Restructuring protobuf to multiple modules

protobuf/java will become a parent pom that will contain two modules:

core - contains all of the code for the protobuf-java artifact
util - contains all of the code for the protobuf-java-util artifact

Also cleaned up various Maven warnings.

66 files changed, 29231 insertions, 0 deletions

diff --git a/java/core/src/main/java/com/google/protobuf/AbstractMessage.java b/java/core/src/main/java/com/google/protobuf/AbstractMessage.java
new file mode 100644
index 00000000..9f418f2b
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/AbstractMessage.java
@@ -0,0 +1,533 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import com.google.protobuf.Descriptors.EnumValueDescriptor;
+import com.google.protobuf.Descriptors.FieldDescriptor;
+import com.google.protobuf.Descriptors.OneofDescriptor;
+import com.google.protobuf.Internal.EnumLite;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * A partial implementation of the {@link Message} interface which implements
+ * as many methods of that interface as possible in terms of other methods.
+ *
+ * @author kenton@google.com Kenton Varda
+ */
+public abstract class AbstractMessage extends AbstractMessageLite
+                                      implements Message {
+  public boolean isInitialized() {
+    return MessageReflection.isInitialized(this);
+  }
+
+
+  public List<String> findInitializationErrors() {
+    return MessageReflection.findMissingFields(this);
+  }
+
+  public String getInitializationErrorString() {
+    return MessageReflection.delimitWithCommas(findInitializationErrors());
+  }
+
+  /** TODO(jieluo): Clear it when all subclasses have implemented this method. */
+  @Override
+  public boolean hasOneof(OneofDescriptor oneof) {
+    throw new UnsupportedOperationException("hasOneof() is not implemented.");
+  }
+
+  /** TODO(jieluo): Clear it when all subclasses have implemented this method. */
+  @Override
+  public FieldDescriptor getOneofFieldDescriptor(OneofDescriptor oneof) {
+    throw new UnsupportedOperationException(
+        "getOneofFieldDescriptor() is not implemented.");
+  }
+
+  @Override
+  public final String toString() {
+    return TextFormat.printToString(this);
+  }
+
+  public void writeTo(final CodedOutputStream output) throws IOException {
+    MessageReflection.writeMessageTo(this, getAllFields(), output, false);
+  }
+
+  protected int memoizedSize = -1;
+
+  public int getSerializedSize() {
+    int size = memoizedSize;
+    if (size != -1) {
+      return size;
+    }
+
+    memoizedSize = MessageReflection.getSerializedSize(this, getAllFields());
+    return memoizedSize;
+  }
+
+  @Override
+  public boolean equals(final Object other) {
+    if (other == this) {
+      return true;
+    }
+    if (!(other instanceof Message)) {
+      return false;
+    }
+    final Message otherMessage = (Message) other;
+    if (getDescriptorForType() != otherMessage.getDescriptorForType()) {
+      return false;
+    }
+    return compareFields(getAllFields(), otherMessage.getAllFields()) &&
+        getUnknownFields().equals(otherMessage.getUnknownFields());
+  }
+
+  @Override
+  public int hashCode() {
+    int hash = memoizedHashCode;
+    if (hash == 0) {
+      hash = 41;
+      hash = (19 * hash) + getDescriptorForType().hashCode();
+      hash = hashFields(hash, getAllFields());
+      hash = (29 * hash) + getUnknownFields().hashCode();
+      memoizedHashCode = hash;
+    }
+    return hash;
+  }
+  
+  private static ByteString toByteString(Object value) {
+    if (value instanceof byte[]) {
+      return ByteString.copyFrom((byte[]) value);
+    } else {
+      return (ByteString) value;
+    }
+  }
+ 
+  /**
+   * Compares two bytes fields. The parameters must be either a byte array or a
+   * ByteString object. They can be of different type though.
+   */
+  private static boolean compareBytes(Object a, Object b) {
+    if (a instanceof byte[] && b instanceof byte[]) {
+      return Arrays.equals((byte[])a, (byte[])b);
+    }
+    return toByteString(a).equals(toByteString(b));
+  }
+  
+  /**
+   * Converts a list of MapEntry messages into a Map used for equals() and
+   * hashCode().
+   */
+  @SuppressWarnings({"rawtypes", "unchecked"})
+  private static Map convertMapEntryListToMap(List list) {
+    if (list.isEmpty()) {
+      return Collections.emptyMap();
+    }
+    Map result = new HashMap();
+    Iterator iterator = list.iterator();
+    Message entry = (Message) iterator.next();
+    Descriptors.Descriptor descriptor = entry.getDescriptorForType();
+    Descriptors.FieldDescriptor key = descriptor.findFieldByName("key");
+    Descriptors.FieldDescriptor value = descriptor.findFieldByName("value");
+    Object fieldValue = entry.getField(value);
+    if (fieldValue instanceof EnumValueDescriptor) {
+      fieldValue = ((EnumValueDescriptor) fieldValue).getNumber();
+    }
+    result.put(entry.getField(key), fieldValue);
+    while (iterator.hasNext()) {
+      entry = (Message) iterator.next();
+      fieldValue = entry.getField(value);
+      if (fieldValue instanceof EnumValueDescriptor) {
+        fieldValue = ((EnumValueDescriptor) fieldValue).getNumber();
+      }
+      result.put(entry.getField(key), fieldValue);
+    }
+    return result;
+  }
+  
+  /**
+   * Compares two map fields. The parameters must be a list of MapEntry
+   * messages.
+   */
+  @SuppressWarnings({"rawtypes", "unchecked"})
+  private static boolean compareMapField(Object a, Object b) {
+    Map ma = convertMapEntryListToMap((List) a);
+    Map mb = convertMapEntryListToMap((List) b);
+    return MapFieldLite.equals(ma, mb);
+  }
+  
+  /**
+   * Compares two set of fields.
+   * This method is used to implement {@link AbstractMessage#equals(Object)}
+   * and {@link AbstractMutableMessage#equals(Object)}. It takes special care
+   * of bytes fields because immutable messages and mutable messages use
+   * different Java type to reprensent a bytes field and this method should be
+   * able to compare immutable messages, mutable messages and also an immutable
+   * message to a mutable message.
+   */
+  static boolean compareFields(Map<FieldDescriptor, Object> a,
+      Map<FieldDescriptor, Object> b) {
+    if (a.size() != b.size()) {
+      return false;
+    }
+    for (FieldDescriptor descriptor : a.keySet()) {
+      if (!b.containsKey(descriptor)) {
+        return false;
+      }
+      Object value1 = a.get(descriptor);
+      Object value2 = b.get(descriptor);
+      if (descriptor.getType() == FieldDescriptor.Type.BYTES) {
+        if (descriptor.isRepeated()) {
+          List list1 = (List) value1;
+          List list2 = (List) value2;
+          if (list1.size() != list2.size()) {
+            return false;
+          }
+          for (int i = 0; i < list1.size(); i++) {
+            if (!compareBytes(list1.get(i), list2.get(i))) {
+              return false;
+            }
+          }
+        } else {
+          // Compares a singular bytes field.
+          if (!compareBytes(value1, value2)) {
+            return false;
+          }
+        }
+      } else if (descriptor.isMapField()) {
+        if (!compareMapField(value1, value2)) {
+          return false;
+        }
+      } else {
+        // Compare non-bytes fields.
+        if (!value1.equals(value2)) {
+          return false;
+        }
+      }
+    }
+    return true;
+  }
+  
+  /**
+   * Calculates the hash code of a map field. {@code value} must be a list of
+   * MapEntry messages.
+   */
+  @SuppressWarnings("unchecked")
+  private static int hashMapField(Object value) {
+    return MapFieldLite.calculateHashCodeForMap(convertMapEntryListToMap((List) value));
+  }
+
+  /** Get a hash code for given fields and values, using the given seed. */
+  @SuppressWarnings("unchecked")
+  protected static int hashFields(int hash, Map<FieldDescriptor, Object> map) {
+    for (Map.Entry<FieldDescriptor, Object> entry : map.entrySet()) {
+      FieldDescriptor field = entry.getKey();
+      Object value = entry.getValue();
+      hash = (37 * hash) + field.getNumber();
+      if (field.isMapField()) {
+        hash = (53 * hash) + hashMapField(value);
+      } else if (field.getType() != FieldDescriptor.Type.ENUM){
+        hash = (53 * hash) + value.hashCode();
+      } else if (field.isRepeated()) {
+        List<? extends EnumLite> list = (List<? extends EnumLite>) value;
+        hash = (53 * hash) + Internal.hashEnumList(list);
+      } else {
+        hash = (53 * hash) + Internal.hashEnum((EnumLite) value);
+      }
+    }
+    return hash;
+  }
+
+  /**
+   * Package private helper method for AbstractParser to create
+   * UninitializedMessageException with missing field information.
+   */
+  @Override
+  UninitializedMessageException newUninitializedMessageException() {
+    return Builder.newUninitializedMessageException(this);
+  }
+
+  // =================================================================
+
+  /**
+   * A partial implementation of the {@link Message.Builder} interface which
+   * implements as many methods of that interface as possible in terms of
+   * other methods.
+   */
+  @SuppressWarnings("unchecked")
+  public static abstract class Builder<BuilderType extends Builder>
+      extends AbstractMessageLite.Builder<BuilderType>
+      implements Message.Builder {
+    // The compiler produces an error if this is not declared explicitly.
+    @Override
+    public abstract BuilderType clone();
+
+    /** TODO(jieluo): Clear it when all subclasses have implemented this method. */
+    @Override
+    public boolean hasOneof(OneofDescriptor oneof) {
+      throw new UnsupportedOperationException("hasOneof() is not implemented.");
+    }
+
+    /** TODO(jieluo): Clear it when all subclasses have implemented this method. */
+    @Override
+    public FieldDescriptor getOneofFieldDescriptor(OneofDescriptor oneof) {
+      throw new UnsupportedOperationException(
+          "getOneofFieldDescriptor() is not implemented.");
+    }
+
+    /** TODO(jieluo): Clear it when all subclasses have implemented this method. */
+    @Override
+    public BuilderType clearOneof(OneofDescriptor oneof) {
+      throw new UnsupportedOperationException("clearOneof() is not implemented.");
+    }
+
+    public BuilderType clear() {
+      for (final Map.Entry<FieldDescriptor, Object> entry :
+           getAllFields().entrySet()) {
+        clearField(entry.getKey());
+      }
+      return (BuilderType) this;
+    }
+
+    public List<String> findInitializationErrors() {
+      return MessageReflection.findMissingFields(this);
+    }
+
+    public String getInitializationErrorString() {
+      return MessageReflection.delimitWithCommas(findInitializationErrors());
+    }
+
+    public BuilderType mergeFrom(final Message other) {
+      if (other.getDescriptorForType() != getDescriptorForType()) {
+        throw new IllegalArgumentException(
+          "mergeFrom(Message) can only merge messages of the same type.");
+      }
+
+      // Note:  We don't attempt to verify that other's fields have valid
+      //   types.  Doing so would be a losing battle.  We'd have to verify
+      //   all sub-messages as well, and we'd have to make copies of all of
+      //   them to insure that they don't change after verification (since
+      //   the Message interface itself cannot enforce immutability of
+      //   implementations).
+      // TODO(kenton):  Provide a function somewhere called makeDeepCopy()
+      //   which allows people to make secure deep copies of messages.
+
+      for (final Map.Entry<FieldDescriptor, Object> entry :
+           other.getAllFields().entrySet()) {
+        final FieldDescriptor field = entry.getKey();
+        if (field.isRepeated()) {
+          for (final Object element : (List)entry.getValue()) {
+            addRepeatedField(field, element);
+          }
+        } else if (field.getJavaType() == FieldDescriptor.JavaType.MESSAGE) {
+          final Message existingValue = (Message)getField(field);
+          if (existingValue == existingValue.getDefaultInstanceForType()) {
+            setField(field, entry.getValue());
+          } else {
+            setField(field,
+              existingValue.newBuilderForType()
+                .mergeFrom(existingValue)
+                .mergeFrom((Message)entry.getValue())
+                .build());
+          }
+        } else {
+          setField(field, entry.getValue());
+        }
+      }
+
+      mergeUnknownFields(other.getUnknownFields());
+
+      return (BuilderType) this;
+    }
+
+    @Override
+    public BuilderType mergeFrom(final CodedInputStream input)
+                                 throws IOException {
+      return mergeFrom(input, ExtensionRegistry.getEmptyRegistry());
+    }
+
+    @Override
+    public BuilderType mergeFrom(
+        final CodedInputStream input,
+        final ExtensionRegistryLite extensionRegistry)
+        throws IOException {
+      final UnknownFieldSet.Builder unknownFields =
+        UnknownFieldSet.newBuilder(getUnknownFields());
+      while (true) {
+        final int tag = input.readTag();
+        if (tag == 0) {
+          break;
+        }
+
+        MessageReflection.BuilderAdapter builderAdapter =
+            new MessageReflection.BuilderAdapter(this);
+        if (!MessageReflection.mergeFieldFrom(input, unknownFields,
+                                              extensionRegistry,
+                                              getDescriptorForType(),
+                                              builderAdapter,
+                                              tag)) {
+          // end group tag
+          break;
+        }
+      }
+      setUnknownFields(unknownFields.build());
+      return (BuilderType) this;
+    }
+
+    public BuilderType mergeUnknownFields(final UnknownFieldSet unknownFields) {
+      setUnknownFields(
+        UnknownFieldSet.newBuilder(getUnknownFields())
+                       .mergeFrom(unknownFields)
+                       .build());
+      return (BuilderType) this;
+    }
+
+    public Message.Builder getFieldBuilder(final FieldDescriptor field) {
+      throw new UnsupportedOperationException(
+          "getFieldBuilder() called on an unsupported message type.");
+    }
+
+    public Message.Builder getRepeatedFieldBuilder(final FieldDescriptor field,
+        int index) {
+      throw new UnsupportedOperationException(
+          "getRepeatedFieldBuilder() called on an unsupported message type.");
+    }
+
+    public String toString() {
+      return TextFormat.printToString(this);
+    }
+
+    /**
+     * Construct an UninitializedMessageException reporting missing fields in
+     * the given message.
+     */
+    protected static UninitializedMessageException
+        newUninitializedMessageException(Message message) {
+      return new UninitializedMessageException(
+          MessageReflection.findMissingFields(message));
+    }
+
+    // ===============================================================
+    // The following definitions seem to be required in order to make javac
+    // not produce weird errors like:
+    //
+    // java/com/google/protobuf/DynamicMessage.java:203: types
+    //   com.google.protobuf.AbstractMessage.Builder<
+    //     com.google.protobuf.DynamicMessage.Builder> and
+    //   com.google.protobuf.AbstractMessage.Builder<
+    //     com.google.protobuf.DynamicMessage.Builder> are incompatible; both
+    //   define mergeFrom(com.google.protobuf.ByteString), but with unrelated
+    //   return types.
+    //
+    // Strangely, these lines are only needed if javac is invoked separately
+    // on AbstractMessage.java and AbstractMessageLite.java.  If javac is
+    // invoked on both simultaneously, it works.  (Or maybe the important
+    // point is whether or not DynamicMessage.java is compiled together with
+    // AbstractMessageLite.java -- not sure.)  I suspect this is a compiler
+    // bug.
+
+    @Override
+    public BuilderType mergeFrom(final ByteString data)
+        throws InvalidProtocolBufferException {
+      return super.mergeFrom(data);
+    }
+
+    @Override
+    public BuilderType mergeFrom(
+        final ByteString data,
+        final ExtensionRegistryLite extensionRegistry)
+        throws InvalidProtocolBufferException {
+      return super.mergeFrom(data, extensionRegistry);
+    }
+
+    @Override
+    public BuilderType mergeFrom(final byte[] data)
+        throws InvalidProtocolBufferException {
+      return super.mergeFrom(data);
+    }
+
+    @Override
+    public BuilderType mergeFrom(
+        final byte[] data, final int off, final int len)
+        throws InvalidProtocolBufferException {
+      return super.mergeFrom(data, off, len);
+    }
+
+    @Override
+    public BuilderType mergeFrom(
+        final byte[] data,
+        final ExtensionRegistryLite extensionRegistry)
+        throws InvalidProtocolBufferException {
+      return super.mergeFrom(data, extensionRegistry);
+    }
+
+    @Override
+    public BuilderType mergeFrom(
+        final byte[] data, final int off, final int len,
+        final ExtensionRegistryLite extensionRegistry)
+        throws InvalidProtocolBufferException {
+      return super.mergeFrom(data, off, len, extensionRegistry);
+    }
+
+    @Override
+    public BuilderType mergeFrom(final InputStream input)
+        throws IOException {
+      return super.mergeFrom(input);
+    }
+
+    @Override
+    public BuilderType mergeFrom(
+        final InputStream input,
+        final ExtensionRegistryLite extensionRegistry)
+        throws IOException {
+      return super.mergeFrom(input, extensionRegistry);
+    }
+
+    @Override
+    public boolean mergeDelimitedFrom(final InputStream input)
+        throws IOException {
+      return super.mergeDelimitedFrom(input);
+    }
+
+    @Override
+    public boolean mergeDelimitedFrom(
+        final InputStream input,
+        final ExtensionRegistryLite extensionRegistry)
+        throws IOException {
+      return super.mergeDelimitedFrom(input, extensionRegistry);
+    }
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/AbstractMessageLite.java b/java/core/src/main/java/com/google/protobuf/AbstractMessageLite.java
new file mode 100644
index 00000000..12384983
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/AbstractMessageLite.java
@@ -0,0 +1,363 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import java.io.FilterInputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.util.Collection;
+
+/**
+ * A partial implementation of the {@link MessageLite} interface which
+ * implements as many methods of that interface as possible in terms of other
+ * methods.
+ *
+ * @author kenton@google.com Kenton Varda
+ */
+public abstract class AbstractMessageLite implements MessageLite {
+  protected int memoizedHashCode = 0;
+
+  public ByteString toByteString() {
+    try {
+      final ByteString.CodedBuilder out =
+        ByteString.newCodedBuilder(getSerializedSize());
+      writeTo(out.getCodedOutput());
+      return out.build();
+    } catch (IOException e) {
+      throw new RuntimeException(
+        "Serializing to a ByteString threw an IOException (should " +
+        "never happen).", e);
+    }
+  }
+
+  public byte[] toByteArray() {
+    try {
+      final byte[] result = new byte[getSerializedSize()];
+      final CodedOutputStream output = CodedOutputStream.newInstance(result);
+      writeTo(output);
+      output.checkNoSpaceLeft();
+      return result;
+    } catch (IOException e) {
+      throw new RuntimeException(
+        "Serializing to a byte array threw an IOException " +
+        "(should never happen).", e);
+    }
+  }
+
+  public void writeTo(final OutputStream output) throws IOException {
+    final int bufferSize =
+        CodedOutputStream.computePreferredBufferSize(getSerializedSize());
+    final CodedOutputStream codedOutput =
+        CodedOutputStream.newInstance(output, bufferSize);
+    writeTo(codedOutput);
+    codedOutput.flush();
+  }
+
+  public void writeDelimitedTo(final OutputStream output) throws IOException {
+    final int serialized = getSerializedSize();
+    final int bufferSize = CodedOutputStream.computePreferredBufferSize(
+        CodedOutputStream.computeRawVarint32Size(serialized) + serialized);
+    final CodedOutputStream codedOutput =
+        CodedOutputStream.newInstance(output, bufferSize);
+    codedOutput.writeRawVarint32(serialized);
+    writeTo(codedOutput);
+    codedOutput.flush();
+  }
+
+
+  /**
+   * Package private helper method for AbstractParser to create
+   * UninitializedMessageException.
+   */
+  UninitializedMessageException newUninitializedMessageException() {
+    return new UninitializedMessageException(this);
+  }
+
+  protected static void checkByteStringIsUtf8(ByteString byteString)
+      throws IllegalArgumentException {
+    if (!byteString.isValidUtf8()) {
+      throw new IllegalArgumentException("Byte string is not UTF-8.");
+    }
+  }
+
+  protected static <T> void addAll(final Iterable<T> values,
+      final Collection<? super T> list) {
+    Builder.addAll(values, list);
+  }
+  
+  /**
+   * A partial implementation of the {@link Message.Builder} interface which
+   * implements as many methods of that interface as possible in terms of
+   * other methods.
+   */
+  @SuppressWarnings("unchecked")
+  public static abstract class Builder<BuilderType extends Builder>
+      implements MessageLite.Builder {
+    // The compiler produces an error if this is not declared explicitly.
+    @Override
+    public abstract BuilderType clone();
+
+    public BuilderType mergeFrom(final CodedInputStream input)
+                                 throws IOException {
+      return mergeFrom(input, ExtensionRegistryLite.getEmptyRegistry());
+    }
+
+    // Re-defined here for return type covariance.
+    public abstract BuilderType mergeFrom(
+        final CodedInputStream input,
+        final ExtensionRegistryLite extensionRegistry)
+        throws IOException;
+
+    public BuilderType mergeFrom(final ByteString data)
+        throws InvalidProtocolBufferException {
+      try {
+        final CodedInputStream input = data.newCodedInput();
+        mergeFrom(input);
+        input.checkLastTagWas(0);
+        return (BuilderType) this;
+      } catch (InvalidProtocolBufferException e) {
+        throw e;
+      } catch (IOException e) {
+        throw new RuntimeException(
+          "Reading from a ByteString threw an IOException (should " +
+          "never happen).", e);
+      }
+    }
+
+    public BuilderType mergeFrom(
+        final ByteString data,
+        final ExtensionRegistryLite extensionRegistry)
+        throws InvalidProtocolBufferException {
+      try {
+        final CodedInputStream input = data.newCodedInput();
+        mergeFrom(input, extensionRegistry);
+        input.checkLastTagWas(0);
+        return (BuilderType) this;
+      } catch (InvalidProtocolBufferException e) {
+        throw e;
+      } catch (IOException e) {
+        throw new RuntimeException(
+          "Reading from a ByteString threw an IOException (should " +
+          "never happen).", e);
+      }
+    }
+
+    public BuilderType mergeFrom(final byte[] data)
+        throws InvalidProtocolBufferException {
+      return mergeFrom(data, 0, data.length);
+    }
+
+    public BuilderType mergeFrom(final byte[] data, final int off,
+                                 final int len)
+                                 throws InvalidProtocolBufferException {
+      try {
+        final CodedInputStream input =
+            CodedInputStream.newInstance(data, off, len);
+        mergeFrom(input);
+        input.checkLastTagWas(0);
+        return (BuilderType) this;
+      } catch (InvalidProtocolBufferException e) {
+        throw e;
+      } catch (IOException e) {
+        throw new RuntimeException(
+          "Reading from a byte array threw an IOException (should " +
+          "never happen).", e);
+      }
+    }
+
+    public BuilderType mergeFrom(
+        final byte[] data,
+        final ExtensionRegistryLite extensionRegistry)
+        throws InvalidProtocolBufferException {
+      return mergeFrom(data, 0, data.length, extensionRegistry);
+    }
+
+    public BuilderType mergeFrom(
+        final byte[] data, final int off, final int len,
+        final ExtensionRegistryLite extensionRegistry)
+        throws InvalidProtocolBufferException {
+      try {
+        final CodedInputStream input =
+            CodedInputStream.newInstance(data, off, len);
+        mergeFrom(input, extensionRegistry);
+        input.checkLastTagWas(0);
+        return (BuilderType) this;
+      } catch (InvalidProtocolBufferException e) {
+        throw e;
+      } catch (IOException e) {
+        throw new RuntimeException(
+          "Reading from a byte array threw an IOException (should " +
+          "never happen).", e);
+      }
+    }
+
+    public BuilderType mergeFrom(final InputStream input) throws IOException {
+      final CodedInputStream codedInput = CodedInputStream.newInstance(input);
+      mergeFrom(codedInput);
+      codedInput.checkLastTagWas(0);
+      return (BuilderType) this;
+    }
+
+    public BuilderType mergeFrom(
+        final InputStream input,
+        final ExtensionRegistryLite extensionRegistry)
+        throws IOException {
+      final CodedInputStream codedInput = CodedInputStream.newInstance(input);
+      mergeFrom(codedInput, extensionRegistry);
+      codedInput.checkLastTagWas(0);
+      return (BuilderType) this;
+    }
+
+    /**
+     * An InputStream implementations which reads from some other InputStream
+     * but is limited to a particular number of bytes.  Used by
+     * mergeDelimitedFrom().  This is intentionally package-private so that
+     * UnknownFieldSet can share it.
+     */
+    static final class LimitedInputStream extends FilterInputStream {
+      private int limit;
+
+      LimitedInputStream(InputStream in, int limit) {
+        super(in);
+        this.limit = limit;
+      }
+
+      @Override
+      public int available() throws IOException {
+        return Math.min(super.available(), limit);
+      }
+
+      @Override
+      public int read() throws IOException {
+        if (limit <= 0) {
+          return -1;
+        }
+        final int result = super.read();
+        if (result >= 0) {
+          --limit;
+        }
+        return result;
+      }
+
+      @Override
+      public int read(final byte[] b, final int off, int len)
+                      throws IOException {
+        if (limit <= 0) {
+          return -1;
+        }
+        len = Math.min(len, limit);
+        final int result = super.read(b, off, len);
+        if (result >= 0) {
+          limit -= result;
+        }
+        return result;
+      }
+
+      @Override
+      public long skip(final long n) throws IOException {
+        final long result = super.skip(Math.min(n, limit));
+        if (result >= 0) {
+          limit -= result;
+        }
+        return result;
+      }
+    }
+
+    public boolean mergeDelimitedFrom(
+        final InputStream input,
+        final ExtensionRegistryLite extensionRegistry)
+        throws IOException {
+      final int firstByte = input.read();
+      if (firstByte == -1) {
+        return false;
+      }
+      final int size = CodedInputStream.readRawVarint32(firstByte, input);
+      final InputStream limitedInput = new LimitedInputStream(input, size);
+      mergeFrom(limitedInput, extensionRegistry);
+      return true;
+    }
+
+    public boolean mergeDelimitedFrom(final InputStream input)
+        throws IOException {
+      return mergeDelimitedFrom(input,
+          ExtensionRegistryLite.getEmptyRegistry());
+    }
+
+    /**
+     * Construct an UninitializedMessageException reporting missing fields in
+     * the given message.
+     */
+    protected static UninitializedMessageException
+        newUninitializedMessageException(MessageLite message) {
+      return new UninitializedMessageException(message);
+    }
+
+    /**
+     * Adds the {@code values} to the {@code list}.  This is a helper method
+     * used by generated code.  Users should ignore it.
+     *
+     * @throws NullPointerException if {@code values} or any of the elements of
+     * {@code values} is null. When that happens, some elements of
+     * {@code values} may have already been added to the result {@code list}.
+     */
+    protected static <T> void addAll(final Iterable<T> values,
+                                     final Collection<? super T> list) {
+      if (values == null) {
+        throw new NullPointerException();
+      }
+      if (values instanceof LazyStringList) {
+        // For StringOrByteStringLists, check the underlying elements to avoid
+        // forcing conversions of ByteStrings to Strings.
+        checkForNullValues(((LazyStringList) values).getUnderlyingElements());
+        list.addAll((Collection<T>) values);
+      } else if (values instanceof Collection) {
+        checkForNullValues(values);
+        list.addAll((Collection<T>) values);
+      } else {
+        for (final T value : values) {
+          if (value == null) {
+            throw new NullPointerException();
+          }
+          list.add(value);
+        }
+      }
+    }
+
+    private static void checkForNullValues(final Iterable<?> values) {
+      for (final Object value : values) {
+        if (value == null) {
+          throw new NullPointerException();
+        }
+      }
+    }
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/AbstractParser.java b/java/core/src/main/java/com/google/protobuf/AbstractParser.java
new file mode 100644
index 00000000..1a4c6311
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/AbstractParser.java
@@ -0,0 +1,253 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import com.google.protobuf.AbstractMessageLite.Builder.LimitedInputStream;
+
+import java.io.IOException;
+import java.io.InputStream;
+
+/**
+ * A partial implementation of the {@link Parser} interface which implements
+ * as many methods of that interface as possible in terms of other methods.
+ *
+ * Note: This class implements all the convenience methods in the
+ * {@link Parser} interface. See {@link Parser} for related javadocs.
+ * Subclasses need to implement
+ * {@link Parser#parsePartialFrom(CodedInputStream, ExtensionRegistryLite)}
+ *
+ * @author liujisi@google.com (Pherl Liu)
+ */
+public abstract class AbstractParser<MessageType extends MessageLite>
+    implements Parser<MessageType> {
+  /**
+   * Creates an UninitializedMessageException for MessageType.
+   */
+  private UninitializedMessageException
+      newUninitializedMessageException(MessageType message) {
+    if (message instanceof AbstractMessageLite) {
+      return ((AbstractMessageLite) message).newUninitializedMessageException();
+    }
+    return new UninitializedMessageException(message);
+  }
+
+  /**
+   * Helper method to check if message is initialized.
+   *
+   * @throws InvalidProtocolBufferException if it is not initialized.
+   * @return The message to check.
+   */
+  private MessageType checkMessageInitialized(MessageType message)
+      throws InvalidProtocolBufferException {
+    if (message != null && !message.isInitialized()) {
+      throw newUninitializedMessageException(message)
+          .asInvalidProtocolBufferException()
+          .setUnfinishedMessage(message);
+    }
+    return message;
+  }
+
+  private static final ExtensionRegistryLite EMPTY_REGISTRY
+      = ExtensionRegistryLite.getEmptyRegistry();
+
+  public MessageType parsePartialFrom(CodedInputStream input)
+      throws InvalidProtocolBufferException {
+    return parsePartialFrom(input, EMPTY_REGISTRY);
+  }
+
+  public MessageType parseFrom(CodedInputStream input,
+                               ExtensionRegistryLite extensionRegistry)
+      throws InvalidProtocolBufferException {
+    return checkMessageInitialized(
+        parsePartialFrom(input, extensionRegistry));
+  }
+
+  public MessageType parseFrom(CodedInputStream input)
+      throws InvalidProtocolBufferException {
+    return parseFrom(input, EMPTY_REGISTRY);
+  }
+
+  public MessageType parsePartialFrom(ByteString data,
+                                      ExtensionRegistryLite extensionRegistry)
+    throws InvalidProtocolBufferException {
+    MessageType message;
+    try {
+      CodedInputStream input = data.newCodedInput();
+      message = parsePartialFrom(input, extensionRegistry);
+      try {
+        input.checkLastTagWas(0);
+      } catch (InvalidProtocolBufferException e) {
+        throw e.setUnfinishedMessage(message);
+      }
+      return message;
+    } catch (InvalidProtocolBufferException e) {
+      throw e;
+    }
+  }
+
+  public MessageType parsePartialFrom(ByteString data)
+      throws InvalidProtocolBufferException {
+    return parsePartialFrom(data, EMPTY_REGISTRY);
+  }
+
+  public MessageType parseFrom(ByteString data,
+                               ExtensionRegistryLite extensionRegistry)
+      throws InvalidProtocolBufferException {
+    return checkMessageInitialized(parsePartialFrom(data, extensionRegistry));
+  }
+
+  public MessageType parseFrom(ByteString data)
+      throws InvalidProtocolBufferException {
+    return parseFrom(data, EMPTY_REGISTRY);
+  }
+
+  public MessageType parsePartialFrom(byte[] data, int off, int len,
+                                      ExtensionRegistryLite extensionRegistry)
+      throws InvalidProtocolBufferException {
+    try {
+      CodedInputStream input = CodedInputStream.newInstance(data, off, len);
+      MessageType message = parsePartialFrom(input, extensionRegistry);
+      try {
+        input.checkLastTagWas(0);
+      } catch (InvalidProtocolBufferException e) {
+        throw e.setUnfinishedMessage(message);
+      }
+      return message;
+    } catch (InvalidProtocolBufferException e) {
+      throw e;
+    }
+  }
+
+  public MessageType parsePartialFrom(byte[] data, int off, int len)
+      throws InvalidProtocolBufferException {
+    return parsePartialFrom(data, off, len, EMPTY_REGISTRY);
+  }
+
+  public MessageType parsePartialFrom(byte[] data,
+                                      ExtensionRegistryLite extensionRegistry)
+      throws InvalidProtocolBufferException {
+    return parsePartialFrom(data, 0, data.length, extensionRegistry);
+  }
+
+  public MessageType parsePartialFrom(byte[] data)
+      throws InvalidProtocolBufferException {
+    return parsePartialFrom(data, 0, data.length, EMPTY_REGISTRY);
+  }
+
+  public MessageType parseFrom(byte[] data, int off, int len,
+                               ExtensionRegistryLite extensionRegistry)
+      throws InvalidProtocolBufferException {
+    return checkMessageInitialized(
+        parsePartialFrom(data, off, len, extensionRegistry));
+  }
+
+  public MessageType parseFrom(byte[] data, int off, int len)
+      throws InvalidProtocolBufferException {
+    return parseFrom(data, off, len, EMPTY_REGISTRY);
+  }
+
+  public MessageType parseFrom(byte[] data,
+                               ExtensionRegistryLite extensionRegistry)
+      throws InvalidProtocolBufferException {
+    return parseFrom(data, 0, data.length, extensionRegistry);
+  }
+
+  public MessageType parseFrom(byte[] data)
+      throws InvalidProtocolBufferException {
+    return parseFrom(data, EMPTY_REGISTRY);
+  }
+
+  public MessageType parsePartialFrom(InputStream input,
+                                      ExtensionRegistryLite extensionRegistry)
+      throws InvalidProtocolBufferException {
+    CodedInputStream codedInput = CodedInputStream.newInstance(input);
+    MessageType message = parsePartialFrom(codedInput, extensionRegistry);
+    try {
+      codedInput.checkLastTagWas(0);
+    } catch (InvalidProtocolBufferException e) {
+      throw e.setUnfinishedMessage(message);
+    }
+    return message;
+  }
+
+  public MessageType parsePartialFrom(InputStream input)
+      throws InvalidProtocolBufferException {
+    return parsePartialFrom(input, EMPTY_REGISTRY);
+  }
+
+  public MessageType parseFrom(InputStream input,
+                               ExtensionRegistryLite extensionRegistry)
+      throws InvalidProtocolBufferException {
+    return checkMessageInitialized(
+        parsePartialFrom(input, extensionRegistry));
+  }
+
+  public MessageType parseFrom(InputStream input)
+      throws InvalidProtocolBufferException {
+    return parseFrom(input, EMPTY_REGISTRY);
+  }
+
+  public MessageType parsePartialDelimitedFrom(
+      InputStream input,
+      ExtensionRegistryLite extensionRegistry)
+      throws InvalidProtocolBufferException {
+    int size;
+    try {
+      int firstByte = input.read();
+      if (firstByte == -1) {
+        return null;
+      }
+      size = CodedInputStream.readRawVarint32(firstByte, input);
+    } catch (IOException e) {
+      throw new InvalidProtocolBufferException(e.getMessage());
+    }
+    InputStream limitedInput = new LimitedInputStream(input, size);
+    return parsePartialFrom(limitedInput, extensionRegistry);
+  }
+
+  public MessageType parsePartialDelimitedFrom(InputStream input)
+      throws InvalidProtocolBufferException {
+    return parsePartialDelimitedFrom(input, EMPTY_REGISTRY);
+  }
+
+  public MessageType parseDelimitedFrom(
+      InputStream input,
+      ExtensionRegistryLite extensionRegistry)
+      throws InvalidProtocolBufferException {
+    return checkMessageInitialized(
+        parsePartialDelimitedFrom(input, extensionRegistry));
+  }
+
+  public MessageType parseDelimitedFrom(InputStream input)
+      throws InvalidProtocolBufferException {
+    return parseDelimitedFrom(input, EMPTY_REGISTRY);
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/AbstractProtobufList.java b/java/core/src/main/java/com/google/protobuf/AbstractProtobufList.java
new file mode 100644
index 00000000..bb6446b2
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/AbstractProtobufList.java
@@ -0,0 +1,136 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import com.google.protobuf.Internal.ProtobufList;
+
+import java.util.AbstractList;
+import java.util.Collection;
+
+/**
+ * An abstract implementation of {@link ProtobufList} which manages mutability semantics. All mutate
+ * methods are check if the list is mutable before proceeding. Subclasses must invoke
+ * {@link #ensureIsMutable()} manually when overriding those methods.
+ */
+abstract class AbstractProtobufList<E> extends AbstractList<E> implements ProtobufList<E> {
+
+  /**
+   * Whether or not this list is modifiable.
+   */
+  private boolean isMutable;
+  
+  /**
+   * Constructs a mutable list by default.
+   */
+  AbstractProtobufList() {
+    isMutable = true;
+  }
+
+  @Override
+  public boolean add(E e) {
+    ensureIsMutable();
+    return super.add(e);
+  }
+
+  @Override
+  public void add(int index, E element) {
+    ensureIsMutable();
+    super.add(index, element);
+  }
+
+  @Override
+  public boolean addAll(Collection<? extends E> c) {
+    ensureIsMutable();
+    return super.addAll(c);
+  }
+  
+  @Override
+  public boolean addAll(int index, Collection<? extends E> c) {
+    ensureIsMutable();
+    return super.addAll(index, c);
+  }
+
+  @Override
+  public void clear() {
+    ensureIsMutable();
+    super.clear();
+  }
+  
+  @Override
+  public boolean isModifiable() {
+    return isMutable;
+  }
+  
+  @Override
+  public final void makeImmutable() {
+    isMutable = false;
+  }
+  
+  @Override
+  public E remove(int index) {
+    ensureIsMutable();
+    return super.remove(index);
+  }
+  
+  @Override
+  public boolean remove(Object o) {
+    ensureIsMutable();
+    return super.remove(o);
+  }
+  
+  @Override
+  public boolean removeAll(Collection<?> c) {
+    ensureIsMutable();
+    return super.removeAll(c);
+  }
+  
+  @Override
+  public boolean retainAll(Collection<?> c) {
+    ensureIsMutable();
+    return super.retainAll(c);
+  }
+  
+  @Override
+  public E set(int index, E element) {
+    ensureIsMutable();
+    return super.set(index, element);
+  }
+  
+  /**
+   * Throws an {@link UnsupportedOperationException} if the list is immutable. Subclasses are
+   * responsible for invoking this method on mutate operations.
+   */
+  protected void ensureIsMutable() {
+    if (!isMutable) {
+      throw new UnsupportedOperationException();
+    }
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/BlockingRpcChannel.java b/java/core/src/main/java/com/google/protobuf/BlockingRpcChannel.java
new file mode 100644
index 00000000..d535efb9
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/BlockingRpcChannel.java
@@ -0,0 +1,51 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+/**
+ * <p>Abstract interface for a blocking RPC channel.  {@code BlockingRpcChannel}
+ * is the blocking equivalent to {@link RpcChannel}.
+ *
+ * @author kenton@google.com Kenton Varda
+ * @author cpovirk@google.com Chris Povirk
+ */
+public interface BlockingRpcChannel {
+  /**
+   * Call the given method of the remote service and blocks until it returns.
+   * {@code callBlockingMethod()} is the blocking equivalent to
+   * {@link RpcChannel#callMethod}.
+   */
+  Message callBlockingMethod(
+      Descriptors.MethodDescriptor method,
+      RpcController controller,
+      Message request,
+      Message responsePrototype) throws ServiceException;
+}
diff --git a/java/core/src/main/java/com/google/protobuf/BlockingService.java b/java/core/src/main/java/com/google/protobuf/BlockingService.java
new file mode 100644
index 00000000..d01f0b8f
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/BlockingService.java
@@ -0,0 +1,64 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+/**
+ * Blocking equivalent to {@link Service}.
+ *
+ * @author kenton@google.com Kenton Varda
+ * @author cpovirk@google.com Chris Povirk
+ */
+public interface BlockingService {
+  /**
+   * Equivalent to {@link Service#getDescriptorForType}.
+   */
+  Descriptors.ServiceDescriptor getDescriptorForType();
+
+  /**
+   * Equivalent to {@link Service#callMethod}, except that
+   * {@code callBlockingMethod()} returns the result of the RPC or throws a
+   * {@link ServiceException} if there is a failure, rather than passing the
+   * information to a callback.
+   */
+  Message callBlockingMethod(Descriptors.MethodDescriptor method,
+                             RpcController controller,
+                             Message request) throws ServiceException;
+
+  /**
+   * Equivalent to {@link Service#getRequestPrototype}.
+   */
+  Message getRequestPrototype(Descriptors.MethodDescriptor method);
+
+  /**
+   * Equivalent to {@link Service#getResponsePrototype}.
+   */
+  Message getResponsePrototype(Descriptors.MethodDescriptor method);
+}
diff --git a/java/core/src/main/java/com/google/protobuf/BooleanArrayList.java b/java/core/src/main/java/com/google/protobuf/BooleanArrayList.java
new file mode 100644
index 00000000..70e042f5
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/BooleanArrayList.java
@@ -0,0 +1,251 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import com.google.protobuf.Internal.BooleanList;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.List;
+import java.util.RandomAccess;
+
+/**
+ * An implementation of {@link BooleanList} on top of a primitive array.
+ * 
+ * @author dweis@google.com (Daniel Weis)
+ */
+final class BooleanArrayList
+    extends AbstractProtobufList<Boolean> implements BooleanList, RandomAccess {
+  
+  private static final int DEFAULT_CAPACITY = 10;
+  
+  private static final BooleanArrayList EMPTY_LIST = new BooleanArrayList();
+  static {
+    EMPTY_LIST.makeImmutable();
+  }
+  
+  public static BooleanArrayList emptyList() {
+    return EMPTY_LIST;
+  }
+  
+  /**
+   * The backing store for the list.
+   */
+  private boolean[] array;
+  
+  /**
+   * The size of the list distinct from the length of the array. That is, it is the number of
+   * elements set in the list.
+   */
+  private int size;
+
+  /**
+   * Constructs a new mutable {@code BooleanArrayList} with default capacity.
+   */
+  BooleanArrayList() {
+    this(DEFAULT_CAPACITY);
+  }
+
+  /**
+   * Constructs a new mutable {@code BooleanArrayList} with the provided capacity.
+   */
+  BooleanArrayList(int capacity) {
+    array = new boolean[capacity];
+    size = 0;
+  }
+
+  /**
+   * Constructs a new mutable {@code BooleanArrayList} containing the same elements as
+   * {@code other}.
+   */
+  BooleanArrayList(List<Boolean> other) {
+    if (other instanceof BooleanArrayList) {
+      BooleanArrayList list = (BooleanArrayList) other;
+      array = list.array.clone();
+      size = list.size;
+    } else {
+      size = other.size();
+      array = new boolean[size];
+      for (int i = 0; i < size; i++) {
+        array[i] = other.get(i);
+      }
+    }
+  }
+  
+  @Override
+  public Boolean get(int index) {
+    return getBoolean(index);
+  }
+
+  @Override
+  public boolean getBoolean(int index) {
+    ensureIndexInRange(index);
+    return array[index];
+  }
+
+  @Override
+  public int size() {
+    return size;
+  }
+
+  @Override
+  public Boolean set(int index, Boolean element) {
+    return setBoolean(index, element);
+  }
+
+  @Override
+  public boolean setBoolean(int index, boolean element) {
+    ensureIsMutable();
+    ensureIndexInRange(index);
+    boolean previousValue = array[index];
+    array[index] = element;
+    return previousValue;
+  }
+
+  @Override
+  public void add(int index, Boolean element) {
+    addBoolean(index, element);
+  }
+
+  /**
+   * Like {@link #add(Boolean)} but more efficient in that it doesn't box the element.
+   */
+  @Override
+  public void addBoolean(boolean element) {
+    addBoolean(size, element);
+  }
+
+  /**
+   * Like {@link #add(int, Boolean)} but more efficient in that it doesn't box the element.
+   */
+  private void addBoolean(int index, boolean element) {
+    ensureIsMutable();
+    if (index < 0 || index > size) {
+      throw new IndexOutOfBoundsException(makeOutOfBoundsExceptionMessage(index));
+    }
+    
+    if (size < array.length) {
+      // Shift everything over to make room
+      System.arraycopy(array, index, array, index + 1, size - index);
+    } else {
+      // Resize to 1.5x the size
+      int length = ((size * 3) / 2) + 1;
+      boolean[] newArray = new boolean[length];
+      
+      // Copy the first part directly
+      System.arraycopy(array, 0, newArray, 0, index);
+      
+      // Copy the rest shifted over by one to make room
+      System.arraycopy(array, index, newArray, index + 1, size - index);
+      array = newArray;
+    }
+
+    array[index] = element;
+    size++;
+    modCount++;
+  }
+
+  @Override
+  public boolean addAll(Collection<? extends Boolean> collection) {
+    ensureIsMutable();
+    
+    if (collection == null) {
+      throw new NullPointerException();
+    }
+    
+    // We specialize when adding another BooleanArrayList to avoid boxing elements.
+    if (!(collection instanceof BooleanArrayList)) {
+      return super.addAll(collection);
+    }
+    
+    BooleanArrayList list = (BooleanArrayList) collection;
+    if (list.size == 0) {
+      return false;
+    }
+    
+    int overflow = Integer.MAX_VALUE - size;
+    if (overflow < list.size) {
+      // We can't actually represent a list this large.
+      throw new OutOfMemoryError();
+    }
+    
+    int newSize = size + list.size;
+    if (newSize > array.length) {
+      array = Arrays.copyOf(array, newSize);
+    }
+    
+    System.arraycopy(list.array, 0, array, size, list.size);
+    size = newSize;
+    modCount++;
+    return true;
+  }
+  
+  @Override
+  public boolean remove(Object o) {
+    ensureIsMutable();
+    for (int i = 0; i < size; i++) {
+      if (o.equals(array[i])) {
+        System.arraycopy(array, i + 1, array, i, size - i);
+        size--;
+        modCount++;
+        return true;
+      }
+    }
+    return false;
+  }
+
+  @Override
+  public Boolean remove(int index) {
+    ensureIsMutable();
+    ensureIndexInRange(index);
+    boolean value = array[index];
+    System.arraycopy(array, index + 1, array, index, size - index);
+    size--;
+    modCount++;
+    return value;
+  }
+
+  /**
+   * Ensures that the provided {@code index} is within the range of {@code [0, size]}. Throws an
+   * {@link IndexOutOfBoundsException} if it is not.
+   * 
+   * @param index the index to verify is in range
+   */
+  private void ensureIndexInRange(int index) {
+    if (index < 0 || index >= size) {
+      throw new IndexOutOfBoundsException(makeOutOfBoundsExceptionMessage(index));
+    }
+  }
+
+  private String makeOutOfBoundsExceptionMessage(int index) {
+    return "Index:" + index + ", Size:" + size;
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/BoundedByteString.java b/java/core/src/main/java/com/google/protobuf/BoundedByteString.java
new file mode 100644
index 00000000..934c9030
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/BoundedByteString.java
@@ -0,0 +1,124 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import java.io.IOException;
+import java.io.InvalidObjectException;
+import java.io.ObjectInputStream;
+
+/**
+ * This class is used to represent the substring of a {@link ByteString} over a
+ * single byte array. In terms of the public API of {@link ByteString}, you end
+ * up here by calling {@link ByteString#copyFrom(byte[])} followed by {@link
+ * ByteString#substring(int, int)}.
+ *
+ * <p>This class contains most of the overhead involved in creating a substring
+ * from a {@link LiteralByteString}.  The overhead involves some range-checking
+ * and two extra fields.
+ *
+ * @author carlanton@google.com (Carl Haverl)
+ */
+final class BoundedByteString extends LiteralByteString {
+
+  private final int bytesOffset;
+  private final int bytesLength;
+
+  /**
+   * Creates a {@code BoundedByteString} backed by the sub-range of given array,
+   * without copying.
+   *
+   * @param bytes  array to wrap
+   * @param offset index to first byte to use in bytes
+   * @param length number of bytes to use from bytes
+   * @throws IllegalArgumentException if {@code offset < 0}, {@code length < 0},
+   *                                  or if {@code offset + length >
+   *                                  bytes.length}.
+   */
+  BoundedByteString(byte[] bytes, int offset, int length) {
+    super(bytes);
+    checkRange(offset, offset + length, bytes.length);
+
+    this.bytesOffset = offset;
+    this.bytesLength = length;
+  }
+
+  /**
+   * Gets the byte at the given index.
+   * Throws {@link ArrayIndexOutOfBoundsException}
+   * for backwards-compatibility reasons although it would more properly be
+   * {@link IndexOutOfBoundsException}.
+   *
+   * @param index index of byte
+   * @return the value
+   * @throws ArrayIndexOutOfBoundsException {@code index} is < 0 or >= size
+   */
+  @Override
+  public byte byteAt(int index) {
+    // We must check the index ourselves as we cannot rely on Java array index
+    // checking for substrings.
+    checkIndex(index, size());
+    return bytes[bytesOffset + index];
+  }
+
+  @Override
+  public int size() {
+    return bytesLength;
+  }
+
+  @Override
+  protected int getOffsetIntoBytes() {
+    return bytesOffset;
+  }
+
+  // =================================================================
+  // ByteString -> byte[]
+
+  @Override
+  protected void copyToInternal(byte[] target, int sourceOffset, int targetOffset,
+      int numberToCopy) {
+    System.arraycopy(bytes, getOffsetIntoBytes() + sourceOffset, target,
+        targetOffset, numberToCopy);
+  }
+
+  // =================================================================
+  // Serializable
+
+  private static final long serialVersionUID = 1L;
+
+  Object writeReplace() {
+    return new LiteralByteString(toByteArray());
+  }
+
+  private void readObject(@SuppressWarnings("unused") ObjectInputStream in) throws IOException {
+    throw new InvalidObjectException(
+        "BoundedByteStream instances are not to be serialized directly");
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/ByteString.java b/java/core/src/main/java/com/google/protobuf/ByteString.java
new file mode 100644
index 00000000..68f20d51
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/ByteString.java
@@ -0,0 +1,1152 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.io.Serializable;
+import java.io.UnsupportedEncodingException;
+import java.nio.ByteBuffer;
+import java.nio.charset.Charset;
+import java.nio.charset.UnsupportedCharsetException;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Iterator;
+import java.util.List;
+import java.util.NoSuchElementException;
+
+/**
+ * Immutable sequence of bytes.  Substring is supported by sharing the reference
+ * to the immutable underlying bytes, as with {@link String}.  Concatenation is
+ * likewise supported without copying (long strings) by building a tree of
+ * pieces in {@link RopeByteString}.
+ * <p>
+ * Like {@link String}, the contents of a {@link ByteString} can never be
+ * observed to change, not even in the presence of a data race or incorrect
+ * API usage in the client code.
+ *
+ * @author crazybob@google.com Bob Lee
+ * @author kenton@google.com Kenton Varda
+ * @author carlanton@google.com Carl Haverl
+ * @author martinrb@google.com Martin Buchholz
+ */
+public abstract class ByteString implements Iterable<Byte>, Serializable {
+
+  /**
+   * When two strings to be concatenated have a combined length shorter than
+   * this, we just copy their bytes on {@link #concat(ByteString)}.
+   * The trade-off is copy size versus the overhead of creating tree nodes
+   * in {@link RopeByteString}.
+   */
+  static final int CONCATENATE_BY_COPY_SIZE = 128;
+
+  /**
+   * When copying an InputStream into a ByteString with .readFrom(),
+   * the chunks in the underlying rope start at 256 bytes, but double
+   * each iteration up to 8192 bytes.
+   */
+  static final int MIN_READ_FROM_CHUNK_SIZE = 0x100;  // 256b
+  static final int MAX_READ_FROM_CHUNK_SIZE = 0x2000;  // 8k
+
+  /**
+   * Empty {@code ByteString}.
+   */
+  public static final ByteString EMPTY = new LiteralByteString(new byte[0]);
+
+  /**
+   * Cached hash value. Intentionally accessed via a data race, which
+   * is safe because of the Java Memory Model's "no out-of-thin-air values"
+   * guarantees for ints. A value of 0 implies that the hash has not been set.
+   */
+  private int hash = 0;
+
+  // This constructor is here to prevent subclassing outside of this package,
+  ByteString() {}
+
+  /**
+   * Gets the byte at the given index. This method should be used only for
+   * random access to individual bytes. To access bytes sequentially, use the
+   * {@link ByteIterator} returned by {@link #iterator()}, and call {@link
+   * #substring(int, int)} first if necessary.
+   *
+   * @param index index of byte
+   * @return the value
+   * @throws ArrayIndexOutOfBoundsException {@code index < 0 or index >= size}
+   */
+  public abstract byte byteAt(int index);
+
+  /**
+   * Return a {@link ByteString.ByteIterator} over the bytes in the ByteString.
+   * To avoid auto-boxing, you may get the iterator manually and call
+   * {@link ByteIterator#nextByte()}.
+   *
+   * @return the iterator
+   */
+  @Override
+  public final ByteIterator iterator() {
+    return new ByteIterator() {
+      private int position = 0;
+      private final int limit = size();
+
+      @Override
+      public boolean hasNext() {
+        return position < limit;
+      }
+
+      @Override
+      public Byte next() {
+        // Boxing calls Byte.valueOf(byte), which does not instantiate.
+        return nextByte();
+      }
+
+      @Override
+      public byte nextByte() {
+        try {
+          return byteAt(position++);
+        } catch (ArrayIndexOutOfBoundsException e) {
+          throw new NoSuchElementException(e.getMessage());
+        }
+      }
+
+      @Override
+      public void remove() {
+        throw new UnsupportedOperationException();
+      }
+    };
+  }
+
+  /**
+   * This interface extends {@code Iterator<Byte>}, so that we can return an
+   * unboxed {@code byte}.
+   */
+  public interface ByteIterator extends Iterator<Byte> {
+    /**
+     * An alternative to {@link Iterator#next()} that returns an
+     * unboxed primitive {@code byte}.
+     *
+     * @return the next {@code byte} in the iteration
+     * @throws NoSuchElementException if the iteration has no more elements
+     */
+    byte nextByte();
+  }
+
+  /**
+   * Gets the number of bytes.
+   *
+   * @return size in bytes
+   */
+  public abstract int size();
+
+  /**
+   * Returns {@code true} if the size is {@code 0}, {@code false} otherwise.
+   *
+   * @return true if this is zero bytes long
+   */
+  public final boolean isEmpty() {
+    return size() == 0;
+  }
+
+  // =================================================================
+  // ByteString -> substring
+
+  /**
+   * Return the substring from {@code beginIndex}, inclusive, to the end of the
+   * string.
+   *
+   * @param beginIndex start at this index
+   * @return substring sharing underlying data
+   * @throws IndexOutOfBoundsException if {@code beginIndex < 0} or
+   *     {@code beginIndex > size()}.
+   */
+  public final ByteString substring(int beginIndex) {
+    return substring(beginIndex, size());
+  }
+
+  /**
+   * Return the substring from {@code beginIndex}, inclusive, to {@code
+   * endIndex}, exclusive.
+   *
+   * @param beginIndex start at this index
+   * @param endIndex   the last character is the one before this index
+   * @return substring sharing underlying data
+   * @throws IndexOutOfBoundsException if {@code beginIndex < 0},
+   *     {@code endIndex > size()}, or {@code beginIndex > endIndex}.
+   */
+  public abstract ByteString substring(int beginIndex, int endIndex);
+
+  /**
+   * Tests if this bytestring starts with the specified prefix.
+   * Similar to {@link String#startsWith(String)}
+   *
+   * @param prefix the prefix.
+   * @return <code>true</code> if the byte sequence represented by the
+   *         argument is a prefix of the byte sequence represented by
+   *         this string; <code>false</code> otherwise.
+   */
+  public final boolean startsWith(ByteString prefix) {
+    return size() >= prefix.size() &&
+           substring(0, prefix.size()).equals(prefix);
+  }
+
+  /**
+   * Tests if this bytestring ends with the specified suffix.
+   * Similar to {@link String#endsWith(String)}
+   *
+   * @param suffix the suffix.
+   * @return <code>true</code> if the byte sequence represented by the
+   *         argument is a suffix of the byte sequence represented by
+   *         this string; <code>false</code> otherwise.
+   */
+  public final boolean endsWith(ByteString suffix) {
+    return size() >= suffix.size() &&
+        substring(size() - suffix.size()).equals(suffix);
+  }
+
+  // =================================================================
+  // byte[] -> ByteString
+
+  /**
+   * Copies the given bytes into a {@code ByteString}.
+   *
+   * @param bytes source array
+   * @param offset offset in source array
+   * @param size number of bytes to copy
+   * @return new {@code ByteString}
+   */
+  public static ByteString copyFrom(byte[] bytes, int offset, int size) {
+    byte[] copy = new byte[size];
+    System.arraycopy(bytes, offset, copy, 0, size);
+    return new LiteralByteString(copy);
+  }
+
+  /**
+   * Copies the given bytes into a {@code ByteString}.
+   *
+   * @param bytes to copy
+   * @return new {@code ByteString}
+   */
+  public static ByteString copyFrom(byte[] bytes) {
+    return copyFrom(bytes, 0, bytes.length);
+  }
+
+  /**
+   * Copies the next {@code size} bytes from a {@code java.nio.ByteBuffer} into
+   * a {@code ByteString}.
+   *
+   * @param bytes source buffer
+   * @param size number of bytes to copy
+   * @return new {@code ByteString}
+   */
+  public static ByteString copyFrom(ByteBuffer bytes, int size) {
+    byte[] copy = new byte[size];
+    bytes.get(copy);
+    return new LiteralByteString(copy);
+  }
+
+  /**
+   * Copies the remaining bytes from a {@code java.nio.ByteBuffer} into
+   * a {@code ByteString}.
+   *
+   * @param bytes sourceBuffer
+   * @return new {@code ByteString}
+   */
+  public static ByteString copyFrom(ByteBuffer bytes) {
+    return copyFrom(bytes, bytes.remaining());
+  }
+
+  /**
+   * Encodes {@code text} into a sequence of bytes using the named charset
+   * and returns the result as a {@code ByteString}.
+   *
+   * @param text source string
+   * @param charsetName encoding to use
+   * @return new {@code ByteString}
+   * @throws UnsupportedEncodingException if the encoding isn't found
+   */
+  public static ByteString copyFrom(String text, String charsetName)
+      throws UnsupportedEncodingException {
+    return new LiteralByteString(text.getBytes(charsetName));
+  }
+
+  /**
+   * Encodes {@code text} into a sequence of bytes using the named charset
+   * and returns the result as a {@code ByteString}.
+   *
+   * @param text source string
+   * @param charset encode using this charset
+   * @return new {@code ByteString}
+   */
+  public static ByteString copyFrom(String text, Charset charset) {
+    return new LiteralByteString(text.getBytes(charset));
+  }
+
+  /**
+   * Encodes {@code text} into a sequence of UTF-8 bytes and returns the
+   * result as a {@code ByteString}.
+   *
+   * @param text source string
+   * @return new {@code ByteString}
+   */
+  public static ByteString copyFromUtf8(String text) {
+    return new LiteralByteString(text.getBytes(Internal.UTF_8));
+  }
+
+  // =================================================================
+  // InputStream -> ByteString
+
+  /**
+   * Completely reads the given stream's bytes into a
+   * {@code ByteString}, blocking if necessary until all bytes are
+   * read through to the end of the stream.
+   *
+   * <b>Performance notes:</b> The returned {@code ByteString} is an
+   * immutable tree of byte arrays ("chunks") of the stream data.  The
+   * first chunk is small, with subsequent chunks each being double
+   * the size, up to 8K.
+   * 
+   * <p>Each byte read from the input stream will be copied twice to ensure
+   * that the resulting ByteString is truly immutable.
+   *
+   * @param streamToDrain The source stream, which is read completely
+   *     but not closed.
+   * @return A new {@code ByteString} which is made up of chunks of
+   *     various sizes, depending on the behavior of the underlying
+   *     stream.
+   * @throws IOException IOException is thrown if there is a problem
+   *     reading the underlying stream.
+   */
+  public static ByteString readFrom(InputStream streamToDrain)
+      throws IOException {
+    return readFrom(streamToDrain, MIN_READ_FROM_CHUNK_SIZE, MAX_READ_FROM_CHUNK_SIZE);
+  }
+
+  /**
+   * Completely reads the given stream's bytes into a
+   * {@code ByteString}, blocking if necessary until all bytes are
+   * read through to the end of the stream.
+   *
+   * <b>Performance notes:</b> The returned {@code ByteString} is an
+   * immutable tree of byte arrays ("chunks") of the stream data.  The
+   * chunkSize parameter sets the size of these byte arrays.
+   *
+   * <p>Each byte read from the input stream will be copied twice to ensure
+   * that the resulting ByteString is truly immutable.
+   *
+   * @param streamToDrain The source stream, which is read completely
+   *     but not closed.
+   * @param chunkSize The size of the chunks in which to read the
+   *     stream.
+   * @return A new {@code ByteString} which is made up of chunks of
+   *     the given size.
+   * @throws IOException IOException is thrown if there is a problem
+   *     reading the underlying stream.
+   */
+  public static ByteString readFrom(InputStream streamToDrain, int chunkSize)
+      throws IOException {
+    return readFrom(streamToDrain, chunkSize, chunkSize);
+  }
+
+  // Helper method that takes the chunk size range as a parameter.
+  public static ByteString readFrom(InputStream streamToDrain, int minChunkSize,
+      int maxChunkSize) throws IOException {
+    Collection<ByteString> results = new ArrayList<ByteString>();
+
+    // copy the inbound bytes into a list of chunks; the chunk size
+    // grows exponentially to support both short and long streams.
+    int chunkSize = minChunkSize;
+    while (true) {
+      ByteString chunk = readChunk(streamToDrain, chunkSize);
+      if (chunk == null) {
+        break;
+      }
+      results.add(chunk);
+      chunkSize = Math.min(chunkSize * 2, maxChunkSize);
+    }
+
+    return ByteString.copyFrom(results);
+  }
+
+  /**
+   * Blocks until a chunk of the given size can be made from the
+   * stream, or EOF is reached.  Calls read() repeatedly in case the
+   * given stream implementation doesn't completely fill the given
+   * buffer in one read() call.
+   *
+   * @return A chunk of the desired size, or else a chunk as large as
+   * was available when end of stream was reached. Returns null if the
+   * given stream had no more data in it.
+   */
+  private static ByteString readChunk(InputStream in, final int chunkSize)
+      throws IOException {
+      final byte[] buf = new byte[chunkSize];
+      int bytesRead = 0;
+      while (bytesRead < chunkSize) {
+        final int count = in.read(buf, bytesRead, chunkSize - bytesRead);
+        if (count == -1) {
+          break;
+        }
+        bytesRead += count;
+      }
+
+      if (bytesRead == 0) {
+        return null;
+      }
+
+      // Always make a copy since InputStream could steal a reference to buf.
+      return ByteString.copyFrom(buf, 0, bytesRead);
+  }
+
+  // =================================================================
+  // Multiple ByteStrings -> One ByteString
+
+  /**
+   * Concatenate the given {@code ByteString} to this one. Short concatenations,
+   * of total size smaller than {@link ByteString#CONCATENATE_BY_COPY_SIZE}, are
+   * produced by copying the underlying bytes (as per Rope.java, <a
+   * href="http://www.cs.ubc.ca/local/reading/proceedings/spe91-95/spe/vol25/issue12/spe986.pdf">
+   * BAP95 </a>. In general, the concatenate involves no copying.
+   *
+   * @param other string to concatenate
+   * @return a new {@code ByteString} instance
+   */
+  public final ByteString concat(ByteString other) {
+    if (Integer.MAX_VALUE - size() < other.size()) {
+      throw new IllegalArgumentException("ByteString would be too long: " +
+          size() + "+" + other.size());
+    }
+
+    return RopeByteString.concatenate(this, other);
+  }
+
+  /**
+   * Concatenates all byte strings in the iterable and returns the result.
+   * This is designed to run in O(list size), not O(total bytes).
+   *
+   * <p>The returned {@code ByteString} is not necessarily a unique object.
+   * If the list is empty, the returned object is the singleton empty
+   * {@code ByteString}.  If the list has only one element, that
+   * {@code ByteString} will be returned without copying.
+   *
+   * @param byteStrings strings to be concatenated
+   * @return new {@code ByteString}
+   */
+  public static ByteString copyFrom(Iterable<ByteString> byteStrings) {
+    // Determine the size;
+    final int size;
+    if (!(byteStrings instanceof Collection)) {
+      int tempSize = 0;
+      for (Iterator<ByteString> iter = byteStrings.iterator(); iter.hasNext();
+          iter.next(), ++tempSize) {
+      }
+      size = tempSize;
+    } else {
+      size = ((Collection<ByteString>) byteStrings).size();
+    }
+
+    if (size == 0) {
+      return EMPTY;
+    }
+
+    return balancedConcat(byteStrings.iterator(), size);
+  }
+
+  // Internal function used by copyFrom(Iterable<ByteString>).
+  // Create a balanced concatenation of the next "length" elements from the
+  // iterable.
+  private static ByteString balancedConcat(Iterator<ByteString> iterator, int length) {
+    assert length >= 1;
+    ByteString result;
+    if (length == 1) {
+      result = iterator.next();
+    } else {
+      int halfLength = length >>> 1;
+      ByteString left = balancedConcat(iterator, halfLength);
+      ByteString right = balancedConcat(iterator, length - halfLength);
+      result = left.concat(right);
+    }
+    return result;
+  }
+
+  // =================================================================
+  // ByteString -> byte[]
+
+  /**
+   * Copies bytes into a buffer at the given offset.
+   *
+   * @param target buffer to copy into
+   * @param offset in the target buffer
+   * @throws IndexOutOfBoundsException if the offset is negative or too large
+   */
+  public void copyTo(byte[] target, int offset) {
+    copyTo(target, 0, offset, size());
+  }
+
+  /**
+   * Copies bytes into a buffer.
+   *
+   * @param target       buffer to copy into
+   * @param sourceOffset offset within these bytes
+   * @param targetOffset offset within the target buffer
+   * @param numberToCopy number of bytes to copy
+   * @throws IndexOutOfBoundsException if an offset or size is negative or too
+   *     large
+   */
+  public final void copyTo(byte[] target, int sourceOffset, int targetOffset,
+      int numberToCopy) {
+    checkRange(sourceOffset, sourceOffset + numberToCopy, size());
+    checkRange(targetOffset, targetOffset + numberToCopy, target.length);
+    if (numberToCopy > 0) {
+      copyToInternal(target, sourceOffset, targetOffset, numberToCopy);
+    }
+  }
+
+  /**
+   * Internal (package private) implementation of
+   * {@link #copyTo(byte[],int,int,int)}.
+   * It assumes that all error checking has already been performed and that
+   * {@code numberToCopy > 0}.
+   */
+  protected abstract void copyToInternal(byte[] target, int sourceOffset,
+      int targetOffset, int numberToCopy);
+
+  /**
+   * Copies bytes into a ByteBuffer.
+   *
+   * @param target ByteBuffer to copy into.
+   * @throws java.nio.ReadOnlyBufferException if the {@code target} is read-only
+   * @throws java.nio.BufferOverflowException if the {@code target}'s
+   *     remaining() space is not large enough to hold the data.
+   */
+  public abstract void copyTo(ByteBuffer target);
+
+  /**
+   * Copies bytes to a {@code byte[]}.
+   *
+   * @return copied bytes
+   */
+  public final byte[] toByteArray() {
+    final int size = size();
+    if (size == 0) {
+      return Internal.EMPTY_BYTE_ARRAY;
+    }
+    byte[] result = new byte[size];
+    copyToInternal(result, 0, 0, size);
+    return result;
+  }
+
+  /**
+   * Writes the complete contents of this byte string to
+   * the specified output stream argument.
+   *
+   * <p>It is assumed that the {@link OutputStream} will not modify the contents passed it
+   * it. It may be possible for a malicious {@link OutputStream} to corrupt
+   * the data underlying the {@link ByteString}.
+   *
+   * @param  out  the output stream to which to write the data.
+   * @throws IOException  if an I/O error occurs.
+   */
+  public abstract void writeTo(OutputStream out) throws IOException;
+
+  /**
+   * Writes a specified part of this byte string to an output stream.
+   *
+   * @param  out  the output stream to which to write the data.
+   * @param  sourceOffset offset within these bytes
+   * @param  numberToWrite number of bytes to write
+   * @throws IOException  if an I/O error occurs.
+   * @throws IndexOutOfBoundsException if an offset or size is negative or too
+   *     large
+   */
+  final void writeTo(OutputStream out, int sourceOffset, int numberToWrite)
+      throws IOException {
+    checkRange(sourceOffset, sourceOffset + numberToWrite, size());
+    if (numberToWrite > 0) {
+      writeToInternal(out, sourceOffset, numberToWrite);
+    }
+  }
+
+  /**
+   * Internal version of {@link #writeTo(OutputStream,int,int)} that assumes
+   * all error checking has already been done.
+   */
+  abstract void writeToInternal(OutputStream out, int sourceOffset, int numberToWrite)
+      throws IOException;
+
+  /**
+   * Constructs a read-only {@code java.nio.ByteBuffer} whose content
+   * is equal to the contents of this byte string.
+   * The result uses the same backing array as the byte string, if possible.
+   *
+   * @return wrapped bytes
+   */
+  public abstract ByteBuffer asReadOnlyByteBuffer();
+
+  /**
+   * Constructs a list of read-only {@code java.nio.ByteBuffer} objects
+   * such that the concatenation of their contents is equal to the contents
+   * of this byte string.  The result uses the same backing arrays as the
+   * byte string.
+   * <p>
+   * By returning a list, implementations of this method may be able to avoid
+   * copying even when there are multiple backing arrays.
+   *
+   * @return a list of wrapped bytes
+   */
+  public abstract List<ByteBuffer> asReadOnlyByteBufferList();
+
+  /**
+   * Constructs a new {@code String} by decoding the bytes using the
+   * specified charset.
+   *
+   * @param charsetName encode using this charset
+   * @return new string
+   * @throws UnsupportedEncodingException if charset isn't recognized
+   */
+  public final String toString(String charsetName)
+      throws UnsupportedEncodingException {
+    try {
+      return toString(Charset.forName(charsetName));
+    } catch (UnsupportedCharsetException e) {
+      UnsupportedEncodingException exception = new UnsupportedEncodingException(charsetName);
+      exception.initCause(e);
+      throw exception;
+    }
+  }
+
+  /**
+   * Constructs a new {@code String} by decoding the bytes using the
+   * specified charset. Returns the same empty String if empty.
+   *
+   * @param charset encode using this charset
+   * @return new string
+   */
+  public final String toString(Charset charset) {
+    return size() == 0 ? "" : toStringInternal(charset);
+  }
+
+  /**
+   * Constructs a new {@code String} by decoding the bytes using the
+   * specified charset.
+   *
+   * @param charset encode using this charset
+   * @return new string
+   */
+  protected abstract String toStringInternal(Charset charset);
+
+  // =================================================================
+  // UTF-8 decoding
+
+  /**
+   * Constructs a new {@code String} by decoding the bytes as UTF-8.
+   *
+   * @return new string using UTF-8 encoding
+   */
+  public final String toStringUtf8() {
+    return toString(Internal.UTF_8);
+  }
+
+  /**
+   * Tells whether this {@code ByteString} represents a well-formed UTF-8
+   * byte sequence, such that the original bytes can be converted to a
+   * String object and then round tripped back to bytes without loss.
+   *
+   * <p>More precisely, returns {@code true} whenever: <pre> {@code
+   * Arrays.equals(byteString.toByteArray(),
+   *     new String(byteString.toByteArray(), "UTF-8").getBytes("UTF-8"))
+   * }</pre>
+   *
+   * <p>This method returns {@code false} for "overlong" byte sequences,
+   * as well as for 3-byte sequences that would map to a surrogate
+   * character, in accordance with the restricted definition of UTF-8
+   * introduced in Unicode 3.1.  Note that the UTF-8 decoder included in
+   * Oracle's JDK has been modified to also reject "overlong" byte
+   * sequences, but (as of 2011) still accepts 3-byte surrogate
+   * character byte sequences.
+   *
+   * <p>See the Unicode Standard,<br>
+   * Table 3-6. <em>UTF-8 Bit Distribution</em>,<br>
+   * Table 3-7. <em>Well Formed UTF-8 Byte Sequences</em>.
+   *
+   * @return whether the bytes in this {@code ByteString} are a
+   * well-formed UTF-8 byte sequence
+   */
+  public abstract boolean isValidUtf8();
+
+  /**
+   * Tells whether the given byte sequence is a well-formed, malformed, or
+   * incomplete UTF-8 byte sequence.  This method accepts and returns a partial
+   * state result, allowing the bytes for a complete UTF-8 byte sequence to be
+   * composed from multiple {@code ByteString} segments.
+   *
+   * @param state either {@code 0} (if this is the initial decoding operation)
+   *     or the value returned from a call to a partial decoding method for the
+   *     previous bytes
+   * @param offset offset of the first byte to check
+   * @param length number of bytes to check
+   *
+   * @return {@code -1} if the partial byte sequence is definitely malformed,
+   * {@code 0} if it is well-formed (no additional input needed), or, if the
+   * byte sequence is "incomplete", i.e. apparently terminated in the middle of
+   * a character, an opaque integer "state" value containing enough information
+   * to decode the character when passed to a subsequent invocation of a
+   * partial decoding method.
+   */
+  protected abstract int partialIsValidUtf8(int state, int offset, int length);
+
+  // =================================================================
+  // equals() and hashCode()
+
+  @Override
+  public abstract boolean equals(Object o);
+
+  /**
+   * Base class for leaf {@link ByteString}s (i.e. non-ropes).
+   */
+  abstract static class LeafByteString extends ByteString {
+    @Override
+    protected final int getTreeDepth() {
+      return 0;
+    }
+
+    @Override
+    protected final boolean isBalanced() {
+      return true;
+    }
+
+    /**
+     * Check equality of the substring of given length of this object starting at
+     * zero with another {@code ByteString} substring starting at offset.
+     *
+     * @param other  what to compare a substring in
+     * @param offset offset into other
+     * @param length number of bytes to compare
+     * @return true for equality of substrings, else false.
+     */
+    abstract boolean equalsRange(ByteString other, int offset, int length);
+  }
+
+  /**
+   * Compute the hashCode using the traditional algorithm from {@link
+   * ByteString}.
+   *
+   * @return hashCode value
+   */
+  @Override
+  public final int hashCode() {
+    int h = hash;
+
+    if (h == 0) {
+      int size = size();
+      h = partialHash(size, 0, size);
+      if (h == 0) {
+        h = 1;
+      }
+      hash = h;
+    }
+    return h;
+  }
+
+  // =================================================================
+  // Input stream
+
+  /**
+   * Creates an {@code InputStream} which can be used to read the bytes.
+   * <p>
+   * The {@link InputStream} returned by this method is guaranteed to be
+   * completely non-blocking.  The method {@link InputStream#available()}
+   * returns the number of bytes remaining in the stream. The methods
+   * {@link InputStream#read(byte[])}, {@link InputStream#read(byte[],int,int)}
+   * and {@link InputStream#skip(long)} will read/skip as many bytes as are
+   * available.  The method {@link InputStream#markSupported()} returns
+   * {@code true}.
+   * <p>
+   * The methods in the returned {@link InputStream} might <b>not</b> be
+   * thread safe.
+   *
+   * @return an input stream that returns the bytes of this byte string.
+   */
+  public abstract InputStream newInput();
+
+  /**
+   * Creates a {@link CodedInputStream} which can be used to read the bytes.
+   * Using this is often more efficient than creating a {@link CodedInputStream}
+   * that wraps the result of {@link #newInput()}.
+   *
+   * @return stream based on wrapped data
+   */
+  public abstract CodedInputStream newCodedInput();
+
+  // =================================================================
+  // Output stream
+
+  /**
+   * Creates a new {@link Output} with the given initial capacity. Call {@link
+   * Output#toByteString()} to create the {@code ByteString} instance.
+   * <p>
+   * A {@link ByteString.Output} offers the same functionality as a
+   * {@link ByteArrayOutputStream}, except that it returns a {@link ByteString}
+   * rather than a {@code byte} array.
+   *
+   * @param initialCapacity estimate of number of bytes to be written
+   * @return {@code OutputStream} for building a {@code ByteString}
+   */
+  public static Output newOutput(int initialCapacity) {
+    return new Output(initialCapacity);
+  }
+
+  /**
+   * Creates a new {@link Output}. Call {@link Output#toByteString()} to create
+   * the {@code ByteString} instance.
+   * <p>
+   * A {@link ByteString.Output} offers the same functionality as a
+   * {@link ByteArrayOutputStream}, except that it returns a {@link ByteString}
+   * rather than a {@code byte array}.
+   *
+   * @return {@code OutputStream} for building a {@code ByteString}
+   */
+  public static Output newOutput() {
+    return new Output(CONCATENATE_BY_COPY_SIZE);
+  }
+
+  /**
+   * Outputs to a {@code ByteString} instance. Call {@link #toByteString()} to
+   * create the {@code ByteString} instance.
+   */
+  public static final class Output extends OutputStream {
+    // Implementation note.
+    // The public methods of this class must be synchronized.  ByteStrings
+    // are guaranteed to be immutable.  Without some sort of locking, it could
+    // be possible for one thread to call toByteSring(), while another thread
+    // is still modifying the underlying byte array.
+
+    private static final byte[] EMPTY_BYTE_ARRAY = new byte[0];
+    // argument passed by user, indicating initial capacity.
+    private final int initialCapacity;
+    // ByteStrings to be concatenated to create the result
+    private final ArrayList<ByteString> flushedBuffers;
+    // Total number of bytes in the ByteStrings of flushedBuffers
+    private int flushedBuffersTotalBytes;
+    // Current buffer to which we are writing
+    private byte[] buffer;
+    // Location in buffer[] to which we write the next byte.
+    private int bufferPos;
+
+    /**
+     * Creates a new ByteString output stream with the specified
+     * initial capacity.
+     *
+     * @param initialCapacity  the initial capacity of the output stream.
+     */
+    Output(int initialCapacity) {
+      if (initialCapacity < 0) {
+        throw new IllegalArgumentException("Buffer size < 0");
+      }
+      this.initialCapacity = initialCapacity;
+      this.flushedBuffers = new ArrayList<ByteString>();
+      this.buffer = new byte[initialCapacity];
+    }
+
+    @Override
+    public synchronized void write(int b) {
+      if (bufferPos == buffer.length) {
+        flushFullBuffer(1);
+      }
+      buffer[bufferPos++] = (byte)b;
+    }
+
+    @Override
+    public synchronized void write(byte[] b, int offset, int length)  {
+      if (length <= buffer.length - bufferPos) {
+        // The bytes can fit into the current buffer.
+        System.arraycopy(b, offset, buffer, bufferPos, length);
+        bufferPos += length;
+      } else {
+        // Use up the current buffer
+        int copySize  = buffer.length - bufferPos;
+        System.arraycopy(b, offset, buffer, bufferPos, copySize);
+        offset += copySize;
+        length -= copySize;
+        // Flush the buffer, and get a new buffer at least big enough to cover
+        // what we still need to output
+        flushFullBuffer(length);
+        System.arraycopy(b, offset, buffer, 0 /* count */, length);
+        bufferPos = length;
+      }
+    }
+
+    /**
+     * Creates a byte string. Its size is the current size of this output
+     * stream and its output has been copied to it.
+     *
+     * @return  the current contents of this output stream, as a byte string.
+     */
+    public synchronized ByteString toByteString() {
+      flushLastBuffer();
+      return ByteString.copyFrom(flushedBuffers);
+    }
+
+    /**
+     * Implement java.util.Arrays.copyOf() for jdk 1.5.
+     */
+    private byte[] copyArray(byte[] buffer, int length) {
+      byte[] result = new byte[length];
+      System.arraycopy(buffer, 0, result, 0, Math.min(buffer.length, length));
+      return result;
+    }
+
+    /**
+     * Writes the complete contents of this byte array output stream to
+     * the specified output stream argument.
+     *
+     * @param out the output stream to which to write the data.
+     * @throws IOException  if an I/O error occurs.
+     */
+    public void writeTo(OutputStream out) throws IOException {
+      ByteString[] cachedFlushBuffers;
+      byte[] cachedBuffer;
+      int cachedBufferPos;
+      synchronized (this) {
+        // Copy the information we need into local variables so as to hold
+        // the lock for as short a time as possible.
+        cachedFlushBuffers =
+            flushedBuffers.toArray(new ByteString[flushedBuffers.size()]);
+        cachedBuffer = buffer;
+        cachedBufferPos = bufferPos;
+      }
+      for (ByteString byteString : cachedFlushBuffers) {
+        byteString.writeTo(out);
+      }
+
+      out.write(copyArray(cachedBuffer, cachedBufferPos));
+    }
+
+    /**
+     * Returns the current size of the output stream.
+     *
+     * @return  the current size of the output stream
+     */
+    public synchronized int size() {
+      return flushedBuffersTotalBytes + bufferPos;
+    }
+
+    /**
+     * Resets this stream, so that all currently accumulated output in the
+     * output stream is discarded. The output stream can be used again,
+     * reusing the already allocated buffer space.
+     */
+    public synchronized void reset() {
+      flushedBuffers.clear();
+      flushedBuffersTotalBytes = 0;
+      bufferPos = 0;
+    }
+
+    @Override
+    public String toString() {
+      return String.format("<ByteString.Output@%s size=%d>",
+          Integer.toHexString(System.identityHashCode(this)), size());
+    }
+
+    /**
+     * Internal function used by writers.  The current buffer is full, and the
+     * writer needs a new buffer whose size is at least the specified minimum
+     * size.
+     */
+    private void flushFullBuffer(int minSize)  {
+      flushedBuffers.add(new LiteralByteString(buffer));
+      flushedBuffersTotalBytes += buffer.length;
+      // We want to increase our total capacity by 50%, but as a minimum,
+      // the new buffer should also at least be >= minSize and
+      // >= initial Capacity.
+      int newSize = Math.max(initialCapacity,
+          Math.max(minSize, flushedBuffersTotalBytes >>> 1));
+      buffer = new byte[newSize];
+      bufferPos = 0;
+    }
+
+    /**
+     * Internal function used by {@link #toByteString()}. The current buffer may
+     * or may not be full, but it needs to be flushed.
+     */
+    private void flushLastBuffer()  {
+      if (bufferPos < buffer.length) {
+        if (bufferPos > 0) {
+          byte[] bufferCopy = copyArray(buffer, bufferPos);
+          flushedBuffers.add(new LiteralByteString(bufferCopy));
+        }
+        // We reuse this buffer for further writes.
+      } else {
+        // Buffer is completely full.  Huzzah.
+        flushedBuffers.add(new LiteralByteString(buffer));
+        // 99% of the time, we're not going to use this OutputStream again.
+        // We set buffer to an empty byte stream so that we're handling this
+        // case without wasting space.  In the rare case that more writes
+        // *do* occur, this empty buffer will be flushed and an appropriately
+        // sized new buffer will be created.
+        buffer = EMPTY_BYTE_ARRAY;
+      }
+      flushedBuffersTotalBytes += bufferPos;
+      bufferPos = 0;
+    }
+  }
+
+  /**
+   * Constructs a new {@code ByteString} builder, which allows you to
+   * efficiently construct a {@code ByteString} by writing to a {@link
+   * CodedOutputStream}. Using this is much more efficient than calling {@code
+   * newOutput()} and wrapping that in a {@code CodedOutputStream}.
+   *
+   * <p>This is package-private because it's a somewhat confusing interface.
+   * Users can call {@link Message#toByteString()} instead of calling this
+   * directly.
+   *
+   * @param size The target byte size of the {@code ByteString}.  You must write
+   *     exactly this many bytes before building the result.
+   * @return the builder
+   */
+  static CodedBuilder newCodedBuilder(int size) {
+    return new CodedBuilder(size);
+  }
+
+  /** See {@link ByteString#newCodedBuilder(int)}. */
+  static final class CodedBuilder {
+    private final CodedOutputStream output;
+    private final byte[] buffer;
+
+    private CodedBuilder(int size) {
+      buffer = new byte[size];
+      output = CodedOutputStream.newInstance(buffer);
+    }
+
+    public ByteString build() {
+      output.checkNoSpaceLeft();
+
+      // We can be confident that the CodedOutputStream will not modify the
+      // underlying bytes anymore because it already wrote all of them.  So,
+      // no need to make a copy.
+      return new LiteralByteString(buffer);
+    }
+
+    public CodedOutputStream getCodedOutput() {
+      return output;
+    }
+  }
+
+  // =================================================================
+  // Methods {@link RopeByteString} needs on instances, which aren't part of the
+  // public API.
+
+  /**
+   * Return the depth of the tree representing this {@code ByteString}, if any,
+   * whose root is this node. If this is a leaf node, return 0.
+   *
+   * @return tree depth or zero
+   */
+  protected abstract int getTreeDepth();
+
+  /**
+   * Return {@code true} if this ByteString is literal (a leaf node) or a
+   * flat-enough tree in the sense of {@link RopeByteString}.
+   *
+   * @return true if the tree is flat enough
+   */
+  protected abstract boolean isBalanced();
+
+  /**
+   * Return the cached hash code if available.
+   *
+   * @return value of cached hash code or 0 if not computed yet
+   */
+  protected final int peekCachedHashCode() {
+    return hash;
+  }
+
+  /**
+   * Compute the hash across the value bytes starting with the given hash, and
+   * return the result.  This is used to compute the hash across strings
+   * represented as a set of pieces by allowing the hash computation to be
+   * continued from piece to piece.
+   *
+   * @param h starting hash value
+   * @param offset offset into this value to start looking at data values
+   * @param length number of data values to include in the hash computation
+   * @return ending hash value
+   */
+  protected abstract int partialHash(int h, int offset, int length);
+
+  /**
+   * Checks that the given index falls within the specified array size.
+   *
+   * @param index the index position to be tested
+   * @param size the length of the array
+   * @throws ArrayIndexOutOfBoundsException if the index does not fall within the array.
+   */
+  static void checkIndex(int index, int size) {
+    if ((index | (size - (index + 1))) < 0) {
+      if (index < 0) {
+        throw new ArrayIndexOutOfBoundsException("Index < 0: " + index);
+      }
+      throw new ArrayIndexOutOfBoundsException("Index > length: " + index + ", " + size);
+    }
+  }
+
+  /**
+   * Checks that the given range falls within the bounds of an array
+   *
+   * @param startIndex the start index of the range (inclusive)
+   * @param endIndex the end index of the range (exclusive)
+   * @param size the size of the array.
+   * @return the length of the range.
+   * @throws ArrayIndexOutOfBoundsException some or all of the range falls outside of the array.
+   */
+  static int checkRange(int startIndex, int endIndex, int size) {
+    final int length = endIndex - startIndex;
+    if ((startIndex | endIndex | length | (size - endIndex)) < 0) {
+      if (startIndex < 0) {
+        throw new IndexOutOfBoundsException("Beginning index: " + startIndex + " < 0");
+      }
+      if (endIndex < startIndex) {
+        throw new IndexOutOfBoundsException(
+            "Beginning index larger than ending index: " + startIndex + ", " + endIndex);
+      }
+      // endIndex >= size
+      throw new IndexOutOfBoundsException("End index: " + endIndex + " >= " + size);
+    }
+    return length;
+  }
+
+  @Override
+  public final String toString() {
+    return String.format("<ByteString@%s size=%d>",
+        Integer.toHexString(System.identityHashCode(this)), size());
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/CodedInputStream.java b/java/core/src/main/java/com/google/protobuf/CodedInputStream.java
new file mode 100644
index 00000000..adc91536
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/CodedInputStream.java
@@ -0,0 +1,1308 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.nio.ByteBuffer;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+/**
+ * Reads and decodes protocol message fields.
+ *
+ * This class contains two kinds of methods:  methods that read specific
+ * protocol message constructs and field types (e.g. {@link #readTag()} and
+ * {@link #readInt32()}) and methods that read low-level values (e.g.
+ * {@link #readRawVarint32()} and {@link #readRawBytes}).  If you are reading
+ * encoded protocol messages, you should use the former methods, but if you are
+ * reading some other format of your own design, use the latter.
+ *
+ * @author kenton@google.com Kenton Varda
+ */
+public final class CodedInputStream {
+  /**
+   * Create a new CodedInputStream wrapping the given InputStream.
+   */
+  public static CodedInputStream newInstance(final InputStream input) {
+    return new CodedInputStream(input);
+  }
+
+  /**
+   * Create a new CodedInputStream wrapping the given byte array.
+   */
+  public static CodedInputStream newInstance(final byte[] buf) {
+    return newInstance(buf, 0, buf.length);
+  }
+
+  /**
+   * Create a new CodedInputStream wrapping the given byte array slice.
+   */
+  public static CodedInputStream newInstance(final byte[] buf, final int off,
+                                             final int len) {
+    CodedInputStream result = new CodedInputStream(buf, off, len);
+    try {
+      // Some uses of CodedInputStream can be more efficient if they know
+      // exactly how many bytes are available.  By pushing the end point of the
+      // buffer as a limit, we allow them to get this information via
+      // getBytesUntilLimit().  Pushing a limit that we know is at the end of
+      // the stream can never hurt, since we can never past that point anyway.
+      result.pushLimit(len);
+    } catch (InvalidProtocolBufferException ex) {
+      // The only reason pushLimit() might throw an exception here is if len
+      // is negative. Normally pushLimit()'s parameter comes directly off the
+      // wire, so it's important to catch exceptions in case of corrupt or
+      // malicious data. However, in this case, we expect that len is not a
+      // user-supplied value, so we can assume that it being negative indicates
+      // a programming error. Therefore, throwing an unchecked exception is
+      // appropriate.
+      throw new IllegalArgumentException(ex);
+    }
+    return result;
+  }
+
+  /**
+   * Create a new CodedInputStream wrapping the given ByteBuffer. The data
+   * starting from the ByteBuffer's current position to its limit will be read.
+   * The returned CodedInputStream may or may not share the underlying data
+   * in the ByteBuffer, therefore the ByteBuffer cannot be changed while the
+   * CodedInputStream is in use.
+   * Note that the ByteBuffer's position won't be changed by this function.
+   * Concurrent calls with the same ByteBuffer object are safe if no other
+   * thread is trying to alter the ByteBuffer's status.
+   */
+  public static CodedInputStream newInstance(ByteBuffer buf) {
+    if (buf.hasArray()) {
+      return newInstance(buf.array(), buf.arrayOffset() + buf.position(),
+          buf.remaining());
+    } else {
+      ByteBuffer temp = buf.duplicate();
+      byte[] buffer = new byte[temp.remaining()];
+      temp.get(buffer);
+      return newInstance(buffer);
+    }
+  }
+
+  /**
+   * Create a new CodedInputStream wrapping a LiteralByteString.
+   */
+  static CodedInputStream newInstance(LiteralByteString byteString) {
+    CodedInputStream result = new CodedInputStream(byteString);
+    try {
+      // Some uses of CodedInputStream can be more efficient if they know
+      // exactly how many bytes are available.  By pushing the end point of the
+      // buffer as a limit, we allow them to get this information via
+      // getBytesUntilLimit().  Pushing a limit that we know is at the end of
+      // the stream can never hurt, since we can never past that point anyway.
+      result.pushLimit(byteString.size());
+    } catch (InvalidProtocolBufferException ex) {
+      // The only reason pushLimit() might throw an exception here is if len
+      // is negative. Normally pushLimit()'s parameter comes directly off the
+      // wire, so it's important to catch exceptions in case of corrupt or
+      // malicious data. However, in this case, we expect that len is not a
+      // user-supplied value, so we can assume that it being negative indicates
+      // a programming error. Therefore, throwing an unchecked exception is
+      // appropriate.
+      throw new IllegalArgumentException(ex);
+    }
+    return result;
+  }
+
+  // -----------------------------------------------------------------
+
+  /**
+   * Attempt to read a field tag, returning zero if we have reached EOF.
+   * Protocol message parsers use this to read tags, since a protocol message
+   * may legally end wherever a tag occurs, and zero is not a valid tag number.
+   */
+  public int readTag() throws IOException {
+    if (isAtEnd()) {
+      lastTag = 0;
+      return 0;
+    }
+
+    lastTag = readRawVarint32();
+    if (WireFormat.getTagFieldNumber(lastTag) == 0) {
+      // If we actually read zero (or any tag number corresponding to field
+      // number zero), that's not a valid tag.
+      throw InvalidProtocolBufferException.invalidTag();
+    }
+    return lastTag;
+  }
+
+  /**
+   * Verifies that the last call to readTag() returned the given tag value.
+   * This is used to verify that a nested group ended with the correct
+   * end tag.
+   *
+   * @throws InvalidProtocolBufferException {@code value} does not match the
+   *                                        last tag.
+   */
+  public void checkLastTagWas(final int value)
+                              throws InvalidProtocolBufferException {
+    if (lastTag != value) {
+      throw InvalidProtocolBufferException.invalidEndTag();
+    }
+  }
+
+  public int getLastTag() {
+    return lastTag;
+  }
+
+  /**
+   * Reads and discards a single field, given its tag value.
+   *
+   * @return {@code false} if the tag is an endgroup tag, in which case
+   *         nothing is skipped.  Otherwise, returns {@code true}.
+   */
+  public boolean skipField(final int tag) throws IOException {
+    switch (WireFormat.getTagWireType(tag)) {
+      case WireFormat.WIRETYPE_VARINT:
+        skipRawVarint();
+        return true;
+      case WireFormat.WIRETYPE_FIXED64:
+        skipRawBytes(8);
+        return true;
+      case WireFormat.WIRETYPE_LENGTH_DELIMITED:
+        skipRawBytes(readRawVarint32());
+        return true;
+      case WireFormat.WIRETYPE_START_GROUP:
+        skipMessage();
+        checkLastTagWas(
+          WireFormat.makeTag(WireFormat.getTagFieldNumber(tag),
+                             WireFormat.WIRETYPE_END_GROUP));
+        return true;
+      case WireFormat.WIRETYPE_END_GROUP:
+        return false;
+      case WireFormat.WIRETYPE_FIXED32:
+        skipRawBytes(4);
+        return true;
+      default:
+        throw InvalidProtocolBufferException.invalidWireType();
+    }
+  }
+
+  /**
+   * Reads a single field and writes it to output in wire format,
+   * given its tag value.
+   *
+   * @return {@code false} if the tag is an endgroup tag, in which case
+   *         nothing is skipped.  Otherwise, returns {@code true}.
+   */
+  public boolean skipField(final int tag, final CodedOutputStream output)
+      throws IOException {
+    switch (WireFormat.getTagWireType(tag)) {
+      case WireFormat.WIRETYPE_VARINT: {
+        long value = readInt64();
+        output.writeRawVarint32(tag);
+        output.writeUInt64NoTag(value);
+        return true;
+      }
+      case WireFormat.WIRETYPE_FIXED64: {
+        long value = readRawLittleEndian64();
+        output.writeRawVarint32(tag);
+        output.writeFixed64NoTag(value);
+        return true;
+      }
+      case WireFormat.WIRETYPE_LENGTH_DELIMITED: {
+        ByteString value = readBytes();
+        output.writeRawVarint32(tag);
+        output.writeBytesNoTag(value);
+        return true;
+      }
+      case WireFormat.WIRETYPE_START_GROUP: {
+        output.writeRawVarint32(tag);
+        skipMessage(output);
+        int endtag = WireFormat.makeTag(WireFormat.getTagFieldNumber(tag),
+                                        WireFormat.WIRETYPE_END_GROUP);
+        checkLastTagWas(endtag);
+        output.writeRawVarint32(endtag);
+        return true;
+      }
+      case WireFormat.WIRETYPE_END_GROUP: {
+        return false;
+      }
+      case WireFormat.WIRETYPE_FIXED32: {
+        int value = readRawLittleEndian32();
+        output.writeRawVarint32(tag);
+        output.writeFixed32NoTag(value);
+        return true;
+      }
+      default:
+        throw InvalidProtocolBufferException.invalidWireType();
+    }
+  }
+
+  /**
+   * Reads and discards an entire message.  This will read either until EOF
+   * or until an endgroup tag, whichever comes first.
+   */
+  public void skipMessage() throws IOException {
+    while (true) {
+      final int tag = readTag();
+      if (tag == 0 || !skipField(tag)) {
+        return;
+      }
+    }
+  }
+
+  /**
+   * Reads an entire message and writes it to output in wire format.
+   * This will read either until EOF or until an endgroup tag,
+   * whichever comes first.
+   */
+  public void skipMessage(CodedOutputStream output) throws IOException {
+    while (true) {
+      final int tag = readTag();
+      if (tag == 0 || !skipField(tag, output)) {
+        return;
+      }
+    }
+  }
+
+  /**
+   * Collects the bytes skipped and returns the data in a ByteBuffer.
+   */
+  private class SkippedDataSink implements RefillCallback {
+    private int lastPos = bufferPos;
+    private ByteArrayOutputStream byteArrayStream;
+
+    @Override
+    public void onRefill() {
+      if (byteArrayStream == null) {
+        byteArrayStream = new ByteArrayOutputStream();
+      }
+      byteArrayStream.write(buffer, lastPos, bufferPos - lastPos);
+      lastPos = 0;
+    }
+
+    /**
+     * Gets skipped data in a ByteBuffer. This method should only be
+     * called once.
+     */
+    ByteBuffer getSkippedData() {
+      if (byteArrayStream == null) {
+        return ByteBuffer.wrap(buffer, lastPos, bufferPos - lastPos);
+      } else {
+        byteArrayStream.write(buffer, lastPos, bufferPos);
+        return ByteBuffer.wrap(byteArrayStream.toByteArray());
+      }
+    }
+  }
+
+
+  // -----------------------------------------------------------------
+
+  /** Read a {@code double} field value from the stream. */
+  public double readDouble() throws IOException {
+    return Double.longBitsToDouble(readRawLittleEndian64());
+  }
+
+  /** Read a {@code float} field value from the stream. */
+  public float readFloat() throws IOException {
+    return Float.intBitsToFloat(readRawLittleEndian32());
+  }
+
+  /** Read a {@code uint64} field value from the stream. */
+  public long readUInt64() throws IOException {
+    return readRawVarint64();
+  }
+
+  /** Read an {@code int64} field value from the stream. */
+  public long readInt64() throws IOException {
+    return readRawVarint64();
+  }
+
+  /** Read an {@code int32} field value from the stream. */
+  public int readInt32() throws IOException {
+    return readRawVarint32();
+  }
+
+  /** Read a {@code fixed64} field value from the stream. */
+  public long readFixed64() throws IOException {
+    return readRawLittleEndian64();
+  }
+
+  /** Read a {@code fixed32} field value from the stream. */
+  public int readFixed32() throws IOException {
+    return readRawLittleEndian32();
+  }
+
+  /** Read a {@code bool} field value from the stream. */
+  public boolean readBool() throws IOException {
+    return readRawVarint64() != 0;
+  }
+
+  /**
+   * Read a {@code string} field value from the stream.
+   * If the stream contains malformed UTF-8,
+   * replace the offending bytes with the standard UTF-8 replacement character.
+   */
+  public String readString() throws IOException {
+    final int size = readRawVarint32();
+    if (size <= (bufferSize - bufferPos) && size > 0) {
+      // Fast path:  We already have the bytes in a contiguous buffer, so
+      //   just copy directly from it.
+      final String result = new String(buffer, bufferPos, size, Internal.UTF_8);
+      bufferPos += size;
+      return result;
+    } else if (size == 0) {
+      return "";
+    } else {
+      // Slow path:  Build a byte array first then copy it.
+      return new String(readRawBytesSlowPath(size), Internal.UTF_8);
+    }
+  }
+
+  /**
+   * Read a {@code string} field value from the stream.
+   * If the stream contains malformed UTF-8,
+   * throw exception {@link InvalidProtocolBufferException}.
+   */
+  public String readStringRequireUtf8() throws IOException {
+    final int size = readRawVarint32();
+    final byte[] bytes;
+    int pos = bufferPos;
+    if (size <= (bufferSize - pos) && size > 0) {
+      // Fast path:  We already have the bytes in a contiguous buffer, so
+      //   just copy directly from it.
+      bytes = buffer;
+      bufferPos = pos + size;
+    } else if (size == 0) {
+      return "";
+    } else {
+      // Slow path:  Build a byte array first then copy it.
+      bytes = readRawBytesSlowPath(size);
+      pos = 0;
+    }
+    // TODO(martinrb): We could save a pass by validating while decoding.
+    if (!Utf8.isValidUtf8(bytes, pos, pos + size)) {
+      throw InvalidProtocolBufferException.invalidUtf8();
+    }
+    return new String(bytes, pos, size, Internal.UTF_8);
+  }
+
+  /** Read a {@code group} field value from the stream. */
+  public void readGroup(final int fieldNumber,
+                        final MessageLite.Builder builder,
+                        final ExtensionRegistryLite extensionRegistry)
+      throws IOException {
+    if (recursionDepth >= recursionLimit) {
+      throw InvalidProtocolBufferException.recursionLimitExceeded();
+    }
+    ++recursionDepth;
+    builder.mergeFrom(this, extensionRegistry);
+    checkLastTagWas(
+      WireFormat.makeTag(fieldNumber, WireFormat.WIRETYPE_END_GROUP));
+    --recursionDepth;
+  }
+
+
+  /** Read a {@code group} field value from the stream. */
+  public <T extends MessageLite> T readGroup(
+      final int fieldNumber,
+      final Parser<T> parser,
+      final ExtensionRegistryLite extensionRegistry)
+      throws IOException {
+    if (recursionDepth >= recursionLimit) {
+      throw InvalidProtocolBufferException.recursionLimitExceeded();
+    }
+    ++recursionDepth;
+    T result = parser.parsePartialFrom(this, extensionRegistry);
+    checkLastTagWas(
+      WireFormat.makeTag(fieldNumber, WireFormat.WIRETYPE_END_GROUP));
+    --recursionDepth;
+    return result;
+  }
+
+  /**
+   * Reads a {@code group} field value from the stream and merges it into the
+   * given {@link UnknownFieldSet}.
+   *
+   * @deprecated UnknownFieldSet.Builder now implements MessageLite.Builder, so
+   *             you can just call {@link #readGroup}.
+   */
+  @Deprecated
+  public void readUnknownGroup(final int fieldNumber,
+                               final MessageLite.Builder builder)
+      throws IOException {
+    // We know that UnknownFieldSet will ignore any ExtensionRegistry so it
+    // is safe to pass null here.  (We can't call
+    // ExtensionRegistry.getEmptyRegistry() because that would make this
+    // class depend on ExtensionRegistry, which is not part of the lite
+    // library.)
+    readGroup(fieldNumber, builder, null);
+  }
+
+  /** Read an embedded message field value from the stream. */
+  public void readMessage(final MessageLite.Builder builder,
+                          final ExtensionRegistryLite extensionRegistry)
+      throws IOException {
+    final int length = readRawVarint32();
+    if (recursionDepth >= recursionLimit) {
+      throw InvalidProtocolBufferException.recursionLimitExceeded();
+    }
+    final int oldLimit = pushLimit(length);
+    ++recursionDepth;
+    builder.mergeFrom(this, extensionRegistry);
+    checkLastTagWas(0);
+    --recursionDepth;
+    popLimit(oldLimit);
+  }
+
+
+  /** Read an embedded message field value from the stream. */
+  public <T extends MessageLite> T readMessage(
+      final Parser<T> parser,
+      final ExtensionRegistryLite extensionRegistry)
+      throws IOException {
+    int length = readRawVarint32();
+    if (recursionDepth >= recursionLimit) {
+      throw InvalidProtocolBufferException.recursionLimitExceeded();
+    }
+    final int oldLimit = pushLimit(length);
+    ++recursionDepth;
+    T result = parser.parsePartialFrom(this, extensionRegistry);
+    checkLastTagWas(0);
+    --recursionDepth;
+    popLimit(oldLimit);
+    return result;
+  }
+
+  /** Read a {@code bytes} field value from the stream. */
+  public ByteString readBytes() throws IOException {
+    final int size = readRawVarint32();
+    if (size <= (bufferSize - bufferPos) && size > 0) {
+      // Fast path:  We already have the bytes in a contiguous buffer, so
+      //   just copy directly from it.
+      final ByteString result = bufferIsImmutable && enableAliasing
+          ? new BoundedByteString(buffer, bufferPos, size)
+          : ByteString.copyFrom(buffer, bufferPos, size);
+      bufferPos += size;
+      return result;
+    } else if (size == 0) {
+      return ByteString.EMPTY;
+    } else {
+      // Slow path:  Build a byte array first then copy it.
+      return new LiteralByteString(readRawBytesSlowPath(size));
+    }
+  }
+
+  /** Read a {@code bytes} field value from the stream. */
+  public byte[] readByteArray() throws IOException {
+    final int size = readRawVarint32();
+    if (size <= (bufferSize - bufferPos) && size > 0) {
+      // Fast path: We already have the bytes in a contiguous buffer, so
+      // just copy directly from it.
+      final byte[] result =
+          Arrays.copyOfRange(buffer, bufferPos, bufferPos + size);
+      bufferPos += size;
+      return result;
+    } else {
+      // Slow path: Build a byte array first then copy it.
+      return readRawBytesSlowPath(size);
+    }
+  }
+
+  /** Read a {@code bytes} field value from the stream. */
+  public ByteBuffer readByteBuffer() throws IOException {
+    final int size = readRawVarint32();
+    if (size <= (bufferSize - bufferPos) && size > 0) {
+      // Fast path: We already have the bytes in a contiguous buffer.
+      // When aliasing is enabled, we can return a ByteBuffer pointing directly
+      // into the underlying byte array without copy if the CodedInputStream is
+      // constructed from a byte array. If aliasing is disabled or the input is
+      // from an InputStream or ByteString, we have to make a copy of the bytes.
+      ByteBuffer result = input == null && !bufferIsImmutable && enableAliasing
+          ? ByteBuffer.wrap(buffer, bufferPos, size).slice()
+          : ByteBuffer.wrap(Arrays.copyOfRange(
+              buffer, bufferPos, bufferPos + size));
+      bufferPos += size;
+      return result;
+    } else if (size == 0) {
+      return Internal.EMPTY_BYTE_BUFFER;
+    } else {
+      // Slow path: Build a byte array first then copy it.
+      return ByteBuffer.wrap(readRawBytesSlowPath(size));
+    }
+  }
+
+  /** Read a {@code uint32} field value from the stream. */
+  public int readUInt32() throws IOException {
+    return readRawVarint32();
+  }
+
+  /**
+   * Read an enum field value from the stream.  Caller is responsible
+   * for converting the numeric value to an actual enum.
+   */
+  public int readEnum() throws IOException {
+    return readRawVarint32();
+  }
+
+  /** Read an {@code sfixed32} field value from the stream. */
+  public int readSFixed32() throws IOException {
+    return readRawLittleEndian32();
+  }
+
+  /** Read an {@code sfixed64} field value from the stream. */
+  public long readSFixed64() throws IOException {
+    return readRawLittleEndian64();
+  }
+
+  /** Read an {@code sint32} field value from the stream. */
+  public int readSInt32() throws IOException {
+    return decodeZigZag32(readRawVarint32());
+  }
+
+  /** Read an {@code sint64} field value from the stream. */
+  public long readSInt64() throws IOException {
+    return decodeZigZag64(readRawVarint64());
+  }
+
+  // =================================================================
+
+  /**
+   * Read a raw Varint from the stream.  If larger than 32 bits, discard the
+   * upper bits.
+   */
+  public int readRawVarint32() throws IOException {
+    // See implementation notes for readRawVarint64
+ fastpath: {
+      int pos = bufferPos;
+
+      if (bufferSize == pos) {
+        break fastpath;
+      }
+
+      final byte[] buffer = this.buffer;
+      int x;
+      if ((x = buffer[pos++]) >= 0) {
+        bufferPos = pos;
+        return x;
+      } else if (bufferSize - pos < 9) {
+        break fastpath;
+      } else if ((x ^= (buffer[pos++] << 7)) < 0) {
+        x ^= (~0 << 7);
+      } else if ((x ^= (buffer[pos++] << 14)) >= 0) {
+        x ^= (~0 << 7) ^ (~0 << 14);
+      } else if ((x ^= (buffer[pos++] << 21)) < 0) {
+        x ^= (~0 << 7) ^ (~0 << 14) ^ (~0 << 21);
+      } else {
+        int y = buffer[pos++];
+        x ^= y << 28;
+        x ^= (~0 << 7) ^ (~0 << 14) ^ (~0 << 21) ^ (~0 << 28);
+        if (y < 0 &&
+            buffer[pos++] < 0 &&
+            buffer[pos++] < 0 &&
+            buffer[pos++] < 0 &&
+            buffer[pos++] < 0 &&
+            buffer[pos++] < 0) {
+          break fastpath;  // Will throw malformedVarint()
+        }
+      }
+      bufferPos = pos;
+      return x;
+    }
+    return (int) readRawVarint64SlowPath();
+  }
+
+  private void skipRawVarint() throws IOException {
+    if (bufferSize - bufferPos >= 10) {
+      final byte[] buffer = this.buffer;
+      int pos = bufferPos;
+      for (int i = 0; i < 10; i++) {
+        if (buffer[pos++] >= 0) {
+          bufferPos = pos;
+          return;
+        }
+      }
+    }
+    skipRawVarintSlowPath();
+  }
+
+  private void skipRawVarintSlowPath() throws IOException {
+    for (int i = 0; i < 10; i++) {
+      if (readRawByte() >= 0) {
+        return;
+      }
+    }
+    throw InvalidProtocolBufferException.malformedVarint();
+  }
+
+  /**
+   * Reads a varint from the input one byte at a time, so that it does not
+   * read any bytes after the end of the varint.  If you simply wrapped the
+   * stream in a CodedInputStream and used {@link #readRawVarint32(InputStream)}
+   * then you would probably end up reading past the end of the varint since
+   * CodedInputStream buffers its input.
+   */
+  static int readRawVarint32(final InputStream input) throws IOException {
+    final int firstByte = input.read();
+    if (firstByte == -1) {
+      throw InvalidProtocolBufferException.truncatedMessage();
+    }
+    return readRawVarint32(firstByte, input);
+  }
+
+  /**
+   * Like {@link #readRawVarint32(InputStream)}, but expects that the caller
+   * has already read one byte.  This allows the caller to determine if EOF
+   * has been reached before attempting to read.
+   */
+  public static int readRawVarint32(
+      final int firstByte, final InputStream input) throws IOException {
+    if ((firstByte & 0x80) == 0) {
+      return firstByte;
+    }
+
+    int result = firstByte & 0x7f;
+    int offset = 7;
+    for (; offset < 32; offset += 7) {
+      final int b = input.read();
+      if (b == -1) {
+        throw InvalidProtocolBufferException.truncatedMessage();
+      }
+      result |= (b & 0x7f) << offset;
+      if ((b & 0x80) == 0) {
+        return result;
+      }
+    }
+    // Keep reading up to 64 bits.
+    for (; offset < 64; offset += 7) {
+      final int b = input.read();
+      if (b == -1) {
+        throw InvalidProtocolBufferException.truncatedMessage();
+      }
+      if ((b & 0x80) == 0) {
+        return result;
+      }
+    }
+    throw InvalidProtocolBufferException.malformedVarint();
+  }
+
+  /** Read a raw Varint from the stream. */
+  public long readRawVarint64() throws IOException {
+    // Implementation notes:
+    //
+    // Optimized for one-byte values, expected to be common.
+    // The particular code below was selected from various candidates
+    // empirically, by winning VarintBenchmark.
+    //
+    // Sign extension of (signed) Java bytes is usually a nuisance, but
+    // we exploit it here to more easily obtain the sign of bytes read.
+    // Instead of cleaning up the sign extension bits by masking eagerly,
+    // we delay until we find the final (positive) byte, when we clear all
+    // accumulated bits with one xor.  We depend on javac to constant fold.
+ fastpath: {
+      int pos = bufferPos;
+
+      if (bufferSize == pos) {
+        break fastpath;
+      }
+
+      final byte[] buffer = this.buffer;
+      long x;
+      int y;
+      if ((y = buffer[pos++]) >= 0) {
+        bufferPos = pos;
+        return y;
+      } else if (bufferSize - pos < 9) {
+        break fastpath;
+      } else if ((y ^= (buffer[pos++] << 7)) < 0) {
+        x = y ^ (~0 << 7);
+      } else if ((y ^= (buffer[pos++] << 14)) >= 0) {
+        x = y ^ ((~0 << 7) ^ (~0 << 14));
+      } else if ((y ^= (buffer[pos++] << 21)) < 0) {
+        x = y ^ ((~0 << 7) ^ (~0 << 14) ^ (~0 << 21));
+      } else if ((x = ((long) y) ^ ((long) buffer[pos++] << 28)) >= 0L) {
+        x ^= (~0L << 7) ^ (~0L << 14) ^ (~0L << 21) ^ (~0L << 28);
+      } else if ((x ^= ((long) buffer[pos++] << 35)) < 0L) {
+        x ^= (~0L << 7) ^ (~0L << 14) ^ (~0L << 21) ^ (~0L << 28) ^ (~0L << 35);
+      } else if ((x ^= ((long) buffer[pos++] << 42)) >= 0L) {
+        x ^= (~0L << 7) ^ (~0L << 14) ^ (~0L << 21) ^ (~0L << 28) ^ (~0L << 35) ^ (~0L << 42);
+      } else if ((x ^= ((long) buffer[pos++] << 49)) < 0L) {
+        x ^= (~0L << 7) ^ (~0L << 14) ^ (~0L << 21) ^ (~0L << 28) ^ (~0L << 35) ^ (~0L << 42)
+            ^ (~0L << 49);
+      } else {
+        x ^= ((long) buffer[pos++] << 56);
+        x ^= (~0L << 7) ^ (~0L << 14) ^ (~0L << 21) ^ (~0L << 28) ^ (~0L << 35) ^ (~0L << 42)
+            ^ (~0L << 49) ^ (~0L << 56);
+        if (x < 0L) {
+          if (buffer[pos++] < 0L) {
+            break fastpath;  // Will throw malformedVarint()
+          }
+        }
+      }
+      bufferPos = pos;
+      return x;
+    }
+    return readRawVarint64SlowPath();
+  }
+
+  /** Variant of readRawVarint64 for when uncomfortably close to the limit. */
+  /* Visible for testing */
+  long readRawVarint64SlowPath() throws IOException {
+    long result = 0;
+    for (int shift = 0; shift < 64; shift += 7) {
+      final byte b = readRawByte();
+      result |= (long) (b & 0x7F) << shift;
+      if ((b & 0x80) == 0) {
+        return result;
+      }
+    }
+    throw InvalidProtocolBufferException.malformedVarint();
+  }
+
+  /** Read a 32-bit little-endian integer from the stream. */
+  public int readRawLittleEndian32() throws IOException {
+    int pos = bufferPos;
+
+    // hand-inlined ensureAvailable(4);
+    if (bufferSize - pos < 4) {
+      refillBuffer(4);
+      pos = bufferPos;
+    }
+
+    final byte[] buffer = this.buffer;
+    bufferPos = pos + 4;
+    return (((buffer[pos]     & 0xff))       |
+            ((buffer[pos + 1] & 0xff) <<  8) |
+            ((buffer[pos + 2] & 0xff) << 16) |
+            ((buffer[pos + 3] & 0xff) << 24));
+  }
+
+  /** Read a 64-bit little-endian integer from the stream. */
+  public long readRawLittleEndian64() throws IOException {
+    int pos = bufferPos;
+
+    // hand-inlined ensureAvailable(8);
+    if (bufferSize - pos < 8) {
+      refillBuffer(8);
+      pos = bufferPos;
+    }
+
+    final byte[] buffer = this.buffer;
+    bufferPos = pos + 8;
+    return ((((long) buffer[pos]     & 0xffL))       |
+            (((long) buffer[pos + 1] & 0xffL) <<  8) |
+            (((long) buffer[pos + 2] & 0xffL) << 16) |
+            (((long) buffer[pos + 3] & 0xffL) << 24) |
+            (((long) buffer[pos + 4] & 0xffL) << 32) |
+            (((long) buffer[pos + 5] & 0xffL) << 40) |
+            (((long) buffer[pos + 6] & 0xffL) << 48) |
+            (((long) buffer[pos + 7] & 0xffL) << 56));
+  }
+
+  /**
+   * Decode a ZigZag-encoded 32-bit value.  ZigZag encodes signed integers
+   * into values that can be efficiently encoded with varint.  (Otherwise,
+   * negative values must be sign-extended to 64 bits to be varint encoded,
+   * thus always taking 10 bytes on the wire.)
+   *
+   * @param n An unsigned 32-bit integer, stored in a signed int because
+   *          Java has no explicit unsigned support.
+   * @return A signed 32-bit integer.
+   */
+  public static int decodeZigZag32(final int n) {
+    return (n >>> 1) ^ -(n & 1);
+  }
+
+  /**
+   * Decode a ZigZag-encoded 64-bit value.  ZigZag encodes signed integers
+   * into values that can be efficiently encoded with varint.  (Otherwise,
+   * negative values must be sign-extended to 64 bits to be varint encoded,
+   * thus always taking 10 bytes on the wire.)
+   *
+   * @param n An unsigned 64-bit integer, stored in a signed int because
+   *          Java has no explicit unsigned support.
+   * @return A signed 64-bit integer.
+   */
+  public static long decodeZigZag64(final long n) {
+    return (n >>> 1) ^ -(n & 1);
+  }
+
+  // -----------------------------------------------------------------
+
+  private final byte[] buffer;
+  private final boolean bufferIsImmutable;
+  private int bufferSize;
+  private int bufferSizeAfterLimit;
+  private int bufferPos;
+  private final InputStream input;
+  private int lastTag;
+  private boolean enableAliasing = false;
+
+  /**
+   * The total number of bytes read before the current buffer.  The total
+   * bytes read up to the current position can be computed as
+   * {@code totalBytesRetired + bufferPos}.  This value may be negative if
+   * reading started in the middle of the current buffer (e.g. if the
+   * constructor that takes a byte array and an offset was used).
+   */
+  private int totalBytesRetired;
+
+  /** The absolute position of the end of the current message. */
+  private int currentLimit = Integer.MAX_VALUE;
+
+  /** See setRecursionLimit() */
+  private int recursionDepth;
+  private int recursionLimit = DEFAULT_RECURSION_LIMIT;
+
+  /** See setSizeLimit() */
+  private int sizeLimit = DEFAULT_SIZE_LIMIT;
+
+  private static final int DEFAULT_RECURSION_LIMIT = 100;
+  private static final int DEFAULT_SIZE_LIMIT = 64 << 20;  // 64MB
+  private static final int BUFFER_SIZE = 4096;
+
+  private CodedInputStream(final byte[] buffer, final int off, final int len) {
+    this.buffer = buffer;
+    bufferSize = off + len;
+    bufferPos = off;
+    totalBytesRetired = -off;
+    input = null;
+    bufferIsImmutable = false;
+  }
+
+  private CodedInputStream(final InputStream input) {
+    buffer = new byte[BUFFER_SIZE];
+    bufferSize = 0;
+    bufferPos = 0;
+    totalBytesRetired = 0;
+    this.input = input;
+    bufferIsImmutable = false;
+  }
+
+  private CodedInputStream(final LiteralByteString byteString) {
+    buffer = byteString.bytes;
+    bufferPos = byteString.getOffsetIntoBytes();
+    bufferSize = bufferPos + byteString.size();
+    totalBytesRetired = -bufferPos;
+    input = null;
+    bufferIsImmutable = true;
+  }
+
+  public void enableAliasing(boolean enabled) {
+    this.enableAliasing = enabled;
+  }
+
+  /**
+   * Set the maximum message recursion depth.  In order to prevent malicious
+   * messages from causing stack overflows, {@code CodedInputStream} limits
+   * how deeply messages may be nested.  The default limit is 64.
+   *
+   * @return the old limit.
+   */
+  public int setRecursionLimit(final int limit) {
+    if (limit < 0) {
+      throw new IllegalArgumentException(
+        "Recursion limit cannot be negative: " + limit);
+    }
+    final int oldLimit = recursionLimit;
+    recursionLimit = limit;
+    return oldLimit;
+  }
+
+  /**
+   * Set the maximum message size.  In order to prevent malicious
+   * messages from exhausting memory or causing integer overflows,
+   * {@code CodedInputStream} limits how large a message may be.
+   * The default limit is 64MB.  You should set this limit as small
+   * as you can without harming your app's functionality.  Note that
+   * size limits only apply when reading from an {@code InputStream}, not
+   * when constructed around a raw byte array (nor with
+   * {@link ByteString#newCodedInput}).
+   * <p>
+   * If you want to read several messages from a single CodedInputStream, you
+   * could call {@link #resetSizeCounter()} after each one to avoid hitting the
+   * size limit.
+   *
+   * @return the old limit.
+   */
+  public int setSizeLimit(final int limit) {
+    if (limit < 0) {
+      throw new IllegalArgumentException(
+        "Size limit cannot be negative: " + limit);
+    }
+    final int oldLimit = sizeLimit;
+    sizeLimit = limit;
+    return oldLimit;
+  }
+
+  /**
+   * Resets the current size counter to zero (see {@link #setSizeLimit(int)}).
+   */
+  public void resetSizeCounter() {
+    totalBytesRetired = -bufferPos;
+  }
+
+  /**
+   * Sets {@code currentLimit} to (current position) + {@code byteLimit}.  This
+   * is called when descending into a length-delimited embedded message.
+   *
+   * <p>Note that {@code pushLimit()} does NOT affect how many bytes the
+   * {@code CodedInputStream} reads from an underlying {@code InputStream} when
+   * refreshing its buffer.  If you need to prevent reading past a certain
+   * point in the underlying {@code InputStream} (e.g. because you expect it to
+   * contain more data after the end of the message which you need to handle
+   * differently) then you must place a wrapper around your {@code InputStream}
+   * which limits the amount of data that can be read from it.
+   *
+   * @return the old limit.
+   */
+  public int pushLimit(int byteLimit) throws InvalidProtocolBufferException {
+    if (byteLimit < 0) {
+      throw InvalidProtocolBufferException.negativeSize();
+    }
+    byteLimit += totalBytesRetired + bufferPos;
+    final int oldLimit = currentLimit;
+    if (byteLimit > oldLimit) {
+      throw InvalidProtocolBufferException.truncatedMessage();
+    }
+    currentLimit = byteLimit;
+
+    recomputeBufferSizeAfterLimit();
+
+    return oldLimit;
+  }
+
+  private void recomputeBufferSizeAfterLimit() {
+    bufferSize += bufferSizeAfterLimit;
+    final int bufferEnd = totalBytesRetired + bufferSize;
+    if (bufferEnd > currentLimit) {
+      // Limit is in current buffer.
+      bufferSizeAfterLimit = bufferEnd - currentLimit;
+      bufferSize -= bufferSizeAfterLimit;
+    } else {
+      bufferSizeAfterLimit = 0;
+    }
+  }
+
+  /**
+   * Discards the current limit, returning to the previous limit.
+   *
+   * @param oldLimit The old limit, as returned by {@code pushLimit}.
+   */
+  public void popLimit(final int oldLimit) {
+    currentLimit = oldLimit;
+    recomputeBufferSizeAfterLimit();
+  }
+
+  /**
+   * Returns the number of bytes to be read before the current limit.
+   * If no limit is set, returns -1.
+   */
+  public int getBytesUntilLimit() {
+    if (currentLimit == Integer.MAX_VALUE) {
+      return -1;
+    }
+
+    final int currentAbsolutePosition = totalBytesRetired + bufferPos;
+    return currentLimit - currentAbsolutePosition;
+  }
+
+  /**
+   * Returns true if the stream has reached the end of the input.  This is the
+   * case if either the end of the underlying input source has been reached or
+   * if the stream has reached a limit created using {@link #pushLimit(int)}.
+   */
+  public boolean isAtEnd() throws IOException {
+    return bufferPos == bufferSize && !tryRefillBuffer(1);
+  }
+
+  /**
+   * The total bytes read up to the current position. Calling
+   * {@link #resetSizeCounter()} resets this value to zero.
+   */
+  public int getTotalBytesRead() {
+      return totalBytesRetired + bufferPos;
+  }
+
+  private interface RefillCallback {
+    void onRefill();
+  }
+
+  private RefillCallback refillCallback = null;
+
+  /**
+   * Reads more bytes from the input, making at least {@code n} bytes available
+   * in the buffer.  Caller must ensure that the requested space is not yet
+   * available, and that the requested space is less than BUFFER_SIZE.
+   *
+   * @throws InvalidProtocolBufferException The end of the stream or the current
+   *                                        limit was reached.
+   */
+  private void refillBuffer(int n) throws IOException {
+    if (!tryRefillBuffer(n)) {
+      throw InvalidProtocolBufferException.truncatedMessage();
+    }
+  }
+
+  /**
+   * Tries to read more bytes from the input, making at least {@code n} bytes
+   * available in the buffer.  Caller must ensure that the requested space is
+   * not yet available, and that the requested space is less than BUFFER_SIZE.
+   *
+   * @return {@code true} if the bytes could be made available; {@code false}
+   *         if the end of the stream or the current limit was reached.
+   */
+  private boolean tryRefillBuffer(int n) throws IOException {
+    if (bufferPos + n <= bufferSize) {
+      throw new IllegalStateException(
+          "refillBuffer() called when " + n +
+          " bytes were already available in buffer");
+    }
+
+    if (totalBytesRetired + bufferPos + n > currentLimit) {
+      // Oops, we hit a limit.
+      return false;
+    }
+
+    if (refillCallback != null) {
+      refillCallback.onRefill();
+    }
+
+    if (input != null) {
+      int pos = bufferPos;
+      if (pos > 0) {
+        if (bufferSize > pos) {
+          System.arraycopy(buffer, pos, buffer, 0, bufferSize - pos);
+        }
+        totalBytesRetired += pos;
+        bufferSize -= pos;
+        bufferPos = 0;
+      }
+
+      int bytesRead = input.read(buffer, bufferSize, buffer.length - bufferSize);
+      if (bytesRead == 0 || bytesRead < -1 || bytesRead > buffer.length) {
+        throw new IllegalStateException(
+            "InputStream#read(byte[]) returned invalid result: " + bytesRead +
+            "\nThe InputStream implementation is buggy.");
+      }
+      if (bytesRead > 0) {
+        bufferSize += bytesRead;
+        // Integer-overflow-conscious check against sizeLimit
+        if (totalBytesRetired + n - sizeLimit > 0) {
+          throw InvalidProtocolBufferException.sizeLimitExceeded();
+        }
+        recomputeBufferSizeAfterLimit();
+        return (bufferSize >= n) ? true : tryRefillBuffer(n);
+      }
+    }
+
+    return false;
+  }
+
+  /**
+   * Read one byte from the input.
+   *
+   * @throws InvalidProtocolBufferException The end of the stream or the current
+   *                                        limit was reached.
+   */
+  public byte readRawByte() throws IOException {
+    if (bufferPos == bufferSize) {
+      refillBuffer(1);
+    }
+    return buffer[bufferPos++];
+  }
+
+  /**
+   * Read a fixed size of bytes from the input.
+   *
+   * @throws InvalidProtocolBufferException The end of the stream or the current
+   *                                        limit was reached.
+   */
+  public byte[] readRawBytes(final int size) throws IOException {
+    final int pos = bufferPos;
+    if (size <= (bufferSize - pos) && size > 0) {
+      bufferPos = pos + size;
+      return Arrays.copyOfRange(buffer, pos, pos + size);
+    } else {
+      return readRawBytesSlowPath(size);
+    }
+  }
+
+  /**
+   * Exactly like readRawBytes, but caller must have already checked the fast
+   * path: (size <= (bufferSize - pos) && size > 0)
+   */
+  private byte[] readRawBytesSlowPath(final int size) throws IOException {
+    if (size <= 0) {
+      if (size == 0) {
+        return Internal.EMPTY_BYTE_ARRAY;
+      } else {
+        throw InvalidProtocolBufferException.negativeSize();
+      }
+    }
+
+    // Verify that the message size so far has not exceeded sizeLimit.
+    int currentMessageSize = totalBytesRetired + bufferPos + size;
+    if (currentMessageSize > sizeLimit) {
+      throw InvalidProtocolBufferException.sizeLimitExceeded();
+    }
+
+    // Verify that the message size so far has not exceeded currentLimit.
+    if (currentMessageSize > currentLimit) {
+      // Read to the end of the stream anyway.
+      skipRawBytes(currentLimit - totalBytesRetired - bufferPos);
+      throw InvalidProtocolBufferException.truncatedMessage();
+    }
+
+    // We need the input stream to proceed.
+    if (input == null) {
+      throw InvalidProtocolBufferException.truncatedMessage();
+    }
+
+    final int originalBufferPos = bufferPos;
+    final int bufferedBytes = bufferSize - bufferPos;
+
+    // Mark the current buffer consumed.
+    totalBytesRetired += bufferSize;
+    bufferPos = 0;
+    bufferSize = 0;
+
+    // Determine the number of bytes we need to read from the input stream.
+    int sizeLeft = size - bufferedBytes;
+    // TODO(nathanmittler): Consider using a value larger than BUFFER_SIZE.
+    if (sizeLeft < BUFFER_SIZE || sizeLeft <= input.available()) {
+      // Either the bytes we need are known to be available, or the required buffer is
+      // within an allowed threshold - go ahead and allocate the buffer now.
+      final byte[] bytes = new byte[size];
+
+      // Copy all of the buffered bytes to the result buffer.
+      System.arraycopy(buffer, originalBufferPos, bytes, 0, bufferedBytes);
+
+      // Fill the remaining bytes from the input stream.
+      int pos = bufferedBytes;
+      while (pos < bytes.length) {
+        int n = input.read(bytes, pos, size - pos);
+        if (n == -1) {
+          throw InvalidProtocolBufferException.truncatedMessage();
+        }
+        totalBytesRetired += n;
+        pos += n;
+      }
+
+      return bytes;
+    }
+
+    // The size is very large.  For security reasons, we can't allocate the
+    // entire byte array yet.  The size comes directly from the input, so a
+    // maliciously-crafted message could provide a bogus very large size in
+    // order to trick the app into allocating a lot of memory.  We avoid this
+    // by allocating and reading only a small chunk at a time, so that the
+    // malicious message must actually *be* extremely large to cause
+    // problems.  Meanwhile, we limit the allowed size of a message elsewhere.
+    final List<byte[]> chunks = new ArrayList<byte[]>();
+
+    while (sizeLeft > 0) {
+      // TODO(nathanmittler): Consider using a value larger than BUFFER_SIZE.
+      final byte[] chunk = new byte[Math.min(sizeLeft, BUFFER_SIZE)];
+      int pos = 0;
+      while (pos < chunk.length) {
+        final int n = input.read(chunk, pos, chunk.length - pos);
+        if (n == -1) {
+          throw InvalidProtocolBufferException.truncatedMessage();
+        }
+        totalBytesRetired += n;
+        pos += n;
+      }
+      sizeLeft -= chunk.length;
+      chunks.add(chunk);
+    }
+
+    // OK, got everything.  Now concatenate it all into one buffer.
+    final byte[] bytes = new byte[size];
+
+    // Start by copying the leftover bytes from this.buffer.
+    System.arraycopy(buffer, originalBufferPos, bytes, 0, bufferedBytes);
+
+    // And now all the chunks.
+    int pos = bufferedBytes;
+    for (final byte[] chunk : chunks) {
+      System.arraycopy(chunk, 0, bytes, pos, chunk.length);
+      pos += chunk.length;
+    }
+
+    // Done.
+    return bytes;
+  }
+
+  /**
+   * Reads and discards {@code size} bytes.
+   *
+   * @throws InvalidProtocolBufferException The end of the stream or the current
+   *                                        limit was reached.
+   */
+  public void skipRawBytes(final int size) throws IOException {
+    if (size <= (bufferSize - bufferPos) && size >= 0) {
+      // We have all the bytes we need already.
+      bufferPos += size;
+    } else {
+      skipRawBytesSlowPath(size);
+    }
+  }
+
+  /**
+   * Exactly like skipRawBytes, but caller must have already checked the fast
+   * path: (size <= (bufferSize - pos) && size >= 0)
+   */
+  private void skipRawBytesSlowPath(final int size) throws IOException {
+    if (size < 0) {
+      throw InvalidProtocolBufferException.negativeSize();
+    }
+
+    if (totalBytesRetired + bufferPos + size > currentLimit) {
+      // Read to the end of the stream anyway.
+      skipRawBytes(currentLimit - totalBytesRetired - bufferPos);
+      // Then fail.
+      throw InvalidProtocolBufferException.truncatedMessage();
+    }
+
+    // Skipping more bytes than are in the buffer.  First skip what we have.
+    int pos = bufferSize - bufferPos;
+    bufferPos = bufferSize;
+
+    // Keep refilling the buffer until we get to the point we wanted to skip to.
+    // This has the side effect of ensuring the limits are updated correctly.
+    refillBuffer(1);
+    while (size - pos > bufferSize) {
+      pos += bufferSize;
+      bufferPos = bufferSize;
+      refillBuffer(1);
+    }
+
+    bufferPos = size - pos;
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/CodedOutputStream.java b/java/core/src/main/java/com/google/protobuf/CodedOutputStream.java
new file mode 100644
index 00000000..d8ebad21
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/CodedOutputStream.java
@@ -0,0 +1,1332 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import com.google.protobuf.Utf8.UnpairedSurrogateException;
+
+import java.io.IOException;
+import java.io.OutputStream;
+import java.nio.ByteBuffer;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+
+/**
+ * Encodes and writes protocol message fields.
+ *
+ * <p>This class contains two kinds of methods:  methods that write specific
+ * protocol message constructs and field types (e.g. {@link #writeTag} and
+ * {@link #writeInt32}) and methods that write low-level values (e.g.
+ * {@link #writeRawVarint32} and {@link #writeRawBytes}).  If you are
+ * writing encoded protocol messages, you should use the former methods, but if
+ * you are writing some other format of your own design, use the latter.
+ *
+ * <p>This class is totally unsynchronized.
+ *
+ * @author kneton@google.com Kenton Varda
+ */
+public final class CodedOutputStream {
+
+  private static final Logger logger = Logger.getLogger(CodedOutputStream.class.getName());
+
+  // TODO(dweis): Consider migrating to a ByteBuffer.
+  private final byte[] buffer;
+  private final int limit;
+  private int position;
+  private int totalBytesWritten = 0;
+
+  private final OutputStream output;
+
+  /**
+   * The buffer size used in {@link #newInstance(OutputStream)}.
+   */
+  public static final int DEFAULT_BUFFER_SIZE = 4096;
+
+  /**
+   * Returns the buffer size to efficiently write dataLength bytes to this
+   * CodedOutputStream. Used by AbstractMessageLite.
+   *
+   * @return the buffer size to efficiently write dataLength bytes to this
+   *         CodedOutputStream.
+   */
+  static int computePreferredBufferSize(int dataLength) {
+    if (dataLength > DEFAULT_BUFFER_SIZE) return DEFAULT_BUFFER_SIZE;
+    return dataLength;
+  }
+
+  private CodedOutputStream(final byte[] buffer, final int offset,
+                            final int length) {
+    output = null;
+    this.buffer = buffer;
+    position = offset;
+    limit = offset + length;
+  }
+
+  private CodedOutputStream(final OutputStream output, final byte[] buffer) {
+    this.output = output;
+    this.buffer = buffer;
+    position = 0;
+    limit = buffer.length;
+  }
+
+  /**
+   * Create a new {@code CodedOutputStream} wrapping the given
+   * {@code OutputStream}.
+   */
+  public static CodedOutputStream newInstance(final OutputStream output) {
+    return newInstance(output, DEFAULT_BUFFER_SIZE);
+  }
+
+  /**
+   * Create a new {@code CodedOutputStream} wrapping the given
+   * {@code OutputStream} with a given buffer size.
+   */
+  public static CodedOutputStream newInstance(final OutputStream output,
+      final int bufferSize) {
+    return new CodedOutputStream(output, new byte[bufferSize]);
+  }
+
+  /**
+   * Create a new {@code CodedOutputStream} that writes directly to the given
+   * byte array.  If more bytes are written than fit in the array,
+   * {@link OutOfSpaceException} will be thrown.  Writing directly to a flat
+   * array is faster than writing to an {@code OutputStream}.  See also
+   * {@link ByteString#newCodedBuilder}.
+   */
+  public static CodedOutputStream newInstance(final byte[] flatArray) {
+    return newInstance(flatArray, 0, flatArray.length);
+  }
+
+  /**
+   * Create a new {@code CodedOutputStream} that writes directly to the given
+   * byte array slice.  If more bytes are written than fit in the slice,
+   * {@link OutOfSpaceException} will be thrown.  Writing directly to a flat
+   * array is faster than writing to an {@code OutputStream}.  See also
+   * {@link ByteString#newCodedBuilder}.
+   */
+  public static CodedOutputStream newInstance(final byte[] flatArray,
+                                              final int offset,
+                                              final int length) {
+    return new CodedOutputStream(flatArray, offset, length);
+  }
+
+  /**
+   * Create a new {@code CodedOutputStream} that writes to the given ByteBuffer.
+   */
+  public static CodedOutputStream newInstance(ByteBuffer byteBuffer) {
+    return newInstance(byteBuffer, DEFAULT_BUFFER_SIZE);
+  }
+
+  /**
+   * Create a new {@code CodedOutputStream} that writes to the given ByteBuffer.
+   */
+  public static CodedOutputStream newInstance(ByteBuffer byteBuffer,
+      int bufferSize) {
+    return newInstance(new ByteBufferOutputStream(byteBuffer), bufferSize);
+  }
+
+  private static class ByteBufferOutputStream extends OutputStream {
+    private final ByteBuffer byteBuffer;
+    public ByteBufferOutputStream(ByteBuffer byteBuffer) {
+      this.byteBuffer = byteBuffer;
+    }
+
+    @Override
+    public void write(int b) throws IOException {
+      byteBuffer.put((byte) b);
+    }
+
+    @Override
+    public void write(byte[] data, int offset, int length) throws IOException {
+      byteBuffer.put(data, offset, length);
+    }
+  }
+
+  // -----------------------------------------------------------------
+
+  /** Write a {@code double} field, including tag, to the stream. */
+  public void writeDouble(final int fieldNumber, final double value)
+                          throws IOException {
+    writeTag(fieldNumber, WireFormat.WIRETYPE_FIXED64);
+    writeDoubleNoTag(value);
+  }
+
+  /** Write a {@code float} field, including tag, to the stream. */
+  public void writeFloat(final int fieldNumber, final float value)
+                         throws IOException {
+    writeTag(fieldNumber, WireFormat.WIRETYPE_FIXED32);
+    writeFloatNoTag(value);
+  }
+
+  /** Write a {@code uint64} field, including tag, to the stream. */
+  public void writeUInt64(final int fieldNumber, final long value)
+                          throws IOException {
+    writeTag(fieldNumber, WireFormat.WIRETYPE_VARINT);
+    writeUInt64NoTag(value);
+  }
+
+  /** Write an {@code int64} field, including tag, to the stream. */
+  public void writeInt64(final int fieldNumber, final long value)
+                         throws IOException {
+    writeTag(fieldNumber, WireFormat.WIRETYPE_VARINT);
+    writeInt64NoTag(value);
+  }
+
+  /** Write an {@code int32} field, including tag, to the stream. */
+  public void writeInt32(final int fieldNumber, final int value)
+                         throws IOException {
+    writeTag(fieldNumber, WireFormat.WIRETYPE_VARINT);
+    writeInt32NoTag(value);
+  }
+
+  /** Write a {@code fixed64} field, including tag, to the stream. */
+  public void writeFixed64(final int fieldNumber, final long value)
+                           throws IOException {
+    writeTag(fieldNumber, WireFormat.WIRETYPE_FIXED64);
+    writeFixed64NoTag(value);
+  }
+
+  /** Write a {@code fixed32} field, including tag, to the stream. */
+  public void writeFixed32(final int fieldNumber, final int value)
+                           throws IOException {
+    writeTag(fieldNumber, WireFormat.WIRETYPE_FIXED32);
+    writeFixed32NoTag(value);
+  }
+
+  /** Write a {@code bool} field, including tag, to the stream. */
+  public void writeBool(final int fieldNumber, final boolean value)
+                        throws IOException {
+    writeTag(fieldNumber, WireFormat.WIRETYPE_VARINT);
+    writeBoolNoTag(value);
+  }
+
+  /** Write a {@code string} field, including tag, to the stream. */
+  public void writeString(final int fieldNumber, final String value)
+                          throws IOException {
+    writeTag(fieldNumber, WireFormat.WIRETYPE_LENGTH_DELIMITED);
+    writeStringNoTag(value);
+  }
+
+  /** Write a {@code group} field, including tag, to the stream. */
+  public void writeGroup(final int fieldNumber, final MessageLite value)
+                         throws IOException {
+    writeTag(fieldNumber, WireFormat.WIRETYPE_START_GROUP);
+    writeGroupNoTag(value);
+    writeTag(fieldNumber, WireFormat.WIRETYPE_END_GROUP);
+  }
+
+
+  /** Write an embedded message field, including tag, to the stream. */
+  public void writeMessage(final int fieldNumber, final MessageLite value)
+                           throws IOException {
+    writeTag(fieldNumber, WireFormat.WIRETYPE_LENGTH_DELIMITED);
+    writeMessageNoTag(value);
+  }
+
+
+  /** Write a {@code bytes} field, including tag, to the stream. */
+  public void writeBytes(final int fieldNumber, final ByteString value)
+                         throws IOException {
+    writeTag(fieldNumber, WireFormat.WIRETYPE_LENGTH_DELIMITED);
+    writeBytesNoTag(value);
+  }
+
+  /** Write a {@code bytes} field, including tag, to the stream. */
+  public void writeByteArray(final int fieldNumber, final byte[] value)
+                             throws IOException {
+    writeTag(fieldNumber, WireFormat.WIRETYPE_LENGTH_DELIMITED);
+    writeByteArrayNoTag(value);
+  }
+
+  /** Write a {@code bytes} field, including tag, to the stream. */
+  public void writeByteArray(final int fieldNumber,
+                             final byte[] value,
+                             final int offset,
+                             final int length)
+                             throws IOException {
+    writeTag(fieldNumber, WireFormat.WIRETYPE_LENGTH_DELIMITED);
+    writeByteArrayNoTag(value, offset, length);
+  }
+
+  /**
+   * Write a {@code bytes} field, including tag, to the stream.
+   * This method will write all content of the ByteBuffer regardless of the
+   * current position and limit (i.e., the number of bytes to be written is
+   * value.capacity(), not value.remaining()). Furthermore, this method doesn't
+   * alter the state of the passed-in ByteBuffer. Its position, limit, mark,
+   * etc. will remain unchanged. If you only want to write the remaining bytes
+   * of a ByteBuffer, you can call
+   * {@code writeByteBuffer(fieldNumber, byteBuffer.slice())}.
+   */
+  public void writeByteBuffer(final int fieldNumber, final ByteBuffer value)
+      throws IOException {
+    writeTag(fieldNumber, WireFormat.WIRETYPE_LENGTH_DELIMITED);
+    writeByteBufferNoTag(value);
+  }
+
+  /** Write a {@code uint32} field, including tag, to the stream. */
+  public void writeUInt32(final int fieldNumber, final int value)
+                          throws IOException {
+    writeTag(fieldNumber, WireFormat.WIRETYPE_VARINT);
+    writeUInt32NoTag(value);
+  }
+
+  /**
+   * Write an enum field, including tag, to the stream.  Caller is responsible
+   * for converting the enum value to its numeric value.
+   */
+  public void writeEnum(final int fieldNumber, final int value)
+                        throws IOException {
+    writeTag(fieldNumber, WireFormat.WIRETYPE_VARINT);
+    writeEnumNoTag(value);
+  }
+
+  /** Write an {@code sfixed32} field, including tag, to the stream. */
+  public void writeSFixed32(final int fieldNumber, final int value)
+                            throws IOException {
+    writeTag(fieldNumber, WireFormat.WIRETYPE_FIXED32);
+    writeSFixed32NoTag(value);
+  }
+
+  /** Write an {@code sfixed64} field, including tag, to the stream. */
+  public void writeSFixed64(final int fieldNumber, final long value)
+                            throws IOException {
+    writeTag(fieldNumber, WireFormat.WIRETYPE_FIXED64);
+    writeSFixed64NoTag(value);
+  }
+
+  /** Write an {@code sint32} field, including tag, to the stream. */
+  public void writeSInt32(final int fieldNumber, final int value)
+                          throws IOException {
+    writeTag(fieldNumber, WireFormat.WIRETYPE_VARINT);
+    writeSInt32NoTag(value);
+  }
+
+  /** Write an {@code sint64} field, including tag, to the stream. */
+  public void writeSInt64(final int fieldNumber, final long value)
+                          throws IOException {
+    writeTag(fieldNumber, WireFormat.WIRETYPE_VARINT);
+    writeSInt64NoTag(value);
+  }
+
+  /**
+   * Write a MessageSet extension field to the stream.  For historical reasons,
+   * the wire format differs from normal fields.
+   */
+  public void writeMessageSetExtension(final int fieldNumber,
+                                       final MessageLite value)
+                                       throws IOException {
+    writeTag(WireFormat.MESSAGE_SET_ITEM, WireFormat.WIRETYPE_START_GROUP);
+    writeUInt32(WireFormat.MESSAGE_SET_TYPE_ID, fieldNumber);
+    writeMessage(WireFormat.MESSAGE_SET_MESSAGE, value);
+    writeTag(WireFormat.MESSAGE_SET_ITEM, WireFormat.WIRETYPE_END_GROUP);
+  }
+
+  /**
+   * Write an unparsed MessageSet extension field to the stream.  For
+   * historical reasons, the wire format differs from normal fields.
+   */
+  public void writeRawMessageSetExtension(final int fieldNumber,
+                                          final ByteString value)
+                                          throws IOException {
+    writeTag(WireFormat.MESSAGE_SET_ITEM, WireFormat.WIRETYPE_START_GROUP);
+    writeUInt32(WireFormat.MESSAGE_SET_TYPE_ID, fieldNumber);
+    writeBytes(WireFormat.MESSAGE_SET_MESSAGE, value);
+    writeTag(WireFormat.MESSAGE_SET_ITEM, WireFormat.WIRETYPE_END_GROUP);
+  }
+
+  // -----------------------------------------------------------------
+
+  /** Write a {@code double} field to the stream. */
+  public void writeDoubleNoTag(final double value) throws IOException {
+    writeRawLittleEndian64(Double.doubleToRawLongBits(value));
+  }
+
+  /** Write a {@code float} field to the stream. */
+  public void writeFloatNoTag(final float value) throws IOException {
+    writeRawLittleEndian32(Float.floatToRawIntBits(value));
+  }
+
+  /** Write a {@code uint64} field to the stream. */
+  public void writeUInt64NoTag(final long value) throws IOException {
+    writeRawVarint64(value);
+  }
+
+  /** Write an {@code int64} field to the stream. */
+  public void writeInt64NoTag(final long value) throws IOException {
+    writeRawVarint64(value);
+  }
+
+  /** Write an {@code int32} field to the stream. */
+  public void writeInt32NoTag(final int value) throws IOException {
+    if (value >= 0) {
+      writeRawVarint32(value);
+    } else {
+      // Must sign-extend.
+      writeRawVarint64(value);
+    }
+  }
+
+  /** Write a {@code fixed64} field to the stream. */
+  public void writeFixed64NoTag(final long value) throws IOException {
+    writeRawLittleEndian64(value);
+  }
+
+  /** Write a {@code fixed32} field to the stream. */
+  public void writeFixed32NoTag(final int value) throws IOException {
+    writeRawLittleEndian32(value);
+  }
+
+  /** Write a {@code bool} field to the stream. */
+  public void writeBoolNoTag(final boolean value) throws IOException {
+    writeRawByte(value ? 1 : 0);
+  }
+
+  /** Write a {@code string} field to the stream. */
+  // TODO(dweis): Document behavior on ill-formed UTF-16 input.
+  public void writeStringNoTag(final String value) throws IOException {
+    try {
+      efficientWriteStringNoTag(value);
+    } catch (UnpairedSurrogateException e) {
+      logger.log(Level.WARNING,
+          "Converting ill-formed UTF-16. Your Protocol Buffer will not round trip correctly!", e);
+      inefficientWriteStringNoTag(value);
+    }
+  }
+
+  /** Write a {@code string} field to the stream. */
+  private void inefficientWriteStringNoTag(final String value) throws IOException {
+    // Unfortunately there does not appear to be any way to tell Java to encode
+    // UTF-8 directly into our buffer, so we have to let it create its own byte
+    // array and then copy.
+    // TODO(dweis): Consider using nio Charset methods instead.
+    final byte[] bytes = value.getBytes(Internal.UTF_8);
+    writeRawVarint32(bytes.length);
+    writeRawBytes(bytes);
+  }
+
+  /**
+   * Write a {@code string} field to the stream efficiently. If the {@code string} is malformed,
+   * this method rolls back its changes and throws an {@link UnpairedSurrogateException} with the
+   * intent that the caller will catch and retry with {@link #inefficientWriteStringNoTag(String)}.
+   *
+   * @param value the string to write to the stream
+   *
+   * @throws UnpairedSurrogateException when {@code value} is ill-formed UTF-16.
+   */
+  private void efficientWriteStringNoTag(final String value) throws IOException {
+    // UTF-8 byte length of the string is at least its UTF-16 code unit length (value.length()),
+    // and at most 3 times of it. We take advantage of this in both branches below.
+    final int maxLength = value.length() * Utf8.MAX_BYTES_PER_CHAR;
+    final int maxLengthVarIntSize = computeRawVarint32Size(maxLength);
+
+    // If we are streaming and the potential length is too big to fit in our buffer, we take the
+    // slower path. Otherwise, we're good to try the fast path.
+    if (output != null && maxLengthVarIntSize + maxLength > limit - position) {
+      // Allocate a byte[] that we know can fit the string and encode into it. String.getBytes()
+      // does the same internally and then does *another copy* to return a byte[] of exactly the
+      // right size. We can skip that copy and just writeRawBytes up to the actualLength of the
+      // UTF-8 encoded bytes.
+      final byte[] encodedBytes = new byte[maxLength];
+      int actualLength = Utf8.encode(value, encodedBytes, 0, maxLength);
+      writeRawVarint32(actualLength);
+      writeRawBytes(encodedBytes, 0, actualLength);
+    } else {
+      // Optimize for the case where we know this length results in a constant varint length as this
+      // saves a pass for measuring the length of the string.
+      final int minLengthVarIntSize = computeRawVarint32Size(value.length());
+      int oldPosition = position;
+      final int length;
+      try {
+        if (minLengthVarIntSize == maxLengthVarIntSize) {
+          position = oldPosition + minLengthVarIntSize;
+          int newPosition = Utf8.encode(value, buffer, position, limit - position);
+          // Since this class is stateful and tracks the position, we rewind and store the state,
+          // prepend the length, then reset it back to the end of the string.
+          position = oldPosition;
+          length = newPosition - oldPosition - minLengthVarIntSize;
+          writeRawVarint32(length);
+          position = newPosition;
+        } else {
+          length = Utf8.encodedLength(value);
+          writeRawVarint32(length);
+          position = Utf8.encode(value, buffer, position, limit - position);
+        }
+      } catch (UnpairedSurrogateException e) {
+        // Be extra careful and restore the original position for retrying the write with the less
+        // efficient path.
+        position = oldPosition;
+        throw e;
+      } catch (ArrayIndexOutOfBoundsException e) {
+        throw new OutOfSpaceException(e);
+      }
+      totalBytesWritten += length;
+    }
+  }
+
+  /** Write a {@code group} field to the stream. */
+  public void writeGroupNoTag(final MessageLite value) throws IOException {
+    value.writeTo(this);
+  }
+
+
+  /** Write an embedded message field to the stream. */
+  public void writeMessageNoTag(final MessageLite value) throws IOException {
+    writeRawVarint32(value.getSerializedSize());
+    value.writeTo(this);
+  }
+
+
+  /** Write a {@code bytes} field to the stream. */
+  public void writeBytesNoTag(final ByteString value) throws IOException {
+    writeRawVarint32(value.size());
+    writeRawBytes(value);
+  }
+
+  /** Write a {@code bytes} field to the stream. */
+  public void writeByteArrayNoTag(final byte[] value) throws IOException {
+    writeRawVarint32(value.length);
+    writeRawBytes(value);
+  }
+
+  /** Write a {@code bytes} field to the stream. */
+  public void writeByteArrayNoTag(final byte[] value,
+                                  final int offset,
+                                  final int length) throws IOException {
+    writeRawVarint32(length);
+    writeRawBytes(value, offset, length);
+  }
+
+  /**
+   * Write a {@code bytes} field to the stream.  This method will write all
+   * content of the ByteBuffer regardless of the current position and limit
+   * (i.e., the number of bytes to be written is value.capacity(), not
+   * value.remaining()). Furthermore, this method doesn't alter the state of
+   * the passed-in ByteBuffer. Its position, limit, mark, etc. will remain
+   * unchanged. If you only want to write the remaining bytes of a ByteBuffer,
+   * you can call {@code writeByteBufferNoTag(byteBuffer.slice())}.
+   */
+  public void writeByteBufferNoTag(final ByteBuffer value) throws IOException {
+    writeRawVarint32(value.capacity());
+    writeRawBytes(value);
+  }
+
+  /** Write a {@code uint32} field to the stream. */
+  public void writeUInt32NoTag(final int value) throws IOException {
+    writeRawVarint32(value);
+  }
+
+  /**
+   * Write an enum field to the stream.  Caller is responsible
+   * for converting the enum value to its numeric value.
+   */
+  public void writeEnumNoTag(final int value) throws IOException {
+    writeInt32NoTag(value);
+  }
+
+  /** Write an {@code sfixed32} field to the stream. */
+  public void writeSFixed32NoTag(final int value) throws IOException {
+    writeRawLittleEndian32(value);
+  }
+
+  /** Write an {@code sfixed64} field to the stream. */
+  public void writeSFixed64NoTag(final long value) throws IOException {
+    writeRawLittleEndian64(value);
+  }
+
+  /** Write an {@code sint32} field to the stream. */
+  public void writeSInt32NoTag(final int value) throws IOException {
+    writeRawVarint32(encodeZigZag32(value));
+  }
+
+  /** Write an {@code sint64} field to the stream. */
+  public void writeSInt64NoTag(final long value) throws IOException {
+    writeRawVarint64(encodeZigZag64(value));
+  }
+
+  // =================================================================
+
+  /**
+   * Compute the number of bytes that would be needed to encode a
+   * {@code double} field, including tag.
+   */
+  public static int computeDoubleSize(final int fieldNumber,
+                                      final double value) {
+    return computeTagSize(fieldNumber) + computeDoubleSizeNoTag(value);
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode a
+   * {@code float} field, including tag.
+   */
+  public static int computeFloatSize(final int fieldNumber, final float value) {
+    return computeTagSize(fieldNumber) + computeFloatSizeNoTag(value);
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode a
+   * {@code uint64} field, including tag.
+   */
+  public static int computeUInt64Size(final int fieldNumber, final long value) {
+    return computeTagSize(fieldNumber) + computeUInt64SizeNoTag(value);
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode an
+   * {@code int64} field, including tag.
+   */
+  public static int computeInt64Size(final int fieldNumber, final long value) {
+    return computeTagSize(fieldNumber) + computeInt64SizeNoTag(value);
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode an
+   * {@code int32} field, including tag.
+   */
+  public static int computeInt32Size(final int fieldNumber, final int value) {
+    return computeTagSize(fieldNumber) + computeInt32SizeNoTag(value);
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode a
+   * {@code fixed64} field, including tag.
+   */
+  public static int computeFixed64Size(final int fieldNumber,
+                                       final long value) {
+    return computeTagSize(fieldNumber) + computeFixed64SizeNoTag(value);
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode a
+   * {@code fixed32} field, including tag.
+   */
+  public static int computeFixed32Size(final int fieldNumber,
+                                       final int value) {
+    return computeTagSize(fieldNumber) + computeFixed32SizeNoTag(value);
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode a
+   * {@code bool} field, including tag.
+   */
+  public static int computeBoolSize(final int fieldNumber,
+                                    final boolean value) {
+    return computeTagSize(fieldNumber) + computeBoolSizeNoTag(value);
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode a
+   * {@code string} field, including tag.
+   */
+  public static int computeStringSize(final int fieldNumber,
+                                      final String value) {
+    return computeTagSize(fieldNumber) + computeStringSizeNoTag(value);
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode a
+   * {@code group} field, including tag.
+   */
+  public static int computeGroupSize(final int fieldNumber,
+                                     final MessageLite value) {
+    return computeTagSize(fieldNumber) * 2 + computeGroupSizeNoTag(value);
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode an
+   * embedded message field, including tag.
+   */
+  public static int computeMessageSize(final int fieldNumber,
+                                       final MessageLite value) {
+    return computeTagSize(fieldNumber) + computeMessageSizeNoTag(value);
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode a
+   * {@code bytes} field, including tag.
+   */
+  public static int computeBytesSize(final int fieldNumber,
+                                     final ByteString value) {
+    return computeTagSize(fieldNumber) + computeBytesSizeNoTag(value);
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode a
+   * {@code bytes} field, including tag.
+   */
+  public static int computeByteArraySize(final int fieldNumber,
+                                         final byte[] value) {
+    return computeTagSize(fieldNumber) + computeByteArraySizeNoTag(value);
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode a
+   * {@code bytes} field, including tag.
+   */
+  public static int computeByteBufferSize(final int fieldNumber,
+                                         final ByteBuffer value) {
+    return computeTagSize(fieldNumber) + computeByteBufferSizeNoTag(value);
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode an
+   * embedded message in lazy field, including tag.
+   */
+  public static int computeLazyFieldSize(final int fieldNumber,
+                                         final LazyFieldLite value) {
+    return computeTagSize(fieldNumber) + computeLazyFieldSizeNoTag(value);
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode a
+   * {@code uint32} field, including tag.
+   */
+  public static int computeUInt32Size(final int fieldNumber, final int value) {
+    return computeTagSize(fieldNumber) + computeUInt32SizeNoTag(value);
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode an
+   * enum field, including tag.  Caller is responsible for converting the
+   * enum value to its numeric value.
+   */
+  public static int computeEnumSize(final int fieldNumber, final int value) {
+    return computeTagSize(fieldNumber) + computeEnumSizeNoTag(value);
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode an
+   * {@code sfixed32} field, including tag.
+   */
+  public static int computeSFixed32Size(final int fieldNumber,
+                                        final int value) {
+    return computeTagSize(fieldNumber) + computeSFixed32SizeNoTag(value);
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode an
+   * {@code sfixed64} field, including tag.
+   */
+  public static int computeSFixed64Size(final int fieldNumber,
+                                        final long value) {
+    return computeTagSize(fieldNumber) + computeSFixed64SizeNoTag(value);
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode an
+   * {@code sint32} field, including tag.
+   */
+  public static int computeSInt32Size(final int fieldNumber, final int value) {
+    return computeTagSize(fieldNumber) + computeSInt32SizeNoTag(value);
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode an
+   * {@code sint64} field, including tag.
+   */
+  public static int computeSInt64Size(final int fieldNumber, final long value) {
+    return computeTagSize(fieldNumber) + computeSInt64SizeNoTag(value);
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode a
+   * MessageSet extension to the stream.  For historical reasons,
+   * the wire format differs from normal fields.
+   */
+  public static int computeMessageSetExtensionSize(
+      final int fieldNumber, final MessageLite value) {
+    return computeTagSize(WireFormat.MESSAGE_SET_ITEM) * 2 +
+           computeUInt32Size(WireFormat.MESSAGE_SET_TYPE_ID, fieldNumber) +
+           computeMessageSize(WireFormat.MESSAGE_SET_MESSAGE, value);
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode an
+   * unparsed MessageSet extension field to the stream.  For
+   * historical reasons, the wire format differs from normal fields.
+   */
+  public static int computeRawMessageSetExtensionSize(
+      final int fieldNumber, final ByteString value) {
+    return computeTagSize(WireFormat.MESSAGE_SET_ITEM) * 2 +
+           computeUInt32Size(WireFormat.MESSAGE_SET_TYPE_ID, fieldNumber) +
+           computeBytesSize(WireFormat.MESSAGE_SET_MESSAGE, value);
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode an
+   * lazily parsed MessageSet extension field to the stream.  For
+   * historical reasons, the wire format differs from normal fields.
+   */
+  public static int computeLazyFieldMessageSetExtensionSize(
+      final int fieldNumber, final LazyFieldLite value) {
+    return computeTagSize(WireFormat.MESSAGE_SET_ITEM) * 2 +
+           computeUInt32Size(WireFormat.MESSAGE_SET_TYPE_ID, fieldNumber) +
+           computeLazyFieldSize(WireFormat.MESSAGE_SET_MESSAGE, value);
+  }
+
+  // -----------------------------------------------------------------
+
+  /**
+   * Compute the number of bytes that would be needed to encode a
+   * {@code double} field, including tag.
+   */
+  public static int computeDoubleSizeNoTag(final double value) {
+    return LITTLE_ENDIAN_64_SIZE;
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode a
+   * {@code float} field, including tag.
+   */
+  public static int computeFloatSizeNoTag(final float value) {
+    return LITTLE_ENDIAN_32_SIZE;
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode a
+   * {@code uint64} field, including tag.
+   */
+  public static int computeUInt64SizeNoTag(final long value) {
+    return computeRawVarint64Size(value);
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode an
+   * {@code int64} field, including tag.
+   */
+  public static int computeInt64SizeNoTag(final long value) {
+    return computeRawVarint64Size(value);
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode an
+   * {@code int32} field, including tag.
+   */
+  public static int computeInt32SizeNoTag(final int value) {
+    if (value >= 0) {
+      return computeRawVarint32Size(value);
+    } else {
+      // Must sign-extend.
+      return 10;
+    }
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode a
+   * {@code fixed64} field.
+   */
+  public static int computeFixed64SizeNoTag(final long value) {
+    return LITTLE_ENDIAN_64_SIZE;
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode a
+   * {@code fixed32} field.
+   */
+  public static int computeFixed32SizeNoTag(final int value) {
+    return LITTLE_ENDIAN_32_SIZE;
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode a
+   * {@code bool} field.
+   */
+  public static int computeBoolSizeNoTag(final boolean value) {
+    return 1;
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode a
+   * {@code string} field.
+   */
+  public static int computeStringSizeNoTag(final String value) {
+    int length;
+    try {
+      length = Utf8.encodedLength(value);
+    } catch (UnpairedSurrogateException e) {
+      // TODO(dweis): Consider using nio Charset methods instead.
+      final byte[] bytes = value.getBytes(Internal.UTF_8);
+      length = bytes.length;
+    }
+
+    return computeRawVarint32Size(length) + length;
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode a
+   * {@code group} field.
+   */
+  public static int computeGroupSizeNoTag(final MessageLite value) {
+    return value.getSerializedSize();
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode an embedded
+   * message field.
+   */
+  public static int computeMessageSizeNoTag(final MessageLite value) {
+    final int size = value.getSerializedSize();
+    return computeRawVarint32Size(size) + size;
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode an embedded
+   * message stored in lazy field.
+   */
+  public static int computeLazyFieldSizeNoTag(final LazyFieldLite value) {
+    final int size = value.getSerializedSize();
+    return computeRawVarint32Size(size) + size;
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode a
+   * {@code bytes} field.
+   */
+  public static int computeBytesSizeNoTag(final ByteString value) {
+    return computeRawVarint32Size(value.size()) +
+           value.size();
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode a
+   * {@code bytes} field.
+   */
+  public static int computeByteArraySizeNoTag(final byte[] value) {
+    return computeRawVarint32Size(value.length) + value.length;
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode a
+   * {@code bytes} field.
+   */
+  public static int computeByteBufferSizeNoTag(final ByteBuffer value) {
+    return computeRawVarint32Size(value.capacity()) + value.capacity();
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode a
+   * {@code uint32} field.
+   */
+  public static int computeUInt32SizeNoTag(final int value) {
+    return computeRawVarint32Size(value);
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode an enum field.
+   * Caller is responsible for converting the enum value to its numeric value.
+   */
+  public static int computeEnumSizeNoTag(final int value) {
+    return computeInt32SizeNoTag(value);
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode an
+   * {@code sfixed32} field.
+   */
+  public static int computeSFixed32SizeNoTag(final int value) {
+    return LITTLE_ENDIAN_32_SIZE;
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode an
+   * {@code sfixed64} field.
+   */
+  public static int computeSFixed64SizeNoTag(final long value) {
+    return LITTLE_ENDIAN_64_SIZE;
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode an
+   * {@code sint32} field.
+   */
+  public static int computeSInt32SizeNoTag(final int value) {
+    return computeRawVarint32Size(encodeZigZag32(value));
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode an
+   * {@code sint64} field.
+   */
+  public static int computeSInt64SizeNoTag(final long value) {
+    return computeRawVarint64Size(encodeZigZag64(value));
+  }
+
+  // =================================================================
+
+  /**
+   * Internal helper that writes the current buffer to the output. The
+   * buffer position is reset to its initial value when this returns.
+   */
+  private void refreshBuffer() throws IOException {
+    if (output == null) {
+      // We're writing to a single buffer.
+      throw new OutOfSpaceException();
+    }
+
+    // Since we have an output stream, this is our buffer
+    // and buffer offset == 0
+    output.write(buffer, 0, position);
+    position = 0;
+  }
+
+  /**
+   * Flushes the stream and forces any buffered bytes to be written.  This
+   * does not flush the underlying OutputStream.
+   */
+  public void flush() throws IOException {
+    if (output != null) {
+      refreshBuffer();
+    }
+  }
+
+  /**
+   * If writing to a flat array, return the space left in the array.
+   * Otherwise, throws {@code UnsupportedOperationException}.
+   */
+  public int spaceLeft() {
+    if (output == null) {
+      return limit - position;
+    } else {
+      throw new UnsupportedOperationException(
+        "spaceLeft() can only be called on CodedOutputStreams that are " +
+        "writing to a flat array.");
+    }
+  }
+
+  /**
+   * Verifies that {@link #spaceLeft()} returns zero.  It's common to create
+   * a byte array that is exactly big enough to hold a message, then write to
+   * it with a {@code CodedOutputStream}.  Calling {@code checkNoSpaceLeft()}
+   * after writing verifies that the message was actually as big as expected,
+   * which can help catch bugs.
+   */
+  public void checkNoSpaceLeft() {
+    if (spaceLeft() != 0) {
+      throw new IllegalStateException(
+        "Did not write as much data as expected.");
+    }
+  }
+
+  /**
+   * If you create a CodedOutputStream around a simple flat array, you must
+   * not attempt to write more bytes than the array has space.  Otherwise,
+   * this exception will be thrown.
+   */
+  public static class OutOfSpaceException extends IOException {
+    private static final long serialVersionUID = -6947486886997889499L;
+
+    private static final String MESSAGE =
+        "CodedOutputStream was writing to a flat byte array and ran out of space.";
+
+    OutOfSpaceException() {
+      super(MESSAGE);
+    }
+
+    OutOfSpaceException(Throwable cause) {
+      super(MESSAGE, cause);
+    }
+  }
+
+  /**
+   * Get the total number of bytes successfully written to this stream.  The
+   * returned value is not guaranteed to be accurate if exceptions have been
+   * found in the middle of writing.
+   */
+  public int getTotalBytesWritten() {
+    return totalBytesWritten;
+  }
+
+  /** Write a single byte. */
+  public void writeRawByte(final byte value) throws IOException {
+    if (position == limit) {
+      refreshBuffer();
+    }
+
+    buffer[position++] = value;
+    ++totalBytesWritten;
+  }
+
+  /** Write a single byte, represented by an integer value. */
+  public void writeRawByte(final int value) throws IOException {
+    writeRawByte((byte) value);
+  }
+
+  /** Write a byte string. */
+  public void writeRawBytes(final ByteString value) throws IOException {
+    writeRawBytes(value, 0, value.size());
+  }
+
+  /** Write an array of bytes. */
+  public void writeRawBytes(final byte[] value) throws IOException {
+    writeRawBytes(value, 0, value.length);
+  }
+
+  /**
+   * Write a ByteBuffer. This method will write all content of the ByteBuffer
+   * regardless of the current position and limit (i.e., the number of bytes
+   * to be written is value.capacity(), not value.remaining()). Furthermore,
+   * this method doesn't alter the state of the passed-in ByteBuffer. Its
+   * position, limit, mark, etc. will remain unchanged. If you only want to
+   * write the remaining bytes of a ByteBuffer, you can call
+   * {@code writeRawBytes(byteBuffer.slice())}.
+   */
+  public void writeRawBytes(final ByteBuffer value) throws IOException {
+    if (value.hasArray()) {
+      writeRawBytes(value.array(), value.arrayOffset(), value.capacity());
+    } else {
+      ByteBuffer duplicated = value.duplicate();
+      duplicated.clear();
+      writeRawBytesInternal(duplicated);
+    }
+  }
+
+  /** Write a ByteBuffer that isn't backed by an array. */
+  private void writeRawBytesInternal(final ByteBuffer value)
+      throws IOException {
+    int length = value.remaining();
+    if (limit - position >= length) {
+      // We have room in the current buffer.
+      value.get(buffer, position, length);
+      position += length;
+      totalBytesWritten += length;
+    } else {
+      // Write extends past current buffer.  Fill the rest of this buffer and
+      // flush.
+      final int bytesWritten = limit - position;
+      value.get(buffer, position, bytesWritten);
+      length -= bytesWritten;
+      position = limit;
+      totalBytesWritten += bytesWritten;
+      refreshBuffer();
+
+      // Now deal with the rest.
+      // Since we have an output stream, this is our buffer
+      // and buffer offset == 0
+      while (length > limit) {
+        // Copy data into the buffer before writing it to OutputStream.
+        // TODO(xiaofeng): Introduce ZeroCopyOutputStream to avoid this copy.
+        value.get(buffer, 0, limit);
+        output.write(buffer, 0, limit);
+        length -= limit;
+        totalBytesWritten += limit;
+      }
+      value.get(buffer, 0, length);
+      position = length;
+      totalBytesWritten += length;
+    }
+  }
+
+  /** Write part of an array of bytes. */
+  public void writeRawBytes(final byte[] value, int offset, int length)
+                            throws IOException {
+    if (limit - position >= length) {
+      // We have room in the current buffer.
+      System.arraycopy(value, offset, buffer, position, length);
+      position += length;
+      totalBytesWritten += length;
+    } else {
+      // Write extends past current buffer.  Fill the rest of this buffer and
+      // flush.
+      final int bytesWritten = limit - position;
+      System.arraycopy(value, offset, buffer, position, bytesWritten);
+      offset += bytesWritten;
+      length -= bytesWritten;
+      position = limit;
+      totalBytesWritten += bytesWritten;
+      refreshBuffer();
+
+      // Now deal with the rest.
+      // Since we have an output stream, this is our buffer
+      // and buffer offset == 0
+      if (length <= limit) {
+        // Fits in new buffer.
+        System.arraycopy(value, offset, buffer, 0, length);
+        position = length;
+      } else {
+        // Write is very big.  Let's do it all at once.
+        output.write(value, offset, length);
+      }
+      totalBytesWritten += length;
+    }
+  }
+
+  /** Write part of a byte string. */
+  public void writeRawBytes(final ByteString value, int offset, int length)
+                            throws IOException {
+    if (limit - position >= length) {
+      // We have room in the current buffer.
+      value.copyTo(buffer, offset, position, length);
+      position += length;
+      totalBytesWritten += length;
+    } else {
+      // Write extends past current buffer.  Fill the rest of this buffer and
+      // flush.
+      final int bytesWritten = limit - position;
+      value.copyTo(buffer, offset, position, bytesWritten);
+      offset += bytesWritten;
+      length -= bytesWritten;
+      position = limit;
+      totalBytesWritten += bytesWritten;
+      refreshBuffer();
+
+      // Now deal with the rest.
+      // Since we have an output stream, this is our buffer
+      // and buffer offset == 0
+      if (length <= limit) {
+        // Fits in new buffer.
+        value.copyTo(buffer, offset, 0, length);
+        position = length;
+      } else {
+        value.writeTo(output, offset, length);
+      }
+      totalBytesWritten += length;
+    }
+  }
+
+  /** Encode and write a tag. */
+  public void writeTag(final int fieldNumber, final int wireType)
+                       throws IOException {
+    writeRawVarint32(WireFormat.makeTag(fieldNumber, wireType));
+  }
+
+  /** Compute the number of bytes that would be needed to encode a tag. */
+  public static int computeTagSize(final int fieldNumber) {
+    return computeRawVarint32Size(WireFormat.makeTag(fieldNumber, 0));
+  }
+
+  /**
+   * Encode and write a varint.  {@code value} is treated as
+   * unsigned, so it won't be sign-extended if negative.
+   */
+  public void writeRawVarint32(int value) throws IOException {
+    while (true) {
+      if ((value & ~0x7F) == 0) {
+        writeRawByte(value);
+        return;
+      } else {
+        writeRawByte((value & 0x7F) | 0x80);
+        value >>>= 7;
+      }
+    }
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode a varint.
+   * {@code value} is treated as unsigned, so it won't be sign-extended if
+   * negative.
+   */
+  public static int computeRawVarint32Size(final int value) {
+    if ((value & (~0 <<  7)) == 0) return 1;
+    if ((value & (~0 << 14)) == 0) return 2;
+    if ((value & (~0 << 21)) == 0) return 3;
+    if ((value & (~0 << 28)) == 0) return 4;
+    return 5;
+  }
+
+  /** Encode and write a varint. */
+  public void writeRawVarint64(long value) throws IOException {
+    while (true) {
+      if ((value & ~0x7FL) == 0) {
+        writeRawByte((int)value);
+        return;
+      } else {
+        writeRawByte(((int)value & 0x7F) | 0x80);
+        value >>>= 7;
+      }
+    }
+  }
+
+  /** Compute the number of bytes that would be needed to encode a varint. */
+  public static int computeRawVarint64Size(long value) {
+    // handle two popular special cases up front ...
+    if ((value & (~0L << 7)) == 0L) return 1;
+    if (value < 0L) return 10;
+    // ... leaving us with 8 remaining, which we can divide and conquer
+    int n = 2;
+    if ((value & (~0L << 35)) != 0L) { n += 4; value >>>= 28; }
+    if ((value & (~0L << 21)) != 0L) { n += 2; value >>>= 14; }
+    if ((value & (~0L << 14)) != 0L) { n += 1; }
+    return n;
+  }
+
+  /** Write a little-endian 32-bit integer. */
+  public void writeRawLittleEndian32(final int value) throws IOException {
+    writeRawByte((value      ) & 0xFF);
+    writeRawByte((value >>  8) & 0xFF);
+    writeRawByte((value >> 16) & 0xFF);
+    writeRawByte((value >> 24) & 0xFF);
+  }
+
+  public static final int LITTLE_ENDIAN_32_SIZE = 4;
+
+  /** Write a little-endian 64-bit integer. */
+  public void writeRawLittleEndian64(final long value) throws IOException {
+    writeRawByte((int)(value      ) & 0xFF);
+    writeRawByte((int)(value >>  8) & 0xFF);
+    writeRawByte((int)(value >> 16) & 0xFF);
+    writeRawByte((int)(value >> 24) & 0xFF);
+    writeRawByte((int)(value >> 32) & 0xFF);
+    writeRawByte((int)(value >> 40) & 0xFF);
+    writeRawByte((int)(value >> 48) & 0xFF);
+    writeRawByte((int)(value >> 56) & 0xFF);
+  }
+
+  public static final int LITTLE_ENDIAN_64_SIZE = 8;
+
+  /**
+   * Encode a ZigZag-encoded 32-bit value.  ZigZag encodes signed integers
+   * into values that can be efficiently encoded with varint.  (Otherwise,
+   * negative values must be sign-extended to 64 bits to be varint encoded,
+   * thus always taking 10 bytes on the wire.)
+   *
+   * @param n A signed 32-bit integer.
+   * @return An unsigned 32-bit integer, stored in a signed int because
+   *         Java has no explicit unsigned support.
+   */
+  public static int encodeZigZag32(final int n) {
+    // Note:  the right-shift must be arithmetic
+    return (n << 1) ^ (n >> 31);
+  }
+
+  /**
+   * Encode a ZigZag-encoded 64-bit value.  ZigZag encodes signed integers
+   * into values that can be efficiently encoded with varint.  (Otherwise,
+   * negative values must be sign-extended to 64 bits to be varint encoded,
+   * thus always taking 10 bytes on the wire.)
+   *
+   * @param n A signed 64-bit integer.
+   * @return An unsigned 64-bit integer, stored in a signed int because
+   *         Java has no explicit unsigned support.
+   */
+  public static long encodeZigZag64(final long n) {
+    // Note:  the right-shift must be arithmetic
+    return (n << 1) ^ (n >> 63);
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/Descriptors.java b/java/core/src/main/java/com/google/protobuf/Descriptors.java
new file mode 100644
index 00000000..5e15cfbe
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/Descriptors.java
@@ -0,0 +1,2439 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import com.google.protobuf.DescriptorProtos.*;
+import com.google.protobuf.Descriptors.FileDescriptor.Syntax;
+
+import java.lang.ref.WeakReference;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.WeakHashMap;
+import java.util.logging.Logger;
+
+/**
+ * Contains a collection of classes which describe protocol message types.
+ *
+ * Every message type has a {@link Descriptor}, which lists all
+ * its fields and other information about a type.  You can get a message
+ * type's descriptor by calling {@code MessageType.getDescriptor()}, or
+ * (given a message object of the type) {@code message.getDescriptorForType()}.
+ * Furthermore, each message is associated with a {@link FileDescriptor} for
+ * a relevant {@code .proto} file. You can obtain it by calling
+ * {@code Descriptor.getFile()}. A {@link FileDescriptor} contains descriptors
+ * for all the messages defined in that file, and file descriptors for all the
+ * imported {@code .proto} files.
+ *
+ * Descriptors are built from DescriptorProtos, as defined in
+ * {@code google/protobuf/descriptor.proto}.
+ *
+ * @author kenton@google.com Kenton Varda
+ */
+public final class Descriptors {
+  private static final Logger logger =
+      Logger.getLogger(Descriptors.class.getName());
+  /**
+   * Describes a {@code .proto} file, including everything defined within.
+   * That includes, in particular, descriptors for all the messages and
+   * file descriptors for all other imported {@code .proto} files
+   * (dependencies).
+   */
+  public static final class FileDescriptor extends GenericDescriptor {
+    /** Convert the descriptor to its protocol message representation. */
+    public FileDescriptorProto toProto() { return proto; }
+
+    /** Get the file name. */
+    public String getName() { return proto.getName(); }
+
+    /** Returns this object. */
+    public FileDescriptor getFile() { return this; }
+
+    /** Returns the same as getName(). */
+    public String getFullName() { return proto.getName(); }
+
+    /**
+     * Get the proto package name.  This is the package name given by the
+     * {@code package} statement in the {@code .proto} file, which differs
+     * from the Java package.
+     */
+    public String getPackage() { return proto.getPackage(); }
+
+    /** Get the {@code FileOptions}, defined in {@code descriptor.proto}. */
+    public FileOptions getOptions() { return proto.getOptions(); }
+
+    /** Get a list of top-level message types declared in this file. */
+    public List<Descriptor> getMessageTypes() {
+      return Collections.unmodifiableList(Arrays.asList(messageTypes));
+    }
+
+    /** Get a list of top-level enum types declared in this file. */
+    public List<EnumDescriptor> getEnumTypes() {
+      return Collections.unmodifiableList(Arrays.asList(enumTypes));
+    }
+
+    /** Get a list of top-level services declared in this file. */
+    public List<ServiceDescriptor> getServices() {
+      return Collections.unmodifiableList(Arrays.asList(services));
+    }
+
+    /** Get a list of top-level extensions declared in this file. */
+    public List<FieldDescriptor> getExtensions() {
+      return Collections.unmodifiableList(Arrays.asList(extensions));
+    }
+
+    /** Get a list of this file's dependencies (imports). */
+    public List<FileDescriptor> getDependencies() {
+      return Collections.unmodifiableList(Arrays.asList(dependencies));
+    }
+
+    /** Get a list of this file's public dependencies (public imports). */
+    public List<FileDescriptor> getPublicDependencies() {
+      return Collections.unmodifiableList(Arrays.asList(publicDependencies));
+    }
+
+    /** The syntax of the .proto file. */
+    public enum Syntax {
+      UNKNOWN("unknown"),
+      PROTO2("proto2"),
+      PROTO3("proto3");
+
+      Syntax(String name) {
+        this.name = name;
+      }
+      private final String name;
+    }
+
+    /** Get the syntax of the .proto file. */
+    public Syntax getSyntax() {
+      if (Syntax.PROTO3.name.equals(proto.getSyntax())) {
+        return Syntax.PROTO3;
+      }
+      return Syntax.PROTO2;
+    }
+
+    /**
+     * Find a message type in the file by name.  Does not find nested types.
+     *
+     * @param name The unqualified type name to look for.
+     * @return The message type's descriptor, or {@code null} if not found.
+     */
+    public Descriptor findMessageTypeByName(String name) {
+      // Don't allow looking up nested types.  This will make optimization
+      // easier later.
+      if (name.indexOf('.') != -1) {
+        return null;
+      }
+      if (getPackage().length() > 0) {
+        name = getPackage() + '.' + name;
+      }
+      final GenericDescriptor result = pool.findSymbol(name);
+      if (result != null && result instanceof Descriptor &&
+          result.getFile() == this) {
+        return (Descriptor)result;
+      } else {
+        return null;
+      }
+    }
+
+    /**
+     * Find an enum type in the file by name.  Does not find nested types.
+     *
+     * @param name The unqualified type name to look for.
+     * @return The enum type's descriptor, or {@code null} if not found.
+     */
+    public EnumDescriptor findEnumTypeByName(String name) {
+      // Don't allow looking up nested types.  This will make optimization
+      // easier later.
+      if (name.indexOf('.') != -1) {
+        return null;
+      }
+      if (getPackage().length() > 0) {
+        name = getPackage() + '.' + name;
+      }
+      final GenericDescriptor result = pool.findSymbol(name);
+      if (result != null && result instanceof EnumDescriptor &&
+          result.getFile() == this) {
+        return (EnumDescriptor)result;
+      } else {
+        return null;
+      }
+    }
+
+    /**
+     * Find a service type in the file by name.
+     *
+     * @param name The unqualified type name to look for.
+     * @return The service type's descriptor, or {@code null} if not found.
+     */
+    public ServiceDescriptor findServiceByName(String name) {
+      // Don't allow looking up nested types.  This will make optimization
+      // easier later.
+      if (name.indexOf('.') != -1) {
+        return null;
+      }
+      if (getPackage().length() > 0) {
+        name = getPackage() + '.' + name;
+      }
+      final GenericDescriptor result = pool.findSymbol(name);
+      if (result != null && result instanceof ServiceDescriptor &&
+          result.getFile() == this) {
+        return (ServiceDescriptor)result;
+      } else {
+        return null;
+      }
+    }
+
+    /**
+     * Find an extension in the file by name.  Does not find extensions nested
+     * inside message types.
+     *
+     * @param name The unqualified extension name to look for.
+     * @return The extension's descriptor, or {@code null} if not found.
+     */
+    public FieldDescriptor findExtensionByName(String name) {
+      if (name.indexOf('.') != -1) {
+        return null;
+      }
+      if (getPackage().length() > 0) {
+        name = getPackage() + '.' + name;
+      }
+      final GenericDescriptor result = pool.findSymbol(name);
+      if (result != null && result instanceof FieldDescriptor &&
+          result.getFile() == this) {
+        return (FieldDescriptor)result;
+      } else {
+        return null;
+      }
+    }
+
+    /**
+     * Construct a {@code FileDescriptor}.
+     *
+     * @param proto The protocol message form of the FileDescriptor.
+     * @param dependencies {@code FileDescriptor}s corresponding to all of
+     *                     the file's dependencies.
+     * @throws DescriptorValidationException {@code proto} is not a valid
+     *           descriptor.  This can occur for a number of reasons, e.g.
+     *           because a field has an undefined type or because two messages
+     *           were defined with the same name.
+     */
+    public static FileDescriptor buildFrom(final FileDescriptorProto proto,
+                                           final FileDescriptor[] dependencies)
+                                    throws DescriptorValidationException {
+      return buildFrom(proto, dependencies, false);
+    }
+
+
+    /**
+     * Construct a {@code FileDescriptor}.
+     *
+     * @param proto The protocol message form of the FileDescriptor.
+     * @param dependencies {@code FileDescriptor}s corresponding to all of
+     *                     the file's dependencies.
+     * @param allowUnknownDependencies If true, non-exist dependenncies will be
+     *           ignored and undefined message types will be replaced with a
+     *           placeholder type.
+     * @throws DescriptorValidationException {@code proto} is not a valid
+     *           descriptor.  This can occur for a number of reasons, e.g.
+     *           because a field has an undefined type or because two messages
+     *           were defined with the same name.
+     */
+    private static FileDescriptor buildFrom(
+        final FileDescriptorProto proto, final FileDescriptor[] dependencies,
+        final boolean allowUnknownDependencies)
+        throws DescriptorValidationException {
+      // Building descriptors involves two steps:  translating and linking.
+      // In the translation step (implemented by FileDescriptor's
+      // constructor), we build an object tree mirroring the
+      // FileDescriptorProto's tree and put all of the descriptors into the
+      // DescriptorPool's lookup tables.  In the linking step, we look up all
+      // type references in the DescriptorPool, so that, for example, a
+      // FieldDescriptor for an embedded message contains a pointer directly
+      // to the Descriptor for that message's type.  We also detect undefined
+      // types in the linking step.
+      final DescriptorPool pool = new DescriptorPool(
+          dependencies, allowUnknownDependencies);
+      final FileDescriptor result = new FileDescriptor(
+          proto, dependencies, pool, allowUnknownDependencies);
+      result.crossLink();
+      return result;
+    }
+
+    /**
+     * This method is to be called by generated code only.  It is equivalent
+     * to {@code buildFrom} except that the {@code FileDescriptorProto} is
+     * encoded in protocol buffer wire format.
+     */
+    public static void internalBuildGeneratedFileFrom(
+        final String[] descriptorDataParts,
+        final FileDescriptor[] dependencies,
+        final InternalDescriptorAssigner descriptorAssigner) {
+      // Hack:  We can't embed a raw byte array inside generated Java code
+      //   (at least, not efficiently), but we can embed Strings.  So, the
+      //   protocol compiler embeds the FileDescriptorProto as a giant
+      //   string literal which is passed to this function to construct the
+      //   file's FileDescriptor.  The string literal contains only 8-bit
+      //   characters, each one representing a byte of the FileDescriptorProto's
+      //   serialized form.  So, if we convert it to bytes in ISO-8859-1, we
+      //   should get the original bytes that we want.
+
+      // descriptorData may contain multiple strings in order to get around the
+      // Java 64k string literal limit.
+      StringBuilder descriptorData = new StringBuilder();
+      for (String part : descriptorDataParts) {
+        descriptorData.append(part);
+      }
+
+      final byte[] descriptorBytes;
+      descriptorBytes = descriptorData.toString().getBytes(Internal.ISO_8859_1);
+
+      FileDescriptorProto proto;
+      try {
+        proto = FileDescriptorProto.parseFrom(descriptorBytes);
+      } catch (InvalidProtocolBufferException e) {
+        throw new IllegalArgumentException(
+          "Failed to parse protocol buffer descriptor for generated code.", e);
+      }
+
+      final FileDescriptor result;
+      try {
+        // When building descriptors for generated code, we allow unknown
+        // dependencies by default.
+        result = buildFrom(proto, dependencies, true);
+      } catch (DescriptorValidationException e) {
+        throw new IllegalArgumentException(
+          "Invalid embedded descriptor for \"" + proto.getName() + "\".", e);
+      }
+
+      final ExtensionRegistry registry =
+          descriptorAssigner.assignDescriptors(result);
+
+      if (registry != null) {
+        // We must re-parse the proto using the registry.
+        try {
+          proto = FileDescriptorProto.parseFrom(descriptorBytes, registry);
+        } catch (InvalidProtocolBufferException e) {
+          throw new IllegalArgumentException(
+            "Failed to parse protocol buffer descriptor for generated code.",
+            e);
+        }
+
+        result.setProto(proto);
+      }
+    }
+
+    /**
+     * This method is to be called by generated code only.  It uses Java
+     * reflection to load the dependencies' descriptors.
+     */
+    public static void internalBuildGeneratedFileFrom(
+        final String[] descriptorDataParts,
+        final Class<?> descriptorOuterClass,
+        final String[] dependencies,
+        final String[] dependencyFileNames,
+        final InternalDescriptorAssigner descriptorAssigner) {
+      List<FileDescriptor> descriptors = new ArrayList<FileDescriptor>();
+      for (int i = 0; i < dependencies.length; i++) {
+        try {
+          Class<?> clazz =
+              descriptorOuterClass.getClassLoader().loadClass(dependencies[i]);
+          descriptors.add(
+              (FileDescriptor) clazz.getField("descriptor").get(null));
+        } catch (Exception e) {
+          // We allow unknown dependencies by default. If a dependency cannot
+          // be found we only generate a warning.
+          logger.warning("Descriptors for \"" + dependencyFileNames[i] +
+              "\" can not be found.");
+        }
+      }
+      FileDescriptor[] descriptorArray = new FileDescriptor[descriptors.size()];
+      descriptors.toArray(descriptorArray);
+      internalBuildGeneratedFileFrom(
+          descriptorDataParts, descriptorArray, descriptorAssigner);
+    }
+
+    /**
+     * This method is to be called by generated code only.  It is used to
+     * update the FileDescriptorProto associated with the descriptor by
+     * parsing it again with the given ExtensionRegistry. This is needed to
+     * recognize custom options.
+     */
+    public static void internalUpdateFileDescriptor(
+        final FileDescriptor descriptor,
+        final ExtensionRegistry registry) {
+      ByteString bytes = descriptor.proto.toByteString();
+      FileDescriptorProto proto;
+      try {
+        proto = FileDescriptorProto.parseFrom(bytes, registry);
+      } catch (InvalidProtocolBufferException e) {
+        throw new IllegalArgumentException(
+          "Failed to parse protocol buffer descriptor for generated code.", e);
+      }
+      descriptor.setProto(proto);
+    }
+
+    /**
+     * This class should be used by generated code only.  When calling
+     * {@link FileDescriptor#internalBuildGeneratedFileFrom}, the caller
+     * provides a callback implementing this interface.  The callback is called
+     * after the FileDescriptor has been constructed, in order to assign all
+     * the global variables defined in the generated code which point at parts
+     * of the FileDescriptor.  The callback returns an ExtensionRegistry which
+     * contains any extensions which might be used in the descriptor -- that
+     * is, extensions of the various "Options" messages defined in
+     * descriptor.proto.  The callback may also return null to indicate that
+     * no extensions are used in the descriptor.
+     */
+    public interface InternalDescriptorAssigner {
+      ExtensionRegistry assignDescriptors(FileDescriptor root);
+    }
+
+    private FileDescriptorProto proto;
+    private final Descriptor[] messageTypes;
+    private final EnumDescriptor[] enumTypes;
+    private final ServiceDescriptor[] services;
+    private final FieldDescriptor[] extensions;
+    private final FileDescriptor[] dependencies;
+    private final FileDescriptor[] publicDependencies;
+    private final DescriptorPool pool;
+
+    private FileDescriptor(final FileDescriptorProto proto,
+                           final FileDescriptor[] dependencies,
+                           final DescriptorPool pool,
+                           boolean allowUnknownDependencies)
+                    throws DescriptorValidationException {
+      this.pool = pool;
+      this.proto = proto;
+      this.dependencies = dependencies.clone();
+      HashMap<String, FileDescriptor> nameToFileMap =
+          new HashMap<String, FileDescriptor>();
+      for (FileDescriptor file : dependencies) {
+        nameToFileMap.put(file.getName(), file);
+      }
+      List<FileDescriptor> publicDependencies = new ArrayList<FileDescriptor>();
+      for (int i = 0; i < proto.getPublicDependencyCount(); i++) {
+        int index = proto.getPublicDependency(i);
+        if (index < 0 || index >= proto.getDependencyCount()) {
+          throw new DescriptorValidationException(this,
+              "Invalid public dependency index.");
+        }
+        String name = proto.getDependency(index);
+        FileDescriptor file = nameToFileMap.get(name);
+        if (file == null) {
+          if (!allowUnknownDependencies) {
+            throw new DescriptorValidationException(this,
+                "Invalid public dependency: " + name);
+          }
+          // Ignore unknown dependencies.
+        } else {
+          publicDependencies.add(file);
+        }
+      }
+      this.publicDependencies = new FileDescriptor[publicDependencies.size()];
+      publicDependencies.toArray(this.publicDependencies);
+
+      pool.addPackage(getPackage(), this);
+
+      messageTypes = new Descriptor[proto.getMessageTypeCount()];
+      for (int i = 0; i < proto.getMessageTypeCount(); i++) {
+        messageTypes[i] =
+          new Descriptor(proto.getMessageType(i), this, null, i);
+      }
+
+      enumTypes = new EnumDescriptor[proto.getEnumTypeCount()];
+      for (int i = 0; i < proto.getEnumTypeCount(); i++) {
+        enumTypes[i] = new EnumDescriptor(proto.getEnumType(i), this, null, i);
+      }
+
+      services = new ServiceDescriptor[proto.getServiceCount()];
+      for (int i = 0; i < proto.getServiceCount(); i++) {
+        services[i] = new ServiceDescriptor(proto.getService(i), this, i);
+      }
+
+      extensions = new FieldDescriptor[proto.getExtensionCount()];
+      for (int i = 0; i < proto.getExtensionCount(); i++) {
+        extensions[i] = new FieldDescriptor(
+          proto.getExtension(i), this, null, i, true);
+      }
+    }
+
+    /**
+     * Create a placeholder FileDescriptor for a message Descriptor.
+     */
+    FileDescriptor(String packageName, Descriptor message)
+        throws DescriptorValidationException {
+      this.pool = new DescriptorPool(new FileDescriptor[0], true);
+      this.proto = FileDescriptorProto.newBuilder()
+          .setName(message.getFullName() + ".placeholder.proto")
+          .setPackage(packageName).addMessageType(message.toProto()).build();
+      this.dependencies = new FileDescriptor[0];
+      this.publicDependencies = new FileDescriptor[0];
+
+      messageTypes = new Descriptor[] {message};
+      enumTypes = new EnumDescriptor[0];
+      services = new ServiceDescriptor[0];
+      extensions = new FieldDescriptor[0];
+
+      pool.addPackage(packageName, this);
+      pool.addSymbol(message);
+    }
+
+    /** Look up and cross-link all field types, etc. */
+    private void crossLink() throws DescriptorValidationException {
+      for (final Descriptor messageType : messageTypes) {
+        messageType.crossLink();
+      }
+
+      for (final ServiceDescriptor service : services) {
+        service.crossLink();
+      }
+
+      for (final FieldDescriptor extension : extensions) {
+        extension.crossLink();
+      }
+    }
+
+    /**
+     * Replace our {@link FileDescriptorProto} with the given one, which is
+     * identical except that it might contain extensions that weren't present
+     * in the original.  This method is needed for bootstrapping when a file
+     * defines custom options.  The options may be defined in the file itself,
+     * so we can't actually parse them until we've constructed the descriptors,
+     * but to construct the descriptors we have to have parsed the descriptor
+     * protos.  So, we have to parse the descriptor protos a second time after
+     * constructing the descriptors.
+     */
+    private void setProto(final FileDescriptorProto proto) {
+      this.proto = proto;
+
+      for (int i = 0; i < messageTypes.length; i++) {
+        messageTypes[i].setProto(proto.getMessageType(i));
+      }
+
+      for (int i = 0; i < enumTypes.length; i++) {
+        enumTypes[i].setProto(proto.getEnumType(i));
+      }
+
+      for (int i = 0; i < services.length; i++) {
+        services[i].setProto(proto.getService(i));
+      }
+
+      for (int i = 0; i < extensions.length; i++) {
+        extensions[i].setProto(proto.getExtension(i));
+      }
+    }
+
+    boolean supportsUnknownEnumValue() {
+      return getSyntax() == Syntax.PROTO3;
+    }
+  }
+
+  // =================================================================
+
+  /** Describes a message type. */
+  public static final class Descriptor extends GenericDescriptor {
+    /**
+     * Get the index of this descriptor within its parent.  In other words,
+     * given a {@link FileDescriptor} {@code file}, the following is true:
+     * <pre>
+     *   for all i in [0, file.getMessageTypeCount()):
+     *     file.getMessageType(i).getIndex() == i
+     * </pre>
+     * Similarly, for a {@link Descriptor} {@code messageType}:
+     * <pre>
+     *   for all i in [0, messageType.getNestedTypeCount()):
+     *     messageType.getNestedType(i).getIndex() == i
+     * </pre>
+     */
+    public int getIndex() { return index; }
+
+    /** Convert the descriptor to its protocol message representation. */
+    public DescriptorProto toProto() { return proto; }
+
+    /** Get the type's unqualified name. */
+    public String getName() { return proto.getName(); }
+
+    /**
+     * Get the type's fully-qualified name, within the proto language's
+     * namespace.  This differs from the Java name.  For example, given this
+     * {@code .proto}:
+     * <pre>
+     *   package foo.bar;
+     *   option java_package = "com.example.protos"
+     *   message Baz {}
+     * </pre>
+     * {@code Baz}'s full name is "foo.bar.Baz".
+     */
+    public String getFullName() { return fullName; }
+
+    /** Get the {@link FileDescriptor} containing this descriptor. */
+    public FileDescriptor getFile() { return file; }
+
+    /** If this is a nested type, get the outer descriptor, otherwise null. */
+    public Descriptor getContainingType() { return containingType; }
+
+    /** Get the {@code MessageOptions}, defined in {@code descriptor.proto}. */
+    public MessageOptions getOptions() { return proto.getOptions(); }
+
+    /** Get a list of this message type's fields. */
+    public List<FieldDescriptor> getFields() {
+      return Collections.unmodifiableList(Arrays.asList(fields));
+    }
+
+    /** Get a list of this message type's oneofs. */
+    public List<OneofDescriptor> getOneofs() {
+      return Collections.unmodifiableList(Arrays.asList(oneofs));
+    }
+
+    /** Get a list of this message type's extensions. */
+    public List<FieldDescriptor> getExtensions() {
+      return Collections.unmodifiableList(Arrays.asList(extensions));
+    }
+
+    /** Get a list of message types nested within this one. */
+    public List<Descriptor> getNestedTypes() {
+      return Collections.unmodifiableList(Arrays.asList(nestedTypes));
+    }
+
+    /** Get a list of enum types nested within this one. */
+    public List<EnumDescriptor> getEnumTypes() {
+      return Collections.unmodifiableList(Arrays.asList(enumTypes));
+    }
+
+    /** Determines if the given field number is an extension. */
+    public boolean isExtensionNumber(final int number) {
+      for (final DescriptorProto.ExtensionRange range :
+          proto.getExtensionRangeList()) {
+        if (range.getStart() <= number && number < range.getEnd()) {
+          return true;
+        }
+      }
+      return false;
+    }
+
+    /** Determines if the given field number is reserved. */
+    public boolean isReservedNumber(final int number) {
+      for (final DescriptorProto.ReservedRange range :
+          proto.getReservedRangeList()) {
+        if (range.getStart() <= number && number < range.getEnd()) {
+          return true;
+        }
+      }
+      return false;
+    }
+
+    /** Determines if the given field name is reserved. */
+    public boolean isReservedName(final String name) {
+      if (name == null) {
+        throw new NullPointerException();
+      }
+      for (final String reservedName : proto.getReservedNameList()) {
+        if (reservedName.equals(name)) {
+          return true;
+        }
+      }
+      return false;
+    }
+
+    /**
+     * Indicates whether the message can be extended.  That is, whether it has
+     * any "extensions x to y" ranges declared on it.
+     */
+    public boolean isExtendable() {
+      return proto.getExtensionRangeList().size() != 0;
+    }
+
+    /**
+     * Finds a field by name.
+     * @param name The unqualified name of the field (e.g. "foo").
+     * @return The field's descriptor, or {@code null} if not found.
+     */
+    public FieldDescriptor findFieldByName(final String name) {
+      final GenericDescriptor result =
+          file.pool.findSymbol(fullName + '.' + name);
+      if (result != null && result instanceof FieldDescriptor) {
+        return (FieldDescriptor)result;
+      } else {
+        return null;
+      }
+    }
+
+    /**
+     * Finds a field by field number.
+     * @param number The field number within this message type.
+     * @return The field's descriptor, or {@code null} if not found.
+     */
+    public FieldDescriptor findFieldByNumber(final int number) {
+      return file.pool.fieldsByNumber.get(
+        new DescriptorPool.DescriptorIntPair(this, number));
+    }
+
+    /**
+     * Finds a nested message type by name.
+     * @param name The unqualified name of the nested type (e.g. "Foo").
+     * @return The types's descriptor, or {@code null} if not found.
+     */
+    public Descriptor findNestedTypeByName(final String name) {
+      final GenericDescriptor result =
+          file.pool.findSymbol(fullName + '.' + name);
+      if (result != null && result instanceof Descriptor) {
+        return (Descriptor)result;
+      } else {
+        return null;
+      }
+    }
+
+    /**
+     * Finds a nested enum type by name.
+     * @param name The unqualified name of the nested type (e.g. "Foo").
+     * @return The types's descriptor, or {@code null} if not found.
+     */
+    public EnumDescriptor findEnumTypeByName(final String name) {
+      final GenericDescriptor result =
+          file.pool.findSymbol(fullName + '.' + name);
+      if (result != null && result instanceof EnumDescriptor) {
+        return (EnumDescriptor)result;
+      } else {
+        return null;
+      }
+    }
+
+    private final int index;
+    private DescriptorProto proto;
+    private final String fullName;
+    private final FileDescriptor file;
+    private final Descriptor containingType;
+    private final Descriptor[] nestedTypes;
+    private final EnumDescriptor[] enumTypes;
+    private final FieldDescriptor[] fields;
+    private final FieldDescriptor[] extensions;
+    private final OneofDescriptor[] oneofs;
+
+    // Used to create a placeholder when the type cannot be found.
+    Descriptor(final String fullname) throws DescriptorValidationException {
+      String name = fullname;
+      String packageName = "";
+      int pos = fullname.lastIndexOf('.');
+      if (pos != -1) {
+        name = fullname.substring(pos + 1);
+        packageName = fullname.substring(0, pos);
+      }
+      this.index = 0;
+      this.proto = DescriptorProto.newBuilder().setName(name).addExtensionRange(
+          DescriptorProto.ExtensionRange.newBuilder().setStart(1)
+          .setEnd(536870912).build()).build();
+      this.fullName = fullname;
+      this.containingType = null;
+
+      this.nestedTypes = new Descriptor[0];
+      this.enumTypes = new EnumDescriptor[0];
+      this.fields = new FieldDescriptor[0];
+      this.extensions = new FieldDescriptor[0];
+      this.oneofs = new OneofDescriptor[0];
+
+      // Create a placeholder FileDescriptor to hold this message.
+      this.file = new FileDescriptor(packageName, this);
+    }
+
+    private Descriptor(final DescriptorProto proto,
+                       final FileDescriptor file,
+                       final Descriptor parent,
+                       final int index)
+                throws DescriptorValidationException {
+      this.index = index;
+      this.proto = proto;
+      fullName = computeFullName(file, parent, proto.getName());
+      this.file = file;
+      containingType = parent;
+
+      oneofs = new OneofDescriptor[proto.getOneofDeclCount()];
+      for (int i = 0; i < proto.getOneofDeclCount(); i++) {
+        oneofs[i] = new OneofDescriptor(
+          proto.getOneofDecl(i), file, this, i);
+      }
+
+      nestedTypes = new Descriptor[proto.getNestedTypeCount()];
+      for (int i = 0; i < proto.getNestedTypeCount(); i++) {
+        nestedTypes[i] = new Descriptor(
+          proto.getNestedType(i), file, this, i);
+      }
+
+      enumTypes = new EnumDescriptor[proto.getEnumTypeCount()];
+      for (int i = 0; i < proto.getEnumTypeCount(); i++) {
+        enumTypes[i] = new EnumDescriptor(
+          proto.getEnumType(i), file, this, i);
+      }
+
+      fields = new FieldDescriptor[proto.getFieldCount()];
+      for (int i = 0; i < proto.getFieldCount(); i++) {
+        fields[i] = new FieldDescriptor(
+          proto.getField(i), file, this, i, false);
+      }
+
+      extensions = new FieldDescriptor[proto.getExtensionCount()];
+      for (int i = 0; i < proto.getExtensionCount(); i++) {
+        extensions[i] = new FieldDescriptor(
+          proto.getExtension(i), file, this, i, true);
+      }
+
+      for (int i = 0; i < proto.getOneofDeclCount(); i++) {
+        oneofs[i].fields = new FieldDescriptor[oneofs[i].getFieldCount()];
+        oneofs[i].fieldCount = 0;
+      }
+      for (int i = 0; i < proto.getFieldCount(); i++) {
+        OneofDescriptor oneofDescriptor = fields[i].getContainingOneof();
+        if (oneofDescriptor != null) {
+          oneofDescriptor.fields[oneofDescriptor.fieldCount++] = fields[i];
+        }
+      }
+
+      file.pool.addSymbol(this);
+    }
+
+    /** Look up and cross-link all field types, etc. */
+    private void crossLink() throws DescriptorValidationException {
+      for (final Descriptor nestedType : nestedTypes) {
+        nestedType.crossLink();
+      }
+
+      for (final FieldDescriptor field : fields) {
+        field.crossLink();
+      }
+
+      for (final FieldDescriptor extension : extensions) {
+        extension.crossLink();
+      }
+    }
+
+    /** See {@link FileDescriptor#setProto}. */
+    private void setProto(final DescriptorProto proto) {
+      this.proto = proto;
+
+      for (int i = 0; i < nestedTypes.length; i++) {
+        nestedTypes[i].setProto(proto.getNestedType(i));
+      }
+
+      for (int i = 0; i < enumTypes.length; i++) {
+        enumTypes[i].setProto(proto.getEnumType(i));
+      }
+
+      for (int i = 0; i < fields.length; i++) {
+        fields[i].setProto(proto.getField(i));
+      }
+
+      for (int i = 0; i < extensions.length; i++) {
+        extensions[i].setProto(proto.getExtension(i));
+      }
+    }
+  }
+
+  // =================================================================
+
+  /** Describes a field of a message type. */
+  public static final class FieldDescriptor
+        extends GenericDescriptor
+        implements Comparable<FieldDescriptor>,
+                 FieldSet.FieldDescriptorLite<FieldDescriptor> {
+    /**
+     * Get the index of this descriptor within its parent.
+     * @see Descriptors.Descriptor#getIndex()
+     */
+    public int getIndex() { return index; }
+
+    /** Convert the descriptor to its protocol message representation. */
+    public FieldDescriptorProto toProto() { return proto; }
+
+    /** Get the field's unqualified name. */
+    public String getName() { return proto.getName(); }
+
+    /** Get the field's number. */
+    public int getNumber() { return proto.getNumber(); }
+
+    /**
+     * Get the field's fully-qualified name.
+     * @see Descriptors.Descriptor#getFullName()
+     */
+    public String getFullName() { return fullName; }
+
+    /** Get the JSON name of this field. */
+    public String getJsonName() {
+      return jsonName;
+    }
+
+    /**
+     * Get the field's java type.  This is just for convenience.  Every
+     * {@code FieldDescriptorProto.Type} maps to exactly one Java type.
+     */
+    public JavaType getJavaType() { return type.getJavaType(); }
+
+    /** For internal use only. */
+    public WireFormat.JavaType getLiteJavaType() {
+      return getLiteType().getJavaType();
+    }
+
+    /** Get the {@code FileDescriptor} containing this descriptor. */
+    public FileDescriptor getFile() { return file; }
+
+    /** Get the field's declared type. */
+    public Type getType() { return type; }
+
+    /** For internal use only. */
+    public WireFormat.FieldType getLiteType() {
+      return table[type.ordinal()];
+    }
+
+    /** For internal use only. */
+    public boolean needsUtf8Check() {
+      if (type != Type.STRING) {
+        return false;
+      }
+      if (getContainingType().getOptions().getMapEntry()) {
+        // Always enforce strict UTF-8 checking for map fields.
+        return true;
+      }
+      if (getFile().getSyntax() == Syntax.PROTO3) {
+        return true;
+      }
+      return getFile().getOptions().getJavaStringCheckUtf8();
+    }
+
+    public boolean isMapField() {
+      return getType() == Type.MESSAGE && isRepeated()
+          && getMessageType().getOptions().getMapEntry();
+    }
+
+    // I'm pretty sure values() constructs a new array every time, since there
+    // is nothing stopping the caller from mutating the array.  Therefore we
+    // make a static copy here.
+    private static final WireFormat.FieldType[] table =
+        WireFormat.FieldType.values();
+
+    /** Is this field declared required? */
+    public boolean isRequired() {
+      return proto.getLabel() == FieldDescriptorProto.Label.LABEL_REQUIRED;
+    }
+
+    /** Is this field declared optional? */
+    public boolean isOptional() {
+      return proto.getLabel() == FieldDescriptorProto.Label.LABEL_OPTIONAL;
+    }
+
+    /** Is this field declared repeated? */
+    public boolean isRepeated() {
+      return proto.getLabel() == FieldDescriptorProto.Label.LABEL_REPEATED;
+    }
+
+    /** Does this field have the {@code [packed = true]} option or is this field
+     *  packable in proto3 and not explicitly setted to unpacked?
+     */
+    public boolean isPacked() {
+      if (!isPackable()) {
+        return false;
+      }
+      if (getFile().getSyntax() == FileDescriptor.Syntax.PROTO2) {
+        return getOptions().getPacked();
+      } else {
+        return !getOptions().hasPacked() || getOptions().getPacked();
+      }
+    }
+
+    /** Can this field be packed? i.e. is it a repeated primitive field? */
+    public boolean isPackable() {
+      return isRepeated() && getLiteType().isPackable();
+    }
+
+    /** Returns true if the field had an explicitly-defined default value. */
+    public boolean hasDefaultValue() { return proto.hasDefaultValue(); }
+
+    /**
+     * Returns the field's default value.  Valid for all types except for
+     * messages and groups.  For all other types, the object returned is of
+     * the same class that would returned by Message.getField(this).
+     */
+    public Object getDefaultValue() {
+      if (getJavaType() == JavaType.MESSAGE) {
+        throw new UnsupportedOperationException(
+          "FieldDescriptor.getDefaultValue() called on an embedded message " +
+          "field.");
+      }
+      return defaultValue;
+    }
+
+    /** Get the {@code FieldOptions}, defined in {@code descriptor.proto}. */
+    public FieldOptions getOptions() { return proto.getOptions(); }
+
+    /** Is this field an extension? */
+    public boolean isExtension() { return proto.hasExtendee(); }
+
+    /**
+     * Get the field's containing type. For extensions, this is the type being
+     * extended, not the location where the extension was defined.  See
+     * {@link #getExtensionScope()}.
+     */
+    public Descriptor getContainingType() { return containingType; }
+
+    /** Get the field's containing oneof. */
+    public OneofDescriptor getContainingOneof() { return containingOneof; }
+
+    /**
+     * For extensions defined nested within message types, gets the outer
+     * type.  Not valid for non-extension fields.  For example, consider
+     * this {@code .proto} file:
+     * <pre>
+     *   message Foo {
+     *     extensions 1000 to max;
+     *   }
+     *   extend Foo {
+     *     optional int32 baz = 1234;
+     *   }
+     *   message Bar {
+     *     extend Foo {
+     *       optional int32 qux = 4321;
+     *     }
+     *   }
+     * </pre>
+     * Both {@code baz}'s and {@code qux}'s containing type is {@code Foo}.
+     * However, {@code baz}'s extension scope is {@code null} while
+     * {@code qux}'s extension scope is {@code Bar}.
+     */
+    public Descriptor getExtensionScope() {
+      if (!isExtension()) {
+        throw new UnsupportedOperationException(
+          "This field is not an extension.");
+      }
+      return extensionScope;
+    }
+
+    /** For embedded message and group fields, gets the field's type. */
+    public Descriptor getMessageType() {
+      if (getJavaType() != JavaType.MESSAGE) {
+        throw new UnsupportedOperationException(
+          "This field is not of message type.");
+      }
+      return messageType;
+    }
+
+    /** For enum fields, gets the field's type. */
+    public EnumDescriptor getEnumType() {
+      if (getJavaType() != JavaType.ENUM) {
+        throw new UnsupportedOperationException(
+          "This field is not of enum type.");
+      }
+      return enumType;
+    }
+
+    /**
+     * Compare with another {@code FieldDescriptor}.  This orders fields in
+     * "canonical" order, which simply means ascending order by field number.
+     * {@code other} must be a field of the same type -- i.e.
+     * {@code getContainingType()} must return the same {@code Descriptor} for
+     * both fields.
+     *
+     * @return negative, zero, or positive if {@code this} is less than,
+     *         equal to, or greater than {@code other}, respectively.
+     */
+    public int compareTo(final FieldDescriptor other) {
+      if (other.containingType != containingType) {
+        throw new IllegalArgumentException(
+          "FieldDescriptors can only be compared to other FieldDescriptors " +
+          "for fields of the same message type.");
+      }
+      return getNumber() - other.getNumber();
+    }
+
+    @Override
+    public String toString() {
+      return getFullName();
+    }
+
+    private final int index;
+
+    private FieldDescriptorProto proto;
+    private final String fullName;
+    private final String jsonName;
+    private final FileDescriptor file;
+    private final Descriptor extensionScope;
+
+    // Possibly initialized during cross-linking.
+    private Type type;
+    private Descriptor containingType;
+    private Descriptor messageType;
+    private OneofDescriptor containingOneof;
+    private EnumDescriptor enumType;
+    private Object defaultValue;
+
+    public enum Type {
+      DOUBLE  (JavaType.DOUBLE     ),
+      FLOAT   (JavaType.FLOAT      ),
+      INT64   (JavaType.LONG       ),
+      UINT64  (JavaType.LONG       ),
+      INT32   (JavaType.INT        ),
+      FIXED64 (JavaType.LONG       ),
+      FIXED32 (JavaType.INT        ),
+      BOOL    (JavaType.BOOLEAN    ),
+      STRING  (JavaType.STRING     ),
+      GROUP   (JavaType.MESSAGE    ),
+      MESSAGE (JavaType.MESSAGE    ),
+      BYTES   (JavaType.BYTE_STRING),
+      UINT32  (JavaType.INT        ),
+      ENUM    (JavaType.ENUM       ),
+      SFIXED32(JavaType.INT        ),
+      SFIXED64(JavaType.LONG       ),
+      SINT32  (JavaType.INT        ),
+      SINT64  (JavaType.LONG       );
+
+      Type(final JavaType javaType) {
+        this.javaType = javaType;
+      }
+
+      private JavaType javaType;
+
+      public FieldDescriptorProto.Type toProto() {
+        return FieldDescriptorProto.Type.valueOf(ordinal() + 1);
+      }
+      public JavaType getJavaType() { return javaType; }
+
+      public static Type valueOf(final FieldDescriptorProto.Type type) {
+        return values()[type.getNumber() - 1];
+      }
+    }
+
+    static {
+      // Refuse to init if someone added a new declared type.
+      if (Type.values().length != FieldDescriptorProto.Type.values().length) {
+        throw new RuntimeException(""
+            + "descriptor.proto has a new declared type but Descriptors.java "
+            + "wasn't updated.");
+      }
+    }
+
+    public enum JavaType {
+      INT(0),
+      LONG(0L),
+      FLOAT(0F),
+      DOUBLE(0D),
+      BOOLEAN(false),
+      STRING(""),
+      BYTE_STRING(ByteString.EMPTY),
+      ENUM(null),
+      MESSAGE(null);
+
+      JavaType(final Object defaultDefault) {
+        this.defaultDefault = defaultDefault;
+      }
+
+      /**
+       * The default default value for fields of this type, if it's a primitive
+       * type.  This is meant for use inside this file only, hence is private.
+       */
+      private final Object defaultDefault;
+    }
+
+    // TODO(xiaofeng): Implement it consistently across different languages. See b/24751348.
+    private static String fieldNameToLowerCamelCase(String name) {
+      StringBuilder result = new StringBuilder(name.length());
+      boolean isNextUpperCase = false;
+      for (int i = 0; i < name.length(); i++) {
+        Character ch = name.charAt(i);
+        if (Character.isLowerCase(ch)) {
+          if (isNextUpperCase) {
+            result.append(Character.toUpperCase(ch));
+          } else {
+            result.append(ch);
+          }
+          isNextUpperCase = false;
+        } else if (Character.isUpperCase(ch)) {
+          if (i == 0) {
+            // Force first letter to lower-case.
+            result.append(Character.toLowerCase(ch));
+          } else {
+            // Capital letters after the first are left as-is.
+            result.append(ch);
+          }
+          isNextUpperCase = false;
+        } else if (Character.isDigit(ch)) {
+          result.append(ch);
+          isNextUpperCase = false;
+        } else {
+          isNextUpperCase = true;
+        }
+      }
+      return result.toString();
+    }
+
+    private FieldDescriptor(final FieldDescriptorProto proto,
+                            final FileDescriptor file,
+                            final Descriptor parent,
+                            final int index,
+                            final boolean isExtension)
+                     throws DescriptorValidationException {
+      this.index = index;
+      this.proto = proto;
+      fullName = computeFullName(file, parent, proto.getName());
+      this.file = file;
+      if (proto.hasJsonName()) {
+        jsonName = proto.getJsonName();
+      } else {
+        jsonName = fieldNameToLowerCamelCase(proto.getName());
+      }
+
+      if (proto.hasType()) {
+        type = Type.valueOf(proto.getType());
+      }
+
+      if (getNumber() <= 0) {
+        throw new DescriptorValidationException(this,
+          "Field numbers must be positive integers.");
+      }
+
+      if (isExtension) {
+        if (!proto.hasExtendee()) {
+          throw new DescriptorValidationException(this,
+            "FieldDescriptorProto.extendee not set for extension field.");
+        }
+        containingType = null;  // Will be filled in when cross-linking
+        if (parent != null) {
+          extensionScope = parent;
+        } else {
+          extensionScope = null;
+        }
+
+        if (proto.hasOneofIndex()) {
+          throw new DescriptorValidationException(this,
+            "FieldDescriptorProto.oneof_index set for extension field.");
+        }
+        containingOneof = null;
+      } else {
+        if (proto.hasExtendee()) {
+          throw new DescriptorValidationException(this,
+            "FieldDescriptorProto.extendee set for non-extension field.");
+        }
+        containingType = parent;
+
+        if (proto.hasOneofIndex()) {
+          if (proto.getOneofIndex() < 0 ||
+              proto.getOneofIndex() >= parent.toProto().getOneofDeclCount()) {
+            throw new DescriptorValidationException(this,
+              "FieldDescriptorProto.oneof_index is out of range for type "
+              + parent.getName());
+          }
+          containingOneof = parent.getOneofs().get(proto.getOneofIndex());
+          containingOneof.fieldCount++;
+        } else {
+          containingOneof = null;
+        }
+        extensionScope = null;
+      }
+
+      file.pool.addSymbol(this);
+    }
+
+    /** Look up and cross-link all field types, etc. */
+    private void crossLink() throws DescriptorValidationException {
+      if (proto.hasExtendee()) {
+        final GenericDescriptor extendee =
+          file.pool.lookupSymbol(proto.getExtendee(), this,
+              DescriptorPool.SearchFilter.TYPES_ONLY);
+        if (!(extendee instanceof Descriptor)) {
+          throw new DescriptorValidationException(this,
+              '\"' + proto.getExtendee() + "\" is not a message type.");
+        }
+        containingType = (Descriptor)extendee;
+
+        if (!getContainingType().isExtensionNumber(getNumber())) {
+          throw new DescriptorValidationException(this,
+              '\"' + getContainingType().getFullName() +
+              "\" does not declare " + getNumber() +
+              " as an extension number.");
+        }
+      }
+
+      if (proto.hasTypeName()) {
+        final GenericDescriptor typeDescriptor =
+          file.pool.lookupSymbol(proto.getTypeName(), this,
+              DescriptorPool.SearchFilter.TYPES_ONLY);
+
+        if (!proto.hasType()) {
+          // Choose field type based on symbol.
+          if (typeDescriptor instanceof Descriptor) {
+            type = Type.MESSAGE;
+          } else if (typeDescriptor instanceof EnumDescriptor) {
+            type = Type.ENUM;
+          } else {
+            throw new DescriptorValidationException(this,
+                '\"' + proto.getTypeName() + "\" is not a type.");
+          }
+        }
+
+        if (getJavaType() == JavaType.MESSAGE) {
+          if (!(typeDescriptor instanceof Descriptor)) {
+            throw new DescriptorValidationException(this,
+                '\"' + proto.getTypeName() + "\" is not a message type.");
+          }
+          messageType = (Descriptor)typeDescriptor;
+
+          if (proto.hasDefaultValue()) {
+            throw new DescriptorValidationException(this,
+              "Messages can't have default values.");
+          }
+        } else if (getJavaType() == JavaType.ENUM) {
+          if (!(typeDescriptor instanceof EnumDescriptor)) {
+            throw new DescriptorValidationException(this,
+                '\"' + proto.getTypeName() + "\" is not an enum type.");
+          }
+          enumType = (EnumDescriptor)typeDescriptor;
+        } else {
+          throw new DescriptorValidationException(this,
+            "Field with primitive type has type_name.");
+        }
+      } else {
+        if (getJavaType() == JavaType.MESSAGE ||
+            getJavaType() == JavaType.ENUM) {
+          throw new DescriptorValidationException(this,
+            "Field with message or enum type missing type_name.");
+        }
+      }
+
+      // Only repeated primitive fields may be packed.
+      if (proto.getOptions().getPacked() && !isPackable()) {
+        throw new DescriptorValidationException(this,
+          "[packed = true] can only be specified for repeated primitive " +
+          "fields.");
+      }
+
+      // We don't attempt to parse the default value until here because for
+      // enums we need the enum type's descriptor.
+      if (proto.hasDefaultValue()) {
+        if (isRepeated()) {
+          throw new DescriptorValidationException(this,
+            "Repeated fields cannot have default values.");
+        }
+
+        try {
+          switch (getType()) {
+            case INT32:
+            case SINT32:
+            case SFIXED32:
+              defaultValue = TextFormat.parseInt32(proto.getDefaultValue());
+              break;
+            case UINT32:
+            case FIXED32:
+              defaultValue = TextFormat.parseUInt32(proto.getDefaultValue());
+              break;
+            case INT64:
+            case SINT64:
+            case SFIXED64:
+              defaultValue = TextFormat.parseInt64(proto.getDefaultValue());
+              break;
+            case UINT64:
+            case FIXED64:
+              defaultValue = TextFormat.parseUInt64(proto.getDefaultValue());
+              break;
+            case FLOAT:
+              if (proto.getDefaultValue().equals("inf")) {
+                defaultValue = Float.POSITIVE_INFINITY;
+              } else if (proto.getDefaultValue().equals("-inf")) {
+                defaultValue = Float.NEGATIVE_INFINITY;
+              } else if (proto.getDefaultValue().equals("nan")) {
+                defaultValue = Float.NaN;
+              } else {
+                defaultValue = Float.valueOf(proto.getDefaultValue());
+              }
+              break;
+            case DOUBLE:
+              if (proto.getDefaultValue().equals("inf")) {
+                defaultValue = Double.POSITIVE_INFINITY;
+              } else if (proto.getDefaultValue().equals("-inf")) {
+                defaultValue = Double.NEGATIVE_INFINITY;
+              } else if (proto.getDefaultValue().equals("nan")) {
+                defaultValue = Double.NaN;
+              } else {
+                defaultValue = Double.valueOf(proto.getDefaultValue());
+              }
+              break;
+            case BOOL:
+              defaultValue = Boolean.valueOf(proto.getDefaultValue());
+              break;
+            case STRING:
+              defaultValue = proto.getDefaultValue();
+              break;
+            case BYTES:
+              try {
+                defaultValue =
+                  TextFormat.unescapeBytes(proto.getDefaultValue());
+              } catch (TextFormat.InvalidEscapeSequenceException e) {
+                throw new DescriptorValidationException(this,
+                  "Couldn't parse default value: " + e.getMessage(), e);
+              }
+              break;
+            case ENUM:
+              defaultValue = enumType.findValueByName(proto.getDefaultValue());
+              if (defaultValue == null) {
+                throw new DescriptorValidationException(this,
+                  "Unknown enum default value: \"" +
+                  proto.getDefaultValue() + '\"');
+              }
+              break;
+            case MESSAGE:
+            case GROUP:
+              throw new DescriptorValidationException(this,
+                "Message type had default value.");
+          }
+        } catch (NumberFormatException e) {
+          throw new DescriptorValidationException(this,
+              "Could not parse default value: \"" +
+              proto.getDefaultValue() + '\"', e);
+        }
+      } else {
+        // Determine the default default for this field.
+        if (isRepeated()) {
+          defaultValue = Collections.emptyList();
+        } else {
+          switch (getJavaType()) {
+            case ENUM:
+              // We guarantee elsewhere that an enum type always has at least
+              // one possible value.
+              defaultValue = enumType.getValues().get(0);
+              break;
+            case MESSAGE:
+              defaultValue = null;
+              break;
+            default:
+              defaultValue = getJavaType().defaultDefault;
+              break;
+          }
+        }
+      }
+
+      if (!isExtension()) {
+        file.pool.addFieldByNumber(this);
+      }
+
+      if (containingType != null &&
+          containingType.getOptions().getMessageSetWireFormat()) {
+        if (isExtension()) {
+          if (!isOptional() || getType() != Type.MESSAGE) {
+            throw new DescriptorValidationException(this,
+              "Extensions of MessageSets must be optional messages.");
+          }
+        } else {
+          throw new DescriptorValidationException(this,
+            "MessageSets cannot have fields, only extensions.");
+        }
+      }
+    }
+
+    /** See {@link FileDescriptor#setProto}. */
+    private void setProto(final FieldDescriptorProto proto) {
+      this.proto = proto;
+    }
+
+    /**
+     * For internal use only.  This is to satisfy the FieldDescriptorLite
+     * interface.
+     */
+    public MessageLite.Builder internalMergeFrom(
+        MessageLite.Builder to, MessageLite from) {
+      // FieldDescriptors are only used with non-lite messages so we can just
+      // down-cast and call mergeFrom directly.
+      return ((Message.Builder) to).mergeFrom((Message) from);
+    }
+
+  }
+
+  // =================================================================
+
+  /** Describes an enum type. */
+  public static final class EnumDescriptor extends GenericDescriptor
+      implements Internal.EnumLiteMap<EnumValueDescriptor> {
+    /**
+     * Get the index of this descriptor within its parent.
+     * @see Descriptors.Descriptor#getIndex()
+     */
+    public int getIndex() { return index; }
+
+    /** Convert the descriptor to its protocol message representation. */
+    public EnumDescriptorProto toProto() { return proto; }
+
+    /** Get the type's unqualified name. */
+    public String getName() { return proto.getName(); }
+
+    /**
+     * Get the type's fully-qualified name.
+     * @see Descriptors.Descriptor#getFullName()
+     */
+    public String getFullName() { return fullName; }
+
+    /** Get the {@link FileDescriptor} containing this descriptor. */
+    public FileDescriptor getFile() { return file; }
+
+    /** If this is a nested type, get the outer descriptor, otherwise null. */
+    public Descriptor getContainingType() { return containingType; }
+
+    /** Get the {@code EnumOptions}, defined in {@code descriptor.proto}. */
+    public EnumOptions getOptions() { return proto.getOptions(); }
+
+    /** Get a list of defined values for this enum. */
+    public List<EnumValueDescriptor> getValues() {
+      return Collections.unmodifiableList(Arrays.asList(values));
+    }
+
+    /**
+     * Find an enum value by name.
+     * @param name The unqualified name of the value (e.g. "FOO").
+     * @return the value's descriptor, or {@code null} if not found.
+     */
+    public EnumValueDescriptor findValueByName(final String name) {
+      final GenericDescriptor result =
+          file.pool.findSymbol(fullName + '.' + name);
+      if (result != null && result instanceof EnumValueDescriptor) {
+        return (EnumValueDescriptor)result;
+      } else {
+        return null;
+      }
+    }
+
+    /**
+     * Find an enum value by number.  If multiple enum values have the same
+     * number, this returns the first defined value with that number.
+     * @param number The value's number.
+     * @return the value's descriptor, or {@code null} if not found.
+     */
+    public EnumValueDescriptor findValueByNumber(final int number) {
+      return file.pool.enumValuesByNumber.get(
+        new DescriptorPool.DescriptorIntPair(this, number));
+    }
+
+    /**
+     * Get the enum value for a number. If no enum value has this number,
+     * construct an EnumValueDescriptor for it.
+     */
+    public EnumValueDescriptor findValueByNumberCreatingIfUnknown(final int number) {
+      EnumValueDescriptor result = findValueByNumber(number);
+      if (result != null) {
+        return result;
+      }
+      // The number represents an unknown enum value.
+      synchronized (this) {
+        // Descriptors are compared by object identity so for the same number
+        // we need to return the same EnumValueDescriptor object. This means
+        // we have to store created EnumValueDescriptors. However, as there
+        // are potentially 2G unknown enum values, storing all of these
+        // objects persistently will consume lots of memory for long-running
+        // services and it's also unnecessary as not many EnumValueDescriptors
+        // will be used at the same time.
+        //
+        // To solve the problem we take advantage of Java's weak references and
+        // rely on gc to release unused descriptors.
+        //
+        // Here is how it works:
+        //   * We store unknown EnumValueDescriptors in a WeakHashMap with the
+        //     value being a weak reference to the descriptor.
+        //   * The descriptor holds a strong reference to the key so as long
+        //     as the EnumValueDescriptor is in use, the key will be there
+        //     and the corresponding map entry will be there. Following-up
+        //     queries with the same number will return the same descriptor.
+        //   * If the user no longer uses an unknown EnumValueDescriptor,
+        //     it will be gc-ed since we only hold a weak reference to it in
+        //     the map. The key in the corresponding map entry will also be
+        //     gc-ed as the only strong reference to it is in the descriptor
+        //     which is just gc-ed. With the key being gone WeakHashMap will
+        //     then remove the whole entry. This way unknown descriptors will
+        //     be freed automatically and we don't need to do anything to
+        //     clean-up unused map entries.
+
+        // Note: We must use "new Integer(number)" here because we don't want
+        // these Integer objects to be cached.
+        Integer key = new Integer(number);
+        WeakReference<EnumValueDescriptor> reference = unknownValues.get(key);
+        if (reference != null) {
+          result = reference.get();
+        }
+        if (result == null) {
+          result = new EnumValueDescriptor(file, this, key);
+          unknownValues.put(key, new WeakReference<EnumValueDescriptor>(result));
+        }
+      }
+      return result;
+    }
+
+    // Used in tests only.
+    int getUnknownEnumValueDescriptorCount() {
+      return unknownValues.size();
+    }
+
+    private final int index;
+    private EnumDescriptorProto proto;
+    private final String fullName;
+    private final FileDescriptor file;
+    private final Descriptor containingType;
+    private EnumValueDescriptor[] values;
+    private final WeakHashMap<Integer, WeakReference<EnumValueDescriptor>> unknownValues =
+        new WeakHashMap<Integer, WeakReference<EnumValueDescriptor>>();
+
+    private EnumDescriptor(final EnumDescriptorProto proto,
+                           final FileDescriptor file,
+                           final Descriptor parent,
+                           final int index)
+                    throws DescriptorValidationException {
+      this.index = index;
+      this.proto = proto;
+      fullName = computeFullName(file, parent, proto.getName());
+      this.file = file;
+      containingType = parent;
+
+      if (proto.getValueCount() == 0) {
+        // We cannot allow enums with no values because this would mean there
+        // would be no valid default value for fields of this type.
+        throw new DescriptorValidationException(this,
+          "Enums must contain at least one value.");
+      }
+
+      values = new EnumValueDescriptor[proto.getValueCount()];
+      for (int i = 0; i < proto.getValueCount(); i++) {
+        values[i] = new EnumValueDescriptor(
+          proto.getValue(i), file, this, i);
+      }
+
+      file.pool.addSymbol(this);
+    }
+
+    /** See {@link FileDescriptor#setProto}. */
+    private void setProto(final EnumDescriptorProto proto) {
+      this.proto = proto;
+
+      for (int i = 0; i < values.length; i++) {
+        values[i].setProto(proto.getValue(i));
+      }
+    }
+  }
+
+  // =================================================================
+
+  /**
+   * Describes one value within an enum type.  Note that multiple defined
+   * values may have the same number.  In generated Java code, all values
+   * with the same number after the first become aliases of the first.
+   * However, they still have independent EnumValueDescriptors.
+   */
+  public static final class EnumValueDescriptor extends GenericDescriptor
+      implements Internal.EnumLite {
+    /**
+     * Get the index of this descriptor within its parent.
+     * @see Descriptors.Descriptor#getIndex()
+     */
+    public int getIndex() { return index; }
+
+    /** Convert the descriptor to its protocol message representation. */
+    public EnumValueDescriptorProto toProto() { return proto; }
+
+    /** Get the value's unqualified name. */
+    public String getName() { return proto.getName(); }
+
+    /** Get the value's number. */
+    public int getNumber() { return proto.getNumber(); }
+
+    @Override
+    public String toString() { return proto.getName(); }
+
+    /**
+     * Get the value's fully-qualified name.
+     * @see Descriptors.Descriptor#getFullName()
+     */
+    public String getFullName() { return fullName; }
+
+    /** Get the {@link FileDescriptor} containing this descriptor. */
+    public FileDescriptor getFile() { return file; }
+
+    /** Get the value's enum type. */
+    public EnumDescriptor getType() { return type; }
+
+    /**
+     * Get the {@code EnumValueOptions}, defined in {@code descriptor.proto}.
+     */
+    public EnumValueOptions getOptions() { return proto.getOptions(); }
+
+    private final int index;
+    private EnumValueDescriptorProto proto;
+    private final String fullName;
+    private final FileDescriptor file;
+    private final EnumDescriptor type;
+
+    private EnumValueDescriptor(final EnumValueDescriptorProto proto,
+                                final FileDescriptor file,
+                                final EnumDescriptor parent,
+                                final int index)
+                         throws DescriptorValidationException {
+      this.index = index;
+      this.proto = proto;
+      this.file = file;
+      type = parent;
+
+      fullName = parent.getFullName() + '.' + proto.getName();
+
+      file.pool.addSymbol(this);
+      file.pool.addEnumValueByNumber(this);
+    }
+
+    private Integer number;
+    // Create an unknown enum value.
+    private EnumValueDescriptor(
+        final FileDescriptor file,
+        final EnumDescriptor parent,
+        final Integer number) {
+      String name = "UNKNOWN_ENUM_VALUE_" + parent.getName() + "_" + number;
+      EnumValueDescriptorProto proto = EnumValueDescriptorProto
+          .newBuilder().setName(name).setNumber(number).build();
+      this.index = -1;
+      this.proto = proto;
+      this.file = file;
+      this.type = parent;
+      this.fullName = parent.getFullName() + '.' + proto.getName();
+      this.number = number;
+
+      // Don't add this descriptor into pool.
+    }
+
+    /** See {@link FileDescriptor#setProto}. */
+    private void setProto(final EnumValueDescriptorProto proto) {
+      this.proto = proto;
+    }
+  }
+
+  // =================================================================
+
+  /** Describes a service type. */
+  public static final class ServiceDescriptor extends GenericDescriptor {
+    /**
+     * Get the index of this descriptor within its parent.
+     * * @see Descriptors.Descriptor#getIndex()
+     */
+    public int getIndex() { return index; }
+
+    /** Convert the descriptor to its protocol message representation. */
+    public ServiceDescriptorProto toProto() { return proto; }
+
+    /** Get the type's unqualified name. */
+    public String getName() { return proto.getName(); }
+
+    /**
+     * Get the type's fully-qualified name.
+     * @see Descriptors.Descriptor#getFullName()
+     */
+    public String getFullName() { return fullName; }
+
+    /** Get the {@link FileDescriptor} containing this descriptor. */
+    public FileDescriptor getFile() { return file; }
+
+    /** Get the {@code ServiceOptions}, defined in {@code descriptor.proto}. */
+    public ServiceOptions getOptions() { return proto.getOptions(); }
+
+    /** Get a list of methods for this service. */
+    public List<MethodDescriptor> getMethods() {
+      return Collections.unmodifiableList(Arrays.asList(methods));
+    }
+
+    /**
+     * Find a method by name.
+     * @param name The unqualified name of the method (e.g. "Foo").
+     * @return the method's descriptor, or {@code null} if not found.
+     */
+    public MethodDescriptor findMethodByName(final String name) {
+      final GenericDescriptor result =
+          file.pool.findSymbol(fullName + '.' + name);
+      if (result != null && result instanceof MethodDescriptor) {
+        return (MethodDescriptor)result;
+      } else {
+        return null;
+      }
+    }
+
+    private final int index;
+    private ServiceDescriptorProto proto;
+    private final String fullName;
+    private final FileDescriptor file;
+    private MethodDescriptor[] methods;
+
+    private ServiceDescriptor(final ServiceDescriptorProto proto,
+                              final FileDescriptor file,
+                              final int index)
+                       throws DescriptorValidationException {
+      this.index = index;
+      this.proto = proto;
+      fullName = computeFullName(file, null, proto.getName());
+      this.file = file;
+
+      methods = new MethodDescriptor[proto.getMethodCount()];
+      for (int i = 0; i < proto.getMethodCount(); i++) {
+        methods[i] = new MethodDescriptor(
+          proto.getMethod(i), file, this, i);
+      }
+
+      file.pool.addSymbol(this);
+    }
+
+    private void crossLink() throws DescriptorValidationException {
+      for (final MethodDescriptor method : methods) {
+        method.crossLink();
+      }
+    }
+
+    /** See {@link FileDescriptor#setProto}. */
+    private void setProto(final ServiceDescriptorProto proto) {
+      this.proto = proto;
+
+      for (int i = 0; i < methods.length; i++) {
+        methods[i].setProto(proto.getMethod(i));
+      }
+    }
+  }
+
+  // =================================================================
+
+  /**
+   * Describes one method within a service type.
+   */
+  public static final class MethodDescriptor extends GenericDescriptor {
+    /**
+     * Get the index of this descriptor within its parent.
+     * * @see Descriptors.Descriptor#getIndex()
+     */
+    public int getIndex() { return index; }
+
+    /** Convert the descriptor to its protocol message representation. */
+    public MethodDescriptorProto toProto() { return proto; }
+
+    /** Get the method's unqualified name. */
+    public String getName() { return proto.getName(); }
+
+    /**
+     * Get the method's fully-qualified name.
+     * @see Descriptors.Descriptor#getFullName()
+     */
+    public String getFullName() { return fullName; }
+
+    /** Get the {@link FileDescriptor} containing this descriptor. */
+    public FileDescriptor getFile() { return file; }
+
+    /** Get the method's service type. */
+    public ServiceDescriptor getService() { return service; }
+
+    /** Get the method's input type. */
+    public Descriptor getInputType() { return inputType; }
+
+    /** Get the method's output type. */
+    public Descriptor getOutputType() { return outputType; }
+
+    /**
+     * Get the {@code MethodOptions}, defined in {@code descriptor.proto}.
+     */
+    public MethodOptions getOptions() { return proto.getOptions(); }
+
+    private final int index;
+    private MethodDescriptorProto proto;
+    private final String fullName;
+    private final FileDescriptor file;
+    private final ServiceDescriptor service;
+
+    // Initialized during cross-linking.
+    private Descriptor inputType;
+    private Descriptor outputType;
+
+    private MethodDescriptor(final MethodDescriptorProto proto,
+                             final FileDescriptor file,
+                             final ServiceDescriptor parent,
+                             final int index)
+                      throws DescriptorValidationException {
+      this.index = index;
+      this.proto = proto;
+      this.file = file;
+      service = parent;
+
+      fullName = parent.getFullName() + '.' + proto.getName();
+
+      file.pool.addSymbol(this);
+    }
+
+    private void crossLink() throws DescriptorValidationException {
+      final GenericDescriptor input =
+        file.pool.lookupSymbol(proto.getInputType(), this,
+            DescriptorPool.SearchFilter.TYPES_ONLY);
+      if (!(input instanceof Descriptor)) {
+        throw new DescriptorValidationException(this,
+            '\"' + proto.getInputType() + "\" is not a message type.");
+      }
+      inputType = (Descriptor)input;
+
+      final GenericDescriptor output =
+        file.pool.lookupSymbol(proto.getOutputType(), this,
+            DescriptorPool.SearchFilter.TYPES_ONLY);
+      if (!(output instanceof Descriptor)) {
+        throw new DescriptorValidationException(this,
+            '\"' + proto.getOutputType() + "\" is not a message type.");
+      }
+      outputType = (Descriptor)output;
+    }
+
+    /** See {@link FileDescriptor#setProto}. */
+    private void setProto(final MethodDescriptorProto proto) {
+      this.proto = proto;
+    }
+  }
+
+  // =================================================================
+
+  private static String computeFullName(final FileDescriptor file,
+                                        final Descriptor parent,
+                                        final String name) {
+    if (parent != null) {
+      return parent.getFullName() + '.' + name;
+    } else if (file.getPackage().length() > 0) {
+      return file.getPackage() + '.' + name;
+    } else {
+      return name;
+    }
+  }
+
+  // =================================================================
+
+  /**
+   * All descriptors implement this to make it easier to implement tools like
+   * {@code DescriptorPool}.<p>
+   *
+   * This class is public so that the methods it exposes can be called from
+   * outside of this package. However, it should only be subclassed from
+   * nested classes of Descriptors.
+   */
+  public abstract static class GenericDescriptor {
+    public abstract Message toProto();
+    public abstract String getName();
+    public abstract String getFullName();
+    public abstract FileDescriptor getFile();
+  }
+
+  /**
+   * Thrown when building descriptors fails because the source DescriptorProtos
+   * are not valid.
+   */
+  public static class DescriptorValidationException extends Exception {
+    private static final long serialVersionUID = 5750205775490483148L;
+
+    /** Gets the full name of the descriptor where the error occurred. */
+    public String getProblemSymbolName() { return name; }
+
+    /**
+     * Gets the protocol message representation of the invalid descriptor.
+     */
+    public Message getProblemProto() { return proto; }
+
+    /**
+     * Gets a human-readable description of the error.
+     */
+    public String getDescription() { return description; }
+
+    private final String name;
+    private final Message proto;
+    private final String description;
+
+    private DescriptorValidationException(
+        final GenericDescriptor problemDescriptor,
+        final String description) {
+      super(problemDescriptor.getFullName() + ": " + description);
+
+      // Note that problemDescriptor may be partially uninitialized, so we
+      // don't want to expose it directly to the user.  So, we only provide
+      // the name and the original proto.
+      name = problemDescriptor.getFullName();
+      proto = problemDescriptor.toProto();
+      this.description = description;
+    }
+
+    private DescriptorValidationException(
+        final GenericDescriptor problemDescriptor,
+        final String description,
+        final Throwable cause) {
+      this(problemDescriptor, description);
+      initCause(cause);
+    }
+
+    private DescriptorValidationException(
+        final FileDescriptor problemDescriptor,
+        final String description) {
+      super(problemDescriptor.getName() + ": " + description);
+
+      // Note that problemDescriptor may be partially uninitialized, so we
+      // don't want to expose it directly to the user.  So, we only provide
+      // the name and the original proto.
+      name = problemDescriptor.getName();
+      proto = problemDescriptor.toProto();
+      this.description = description;
+    }
+  }
+
+  // =================================================================
+
+  /**
+   * A private helper class which contains lookup tables containing all the
+   * descriptors defined in a particular file.
+   */
+  private static final class DescriptorPool {
+
+    /** Defines what subclass of descriptors to search in the descriptor pool.
+     */
+    enum SearchFilter {
+      TYPES_ONLY, AGGREGATES_ONLY, ALL_SYMBOLS
+    }
+
+    DescriptorPool(final FileDescriptor[] dependencies,
+        boolean allowUnknownDependencies) {
+      this.dependencies = new HashSet<FileDescriptor>();
+      this.allowUnknownDependencies = allowUnknownDependencies;
+
+      for (int i = 0; i < dependencies.length; i++) {
+        this.dependencies.add(dependencies[i]);
+        importPublicDependencies(dependencies[i]);
+      }
+
+      for (final FileDescriptor dependency : this.dependencies) {
+        try {
+          addPackage(dependency.getPackage(), dependency);
+        } catch (DescriptorValidationException e) {
+          // Can't happen, because addPackage() only fails when the name
+          // conflicts with a non-package, but we have not yet added any
+          // non-packages at this point.
+          assert false;
+        }
+      }
+    }
+
+    /** Find and put public dependencies of the file into dependencies set.*/
+    private void importPublicDependencies(final FileDescriptor file) {
+      for (FileDescriptor dependency : file.getPublicDependencies()) {
+        if (dependencies.add(dependency)) {
+          importPublicDependencies(dependency);
+        }
+      }
+    }
+
+    private final Set<FileDescriptor> dependencies;
+    private boolean allowUnknownDependencies;
+
+    private final Map<String, GenericDescriptor> descriptorsByName =
+      new HashMap<String, GenericDescriptor>();
+    private final Map<DescriptorIntPair, FieldDescriptor> fieldsByNumber =
+      new HashMap<DescriptorIntPair, FieldDescriptor>();
+    private final Map<DescriptorIntPair, EnumValueDescriptor> enumValuesByNumber
+        = new HashMap<DescriptorIntPair, EnumValueDescriptor>();
+
+    /** Find a generic descriptor by fully-qualified name. */
+    GenericDescriptor findSymbol(final String fullName) {
+      return findSymbol(fullName, SearchFilter.ALL_SYMBOLS);
+    }
+
+    /** Find a descriptor by fully-qualified name and given option to only
+     * search valid field type descriptors.
+     */
+    GenericDescriptor findSymbol(final String fullName,
+                                 final SearchFilter filter) {
+      GenericDescriptor result = descriptorsByName.get(fullName);
+      if (result != null) {
+        if ((filter==SearchFilter.ALL_SYMBOLS) ||
+            ((filter==SearchFilter.TYPES_ONLY) && isType(result)) ||
+            ((filter==SearchFilter.AGGREGATES_ONLY) && isAggregate(result))) {
+          return result;
+        }
+      }
+
+      for (final FileDescriptor dependency : dependencies) {
+        result = dependency.pool.descriptorsByName.get(fullName);
+        if (result != null) {
+          if ((filter==SearchFilter.ALL_SYMBOLS) ||
+              ((filter==SearchFilter.TYPES_ONLY) && isType(result)) ||
+              ((filter==SearchFilter.AGGREGATES_ONLY) && isAggregate(result))) {
+            return result;
+          }
+        }
+      }
+
+      return null;
+    }
+
+    /** Checks if the descriptor is a valid type for a message field. */
+    boolean isType(GenericDescriptor descriptor) {
+      return (descriptor instanceof Descriptor) ||
+        (descriptor instanceof EnumDescriptor);
+    }
+
+    /** Checks if the descriptor is a valid namespace type. */
+    boolean isAggregate(GenericDescriptor descriptor) {
+      return (descriptor instanceof Descriptor) ||
+        (descriptor instanceof EnumDescriptor) ||
+        (descriptor instanceof PackageDescriptor) ||
+        (descriptor instanceof ServiceDescriptor);
+    }
+
+    /**
+     * Look up a type descriptor by name, relative to some other descriptor.
+     * The name may be fully-qualified (with a leading '.'),
+     * partially-qualified, or unqualified.  C++-like name lookup semantics
+     * are used to search for the matching descriptor.
+     */
+    GenericDescriptor lookupSymbol(final String name,
+                                   final GenericDescriptor relativeTo,
+                                   final DescriptorPool.SearchFilter filter)
+                            throws DescriptorValidationException {
+      // TODO(kenton):  This could be optimized in a number of ways.
+
+      GenericDescriptor result;
+      String fullname;
+      if (name.startsWith(".")) {
+        // Fully-qualified name.
+        fullname = name.substring(1);
+        result = findSymbol(fullname, filter);
+      } else {
+        // If "name" is a compound identifier, we want to search for the
+        // first component of it, then search within it for the rest.
+        // If name is something like "Foo.Bar.baz", and symbols named "Foo" are
+        // defined in multiple parent scopes, we only want to find "Bar.baz" in
+        // the innermost one.  E.g., the following should produce an error:
+        //   message Bar { message Baz {} }
+        //   message Foo {
+        //     message Bar {
+        //     }
+        //     optional Bar.Baz baz = 1;
+        //   }
+        // So, we look for just "Foo" first, then look for "Bar.baz" within it
+        // if found.
+        final int firstPartLength = name.indexOf('.');
+        final String firstPart;
+        if (firstPartLength == -1) {
+          firstPart = name;
+        } else {
+          firstPart = name.substring(0, firstPartLength);
+        }
+
+        // We will search each parent scope of "relativeTo" looking for the
+        // symbol.
+        final StringBuilder scopeToTry =
+            new StringBuilder(relativeTo.getFullName());
+
+        while (true) {
+          // Chop off the last component of the scope.
+          final int dotpos = scopeToTry.lastIndexOf(".");
+          if (dotpos == -1) {
+            fullname = name;
+            result = findSymbol(name, filter);
+            break;
+          } else {
+            scopeToTry.setLength(dotpos + 1);
+
+            // Append firstPart and try to find
+            scopeToTry.append(firstPart);
+            result = findSymbol(scopeToTry.toString(),
+                DescriptorPool.SearchFilter.AGGREGATES_ONLY);
+
+            if (result != null) {
+              if (firstPartLength != -1) {
+                // We only found the first part of the symbol.  Now look for
+                // the whole thing.  If this fails, we *don't* want to keep
+                // searching parent scopes.
+                scopeToTry.setLength(dotpos + 1);
+                scopeToTry.append(name);
+                result = findSymbol(scopeToTry.toString(), filter);
+              }
+              fullname = scopeToTry.toString();
+              break;
+            }
+
+            // Not found.  Remove the name so we can try again.
+            scopeToTry.setLength(dotpos);
+          }
+        }
+      }
+
+      if (result == null) {
+        if (allowUnknownDependencies && filter == SearchFilter.TYPES_ONLY) {
+          logger.warning("The descriptor for message type \"" + name +
+              "\" can not be found and a placeholder is created for it");
+          // We create a dummy message descriptor here regardless of the
+          // expected type. If the type should be message, this dummy
+          // descriptor will work well and if the type should be enum, a
+          // DescriptorValidationException will be thrown latter. In either
+          // case, the code works as expected: we allow unknown message types
+          // but not unknwon enum types.
+          result = new Descriptor(fullname);
+          // Add the placeholder file as a dependency so we can find the
+          // placeholder symbol when resolving other references.
+          this.dependencies.add(result.getFile());
+          return result;
+        } else {
+          throw new DescriptorValidationException(relativeTo,
+              '\"' + name + "\" is not defined.");
+        }
+      } else {
+        return result;
+      }
+    }
+
+    /**
+     * Adds a symbol to the symbol table.  If a symbol with the same name
+     * already exists, throws an error.
+     */
+    void addSymbol(final GenericDescriptor descriptor)
+            throws DescriptorValidationException {
+      validateSymbolName(descriptor);
+
+      final String fullName = descriptor.getFullName();
+      final int dotpos = fullName.lastIndexOf('.');
+
+      final GenericDescriptor old = descriptorsByName.put(fullName, descriptor);
+      if (old != null) {
+        descriptorsByName.put(fullName, old);
+
+        if (descriptor.getFile() == old.getFile()) {
+          if (dotpos == -1) {
+            throw new DescriptorValidationException(descriptor,
+                '\"' + fullName + "\" is already defined.");
+          } else {
+            throw new DescriptorValidationException(descriptor,
+                '\"' + fullName.substring(dotpos + 1) +
+              "\" is already defined in \"" +
+              fullName.substring(0, dotpos) + "\".");
+          }
+        } else {
+          throw new DescriptorValidationException(descriptor,
+              '\"' + fullName + "\" is already defined in file \"" +
+            old.getFile().getName() + "\".");
+        }
+      }
+    }
+
+    /**
+     * Represents a package in the symbol table.  We use PackageDescriptors
+     * just as placeholders so that someone cannot define, say, a message type
+     * that has the same name as an existing package.
+     */
+    private static final class PackageDescriptor extends GenericDescriptor {
+      public Message toProto()        { return file.toProto(); }
+      public String getName()         { return name;           }
+      public String getFullName()     { return fullName;       }
+      public FileDescriptor getFile() { return file;           }
+
+      PackageDescriptor(final String name, final String fullName,
+                        final FileDescriptor file) {
+        this.file = file;
+        this.fullName = fullName;
+        this.name = name;
+      }
+
+      private final String name;
+      private final String fullName;
+      private final FileDescriptor file;
+    }
+
+    /**
+     * Adds a package to the symbol tables.  If a package by the same name
+     * already exists, that is fine, but if some other kind of symbol exists
+     * under the same name, an exception is thrown.  If the package has
+     * multiple components, this also adds the parent package(s).
+     */
+    void addPackage(final String fullName, final FileDescriptor file)
+             throws DescriptorValidationException {
+      final int dotpos = fullName.lastIndexOf('.');
+      final String name;
+      if (dotpos == -1) {
+        name = fullName;
+      } else {
+        addPackage(fullName.substring(0, dotpos), file);
+        name = fullName.substring(dotpos + 1);
+      }
+
+      final GenericDescriptor old =
+        descriptorsByName.put(fullName,
+          new PackageDescriptor(name, fullName, file));
+      if (old != null) {
+        descriptorsByName.put(fullName, old);
+        if (!(old instanceof PackageDescriptor)) {
+          throw new DescriptorValidationException(file,
+              '\"' + name + "\" is already defined (as something other than a "
+              + "package) in file \"" + old.getFile().getName() + "\".");
+        }
+      }
+    }
+
+    /** A (GenericDescriptor, int) pair, used as a map key. */
+    private static final class DescriptorIntPair {
+      private final GenericDescriptor descriptor;
+      private final int number;
+
+      DescriptorIntPair(final GenericDescriptor descriptor, final int number) {
+        this.descriptor = descriptor;
+        this.number = number;
+      }
+
+      @Override
+      public int hashCode() {
+        return descriptor.hashCode() * ((1 << 16) - 1) + number;
+      }
+      @Override
+      public boolean equals(final Object obj) {
+        if (!(obj instanceof DescriptorIntPair)) {
+          return false;
+        }
+        final DescriptorIntPair other = (DescriptorIntPair)obj;
+        return descriptor == other.descriptor && number == other.number;
+      }
+    }
+
+    /**
+     * Adds a field to the fieldsByNumber table.  Throws an exception if a
+     * field with the same containing type and number already exists.
+     */
+    void addFieldByNumber(final FieldDescriptor field)
+                   throws DescriptorValidationException {
+      final DescriptorIntPair key =
+        new DescriptorIntPair(field.getContainingType(), field.getNumber());
+      final FieldDescriptor old = fieldsByNumber.put(key, field);
+      if (old != null) {
+        fieldsByNumber.put(key, old);
+        throw new DescriptorValidationException(field,
+          "Field number " + field.getNumber() +
+          " has already been used in \"" +
+          field.getContainingType().getFullName() +
+          "\" by field \"" + old.getName() + "\".");
+      }
+    }
+
+    /**
+     * Adds an enum value to the enumValuesByNumber table.  If an enum value
+     * with the same type and number already exists, does nothing.  (This is
+     * allowed; the first value define with the number takes precedence.)
+     */
+    void addEnumValueByNumber(final EnumValueDescriptor value) {
+      final DescriptorIntPair key =
+        new DescriptorIntPair(value.getType(), value.getNumber());
+      final EnumValueDescriptor old = enumValuesByNumber.put(key, value);
+      if (old != null) {
+        enumValuesByNumber.put(key, old);
+        // Not an error:  Multiple enum values may have the same number, but
+        // we only want the first one in the map.
+      }
+    }
+
+    /**
+     * Verifies that the descriptor's name is valid (i.e. it contains only
+     * letters, digits, and underscores, and does not start with a digit).
+     */
+    static void validateSymbolName(final GenericDescriptor descriptor)
+                                   throws DescriptorValidationException {
+      final String name = descriptor.getName();
+      if (name.length() == 0) {
+        throw new DescriptorValidationException(descriptor, "Missing name.");
+      } else {
+        boolean valid = true;
+        for (int i = 0; i < name.length(); i++) {
+          final char c = name.charAt(i);
+          // Non-ASCII characters are not valid in protobuf identifiers, even
+          // if they are letters or digits.
+          if (c >= 128) {
+            valid = false;
+          }
+          // First character must be letter or _.  Subsequent characters may
+          // be letters, numbers, or digits.
+          if (Character.isLetter(c) || c == '_' ||
+              (Character.isDigit(c) && i > 0)) {
+            // Valid
+          } else {
+            valid = false;
+          }
+        }
+        if (!valid) {
+          throw new DescriptorValidationException(descriptor,
+              '\"' + name + "\" is not a valid identifier.");
+        }
+      }
+    }
+  }
+
+  /** Describes an oneof of a message type. */
+  public static final class OneofDescriptor {
+    /** Get the index of this descriptor within its parent. */
+    public int getIndex() { return index; }
+
+    public String getName() { return proto.getName(); }
+
+    public FileDescriptor getFile() { return file; }
+
+    public String getFullName() { return fullName; }
+
+    public Descriptor getContainingType() { return containingType; }
+
+    public int getFieldCount() { return fieldCount; }
+
+    /** Get a list of this message type's fields. */
+    public List<FieldDescriptor> getFields() {
+      return Collections.unmodifiableList(Arrays.asList(fields));
+    }
+
+    public FieldDescriptor getField(int index) {
+      return fields[index];
+    }
+
+    private OneofDescriptor(final OneofDescriptorProto proto,
+                            final FileDescriptor file,
+                            final Descriptor parent,
+                            final int index)
+                     throws DescriptorValidationException {
+      this.proto = proto;
+      fullName = computeFullName(file, parent, proto.getName());
+      this.file = file;
+      this.index = index;
+
+      containingType = parent;
+      fieldCount = 0;
+    }
+
+    private final int index;
+    private OneofDescriptorProto proto;
+    private final String fullName;
+    private final FileDescriptor file;
+
+    private Descriptor containingType;
+    private int fieldCount;
+    private FieldDescriptor[] fields;
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/DoubleArrayList.java b/java/core/src/main/java/com/google/protobuf/DoubleArrayList.java
new file mode 100644
index 00000000..bcc9d6ee
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/DoubleArrayList.java
@@ -0,0 +1,250 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import com.google.protobuf.Internal.DoubleList;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.List;
+import java.util.RandomAccess;
+
+/**
+ * An implementation of {@link DoubleList} on top of a primitive array.
+ * 
+ * @author dweis@google.com (Daniel Weis)
+ */
+final class DoubleArrayList
+    extends AbstractProtobufList<Double> implements DoubleList, RandomAccess {
+  
+  private static final int DEFAULT_CAPACITY = 10;
+  
+  private static final DoubleArrayList EMPTY_LIST = new DoubleArrayList();
+  static {
+    EMPTY_LIST.makeImmutable();
+  }
+  
+  public static DoubleArrayList emptyList() {
+    return EMPTY_LIST;
+  }
+  
+  /**
+   * The backing store for the list.
+   */
+  private double[] array;
+  
+  /**
+   * The size of the list distinct from the length of the array. That is, it is the number of
+   * elements set in the list.
+   */
+  private int size;
+
+  /**
+   * Constructs a new mutable {@code DoubleArrayList} with default capacity.
+   */
+  DoubleArrayList() {
+    this(DEFAULT_CAPACITY);
+  }
+
+  /**
+   * Constructs a new mutable {@code DoubleArrayList} with the provided capacity.
+   */
+  DoubleArrayList(int capacity) {
+    array = new double[capacity];
+    size = 0;
+  }
+
+  /**
+   * Constructs a new mutable {@code DoubleArrayList} containing the same elements as {@code other}.
+   */
+  DoubleArrayList(List<Double> other) {
+    if (other instanceof DoubleArrayList) {
+      DoubleArrayList list = (DoubleArrayList) other;
+      array = list.array.clone();
+      size = list.size;
+    } else {
+      size = other.size();
+      array = new double[size];
+      for (int i = 0; i < size; i++) {
+        array[i] = other.get(i);
+      }
+    }
+  }
+  
+  @Override
+  public Double get(int index) {
+    return getDouble(index);
+  }
+
+  @Override
+  public double getDouble(int index) {
+    ensureIndexInRange(index);
+    return array[index];
+  }
+
+  @Override
+  public int size() {
+    return size;
+  }
+
+  @Override
+  public Double set(int index, Double element) {
+    return setDouble(index, element);
+  }
+
+  @Override
+  public double setDouble(int index, double element) {
+    ensureIsMutable();
+    ensureIndexInRange(index);
+    double previousValue = array[index];
+    array[index] = element;
+    return previousValue;
+  }
+
+  @Override
+  public void add(int index, Double element) {
+    addDouble(index, element);
+  }
+
+  /**
+   * Like {@link #add(Double)} but more efficient in that it doesn't box the element.
+   */
+  @Override
+  public void addDouble(double element) {
+    addDouble(size, element);
+  }
+
+  /**
+   * Like {@link #add(int, Double)} but more efficient in that it doesn't box the element.
+   */
+  private void addDouble(int index, double element) {
+    ensureIsMutable();
+    if (index < 0 || index > size) {
+      throw new IndexOutOfBoundsException(makeOutOfBoundsExceptionMessage(index));
+    }
+    
+    if (size < array.length) {
+      // Shift everything over to make room
+      System.arraycopy(array, index, array, index + 1, size - index);
+    } else {
+      // Resize to 1.5x the size
+      int length = ((size * 3) / 2) + 1;
+      double[] newArray = new double[length];
+      
+      // Copy the first part directly
+      System.arraycopy(array, 0, newArray, 0, index);
+      
+      // Copy the rest shifted over by one to make room
+      System.arraycopy(array, index, newArray, index + 1, size - index);
+      array = newArray;
+    }
+
+    array[index] = element;
+    size++;
+    modCount++;
+  }
+
+  @Override
+  public boolean addAll(Collection<? extends Double> collection) {
+    ensureIsMutable();
+    
+    if (collection == null) {
+      throw new NullPointerException();
+    }
+    
+    // We specialize when adding another DoubleArrayList to avoid boxing elements.
+    if (!(collection instanceof DoubleArrayList)) {
+      return super.addAll(collection);
+    }
+    
+    DoubleArrayList list = (DoubleArrayList) collection;
+    if (list.size == 0) {
+      return false;
+    }
+    
+    int overflow = Integer.MAX_VALUE - size;
+    if (overflow < list.size) {
+      // We can't actually represent a list this large.
+      throw new OutOfMemoryError();
+    }
+    
+    int newSize = size + list.size;
+    if (newSize > array.length) {
+      array = Arrays.copyOf(array, newSize);
+    }
+    
+    System.arraycopy(list.array, 0, array, size, list.size);
+    size = newSize;
+    modCount++;
+    return true;
+  }
+  
+  @Override
+  public boolean remove(Object o) {
+    ensureIsMutable();
+    for (int i = 0; i < size; i++) {
+      if (o.equals(array[i])) {
+        System.arraycopy(array, i + 1, array, i, size - i);
+        size--;
+        modCount++;
+        return true;
+      }
+    }
+    return false;
+  }
+
+  @Override
+  public Double remove(int index) {
+    ensureIsMutable();
+    ensureIndexInRange(index);
+    double value = array[index];
+    System.arraycopy(array, index + 1, array, index, size - index);
+    size--;
+    modCount++;
+    return value;
+  }
+
+  /**
+   * Ensures that the provided {@code index} is within the range of {@code [0, size]}. Throws an
+   * {@link IndexOutOfBoundsException} if it is not.
+   * 
+   * @param index the index to verify is in range
+   */
+  private void ensureIndexInRange(int index) {
+    if (index < 0 || index >= size) {
+      throw new IndexOutOfBoundsException(makeOutOfBoundsExceptionMessage(index));
+    }
+  }
+
+  private String makeOutOfBoundsExceptionMessage(int index) {
+    return "Index:" + index + ", Size:" + size;
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/DynamicMessage.java b/java/core/src/main/java/com/google/protobuf/DynamicMessage.java
new file mode 100644
index 00000000..3ea1b688
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/DynamicMessage.java
@@ -0,0 +1,644 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import com.google.protobuf.Descriptors.Descriptor;
+import com.google.protobuf.Descriptors.EnumValueDescriptor;
+import com.google.protobuf.Descriptors.FieldDescriptor;
+import com.google.protobuf.Descriptors.OneofDescriptor;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.Collections;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * An implementation of {@link Message} that can represent arbitrary types,
+ * given a {@link Descriptors.Descriptor}.
+ *
+ * @author kenton@google.com Kenton Varda
+ */
+public final class DynamicMessage extends AbstractMessage {
+  private final Descriptor type;
+  private final FieldSet<FieldDescriptor> fields;
+  private final FieldDescriptor[] oneofCases;
+  private final UnknownFieldSet unknownFields;
+  private int memoizedSize = -1;
+
+  /**
+   * Construct a {@code DynamicMessage} using the given {@code FieldSet}.
+   * oneofCases stores the FieldDescriptor for each oneof to indicate
+   * which field is set. Caller should make sure the array is immutable.
+   *
+   * This constructor is package private and will be used in
+   * {@code DynamicMutableMessage} to convert a mutable message to an immutable
+   * message.
+   */
+  DynamicMessage(Descriptor type, FieldSet<FieldDescriptor> fields,
+                 FieldDescriptor[] oneofCases,
+                 UnknownFieldSet unknownFields) {
+    this.type = type;
+    this.fields = fields;
+    this.oneofCases = oneofCases;
+    this.unknownFields = unknownFields;
+  }
+
+  /**
+   * Get a {@code DynamicMessage} representing the default instance of the
+   * given type.
+   */
+  public static DynamicMessage getDefaultInstance(Descriptor type) {
+    int oneofDeclCount = type.toProto().getOneofDeclCount();
+    FieldDescriptor[] oneofCases = new FieldDescriptor[oneofDeclCount];
+    return new DynamicMessage(type, FieldSet.<FieldDescriptor>emptySet(),
+                              oneofCases,
+                              UnknownFieldSet.getDefaultInstance());
+  }
+
+
+  /** Parse a message of the given type from the given input stream. */
+  public static DynamicMessage parseFrom(Descriptor type,
+                                         CodedInputStream input)
+                                         throws IOException {
+    return newBuilder(type).mergeFrom(input).buildParsed();
+  }
+
+  /** Parse a message of the given type from the given input stream. */
+  public static DynamicMessage parseFrom(
+      Descriptor type,
+      CodedInputStream input,
+      ExtensionRegistry extensionRegistry)
+      throws IOException {
+    return newBuilder(type).mergeFrom(input, extensionRegistry).buildParsed();
+  }
+
+  /** Parse {@code data} as a message of the given type and return it. */
+  public static DynamicMessage parseFrom(Descriptor type, ByteString data)
+                                         throws InvalidProtocolBufferException {
+    return newBuilder(type).mergeFrom(data).buildParsed();
+  }
+
+  /** Parse {@code data} as a message of the given type and return it. */
+  public static DynamicMessage parseFrom(Descriptor type, ByteString data,
+                                         ExtensionRegistry extensionRegistry)
+                                         throws InvalidProtocolBufferException {
+    return newBuilder(type).mergeFrom(data, extensionRegistry).buildParsed();
+  }
+
+  /** Parse {@code data} as a message of the given type and return it. */
+  public static DynamicMessage parseFrom(Descriptor type, byte[] data)
+                                         throws InvalidProtocolBufferException {
+    return newBuilder(type).mergeFrom(data).buildParsed();
+  }
+
+  /** Parse {@code data} as a message of the given type and return it. */
+  public static DynamicMessage parseFrom(Descriptor type, byte[] data,
+                                         ExtensionRegistry extensionRegistry)
+                                         throws InvalidProtocolBufferException {
+    return newBuilder(type).mergeFrom(data, extensionRegistry).buildParsed();
+  }
+
+  /** Parse a message of the given type from {@code input} and return it. */
+  public static DynamicMessage parseFrom(Descriptor type, InputStream input)
+                                         throws IOException {
+    return newBuilder(type).mergeFrom(input).buildParsed();
+  }
+
+  /** Parse a message of the given type from {@code input} and return it. */
+  public static DynamicMessage parseFrom(Descriptor type, InputStream input,
+                                         ExtensionRegistry extensionRegistry)
+                                         throws IOException {
+    return newBuilder(type).mergeFrom(input, extensionRegistry).buildParsed();
+  }
+
+  /** Construct a {@link Message.Builder} for the given type. */
+  public static Builder newBuilder(Descriptor type) {
+    return new Builder(type);
+  }
+
+  /**
+   * Construct a {@link Message.Builder} for a message of the same type as
+   * {@code prototype}, and initialize it with {@code prototype}'s contents.
+   */
+  public static Builder newBuilder(Message prototype) {
+    return new Builder(prototype.getDescriptorForType()).mergeFrom(prototype);
+  }
+
+  // -----------------------------------------------------------------
+  // Implementation of Message interface.
+
+  public Descriptor getDescriptorForType() {
+    return type;
+  }
+
+  public DynamicMessage getDefaultInstanceForType() {
+    return getDefaultInstance(type);
+  }
+
+  public Map<FieldDescriptor, Object> getAllFields() {
+    return fields.getAllFields();
+  }
+
+  public boolean hasOneof(OneofDescriptor oneof) {
+    verifyOneofContainingType(oneof);
+    FieldDescriptor field = oneofCases[oneof.getIndex()];
+    if (field == null) {
+      return false;
+    }
+    return true;
+  }
+
+  public FieldDescriptor getOneofFieldDescriptor(OneofDescriptor oneof) {
+    verifyOneofContainingType(oneof);
+    return oneofCases[oneof.getIndex()];
+  }
+
+  public boolean hasField(FieldDescriptor field) {
+    verifyContainingType(field);
+    return fields.hasField(field);
+  }
+
+  public Object getField(FieldDescriptor field) {
+    verifyContainingType(field);
+    Object result = fields.getField(field);
+    if (result == null) {
+      if (field.isRepeated()) {
+        result = Collections.emptyList();
+      } else if (field.getJavaType() == FieldDescriptor.JavaType.MESSAGE) {
+        result = getDefaultInstance(field.getMessageType());
+      } else {
+        result = field.getDefaultValue();
+      }
+    }
+    return result;
+  }
+
+  public int getRepeatedFieldCount(FieldDescriptor field) {
+    verifyContainingType(field);
+    return fields.getRepeatedFieldCount(field);
+  }
+
+  public Object getRepeatedField(FieldDescriptor field, int index) {
+    verifyContainingType(field);
+    return fields.getRepeatedField(field, index);
+  }
+
+  public UnknownFieldSet getUnknownFields() {
+    return unknownFields;
+  }
+
+  static boolean isInitialized(Descriptor type,
+                               FieldSet<FieldDescriptor> fields) {
+    // Check that all required fields are present.
+    for (final FieldDescriptor field : type.getFields()) {
+      if (field.isRequired()) {
+        if (!fields.hasField(field)) {
+          return false;
+        }
+      }
+    }
+
+    // Check that embedded messages are initialized.
+    return fields.isInitialized();
+  }
+
+  @Override
+  public boolean isInitialized() {
+    return isInitialized(type, fields);
+  }
+
+  @Override
+  public void writeTo(CodedOutputStream output) throws IOException {
+    if (type.getOptions().getMessageSetWireFormat()) {
+      fields.writeMessageSetTo(output);
+      unknownFields.writeAsMessageSetTo(output);
+    } else {
+      fields.writeTo(output);
+      unknownFields.writeTo(output);
+    }
+  }
+
+  @Override
+  public int getSerializedSize() {
+    int size = memoizedSize;
+    if (size != -1) return size;
+
+    if (type.getOptions().getMessageSetWireFormat()) {
+      size = fields.getMessageSetSerializedSize();
+      size += unknownFields.getSerializedSizeAsMessageSet();
+    } else {
+      size = fields.getSerializedSize();
+      size += unknownFields.getSerializedSize();
+    }
+
+    memoizedSize = size;
+    return size;
+  }
+
+  public Builder newBuilderForType() {
+    return new Builder(type);
+  }
+
+  public Builder toBuilder() {
+    return newBuilderForType().mergeFrom(this);
+  }
+
+  public Parser<DynamicMessage> getParserForType() {
+    return new AbstractParser<DynamicMessage>() {
+      public DynamicMessage parsePartialFrom(
+          CodedInputStream input,
+          ExtensionRegistryLite extensionRegistry)
+          throws InvalidProtocolBufferException {
+        Builder builder = newBuilder(type);
+        try {
+          builder.mergeFrom(input, extensionRegistry);
+        } catch (InvalidProtocolBufferException e) {
+          throw e.setUnfinishedMessage(builder.buildPartial());
+        } catch (IOException e) {
+          throw new InvalidProtocolBufferException(e.getMessage())
+              .setUnfinishedMessage(builder.buildPartial());
+        }
+        return builder.buildPartial();
+      }
+    };
+  }
+
+  /** Verifies that the field is a field of this message. */
+  private void verifyContainingType(FieldDescriptor field) {
+    if (field.getContainingType() != type) {
+      throw new IllegalArgumentException(
+        "FieldDescriptor does not match message type.");
+    }
+  }
+
+  /** Verifies that the oneof is an oneof of this message. */
+  private void verifyOneofContainingType(OneofDescriptor oneof) {
+    if (oneof.getContainingType() != type) {
+      throw new IllegalArgumentException(
+        "OneofDescriptor does not match message type.");
+    }
+  }
+
+  // =================================================================
+
+  /**
+   * Builder for {@link DynamicMessage}s.
+   */
+  public static final class Builder extends AbstractMessage.Builder<Builder> {
+    private final Descriptor type;
+    private FieldSet<FieldDescriptor> fields;
+    private final FieldDescriptor[] oneofCases;
+    private UnknownFieldSet unknownFields;
+
+    /** Construct a {@code Builder} for the given type. */
+    private Builder(Descriptor type) {
+      this.type = type;
+      this.fields = FieldSet.newFieldSet();
+      this.unknownFields = UnknownFieldSet.getDefaultInstance();
+      this.oneofCases = new FieldDescriptor[type.toProto().getOneofDeclCount()];
+    }
+
+    // ---------------------------------------------------------------
+    // Implementation of Message.Builder interface.
+
+    @Override
+    public Builder clear() {
+      if (fields.isImmutable()) {
+        fields = FieldSet.newFieldSet();
+      } else {
+        fields.clear();
+      }
+      unknownFields = UnknownFieldSet.getDefaultInstance();
+      return this;
+    }
+
+    @Override
+    public Builder mergeFrom(Message other) {
+      if (other instanceof DynamicMessage) {
+        // This should be somewhat faster than calling super.mergeFrom().
+        DynamicMessage otherDynamicMessage = (DynamicMessage) other;
+        if (otherDynamicMessage.type != type) {
+          throw new IllegalArgumentException(
+            "mergeFrom(Message) can only merge messages of the same type.");
+        }
+        ensureIsMutable();
+        fields.mergeFrom(otherDynamicMessage.fields);
+        mergeUnknownFields(otherDynamicMessage.unknownFields);
+        for (int i = 0; i < oneofCases.length; i++) {
+          if (oneofCases[i] == null) {
+            oneofCases[i] = otherDynamicMessage.oneofCases[i];
+          } else {
+            if ((otherDynamicMessage.oneofCases[i] != null)
+                && (oneofCases[i] != otherDynamicMessage.oneofCases[i])) {
+              fields.clearField(oneofCases[i]);
+              oneofCases[i] = otherDynamicMessage.oneofCases[i];
+            }
+          }
+        }
+        return this;
+      } else {
+        return super.mergeFrom(other);
+      }
+    }
+
+    public DynamicMessage build() {
+      if (!isInitialized()) {
+        throw newUninitializedMessageException(
+          new DynamicMessage(type, fields,
+              java.util.Arrays.copyOf(oneofCases, oneofCases.length), unknownFields));
+      }
+      return buildPartial();
+    }
+
+    /**
+     * Helper for DynamicMessage.parseFrom() methods to call.  Throws
+     * {@link InvalidProtocolBufferException} instead of
+     * {@link UninitializedMessageException}.
+     */
+    private DynamicMessage buildParsed() throws InvalidProtocolBufferException {
+      if (!isInitialized()) {
+        throw newUninitializedMessageException(
+          new DynamicMessage(type, fields,
+              java.util.Arrays.copyOf(oneofCases, oneofCases.length), unknownFields))
+          .asInvalidProtocolBufferException();
+      }
+      return buildPartial();
+    }
+
+    public DynamicMessage buildPartial() {
+      fields.makeImmutable();
+      DynamicMessage result =
+        new DynamicMessage(type, fields,
+            java.util.Arrays.copyOf(oneofCases, oneofCases.length), unknownFields);
+      return result;
+    }
+
+    @Override
+    public Builder clone() {
+      Builder result = new Builder(type);
+      result.fields.mergeFrom(fields);
+      result.mergeUnknownFields(unknownFields);
+      System.arraycopy(oneofCases, 0, result.oneofCases, 0 , oneofCases.length);
+      return result;
+    }
+
+    public boolean isInitialized() {
+      return DynamicMessage.isInitialized(type, fields);
+    }
+
+    public Descriptor getDescriptorForType() {
+      return type;
+    }
+
+    public DynamicMessage getDefaultInstanceForType() {
+      return getDefaultInstance(type);
+    }
+
+    public Map<FieldDescriptor, Object> getAllFields() {
+      return fields.getAllFields();
+    }
+
+    public Builder newBuilderForField(FieldDescriptor field) {
+      verifyContainingType(field);
+
+      if (field.getJavaType() != FieldDescriptor.JavaType.MESSAGE) {
+        throw new IllegalArgumentException(
+          "newBuilderForField is only valid for fields with message type.");
+      }
+
+      return new Builder(field.getMessageType());
+    }
+
+    public boolean hasOneof(OneofDescriptor oneof) {
+      verifyOneofContainingType(oneof);
+      FieldDescriptor field = oneofCases[oneof.getIndex()];
+      if (field == null) {
+        return false;
+      }
+      return true;
+    }
+
+    public FieldDescriptor getOneofFieldDescriptor(OneofDescriptor oneof) {
+      verifyOneofContainingType(oneof);
+      return oneofCases[oneof.getIndex()];
+    }
+
+    public Builder clearOneof(OneofDescriptor oneof) {
+      verifyOneofContainingType(oneof);
+      FieldDescriptor field = oneofCases[oneof.getIndex()];
+      if (field != null) {
+        clearField(field);
+      }
+      return this;
+    }
+
+    public boolean hasField(FieldDescriptor field) {
+      verifyContainingType(field);
+      return fields.hasField(field);
+    }
+
+    public Object getField(FieldDescriptor field) {
+      verifyContainingType(field);
+      Object result = fields.getField(field);
+      if (result == null) {
+        if (field.isRepeated()) {
+          result = Collections.emptyList();
+        } else if (field.getJavaType() == FieldDescriptor.JavaType.MESSAGE) {
+          result = getDefaultInstance(field.getMessageType());
+        } else {
+          result = field.getDefaultValue();
+        }
+      }
+      return result;
+    }
+
+    public Builder setField(FieldDescriptor field, Object value) {
+      verifyContainingType(field);
+      ensureIsMutable();
+      // TODO(xiaofeng): This check should really be put in FieldSet.setField()
+      // where all other such checks are done. However, currently
+      // FieldSet.setField() permits Integer value for enum fields probably
+      // because of some internal features we support. Should figure it out
+      // and move this check to a more appropriate place.
+      if (field.getType() == FieldDescriptor.Type.ENUM) {
+        ensureEnumValueDescriptor(field, value);
+      }
+      OneofDescriptor oneofDescriptor = field.getContainingOneof();
+      if (oneofDescriptor != null) {
+        int index = oneofDescriptor.getIndex();
+        FieldDescriptor oldField = oneofCases[index];
+        if ((oldField != null) && (oldField != field)) {
+          fields.clearField(oldField);
+        }
+        oneofCases[index] = field;
+      }
+      fields.setField(field, value);
+      return this;
+    }
+
+    public Builder clearField(FieldDescriptor field) {
+      verifyContainingType(field);
+      ensureIsMutable();
+      OneofDescriptor oneofDescriptor = field.getContainingOneof();
+      if (oneofDescriptor != null) {
+        int index = oneofDescriptor.getIndex();
+        if (oneofCases[index] == field) {
+          oneofCases[index] = null;
+        }
+      }
+      fields.clearField(field);
+      return this;
+    }
+
+    public int getRepeatedFieldCount(FieldDescriptor field) {
+      verifyContainingType(field);
+      return fields.getRepeatedFieldCount(field);
+    }
+
+    public Object getRepeatedField(FieldDescriptor field, int index) {
+      verifyContainingType(field);
+      return fields.getRepeatedField(field, index);
+    }
+
+    public Builder setRepeatedField(FieldDescriptor field,
+                                    int index, Object value) {
+      verifyContainingType(field);
+      ensureIsMutable();
+      fields.setRepeatedField(field, index, value);
+      return this;
+    }
+
+    public Builder addRepeatedField(FieldDescriptor field, Object value) {
+      verifyContainingType(field);
+      ensureIsMutable();
+      fields.addRepeatedField(field, value);
+      return this;
+    }
+
+    public UnknownFieldSet getUnknownFields() {
+      return unknownFields;
+    }
+
+    public Builder setUnknownFields(UnknownFieldSet unknownFields) {
+      if (getDescriptorForType().getFile().getSyntax()
+          == Descriptors.FileDescriptor.Syntax.PROTO3) {
+        // Proto3 discards unknown fields.
+        return this;
+      }
+      this.unknownFields = unknownFields;
+      return this;
+    }
+
+    @Override
+    public Builder mergeUnknownFields(UnknownFieldSet unknownFields) {
+      if (getDescriptorForType().getFile().getSyntax()
+          == Descriptors.FileDescriptor.Syntax.PROTO3) {
+        // Proto3 discards unknown fields.
+        return this;
+      }
+      this.unknownFields =
+        UnknownFieldSet.newBuilder(this.unknownFields)
+                       .mergeFrom(unknownFields)
+                       .build();
+      return this;
+    }
+
+    /** Verifies that the field is a field of this message. */
+    private void verifyContainingType(FieldDescriptor field) {
+      if (field.getContainingType() != type) {
+        throw new IllegalArgumentException(
+          "FieldDescriptor does not match message type.");
+      }
+    }
+
+    /** Verifies that the oneof is an oneof of this message. */
+    private void verifyOneofContainingType(OneofDescriptor oneof) {
+      if (oneof.getContainingType() != type) {
+        throw new IllegalArgumentException(
+          "OneofDescriptor does not match message type.");
+      }
+    }
+
+    /** Verifies that the value is EnumValueDescriptor and matches Enum Type. */
+    private void ensureSingularEnumValueDescriptor(
+        FieldDescriptor field, Object value) {
+      if (value == null) {
+        throw new NullPointerException();
+      }
+      if (!(value instanceof EnumValueDescriptor)) {
+        throw new IllegalArgumentException(
+          "DynamicMessage should use EnumValueDescriptor to set Enum Value.");
+      }
+      // TODO(xiaofeng): Re-enable this check after Orgstore is fixed to not
+      // set incorrect EnumValueDescriptors.
+      // EnumDescriptor fieldType = field.getEnumType();
+      // EnumDescriptor fieldValueType = ((EnumValueDescriptor) value).getType();
+      // if (fieldType != fieldValueType) {
+      //  throw new IllegalArgumentException(String.format(
+      //      "EnumDescriptor %s of field doesn't match EnumDescriptor %s of field value",
+      //      fieldType.getFullName(), fieldValueType.getFullName()));
+      // }
+    }
+
+    /** Verifies the value for an enum field. */
+    private void ensureEnumValueDescriptor(
+        FieldDescriptor field, Object value) {
+      if (field.isRepeated()) {
+        for (Object item : (List) value) {
+          ensureSingularEnumValueDescriptor(field, item);
+        }
+      } else {
+         ensureSingularEnumValueDescriptor(field, value);
+      }
+    }
+
+    private void ensureIsMutable() {
+      if (fields.isImmutable()) {
+        fields = fields.clone();
+      }
+    }
+
+    @Override
+    public com.google.protobuf.Message.Builder getFieldBuilder(FieldDescriptor field) {
+      // TODO(xiangl): need implementation for dynamic message
+      throw new UnsupportedOperationException(
+        "getFieldBuilder() called on a dynamic message type.");
+    }
+
+    @Override
+    public com.google.protobuf.Message.Builder getRepeatedFieldBuilder(FieldDescriptor field,
+        int index) {
+      throw new UnsupportedOperationException(
+        "getRepeatedFieldBuilder() called on a dynamic message type.");
+    }
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/Extension.java b/java/core/src/main/java/com/google/protobuf/Extension.java
new file mode 100644
index 00000000..68d29f33
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/Extension.java
@@ -0,0 +1,85 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+/**
+ * Interface that generated extensions implement.
+ *
+ * @author liujisi@google.com (Jisi Liu)
+ */
+public abstract class Extension<ContainingType extends MessageLite, Type>
+    extends ExtensionLite<ContainingType, Type> {
+
+  /** Returns the descriptor of the extension. */
+  public abstract Descriptors.FieldDescriptor getDescriptor();
+
+  /** Returns whether or not this extension is a Lite Extension. */
+  final boolean isLite() {
+    return false;
+  }
+
+  // All the methods below are extension implementation details.
+
+  /**
+   * The API type that the extension is used for.
+   */
+  protected enum ExtensionType {
+    IMMUTABLE,
+    MUTABLE,
+    PROTO1,
+  }
+
+  protected ExtensionType getExtensionType() {
+    // TODO(liujisi): make this abstract after we fix proto1.
+    return ExtensionType.IMMUTABLE;
+  }
+
+  /**
+   * Type of a message extension.
+   */
+  public enum MessageType {
+    PROTO1,
+    PROTO2,
+  }
+  
+  /**
+   * If the extension is a message extension (i.e., getLiteType() == MESSAGE),
+   * returns the type of the message, otherwise undefined.
+   */
+  public MessageType getMessageType() {
+    return MessageType.PROTO2;
+  }
+
+  protected abstract Object fromReflectionType(Object value);
+  protected abstract Object singularFromReflectionType(Object value);
+  protected abstract Object toReflectionType(Object value);
+  protected abstract Object singularToReflectionType(Object value);
+}
diff --git a/java/core/src/main/java/com/google/protobuf/ExtensionLite.java b/java/core/src/main/java/com/google/protobuf/ExtensionLite.java
new file mode 100644
index 00000000..f8f5bd2c
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/ExtensionLite.java
@@ -0,0 +1,63 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+/**
+ * Lite interface that generated extensions implement.
+ * <p>
+ * Methods are for use by generated code only. You can hold a reference to
+ * extensions using this type name.
+ */
+public abstract class ExtensionLite<ContainingType extends MessageLite, Type> {
+
+  /** Returns the field number of the extension. */
+  public abstract int getNumber();
+
+  /** Returns the type of the field. */
+  public abstract WireFormat.FieldType getLiteType();
+
+  /** Returns whether it is a repeated field. */
+  public abstract boolean isRepeated();
+
+  /** Returns the default value of the extension field. */
+  public abstract Type getDefaultValue();
+
+  /**
+   * Returns the default instance of the extension field, if it's a message
+   * extension.
+   */
+  public abstract MessageLite getMessageDefaultInstance();
+  
+  /** Returns whether or not this extension is a Lite Extension. */
+  boolean isLite() {
+    return true;
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/ExtensionRegistry.java b/java/core/src/main/java/com/google/protobuf/ExtensionRegistry.java
new file mode 100644
index 00000000..0067392f
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/ExtensionRegistry.java
@@ -0,0 +1,392 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import com.google.protobuf.Descriptors.Descriptor;
+import com.google.protobuf.Descriptors.FieldDescriptor;
+
+import java.util.Collection;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Set;
+
+/**
+ * A table of known extensions, searchable by name or field number.  When
+ * parsing a protocol message that might have extensions, you must provide
+ * an {@code ExtensionRegistry} in which you have registered any extensions
+ * that you want to be able to parse.  Otherwise, those extensions will just
+ * be treated like unknown fields.
+ *
+ * <p>For example, if you had the {@code .proto} file:
+ *
+ * <pre>
+ * option java_class = "MyProto";
+ *
+ * message Foo {
+ *   extensions 1000 to max;
+ * }
+ *
+ * extend Foo {
+ *   optional int32 bar;
+ * }
+ * </pre>
+ *
+ * Then you might write code like:
+ *
+ * <pre>
+ * ExtensionRegistry registry = ExtensionRegistry.newInstance();
+ * registry.add(MyProto.bar);
+ * MyProto.Foo message = MyProto.Foo.parseFrom(input, registry);
+ * </pre>
+ *
+ * <p>Background:
+ *
+ * <p>You might wonder why this is necessary.  Two alternatives might come to
+ * mind.  First, you might imagine a system where generated extensions are
+ * automatically registered when their containing classes are loaded.  This
+ * is a popular technique, but is bad design; among other things, it creates a
+ * situation where behavior can change depending on what classes happen to be
+ * loaded.  It also introduces a security vulnerability, because an
+ * unprivileged class could cause its code to be called unexpectedly from a
+ * privileged class by registering itself as an extension of the right type.
+ *
+ * <p>Another option you might consider is lazy parsing: do not parse an
+ * extension until it is first requested, at which point the caller must
+ * provide a type to use.  This introduces a different set of problems.  First,
+ * it would require a mutex lock any time an extension was accessed, which
+ * would be slow.  Second, corrupt data would not be detected until first
+ * access, at which point it would be much harder to deal with it.  Third, it
+ * could violate the expectation that message objects are immutable, since the
+ * type provided could be any arbitrary message class.  An unprivileged user
+ * could take advantage of this to inject a mutable object into a message
+ * belonging to privileged code and create mischief.
+ *
+ * @author kenton@google.com Kenton Varda
+ */
+public class ExtensionRegistry extends ExtensionRegistryLite {
+  /** Construct a new, empty instance. */
+  public static ExtensionRegistry newInstance() {
+    return new ExtensionRegistry();
+  }
+
+  /** Get the unmodifiable singleton empty instance. */
+  public static ExtensionRegistry getEmptyRegistry() {
+    return EMPTY;
+  }
+
+
+  /** Returns an unmodifiable view of the registry. */
+  @Override
+  public ExtensionRegistry getUnmodifiable() {
+    return new ExtensionRegistry(this);
+  }
+
+  /** A (Descriptor, Message) pair, returned by lookup methods. */
+  public static final class ExtensionInfo {
+    /** The extension's descriptor. */
+    public final FieldDescriptor descriptor;
+
+    /**
+     * A default instance of the extension's type, if it has a message type.
+     * Otherwise, {@code null}.
+     */
+    public final Message defaultInstance;
+
+    private ExtensionInfo(final FieldDescriptor descriptor) {
+      this.descriptor = descriptor;
+      defaultInstance = null;
+    }
+    private ExtensionInfo(final FieldDescriptor descriptor,
+                          final Message defaultInstance) {
+      this.descriptor = descriptor;
+      this.defaultInstance = defaultInstance;
+    }
+  }
+
+  /**
+   * Deprecated. Use {@link #findImmutableExtensionByName(String)} instead.
+   */
+  public ExtensionInfo findExtensionByName(final String fullName) {
+    return findImmutableExtensionByName(fullName);
+  }
+
+  /**
+   * Find an extension for immutable APIs by fully-qualified field name,
+   * in the proto namespace. i.e. {@code result.descriptor.fullName()} will
+   * match {@code fullName} if a match is found.
+   *
+   * @return Information about the extension if found, or {@code null}
+   *         otherwise.
+   */
+  public ExtensionInfo findImmutableExtensionByName(final String fullName) {
+    return immutableExtensionsByName.get(fullName);
+  }
+
+  /**
+   * Find an extension for mutable APIs by fully-qualified field name,
+   * in the proto namespace. i.e. {@code result.descriptor.fullName()} will
+   * match {@code fullName} if a match is found.
+   *
+   * @return Information about the extension if found, or {@code null}
+   *         otherwise.
+   */
+  public ExtensionInfo findMutableExtensionByName(final String fullName) {
+    return mutableExtensionsByName.get(fullName);
+  }
+
+  /**
+   * Deprecated. Use {@link #findImmutableExtensionByNumber(
+   * Descriptors.Descriptor, int)}
+   */
+  public ExtensionInfo findExtensionByNumber(
+      final Descriptor containingType, final int fieldNumber) {
+    return findImmutableExtensionByNumber(containingType, fieldNumber);
+  }
+
+  /**
+   * Find an extension by containing type and field number for immutable APIs.
+   *
+   * @return Information about the extension if found, or {@code null}
+   *         otherwise.
+   */
+  public ExtensionInfo findImmutableExtensionByNumber(
+      final Descriptor containingType, final int fieldNumber) {
+    return immutableExtensionsByNumber.get(
+      new DescriptorIntPair(containingType, fieldNumber));
+  }
+
+  /**
+   * Find an extension by containing type and field number for mutable APIs.
+   *
+   * @return Information about the extension if found, or {@code null}
+   *         otherwise.
+   */
+  public ExtensionInfo findMutableExtensionByNumber(
+      final Descriptor containingType, final int fieldNumber) {
+    return mutableExtensionsByNumber.get(
+        new DescriptorIntPair(containingType, fieldNumber));
+  }
+
+  /**
+   * Find all extensions for mutable APIs by fully-qualified name of
+   * extended class. Note that this method is more computationally expensive
+   * than getting a single extension by name or number.
+   *
+   * @return Information about the extensions found, or {@code null} if there
+   *     are none.
+   */
+  public Set<ExtensionInfo> getAllMutableExtensionsByExtendedType(final String fullName) {
+    HashSet<ExtensionInfo> extensions = new HashSet<ExtensionInfo>();
+    for (DescriptorIntPair pair : mutableExtensionsByNumber.keySet()) {
+      if (pair.descriptor.getFullName().equals(fullName)) {
+        extensions.add(mutableExtensionsByNumber.get(pair));
+      }
+    }
+    return extensions;
+  }
+
+  /**
+   * Find all extensions for immutable APIs by fully-qualified name of
+   * extended class. Note that this method is more computationally expensive
+   * than getting a single extension by name or number.
+   *
+   * @return Information about the extensions found, or {@code null} if there
+   *     are none.
+   */
+  public Set<ExtensionInfo> getAllImmutableExtensionsByExtendedType(final String fullName) {
+    HashSet<ExtensionInfo> extensions = new HashSet<ExtensionInfo>();
+    for (DescriptorIntPair pair : immutableExtensionsByNumber.keySet()) {
+      if (pair.descriptor.getFullName().equals(fullName)) {
+        extensions.add(immutableExtensionsByNumber.get(pair));
+      }
+    }
+    return extensions;
+  }
+
+  /** Add an extension from a generated file to the registry. */
+  public void add(final Extension<?, ?> extension) {
+    if (extension.getExtensionType() != Extension.ExtensionType.IMMUTABLE &&
+        extension.getExtensionType() != Extension.ExtensionType.MUTABLE) {
+      // do not support other extension types. ignore
+      return;
+    }
+    add(newExtensionInfo(extension), extension.getExtensionType());
+  }
+
+  static ExtensionInfo newExtensionInfo(final Extension<?, ?> extension) {
+    if (extension.getDescriptor().getJavaType() ==
+        FieldDescriptor.JavaType.MESSAGE) {
+      if (extension.getMessageDefaultInstance() == null) {
+        throw new IllegalStateException(
+            "Registered message-type extension had null default instance: " +
+                extension.getDescriptor().getFullName());
+      }
+      return new ExtensionInfo(extension.getDescriptor(),
+          (Message) extension.getMessageDefaultInstance());
+    } else {
+      return new ExtensionInfo(extension.getDescriptor(), null);
+    }
+  }
+
+  /** Add a non-message-type extension to the registry by descriptor. */
+  public void add(final FieldDescriptor type) {
+    if (type.getJavaType() == FieldDescriptor.JavaType.MESSAGE) {
+      throw new IllegalArgumentException(
+        "ExtensionRegistry.add() must be provided a default instance when " +
+        "adding an embedded message extension.");
+    }
+    ExtensionInfo info = new ExtensionInfo(type, null);
+    add(info, Extension.ExtensionType.IMMUTABLE);
+    add(info, Extension.ExtensionType.MUTABLE);
+  }
+
+  /** Add a message-type extension to the registry by descriptor. */
+  public void add(final FieldDescriptor type, final Message defaultInstance) {
+    if (type.getJavaType() != FieldDescriptor.JavaType.MESSAGE) {
+      throw new IllegalArgumentException(
+        "ExtensionRegistry.add() provided a default instance for a " +
+        "non-message extension.");
+    }
+      add(new ExtensionInfo(type, defaultInstance),
+          Extension.ExtensionType.IMMUTABLE);
+  }
+
+  // =================================================================
+  // Private stuff.
+
+  private ExtensionRegistry() {
+    this.immutableExtensionsByName = new HashMap<String, ExtensionInfo>();
+    this.mutableExtensionsByName = new HashMap<String, ExtensionInfo>();
+    this.immutableExtensionsByNumber =
+        new HashMap<DescriptorIntPair, ExtensionInfo>();
+    this.mutableExtensionsByNumber =
+        new HashMap<DescriptorIntPair, ExtensionInfo>();
+  }
+
+  private ExtensionRegistry(ExtensionRegistry other) {
+    super(other);
+    this.immutableExtensionsByName =
+        Collections.unmodifiableMap(other.immutableExtensionsByName);
+    this.mutableExtensionsByName =
+        Collections.unmodifiableMap(other.mutableExtensionsByName);
+    this.immutableExtensionsByNumber =
+        Collections.unmodifiableMap(other.immutableExtensionsByNumber);
+    this.mutableExtensionsByNumber =
+            Collections.unmodifiableMap(other.mutableExtensionsByNumber);
+  }
+
+  private final Map<String, ExtensionInfo> immutableExtensionsByName;
+  private final Map<String, ExtensionInfo> mutableExtensionsByName;
+  private final Map<DescriptorIntPair, ExtensionInfo> immutableExtensionsByNumber;
+  private final Map<DescriptorIntPair, ExtensionInfo> mutableExtensionsByNumber;
+
+  ExtensionRegistry(boolean empty) {
+    super(ExtensionRegistryLite.getEmptyRegistry());
+    this.immutableExtensionsByName =
+        Collections.<String, ExtensionInfo>emptyMap();
+    this.mutableExtensionsByName =
+        Collections.<String, ExtensionInfo>emptyMap();
+    this.immutableExtensionsByNumber =
+        Collections.<DescriptorIntPair, ExtensionInfo>emptyMap();
+    this.mutableExtensionsByNumber =
+            Collections.<DescriptorIntPair, ExtensionInfo>emptyMap();
+  }
+  private static final ExtensionRegistry EMPTY = new ExtensionRegistry(true);
+
+  private void add(
+      final ExtensionInfo extension,
+      final Extension.ExtensionType extensionType) {
+    if (!extension.descriptor.isExtension()) {
+      throw new IllegalArgumentException(
+          "ExtensionRegistry.add() was given a FieldDescriptor for a regular " +
+              "(non-extension) field.");
+    }
+
+    Map<String, ExtensionInfo> extensionsByName;
+    Map<DescriptorIntPair, ExtensionInfo> extensionsByNumber;
+    switch (extensionType) {
+      case IMMUTABLE:
+        extensionsByName = immutableExtensionsByName;
+        extensionsByNumber = immutableExtensionsByNumber;
+        break;
+      case MUTABLE:
+        extensionsByName = mutableExtensionsByName;
+        extensionsByNumber = mutableExtensionsByNumber;
+        break;
+      default:
+        // Ignore the unknown supported type.
+        return;
+    }
+
+    extensionsByName.put(extension.descriptor.getFullName(), extension);
+    extensionsByNumber.put(
+      new DescriptorIntPair(extension.descriptor.getContainingType(),
+                            extension.descriptor.getNumber()),
+      extension);
+
+    final FieldDescriptor field = extension.descriptor;
+    if (field.getContainingType().getOptions().getMessageSetWireFormat() &&
+        field.getType() == FieldDescriptor.Type.MESSAGE &&
+        field.isOptional() &&
+        field.getExtensionScope() == field.getMessageType()) {
+      // This is an extension of a MessageSet type defined within the extension
+      // type's own scope.  For backwards-compatibility, allow it to be looked
+      // up by type name.
+      extensionsByName.put(field.getMessageType().getFullName(), extension);
+    }
+  }
+
+  /** A (GenericDescriptor, int) pair, used as a map key. */
+  private static final class DescriptorIntPair {
+    private final Descriptor descriptor;
+    private final int number;
+
+    DescriptorIntPair(final Descriptor descriptor, final int number) {
+      this.descriptor = descriptor;
+      this.number = number;
+    }
+
+    @Override
+    public int hashCode() {
+      return descriptor.hashCode() * ((1 << 16) - 1) + number;
+    }
+    @Override
+    public boolean equals(final Object obj) {
+      if (!(obj instanceof DescriptorIntPair)) {
+        return false;
+      }
+      final DescriptorIntPair other = (DescriptorIntPair)obj;
+      return descriptor == other.descriptor && number == other.number;
+    }
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/ExtensionRegistryLite.java b/java/core/src/main/java/com/google/protobuf/ExtensionRegistryLite.java
new file mode 100644
index 00000000..65cf7385
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/ExtensionRegistryLite.java
@@ -0,0 +1,185 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * Equivalent to {@link ExtensionRegistry} but supports only "lite" types.
+ * <p>
+ * If all of your types are lite types, then you only need to use
+ * {@code ExtensionRegistryLite}.  Similarly, if all your types are regular
+ * types, then you only need {@link ExtensionRegistry}.  Typically it does not
+ * make sense to mix the two, since if you have any regular types in your
+ * program, you then require the full runtime and lose all the benefits of
+ * the lite runtime, so you might as well make all your types be regular types.
+ * However, in some cases (e.g. when depending on multiple third-party libraries
+ * where one uses lite types and one uses regular), you may find yourself
+ * wanting to mix the two.  In this case things get more complicated.
+ * <p>
+ * There are three factors to consider:  Whether the type being extended is
+ * lite, whether the embedded type (in the case of a message-typed extension)
+ * is lite, and whether the extension itself is lite.  Since all three are
+ * declared in different files, they could all be different.  Here are all
+ * the combinations and which type of registry to use:
+ * <pre>
+ *   Extended type     Inner type    Extension         Use registry
+ *   =======================================================================
+ *   lite              lite          lite              ExtensionRegistryLite
+ *   lite              regular       lite              ExtensionRegistry
+ *   regular           regular       regular           ExtensionRegistry
+ *   all other combinations                            not supported
+ * </pre>
+ * <p>
+ * Note that just as regular types are not allowed to contain lite-type fields,
+ * they are also not allowed to contain lite-type extensions.  This is because
+ * regular types must be fully accessible via reflection, which in turn means
+ * that all the inner messages must also support reflection.  On the other hand,
+ * since regular types implement the entire lite interface, there is no problem
+ * with embedding regular types inside lite types.
+ *
+ * @author kenton@google.com Kenton Varda
+ */
+public class ExtensionRegistryLite {
+
+  // Set true to enable lazy parsing feature for MessageSet.
+  //
+  // TODO(xiangl): Now we use a global flag to control whether enable lazy
+  // parsing feature for MessageSet, which may be too crude for some
+  // applications. Need to support this feature on smaller granularity.
+  private static volatile boolean eagerlyParseMessageSets = false;
+
+  public static boolean isEagerlyParseMessageSets() {
+    return eagerlyParseMessageSets;
+  }
+
+  public static void setEagerlyParseMessageSets(boolean isEagerlyParse) {
+    eagerlyParseMessageSets = isEagerlyParse;
+  }
+
+  /** Construct a new, empty instance. */
+  public static ExtensionRegistryLite newInstance() {
+    return new ExtensionRegistryLite();
+  }
+
+  /** Get the unmodifiable singleton empty instance. */
+  public static ExtensionRegistryLite getEmptyRegistry() {
+    return EMPTY;
+  }
+
+  /** Returns an unmodifiable view of the registry. */
+  public ExtensionRegistryLite getUnmodifiable() {
+    return new ExtensionRegistryLite(this);
+  }
+
+  /**
+   * Find an extension by containing type and field number.
+   *
+   * @return Information about the extension if found, or {@code null}
+   *         otherwise.
+   */
+  @SuppressWarnings("unchecked")
+  public <ContainingType extends MessageLite>
+      GeneratedMessageLite.GeneratedExtension<ContainingType, ?>
+        findLiteExtensionByNumber(
+          final ContainingType containingTypeDefaultInstance,
+          final int fieldNumber) {
+    return (GeneratedMessageLite.GeneratedExtension<ContainingType, ?>)
+      extensionsByNumber.get(
+        new ObjectIntPair(containingTypeDefaultInstance, fieldNumber));
+  }
+
+  /** Add an extension from a lite generated file to the registry. */
+  public final void add(
+      final GeneratedMessageLite.GeneratedExtension<?, ?> extension) {
+    extensionsByNumber.put(
+      new ObjectIntPair(extension.getContainingTypeDefaultInstance(),
+                        extension.getNumber()),
+      extension);
+  }
+
+  // =================================================================
+  // Private stuff.
+
+  // Constructors are package-private so that ExtensionRegistry can subclass
+  // this.
+
+  ExtensionRegistryLite() {
+    this.extensionsByNumber =
+        new HashMap<ObjectIntPair,
+                    GeneratedMessageLite.GeneratedExtension<?, ?>>();
+  }
+
+  ExtensionRegistryLite(ExtensionRegistryLite other) {
+    if (other == EMPTY) {
+      this.extensionsByNumber = Collections.emptyMap();
+    } else {
+      this.extensionsByNumber =
+        Collections.unmodifiableMap(other.extensionsByNumber);
+    }
+  }
+
+  private final Map<ObjectIntPair,
+                    GeneratedMessageLite.GeneratedExtension<?, ?>>
+      extensionsByNumber;
+
+  private ExtensionRegistryLite(boolean empty) {
+    this.extensionsByNumber = Collections.emptyMap();
+  }
+  private static final ExtensionRegistryLite EMPTY =
+    new ExtensionRegistryLite(true);
+
+  /** A (Object, int) pair, used as a map key. */
+  private static final class ObjectIntPair {
+    private final Object object;
+    private final int number;
+
+    ObjectIntPair(final Object object, final int number) {
+      this.object = object;
+      this.number = number;
+    }
+
+    @Override
+    public int hashCode() {
+      return System.identityHashCode(object) * ((1 << 16) - 1) + number;
+    }
+    @Override
+    public boolean equals(final Object obj) {
+      if (!(obj instanceof ObjectIntPair)) {
+        return false;
+      }
+      final ObjectIntPair other = (ObjectIntPair)obj;
+      return object == other.object && number == other.number;
+    }
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/FieldSet.java b/java/core/src/main/java/com/google/protobuf/FieldSet.java
new file mode 100644
index 00000000..47924b65
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/FieldSet.java
@@ -0,0 +1,889 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import com.google.protobuf.LazyField.LazyIterator;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * A class which represents an arbitrary set of fields of some message type.
+ * This is used to implement {@link DynamicMessage}, and also to represent
+ * extensions in {@link GeneratedMessage}.  This class is package-private,
+ * since outside users should probably be using {@link DynamicMessage}.
+ *
+ * @author kenton@google.com Kenton Varda
+ */
+final class FieldSet<FieldDescriptorType extends
+      FieldSet.FieldDescriptorLite<FieldDescriptorType>> {
+  /**
+   * Interface for a FieldDescriptor or lite extension descriptor.  This
+   * prevents FieldSet from depending on {@link Descriptors.FieldDescriptor}.
+   */
+  public interface FieldDescriptorLite<T extends FieldDescriptorLite<T>>
+      extends Comparable<T> {
+    int getNumber();
+    WireFormat.FieldType getLiteType();
+    WireFormat.JavaType getLiteJavaType();
+    boolean isRepeated();
+    boolean isPacked();
+    Internal.EnumLiteMap<?> getEnumType();
+
+    // If getLiteJavaType() == MESSAGE, this merges a message object of the
+    // type into a builder of the type.  Returns {@code to}.
+    MessageLite.Builder internalMergeFrom(
+        MessageLite.Builder to, MessageLite from);
+  }
+
+  private final SmallSortedMap<FieldDescriptorType, Object> fields;
+  private boolean isImmutable;
+  private boolean hasLazyField = false;
+
+  /** Construct a new FieldSet. */
+  private FieldSet() {
+    this.fields = SmallSortedMap.newFieldMap(16);
+  }
+
+  /**
+   * Construct an empty FieldSet.  This is only used to initialize
+   * DEFAULT_INSTANCE.
+   */
+  private FieldSet(final boolean dummy) {
+    this.fields = SmallSortedMap.newFieldMap(0);
+    makeImmutable();
+  }
+
+  /** Construct a new FieldSet. */
+  public static <T extends FieldSet.FieldDescriptorLite<T>>
+      FieldSet<T> newFieldSet() {
+    return new FieldSet<T>();
+  }
+
+  /** Get an immutable empty FieldSet. */
+  @SuppressWarnings("unchecked")
+  public static <T extends FieldSet.FieldDescriptorLite<T>>
+      FieldSet<T> emptySet() {
+    return DEFAULT_INSTANCE;
+  }
+  @SuppressWarnings("rawtypes")
+  private static final FieldSet DEFAULT_INSTANCE = new FieldSet(true);
+
+  /** Make this FieldSet immutable from this point forward. */
+  @SuppressWarnings("unchecked")
+  public void makeImmutable() {
+    if (isImmutable) {
+      return;
+    }
+    fields.makeImmutable();
+    isImmutable = true;
+  }
+
+  /**
+   * Returns whether the FieldSet is immutable. This is true if it is the
+   * {@link #emptySet} or if {@link #makeImmutable} were called.
+   *
+   * @return whether the FieldSet is immutable.
+   */
+  public boolean isImmutable() {
+    return isImmutable;
+  }
+
+  /**
+   * Clones the FieldSet. The returned FieldSet will be mutable even if the
+   * original FieldSet was immutable.
+   *
+   * @return the newly cloned FieldSet
+   */
+  @Override
+  public FieldSet<FieldDescriptorType> clone() {
+    // We can't just call fields.clone because List objects in the map
+    // should not be shared.
+    FieldSet<FieldDescriptorType> clone = FieldSet.newFieldSet();
+    for (int i = 0; i < fields.getNumArrayEntries(); i++) {
+      Map.Entry<FieldDescriptorType, Object> entry = fields.getArrayEntryAt(i);
+      FieldDescriptorType descriptor = entry.getKey();
+      clone.setField(descriptor, entry.getValue());
+    }
+    for (Map.Entry<FieldDescriptorType, Object> entry :
+             fields.getOverflowEntries()) {
+      FieldDescriptorType descriptor = entry.getKey();
+      clone.setField(descriptor, entry.getValue());
+    }
+    clone.hasLazyField = hasLazyField;
+    return clone;
+  }
+
+
+  // =================================================================
+
+  /** See {@link Message.Builder#clear()}. */
+  public void clear() {
+    fields.clear();
+    hasLazyField = false;
+  }
+
+  /**
+   * Get a simple map containing all the fields.
+   */
+  public Map<FieldDescriptorType, Object> getAllFields() {
+    if (hasLazyField) {
+      SmallSortedMap<FieldDescriptorType, Object> result =
+          SmallSortedMap.newFieldMap(16);
+      for (int i = 0; i < fields.getNumArrayEntries(); i++) {
+        cloneFieldEntry(result, fields.getArrayEntryAt(i));
+      }
+      for (Map.Entry<FieldDescriptorType, Object> entry :
+          fields.getOverflowEntries()) {
+        cloneFieldEntry(result, entry);
+      }
+      if (fields.isImmutable()) {
+        result.makeImmutable();
+      }
+      return result;
+    }
+    return fields.isImmutable() ? fields : Collections.unmodifiableMap(fields);
+  }
+
+  private void cloneFieldEntry(Map<FieldDescriptorType, Object> map,
+      Map.Entry<FieldDescriptorType, Object> entry) {
+    FieldDescriptorType key = entry.getKey();
+    Object value = entry.getValue();
+    if (value instanceof LazyField) {
+      map.put(key, ((LazyField) value).getValue());
+    } else {
+      map.put(key, value);
+    }
+  }
+
+  /**
+   * Get an iterator to the field map. This iterator should not be leaked out
+   * of the protobuf library as it is not protected from mutation when fields
+   * is not immutable.
+   */
+  public Iterator<Map.Entry<FieldDescriptorType, Object>> iterator() {
+    if (hasLazyField) {
+      return new LazyIterator<FieldDescriptorType>(
+          fields.entrySet().iterator());
+    }
+    return fields.entrySet().iterator();
+  }
+
+  /**
+   * Useful for implementing
+   * {@link Message#hasField(Descriptors.FieldDescriptor)}.
+   */
+  public boolean hasField(final FieldDescriptorType descriptor) {
+    if (descriptor.isRepeated()) {
+      throw new IllegalArgumentException(
+        "hasField() can only be called on non-repeated fields.");
+    }
+
+    return fields.get(descriptor) != null;
+  }
+
+  /**
+   * Useful for implementing
+   * {@link Message#getField(Descriptors.FieldDescriptor)}.  This method
+   * returns {@code null} if the field is not set; in this case it is up
+   * to the caller to fetch the field's default value.
+   */
+  public Object getField(final FieldDescriptorType descriptor) {
+    Object o = fields.get(descriptor);
+    if (o instanceof LazyField) {
+      return ((LazyField) o).getValue();
+    }
+    return o;
+  }
+
+  /**
+   * Useful for implementing
+   * {@link Message.Builder#setField(Descriptors.FieldDescriptor,Object)}.
+   */
+  @SuppressWarnings({"unchecked", "rawtypes"})
+  public void setField(final FieldDescriptorType descriptor,
+                       Object value) {
+    if (descriptor.isRepeated()) {
+      if (!(value instanceof List)) {
+        throw new IllegalArgumentException(
+          "Wrong object type used with protocol message reflection.");
+      }
+
+      // Wrap the contents in a new list so that the caller cannot change
+      // the list's contents after setting it.
+      final List newList = new ArrayList();
+      newList.addAll((List) value);
+      for (final Object element : newList) {
+        verifyType(descriptor.getLiteType(), element);
+      }
+      value = newList;
+    } else {
+      verifyType(descriptor.getLiteType(), value);
+    }
+
+    if (value instanceof LazyField) {
+      hasLazyField = true;
+    }
+    fields.put(descriptor, value);
+  }
+
+  /**
+   * Useful for implementing
+   * {@link Message.Builder#clearField(Descriptors.FieldDescriptor)}.
+   */
+  public void clearField(final FieldDescriptorType descriptor) {
+    fields.remove(descriptor);
+    if (fields.isEmpty()) {
+      hasLazyField = false;
+    }
+  }
+
+  /**
+   * Useful for implementing
+   * {@link Message#getRepeatedFieldCount(Descriptors.FieldDescriptor)}.
+   */
+  public int getRepeatedFieldCount(final FieldDescriptorType descriptor) {
+    if (!descriptor.isRepeated()) {
+      throw new IllegalArgumentException(
+        "getRepeatedField() can only be called on repeated fields.");
+    }
+
+    final Object value = getField(descriptor);
+    if (value == null) {
+      return 0;
+    } else {
+      return ((List<?>) value).size();
+    }
+  }
+
+  /**
+   * Useful for implementing
+   * {@link Message#getRepeatedField(Descriptors.FieldDescriptor,int)}.
+   */
+  public Object getRepeatedField(final FieldDescriptorType descriptor,
+                                 final int index) {
+    if (!descriptor.isRepeated()) {
+      throw new IllegalArgumentException(
+        "getRepeatedField() can only be called on repeated fields.");
+    }
+
+    final Object value = getField(descriptor);
+
+    if (value == null) {
+      throw new IndexOutOfBoundsException();
+    } else {
+      return ((List<?>) value).get(index);
+    }
+  }
+
+  /**
+   * Useful for implementing
+   * {@link Message.Builder#setRepeatedField(Descriptors.FieldDescriptor,int,Object)}.
+   */
+  @SuppressWarnings("unchecked")
+  public void setRepeatedField(final FieldDescriptorType descriptor,
+                               final int index,
+                               final Object value) {
+    if (!descriptor.isRepeated()) {
+      throw new IllegalArgumentException(
+        "getRepeatedField() can only be called on repeated fields.");
+    }
+
+    final Object list = getField(descriptor);
+    if (list == null) {
+      throw new IndexOutOfBoundsException();
+    }
+
+    verifyType(descriptor.getLiteType(), value);
+    ((List<Object>) list).set(index, value);
+  }
+
+  /**
+   * Useful for implementing
+   * {@link Message.Builder#addRepeatedField(Descriptors.FieldDescriptor,Object)}.
+   */
+  @SuppressWarnings("unchecked")
+  public void addRepeatedField(final FieldDescriptorType descriptor,
+                               final Object value) {
+    if (!descriptor.isRepeated()) {
+      throw new IllegalArgumentException(
+        "addRepeatedField() can only be called on repeated fields.");
+    }
+
+    verifyType(descriptor.getLiteType(), value);
+
+    final Object existingValue = getField(descriptor);
+    List<Object> list;
+    if (existingValue == null) {
+      list = new ArrayList<Object>();
+      fields.put(descriptor, list);
+    } else {
+      list = (List<Object>) existingValue;
+    }
+
+    list.add(value);
+  }
+
+  /**
+   * Verifies that the given object is of the correct type to be a valid
+   * value for the given field.  (For repeated fields, this checks if the
+   * object is the right type to be one element of the field.)
+   *
+   * @throws IllegalArgumentException The value is not of the right type.
+   */
+  private static void verifyType(final WireFormat.FieldType type,
+                                 final Object value) {
+    if (value == null) {
+      throw new NullPointerException();
+    }
+
+    boolean isValid = false;
+    switch (type.getJavaType()) {
+      case INT:          isValid = value instanceof Integer   ; break;
+      case LONG:         isValid = value instanceof Long      ; break;
+      case FLOAT:        isValid = value instanceof Float     ; break;
+      case DOUBLE:       isValid = value instanceof Double    ; break;
+      case BOOLEAN:      isValid = value instanceof Boolean   ; break;
+      case STRING:       isValid = value instanceof String    ; break;
+      case BYTE_STRING:
+        isValid = value instanceof ByteString || value instanceof byte[];
+        break;
+      case ENUM:
+        // TODO(kenton):  Caller must do type checking here, I guess.
+        isValid =
+            (value instanceof Integer || value instanceof Internal.EnumLite);
+        break;
+      case MESSAGE:
+        // TODO(kenton):  Caller must do type checking here, I guess.
+        isValid =
+            (value instanceof MessageLite) || (value instanceof LazyField);
+        break;
+    }
+
+    if (!isValid) {
+      // TODO(kenton):  When chaining calls to setField(), it can be hard to
+      //   tell from the stack trace which exact call failed, since the whole
+      //   chain is considered one line of code.  It would be nice to print
+      //   more information here, e.g. naming the field.  We used to do that.
+      //   But we can't now that FieldSet doesn't use descriptors.  Maybe this
+      //   isn't a big deal, though, since it would only really apply when using
+      //   reflection and generally people don't chain reflection setters.
+      throw new IllegalArgumentException(
+        "Wrong object type used with protocol message reflection.");
+    }
+  }
+
+  // =================================================================
+  // Parsing and serialization
+
+  /**
+   * See {@link Message#isInitialized()}.  Note:  Since {@code FieldSet}
+   * itself does not have any way of knowing about required fields that
+   * aren't actually present in the set, it is up to the caller to check
+   * that all required fields are present.
+   */
+  public boolean isInitialized() {
+    for (int i = 0; i < fields.getNumArrayEntries(); i++) {
+      if (!isInitialized(fields.getArrayEntryAt(i))) {
+        return false;
+      }
+    }
+    for (final Map.Entry<FieldDescriptorType, Object> entry :
+             fields.getOverflowEntries()) {
+      if (!isInitialized(entry)) {
+        return false;
+      }
+    }
+    return true;
+  }
+
+  @SuppressWarnings("unchecked")
+  private boolean isInitialized(
+      final Map.Entry<FieldDescriptorType, Object> entry) {
+    final FieldDescriptorType descriptor = entry.getKey();
+    if (descriptor.getLiteJavaType() == WireFormat.JavaType.MESSAGE) {
+      if (descriptor.isRepeated()) {
+        for (final MessageLite element:
+                 (List<MessageLite>) entry.getValue()) {
+          if (!element.isInitialized()) {
+            return false;
+          }
+        }
+      } else {
+        Object value = entry.getValue();
+        if (value instanceof MessageLite) {
+          if (!((MessageLite) value).isInitialized()) {
+            return false;
+          }
+        } else if (value instanceof LazyField) {
+          return true;
+        } else {
+          throw new IllegalArgumentException(
+              "Wrong object type used with protocol message reflection.");
+        }
+      }
+    }
+    return true;
+  }
+
+  /**
+   * Given a field type, return the wire type.
+   *
+   * @returns One of the {@code WIRETYPE_} constants defined in
+   *          {@link WireFormat}.
+   */
+  static int getWireFormatForFieldType(final WireFormat.FieldType type,
+                                       boolean isPacked) {
+    if (isPacked) {
+      return WireFormat.WIRETYPE_LENGTH_DELIMITED;
+    } else {
+      return type.getWireType();
+    }
+  }
+
+  /**
+   * Like {@link Message.Builder#mergeFrom(Message)}, but merges from another 
+   * {@link FieldSet}.
+   */
+  public void mergeFrom(final FieldSet<FieldDescriptorType> other) {
+    for (int i = 0; i < other.fields.getNumArrayEntries(); i++) {
+      mergeFromField(other.fields.getArrayEntryAt(i));
+    }
+    for (final Map.Entry<FieldDescriptorType, Object> entry :
+             other.fields.getOverflowEntries()) {
+      mergeFromField(entry);
+    }
+  }
+
+  private Object cloneIfMutable(Object value) {
+    if (value instanceof byte[]) {
+      byte[] bytes = (byte[]) value;
+      byte[] copy = new byte[bytes.length];
+      System.arraycopy(bytes, 0, copy, 0, bytes.length);
+      return copy;
+    } else {
+      return value;
+    }
+  }
+
+  @SuppressWarnings({"unchecked", "rawtypes"})
+  private void mergeFromField(
+      final Map.Entry<FieldDescriptorType, Object> entry) {
+    final FieldDescriptorType descriptor = entry.getKey();
+    Object otherValue = entry.getValue();
+    if (otherValue instanceof LazyField) {
+      otherValue = ((LazyField) otherValue).getValue();
+    }
+
+    if (descriptor.isRepeated()) {
+      Object value = getField(descriptor);
+      if (value == null) {
+        value = new ArrayList();
+      }
+      for (Object element : (List) otherValue) {
+        ((List) value).add(cloneIfMutable(element));
+      }
+      fields.put(descriptor, value);
+    } else if (descriptor.getLiteJavaType() == WireFormat.JavaType.MESSAGE) {
+      Object value = getField(descriptor);
+      if (value == null) {
+        fields.put(descriptor, cloneIfMutable(otherValue));
+      } else {
+        // Merge the messages.
+          value = descriptor.internalMergeFrom(
+                ((MessageLite) value).toBuilder(), (MessageLite) otherValue)
+                .build();
+
+        fields.put(descriptor, value);
+      }
+    } else {
+      fields.put(descriptor, cloneIfMutable(otherValue));
+    }
+  }
+
+  // TODO(kenton):  Move static parsing and serialization methods into some
+  //   other class.  Probably WireFormat.
+
+  /**
+   * Read a field of any primitive type for immutable messages from a
+   * CodedInputStream. Enums, groups, and embedded messages are not handled by
+   * this method.
+   *
+   * @param input The stream from which to read.
+   * @param type Declared type of the field.
+   * @param checkUtf8 When true, check that the input is valid utf8.
+   * @return An object representing the field's value, of the exact
+   *         type which would be returned by
+   *         {@link Message#getField(Descriptors.FieldDescriptor)} for
+   *         this field.
+   */
+  public static Object readPrimitiveField(
+      CodedInputStream input,
+      final WireFormat.FieldType type,
+      boolean checkUtf8) throws IOException {
+    if (checkUtf8) {
+      return WireFormat.readPrimitiveField(input, type,
+          WireFormat.Utf8Validation.STRICT);
+    } else {
+      return WireFormat.readPrimitiveField(input, type,
+          WireFormat.Utf8Validation.LOOSE);
+    }
+  }
+
+
+  /** See {@link Message#writeTo(CodedOutputStream)}. */
+  public void writeTo(final CodedOutputStream output)
+                      throws IOException {
+    for (int i = 0; i < fields.getNumArrayEntries(); i++) {
+      final Map.Entry<FieldDescriptorType, Object> entry =
+          fields.getArrayEntryAt(i);
+      writeField(entry.getKey(), entry.getValue(), output);
+    }
+    for (final Map.Entry<FieldDescriptorType, Object> entry :
+         fields.getOverflowEntries()) {
+      writeField(entry.getKey(), entry.getValue(), output);
+    }
+  }
+
+  /**
+   * Like {@link #writeTo} but uses MessageSet wire format.
+   */
+  public void writeMessageSetTo(final CodedOutputStream output)
+                                throws IOException {
+    for (int i = 0; i < fields.getNumArrayEntries(); i++) {
+      writeMessageSetTo(fields.getArrayEntryAt(i), output);
+    }
+    for (final Map.Entry<FieldDescriptorType, Object> entry :
+             fields.getOverflowEntries()) {
+      writeMessageSetTo(entry, output);
+    }
+  }
+
+  private void writeMessageSetTo(
+      final Map.Entry<FieldDescriptorType, Object> entry,
+      final CodedOutputStream output) throws IOException {
+    final FieldDescriptorType descriptor = entry.getKey();
+    if (descriptor.getLiteJavaType() == WireFormat.JavaType.MESSAGE &&
+        !descriptor.isRepeated() && !descriptor.isPacked()) {
+      Object value = entry.getValue();
+      if (value instanceof LazyField) {
+        value = ((LazyField) value).getValue();
+      }
+      output.writeMessageSetExtension(entry.getKey().getNumber(),
+                                      (MessageLite) value);
+    } else {
+      writeField(descriptor, entry.getValue(), output);
+    }
+  }
+
+  /**
+   * Write a single tag-value pair to the stream.
+   *
+   * @param output The output stream.
+   * @param type   The field's type.
+   * @param number The field's number.
+   * @param value  Object representing the field's value.  Must be of the exact
+   *               type which would be returned by
+   *               {@link Message#getField(Descriptors.FieldDescriptor)} for
+   *               this field.
+   */
+  private static void writeElement(final CodedOutputStream output,
+                                   final WireFormat.FieldType type,
+                                   final int number,
+                                   final Object value) throws IOException {
+    // Special case for groups, which need a start and end tag; other fields
+    // can just use writeTag() and writeFieldNoTag().
+    if (type == WireFormat.FieldType.GROUP) {
+        output.writeGroup(number, (MessageLite) value);
+    } else {
+      output.writeTag(number, getWireFormatForFieldType(type, false));
+      writeElementNoTag(output, type, value);
+    }
+  }
+
+  /**
+   * Write a field of arbitrary type, without its tag, to the stream.
+   *
+   * @param output The output stream.
+   * @param type The field's type.
+   * @param value  Object representing the field's value.  Must be of the exact
+   *               type which would be returned by
+   *               {@link Message#getField(Descriptors.FieldDescriptor)} for
+   *               this field.
+   */
+  static void writeElementNoTag(
+      final CodedOutputStream output,
+      final WireFormat.FieldType type,
+      final Object value) throws IOException {
+    switch (type) {
+      case DOUBLE  : output.writeDoubleNoTag  ((Double     ) value); break;
+      case FLOAT   : output.writeFloatNoTag   ((Float      ) value); break;
+      case INT64   : output.writeInt64NoTag   ((Long       ) value); break;
+      case UINT64  : output.writeUInt64NoTag  ((Long       ) value); break;
+      case INT32   : output.writeInt32NoTag   ((Integer    ) value); break;
+      case FIXED64 : output.writeFixed64NoTag ((Long       ) value); break;
+      case FIXED32 : output.writeFixed32NoTag ((Integer    ) value); break;
+      case BOOL    : output.writeBoolNoTag    ((Boolean    ) value); break;
+      case GROUP   : output.writeGroupNoTag   ((MessageLite) value); break;
+      case MESSAGE : output.writeMessageNoTag ((MessageLite) value); break;
+      case STRING:
+        if (value instanceof ByteString) {
+          output.writeBytesNoTag((ByteString) value);
+        } else {
+          output.writeStringNoTag((String) value);
+        }
+        break;
+      case BYTES:
+        if (value instanceof ByteString) {
+          output.writeBytesNoTag((ByteString) value);
+        } else {
+          output.writeByteArrayNoTag((byte[]) value);
+        }
+        break;
+      case UINT32  : output.writeUInt32NoTag  ((Integer    ) value); break;
+      case SFIXED32: output.writeSFixed32NoTag((Integer    ) value); break;
+      case SFIXED64: output.writeSFixed64NoTag((Long       ) value); break;
+      case SINT32  : output.writeSInt32NoTag  ((Integer    ) value); break;
+      case SINT64  : output.writeSInt64NoTag  ((Long       ) value); break;
+
+      case ENUM:
+        if (value instanceof Internal.EnumLite) {
+          output.writeEnumNoTag(((Internal.EnumLite) value).getNumber());
+        } else {
+          output.writeEnumNoTag(((Integer) value).intValue());
+        }
+        break;
+    }
+  }
+
+  /** Write a single field. */
+  public static void writeField(final FieldDescriptorLite<?> descriptor,
+                                final Object value,
+                                final CodedOutputStream output)
+                                throws IOException {
+    WireFormat.FieldType type = descriptor.getLiteType();
+    int number = descriptor.getNumber();
+    if (descriptor.isRepeated()) {
+      final List<?> valueList = (List<?>)value;
+      if (descriptor.isPacked()) {
+        output.writeTag(number, WireFormat.WIRETYPE_LENGTH_DELIMITED);
+        // Compute the total data size so the length can be written.
+        int dataSize = 0;
+        for (final Object element : valueList) {
+          dataSize += computeElementSizeNoTag(type, element);
+        }
+        output.writeRawVarint32(dataSize);
+        // Write the data itself, without any tags.
+        for (final Object element : valueList) {
+          writeElementNoTag(output, type, element);
+        }
+      } else {
+        for (final Object element : valueList) {
+          writeElement(output, type, number, element);
+        }
+      }
+    } else {
+      if (value instanceof LazyField) {
+        writeElement(output, type, number, ((LazyField) value).getValue());
+      } else {
+        writeElement(output, type, number, value);
+      }
+    }
+  }
+
+  /**
+   * See {@link Message#getSerializedSize()}.  It's up to the caller to cache
+   * the resulting size if desired.
+   */
+  public int getSerializedSize() {
+    int size = 0;
+    for (int i = 0; i < fields.getNumArrayEntries(); i++) {
+      final Map.Entry<FieldDescriptorType, Object> entry =
+          fields.getArrayEntryAt(i);
+      size += computeFieldSize(entry.getKey(), entry.getValue());
+    }
+    for (final Map.Entry<FieldDescriptorType, Object> entry :
+         fields.getOverflowEntries()) {
+      size += computeFieldSize(entry.getKey(), entry.getValue());
+    }
+    return size;
+  }
+
+  /**
+   * Like {@link #getSerializedSize} but uses MessageSet wire format.
+   */
+  public int getMessageSetSerializedSize() {
+    int size = 0;
+    for (int i = 0; i < fields.getNumArrayEntries(); i++) {
+      size += getMessageSetSerializedSize(fields.getArrayEntryAt(i));
+    }
+    for (final Map.Entry<FieldDescriptorType, Object> entry :
+             fields.getOverflowEntries()) {
+      size += getMessageSetSerializedSize(entry);
+    }
+    return size;
+  }
+
+  private int getMessageSetSerializedSize(
+      final Map.Entry<FieldDescriptorType, Object> entry) {
+    final FieldDescriptorType descriptor = entry.getKey();
+    Object value = entry.getValue();
+    if (descriptor.getLiteJavaType() == WireFormat.JavaType.MESSAGE
+        && !descriptor.isRepeated() && !descriptor.isPacked()) {
+      if (value instanceof LazyField) {
+        return CodedOutputStream.computeLazyFieldMessageSetExtensionSize(
+            entry.getKey().getNumber(), (LazyField) value);
+      } else {
+        return CodedOutputStream.computeMessageSetExtensionSize(
+            entry.getKey().getNumber(), (MessageLite) value);
+      }
+    } else {
+      return computeFieldSize(descriptor, value);
+    }
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode a
+   * single tag/value pair of arbitrary type.
+   *
+   * @param type   The field's type.
+   * @param number The field's number.
+   * @param value  Object representing the field's value.  Must be of the exact
+   *               type which would be returned by
+   *               {@link Message#getField(Descriptors.FieldDescriptor)} for
+   *               this field.
+   */
+  private static int computeElementSize(
+      final WireFormat.FieldType type,
+      final int number, final Object value) {
+    int tagSize = CodedOutputStream.computeTagSize(number);
+    if (type == WireFormat.FieldType.GROUP) {
+      // Only count the end group tag for proto2 messages as for proto1 the end
+      // group tag will be counted as a part of getSerializedSize().
+        tagSize *= 2;
+    }
+    return tagSize + computeElementSizeNoTag(type, value);
+  }
+
+  /**
+   * Compute the number of bytes that would be needed to encode a
+   * particular value of arbitrary type, excluding tag.
+   *
+   * @param type   The field's type.
+   * @param value  Object representing the field's value.  Must be of the exact
+   *               type which would be returned by
+   *               {@link Message#getField(Descriptors.FieldDescriptor)} for
+   *               this field.
+   */
+  static int computeElementSizeNoTag(
+      final WireFormat.FieldType type, final Object value) {
+    switch (type) {
+      // Note:  Minor violation of 80-char limit rule here because this would
+      //   actually be harder to read if we wrapped the lines.
+      case DOUBLE  : return CodedOutputStream.computeDoubleSizeNoTag  ((Double     )value);
+      case FLOAT   : return CodedOutputStream.computeFloatSizeNoTag   ((Float      )value);
+      case INT64   : return CodedOutputStream.computeInt64SizeNoTag   ((Long       )value);
+      case UINT64  : return CodedOutputStream.computeUInt64SizeNoTag  ((Long       )value);
+      case INT32   : return CodedOutputStream.computeInt32SizeNoTag   ((Integer    )value);
+      case FIXED64 : return CodedOutputStream.computeFixed64SizeNoTag ((Long       )value);
+      case FIXED32 : return CodedOutputStream.computeFixed32SizeNoTag ((Integer    )value);
+      case BOOL    : return CodedOutputStream.computeBoolSizeNoTag    ((Boolean    )value);
+      case GROUP   : return CodedOutputStream.computeGroupSizeNoTag   ((MessageLite)value);
+      case BYTES   :
+        if (value instanceof ByteString) {
+          return CodedOutputStream.computeBytesSizeNoTag((ByteString) value);
+        } else {
+          return CodedOutputStream.computeByteArraySizeNoTag((byte[]) value);
+        }
+      case STRING  :
+        if (value instanceof ByteString) {
+          return CodedOutputStream.computeBytesSizeNoTag((ByteString) value);
+        } else {
+          return CodedOutputStream.computeStringSizeNoTag((String) value);
+        }
+      case UINT32  : return CodedOutputStream.computeUInt32SizeNoTag  ((Integer    )value);
+      case SFIXED32: return CodedOutputStream.computeSFixed32SizeNoTag((Integer    )value);
+      case SFIXED64: return CodedOutputStream.computeSFixed64SizeNoTag((Long       )value);
+      case SINT32  : return CodedOutputStream.computeSInt32SizeNoTag  ((Integer    )value);
+      case SINT64  : return CodedOutputStream.computeSInt64SizeNoTag  ((Long       )value);
+
+      case MESSAGE:
+        if (value instanceof LazyField) {
+          return CodedOutputStream.computeLazyFieldSizeNoTag((LazyField) value);
+        } else {
+          return CodedOutputStream.computeMessageSizeNoTag((MessageLite) value);
+        }
+
+      case ENUM:
+        if (value instanceof Internal.EnumLite) {
+          return CodedOutputStream.computeEnumSizeNoTag(
+              ((Internal.EnumLite) value).getNumber());
+        } else {
+          return CodedOutputStream.computeEnumSizeNoTag((Integer) value);
+        }
+    }
+
+    throw new RuntimeException(
+      "There is no way to get here, but the compiler thinks otherwise.");
+  }
+
+  /**
+   * Compute the number of bytes needed to encode a particular field.
+   */
+  public static int computeFieldSize(final FieldDescriptorLite<?> descriptor,
+                                     final Object value) {
+    WireFormat.FieldType type = descriptor.getLiteType();
+    int number = descriptor.getNumber();
+    if (descriptor.isRepeated()) {
+      if (descriptor.isPacked()) {
+        int dataSize = 0;
+        for (final Object element : (List<?>)value) {
+          dataSize += computeElementSizeNoTag(type, element);
+        }
+        return dataSize +
+            CodedOutputStream.computeTagSize(number) +
+            CodedOutputStream.computeRawVarint32Size(dataSize);
+      } else {
+        int size = 0;
+        for (final Object element : (List<?>)value) {
+          size += computeElementSize(type, number, element);
+        }
+        return size;
+      }
+    } else {
+      return computeElementSize(type, number, value);
+    }
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/FloatArrayList.java b/java/core/src/main/java/com/google/protobuf/FloatArrayList.java
new file mode 100644
index 00000000..033b5eed
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/FloatArrayList.java
@@ -0,0 +1,249 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import com.google.protobuf.Internal.FloatList;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.List;
+import java.util.RandomAccess;
+
+/**
+ * An implementation of {@link FloatList} on top of a primitive array.
+ * 
+ * @author dweis@google.com (Daniel Weis)
+ */
+final class FloatArrayList extends AbstractProtobufList<Float> implements FloatList, RandomAccess {
+  
+  private static final int DEFAULT_CAPACITY = 10;
+  
+  private static final FloatArrayList EMPTY_LIST = new FloatArrayList();
+  static {
+    EMPTY_LIST.makeImmutable();
+  }
+  
+  public static FloatArrayList emptyList() {
+    return EMPTY_LIST;
+  }
+  
+  /**
+   * The backing store for the list.
+   */
+  private float[] array;
+  
+  /**
+   * The size of the list distinct from the length of the array. That is, it is the number of
+   * elements set in the list.
+   */
+  private int size;
+
+  /**
+   * Constructs a new mutable {@code FloatArrayList} with default capacity.
+   */
+  FloatArrayList() {
+    this(DEFAULT_CAPACITY);
+  }
+
+  /**
+   * Constructs a new mutable {@code FloatArrayList} with the provided capacity.
+   */
+  FloatArrayList(int capacity) {
+    array = new float[capacity];
+    size = 0;
+  }
+
+  /**
+   * Constructs a new mutable {@code FloatArrayList} containing the same elements as {@code other}.
+   */
+  FloatArrayList(List<Float> other) {
+    if (other instanceof FloatArrayList) {
+      FloatArrayList list = (FloatArrayList) other;
+      array = list.array.clone();
+      size = list.size;
+    } else {
+      size = other.size();
+      array = new float[size];
+      for (int i = 0; i < size; i++) {
+        array[i] = other.get(i);
+      }
+    }
+  }
+  
+  @Override
+  public Float get(int index) {
+    return getFloat(index);
+  }
+
+  @Override
+  public float getFloat(int index) {
+    ensureIndexInRange(index);
+    return array[index];
+  }
+
+  @Override
+  public int size() {
+    return size;
+  }
+
+  @Override
+  public Float set(int index, Float element) {
+    return setFloat(index, element);
+  }
+
+  @Override
+  public float setFloat(int index, float element) {
+    ensureIsMutable();
+    ensureIndexInRange(index);
+    float previousValue = array[index];
+    array[index] = element;
+    return previousValue;
+  }
+
+  @Override
+  public void add(int index, Float element) {
+    addFloat(index, element);
+  }
+
+  /**
+   * Like {@link #add(Float)} but more efficient in that it doesn't box the element.
+   */
+  @Override
+  public void addFloat(float element) {
+    addFloat(size, element);
+  }
+
+  /**
+   * Like {@link #add(int, Float)} but more efficient in that it doesn't box the element.
+   */
+  private void addFloat(int index, float element) {
+    ensureIsMutable();
+    if (index < 0 || index > size) {
+      throw new IndexOutOfBoundsException(makeOutOfBoundsExceptionMessage(index));
+    }
+    
+    if (size < array.length) {
+      // Shift everything over to make room
+      System.arraycopy(array, index, array, index + 1, size - index);
+    } else {
+      // Resize to 1.5x the size
+      int length = ((size * 3) / 2) + 1;
+      float[] newArray = new float[length];
+      
+      // Copy the first part directly
+      System.arraycopy(array, 0, newArray, 0, index);
+      
+      // Copy the rest shifted over by one to make room
+      System.arraycopy(array, index, newArray, index + 1, size - index);
+      array = newArray;
+    }
+
+    array[index] = element;
+    size++;
+    modCount++;
+  }
+
+  @Override
+  public boolean addAll(Collection<? extends Float> collection) {
+    ensureIsMutable();
+    
+    if (collection == null) {
+      throw new NullPointerException();
+    }
+    
+    // We specialize when adding another FloatArrayList to avoid boxing elements.
+    if (!(collection instanceof FloatArrayList)) {
+      return super.addAll(collection);
+    }
+    
+    FloatArrayList list = (FloatArrayList) collection;
+    if (list.size == 0) {
+      return false;
+    }
+    
+    int overflow = Integer.MAX_VALUE - size;
+    if (overflow < list.size) {
+      // We can't actually represent a list this large.
+      throw new OutOfMemoryError();
+    }
+    
+    int newSize = size + list.size;
+    if (newSize > array.length) {
+      array = Arrays.copyOf(array, newSize);
+    }
+    
+    System.arraycopy(list.array, 0, array, size, list.size);
+    size = newSize;
+    modCount++;
+    return true;
+  }
+  
+  @Override
+  public boolean remove(Object o) {
+    ensureIsMutable();
+    for (int i = 0; i < size; i++) {
+      if (o.equals(array[i])) {
+        System.arraycopy(array, i + 1, array, i, size - i);
+        size--;
+        modCount++;
+        return true;
+      }
+    }
+    return false;
+  }
+
+  @Override
+  public Float remove(int index) {
+    ensureIsMutable();
+    ensureIndexInRange(index);
+    float value = array[index];
+    System.arraycopy(array, index + 1, array, index, size - index);
+    size--;
+    modCount++;
+    return value;
+  }
+
+  /**
+   * Ensures that the provided {@code index} is within the range of {@code [0, size]}. Throws an
+   * {@link IndexOutOfBoundsException} if it is not.
+   * 
+   * @param index the index to verify is in range
+   */
+  private void ensureIndexInRange(int index) {
+    if (index < 0 || index >= size) {
+      throw new IndexOutOfBoundsException(makeOutOfBoundsExceptionMessage(index));
+    }
+  }
+
+  private String makeOutOfBoundsExceptionMessage(int index) {
+    return "Index:" + index + ", Size:" + size;
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/GeneratedMessage.java b/java/core/src/main/java/com/google/protobuf/GeneratedMessage.java
new file mode 100644
index 00000000..d84fa75c
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/GeneratedMessage.java
@@ -0,0 +1,2778 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import com.google.protobuf.Descriptors.Descriptor;
+import com.google.protobuf.Descriptors.EnumDescriptor;
+import com.google.protobuf.Descriptors.EnumValueDescriptor;
+import com.google.protobuf.Descriptors.FieldDescriptor;
+import com.google.protobuf.Descriptors.FileDescriptor;
+import com.google.protobuf.Descriptors.OneofDescriptor;
+import com.google.protobuf.GeneratedMessageLite.ExtendableMessage;
+import com.google.protobuf.GeneratedMessageLite.GeneratedExtension;
+
+import java.io.IOException;
+import java.io.ObjectStreamException;
+import java.io.Serializable;
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+import java.lang.reflect.Type;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.TreeMap;
+
+/**
+ * All generated protocol message classes extend this class.  This class
+ * implements most of the Message and Builder interfaces using Java reflection.
+ * Users can ignore this class and pretend that generated messages implement
+ * the Message interface directly.
+ *
+ * @author kenton@google.com Kenton Varda
+ */
+public abstract class GeneratedMessage extends AbstractMessage
+    implements Serializable {
+  private static final long serialVersionUID = 1L;
+
+  /**
+   * For testing. Allows a test to disable the optimization that avoids using
+   * field builders for nested messages until they are requested. By disabling
+   * this optimization, existing tests can be reused to test the field builders.
+   */
+  protected static boolean alwaysUseFieldBuilders = false;
+
+  /** For use by generated code only.  */
+  protected UnknownFieldSet unknownFields;
+
+  protected GeneratedMessage() {
+    unknownFields = UnknownFieldSet.getDefaultInstance();
+  }
+
+  protected GeneratedMessage(Builder<?> builder) {
+    unknownFields = builder.getUnknownFields();
+  }
+
+  public Parser<? extends GeneratedMessage> getParserForType() {
+    throw new UnsupportedOperationException(
+        "This is supposed to be overridden by subclasses.");
+  }
+
+ /**
+  * For testing. Allows a test to disable the optimization that avoids using
+  * field builders for nested messages until they are requested. By disabling
+  * this optimization, existing tests can be reused to test the field builders.
+  * See {@link RepeatedFieldBuilder} and {@link SingleFieldBuilder}.
+  */
+  static void enableAlwaysUseFieldBuildersForTesting() {
+    alwaysUseFieldBuilders = true;
+  }
+
+  /**
+   * Get the FieldAccessorTable for this type.  We can't have the message
+   * class pass this in to the constructor because of bootstrapping trouble
+   * with DescriptorProtos.
+   */
+  protected abstract FieldAccessorTable internalGetFieldAccessorTable();
+
+  //@Override (Java 1.6 override semantics, but we must support 1.5)
+  public Descriptor getDescriptorForType() {
+    return internalGetFieldAccessorTable().descriptor;
+  }
+
+  /**
+   * Internal helper to return a modifiable map containing all the fields.
+   * The returned Map is modifialbe so that the caller can add additional
+   * extension fields to implement {@link #getAllFields()}.
+   *
+   * @param getBytesForString whether to generate ByteString for string fields
+   */
+  private Map<FieldDescriptor, Object> getAllFieldsMutable(
+      boolean getBytesForString) {
+    final TreeMap<FieldDescriptor, Object> result =
+      new TreeMap<FieldDescriptor, Object>();
+    final Descriptor descriptor = internalGetFieldAccessorTable().descriptor;
+    final List<FieldDescriptor> fields = descriptor.getFields();
+
+    for (int i = 0; i < fields.size(); i++) {
+      FieldDescriptor field = fields.get(i);
+      final OneofDescriptor oneofDescriptor = field.getContainingOneof();
+
+      /*
+       * If the field is part of a Oneof, then at maximum one field in the Oneof is set
+       * and it is not repeated. There is no need to iterate through the others.
+       */
+      if (oneofDescriptor != null) {
+        // Skip other fields in the Oneof we know are not set
+        i += oneofDescriptor.getFieldCount() - 1;
+        if (!hasOneof(oneofDescriptor)) {
+          // If no field is set in the Oneof, skip all the fields in the Oneof
+          continue;
+        }
+        // Get the pointer to the only field which is set in the Oneof
+        field = getOneofFieldDescriptor(oneofDescriptor);
+      } else {
+        // If we are not in a Oneof, we need to check if the field is set and if it is repeated
+        if (field.isRepeated()) {
+          final List<?> value = (List<?>) getField(field);
+          if (!value.isEmpty()) {
+            result.put(field, value);
+          }
+          continue;
+        }
+        if (!hasField(field)) {
+          continue;
+        }
+      }
+      // Add the field to the map
+      if (getBytesForString && field.getJavaType() == FieldDescriptor.JavaType.STRING) {
+        result.put(field, getFieldRaw(field));
+      } else {
+        result.put(field, getField(field));
+      }
+    }
+    return result;
+  }
+
+  @Override
+  public boolean isInitialized() {
+    for (final FieldDescriptor field : getDescriptorForType().getFields()) {
+      // Check that all required fields are present.
+      if (field.isRequired()) {
+        if (!hasField(field)) {
+          return false;
+        }
+      }
+      // Check that embedded messages are initialized.
+      if (field.getJavaType() == FieldDescriptor.JavaType.MESSAGE) {
+        if (field.isRepeated()) {
+          @SuppressWarnings("unchecked") final
+          List<Message> messageList = (List<Message>) getField(field);
+          for (final Message element : messageList) {
+            if (!element.isInitialized()) {
+              return false;
+            }
+          }
+        } else {
+          if (hasField(field) && !((Message) getField(field)).isInitialized()) {
+            return false;
+          }
+        }
+      }
+    }
+
+    return true;
+  }
+
+  //@Override (Java 1.6 override semantics, but we must support 1.5)
+  public Map<FieldDescriptor, Object> getAllFields() {
+    return Collections.unmodifiableMap(
+        getAllFieldsMutable(/* getBytesForString = */ false));
+  }
+
+  /**
+   * Returns a collection of all the fields in this message which are set
+   * and their corresponding values.  A singular ("required" or "optional")
+   * field is set iff hasField() returns true for that field.  A "repeated"
+   * field is set iff getRepeatedFieldCount() is greater than zero.  The
+   * values are exactly what would be returned by calling
+   * {@link #getFieldRaw(Descriptors.FieldDescriptor)} for each field.  The map
+   * is guaranteed to be a sorted map, so iterating over it will return fields
+   * in order by field number.
+   */
+  Map<FieldDescriptor, Object> getAllFieldsRaw() {
+    return Collections.unmodifiableMap(
+        getAllFieldsMutable(/* getBytesForString = */ true));
+  }
+
+  //@Override (Java 1.6 override semantics, but we must support 1.5)
+  public boolean hasOneof(final OneofDescriptor oneof) {
+    return internalGetFieldAccessorTable().getOneof(oneof).has(this);
+  }
+
+  //@Override (Java 1.6 override semantics, but we must support 1.5)
+  public FieldDescriptor getOneofFieldDescriptor(final OneofDescriptor oneof) {
+    return internalGetFieldAccessorTable().getOneof(oneof).get(this);
+  }
+
+  //@Override (Java 1.6 override semantics, but we must support 1.5)
+  public boolean hasField(final FieldDescriptor field) {
+    return internalGetFieldAccessorTable().getField(field).has(this);
+  }
+
+  //@Override (Java 1.6 override semantics, but we must support 1.5)
+  public Object getField(final FieldDescriptor field) {
+    return internalGetFieldAccessorTable().getField(field).get(this);
+  }
+
+  /**
+   * Obtains the value of the given field, or the default value if it is
+   * not set.  For primitive fields, the boxed primitive value is returned.
+   * For enum fields, the EnumValueDescriptor for the value is returned. For
+   * embedded message fields, the sub-message is returned.  For repeated
+   * fields, a java.util.List is returned. For present string fields, a
+   * ByteString is returned representing the bytes that the field contains.
+   */
+  Object getFieldRaw(final FieldDescriptor field) {
+    return internalGetFieldAccessorTable().getField(field).getRaw(this);
+  }
+
+  //@Override (Java 1.6 override semantics, but we must support 1.5)
+  public int getRepeatedFieldCount(final FieldDescriptor field) {
+    return internalGetFieldAccessorTable().getField(field)
+      .getRepeatedCount(this);
+  }
+
+  //@Override (Java 1.6 override semantics, but we must support 1.5)
+  public Object getRepeatedField(final FieldDescriptor field, final int index) {
+    return internalGetFieldAccessorTable().getField(field)
+      .getRepeated(this, index);
+  }
+
+  //@Override (Java 1.6 override semantics, but we must support 1.5)
+  public UnknownFieldSet getUnknownFields() {
+    throw new UnsupportedOperationException(
+        "This is supposed to be overridden by subclasses.");
+  }
+
+  /**
+   * Called by subclasses to parse an unknown field.
+   * @return {@code true} unless the tag is an end-group tag.
+   */
+  protected boolean parseUnknownField(
+      CodedInputStream input,
+      UnknownFieldSet.Builder unknownFields,
+      ExtensionRegistryLite extensionRegistry,
+      int tag) throws IOException {
+    return unknownFields.mergeFieldFrom(tag, input);
+  }
+
+  @Override
+  public void writeTo(final CodedOutputStream output) throws IOException {
+    MessageReflection.writeMessageTo(this, getAllFieldsRaw(), output, false);
+  }
+
+  @Override
+  public int getSerializedSize() {
+    int size = memoizedSize;
+    if (size != -1) {
+      return size;
+    }
+
+    memoizedSize = MessageReflection.getSerializedSize(
+        this, getAllFieldsRaw());
+    return memoizedSize;
+  }
+
+
+
+  /**
+   * Used by parsing constructors in generated classes.
+   */
+  protected void makeExtensionsImmutable() {
+    // Noop for messages without extensions.
+  }
+
+  protected abstract Message.Builder newBuilderForType(BuilderParent parent);
+
+  /**
+   * Interface for the parent of a Builder that allows the builder to
+   * communicate invalidations back to the parent for use when using nested
+   * builders.
+   */
+  protected interface BuilderParent {
+
+    /**
+     * A builder becomes dirty whenever a field is modified -- including fields
+     * in nested builders -- and becomes clean when build() is called.  Thus,
+     * when a builder becomes dirty, all its parents become dirty as well, and
+     * when it becomes clean, all its children become clean.  The dirtiness
+     * state is used to invalidate certain cached values.
+     * <br>
+     * To this end, a builder calls markAsDirty() on its parent whenever it
+     * transitions from clean to dirty.  The parent must propagate this call to
+     * its own parent, unless it was already dirty, in which case the
+     * grandparent must necessarily already be dirty as well.  The parent can
+     * only transition back to "clean" after calling build() on all children.
+     */
+    void markDirty();
+  }
+
+  @SuppressWarnings("unchecked")
+  public abstract static class Builder <BuilderType extends Builder>
+      extends AbstractMessage.Builder<BuilderType> {
+
+    private BuilderParent builderParent;
+
+    private BuilderParentImpl meAsParent;
+
+    // Indicates that we've built a message and so we are now obligated
+    // to dispatch dirty invalidations. See GeneratedMessage.BuilderListener.
+    private boolean isClean;
+
+    private UnknownFieldSet unknownFields =
+        UnknownFieldSet.getDefaultInstance();
+
+    protected Builder() {
+      this(null);
+    }
+
+    protected Builder(BuilderParent builderParent) {
+      this.builderParent = builderParent;
+    }
+
+    void dispose() {
+      builderParent = null;
+    }
+
+    /**
+     * Called by the subclass when a message is built.
+     */
+    protected void onBuilt() {
+      if (builderParent != null) {
+        markClean();
+      }
+    }
+
+    /**
+     * Called by the subclass or a builder to notify us that a message was
+     * built and may be cached and therefore invalidations are needed.
+     */
+    protected void markClean() {
+      this.isClean = true;
+    }
+
+    /**
+     * Gets whether invalidations are needed
+     *
+     * @return whether invalidations are needed
+     */
+    protected boolean isClean() {
+      return isClean;
+    }
+
+    @Override
+    public BuilderType clone() {
+      BuilderType builder =
+          (BuilderType) getDefaultInstanceForType().newBuilderForType();
+      builder.mergeFrom(buildPartial());
+      return builder;
+    }
+
+    /**
+     * Called by the initialization and clear code paths to allow subclasses to
+     * reset any of their builtin fields back to the initial values.
+     */
+    public BuilderType clear() {
+      unknownFields = UnknownFieldSet.getDefaultInstance();
+      onChanged();
+      return (BuilderType) this;
+    }
+
+    /**
+     * Get the FieldAccessorTable for this type.  We can't have the message
+     * class pass this in to the constructor because of bootstrapping trouble
+     * with DescriptorProtos.
+     */
+    protected abstract FieldAccessorTable internalGetFieldAccessorTable();
+
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    public Descriptor getDescriptorForType() {
+      return internalGetFieldAccessorTable().descriptor;
+    }
+
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    public Map<FieldDescriptor, Object> getAllFields() {
+      return Collections.unmodifiableMap(getAllFieldsMutable());
+    }
+
+    /** Internal helper which returns a mutable map. */
+    private Map<FieldDescriptor, Object> getAllFieldsMutable() {
+      final TreeMap<FieldDescriptor, Object> result =
+        new TreeMap<FieldDescriptor, Object>();
+      final Descriptor descriptor = internalGetFieldAccessorTable().descriptor;
+      final List<FieldDescriptor> fields = descriptor.getFields();
+
+      for (int i = 0; i < fields.size(); i++) {
+        FieldDescriptor field = fields.get(i);
+        final OneofDescriptor oneofDescriptor = field.getContainingOneof();
+
+        /*
+         * If the field is part of a Oneof, then at maximum one field in the Oneof is set
+         * and it is not repeated. There is no need to iterate through the others.
+         */
+        if (oneofDescriptor != null) {
+          // Skip other fields in the Oneof we know are not set
+          i += oneofDescriptor.getFieldCount() - 1;
+          if (!hasOneof(oneofDescriptor)) {
+            // If no field is set in the Oneof, skip all the fields in the Oneof
+            continue;
+          }
+          // Get the pointer to the only field which is set in the Oneof
+          field = getOneofFieldDescriptor(oneofDescriptor);
+        } else {
+          // If we are not in a Oneof, we need to check if the field is set and if it is repeated
+          if (field.isRepeated()) {
+            final List<?> value = (List<?>) getField(field);
+            if (!value.isEmpty()) {
+              result.put(field, value);
+            }
+            continue;
+          }
+          if (!hasField(field)) {
+            continue;
+          }
+        }
+        // Add the field to the map
+        result.put(field, getField(field));
+      }
+      return result;
+    }
+
+    public Message.Builder newBuilderForField(
+        final FieldDescriptor field) {
+      return internalGetFieldAccessorTable().getField(field).newBuilder();
+    }
+
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    public Message.Builder getFieldBuilder(final FieldDescriptor field) {
+      return internalGetFieldAccessorTable().getField(field).getBuilder(this);
+    }
+
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    public Message.Builder getRepeatedFieldBuilder(final FieldDescriptor field,
+        int index) {
+      return internalGetFieldAccessorTable().getField(field).getRepeatedBuilder(
+          this, index);
+    }
+
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    public boolean hasOneof(final OneofDescriptor oneof) {
+      return internalGetFieldAccessorTable().getOneof(oneof).has(this);
+    }
+
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    public FieldDescriptor getOneofFieldDescriptor(final OneofDescriptor oneof) {
+      return internalGetFieldAccessorTable().getOneof(oneof).get(this);
+    }
+
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    public boolean hasField(final FieldDescriptor field) {
+      return internalGetFieldAccessorTable().getField(field).has(this);
+    }
+
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    public Object getField(final FieldDescriptor field) {
+      Object object = internalGetFieldAccessorTable().getField(field).get(this);
+      if (field.isRepeated()) {
+        // The underlying list object is still modifiable at this point.
+        // Make sure not to expose the modifiable list to the caller.
+        return Collections.unmodifiableList((List) object);
+      } else {
+        return object;
+      }
+    }
+
+    public BuilderType setField(final FieldDescriptor field,
+                                final Object value) {
+      internalGetFieldAccessorTable().getField(field).set(this, value);
+      return (BuilderType) this;
+    }
+
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    public BuilderType clearField(final FieldDescriptor field) {
+      internalGetFieldAccessorTable().getField(field).clear(this);
+      return (BuilderType) this;
+    }
+
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    public BuilderType clearOneof(final OneofDescriptor oneof) {
+      internalGetFieldAccessorTable().getOneof(oneof).clear(this);
+      return (BuilderType) this;
+    }
+
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    public int getRepeatedFieldCount(final FieldDescriptor field) {
+      return internalGetFieldAccessorTable().getField(field)
+          .getRepeatedCount(this);
+    }
+
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    public Object getRepeatedField(final FieldDescriptor field,
+                                   final int index) {
+      return internalGetFieldAccessorTable().getField(field)
+          .getRepeated(this, index);
+    }
+
+    public BuilderType setRepeatedField(final FieldDescriptor field,
+                                        final int index, final Object value) {
+      internalGetFieldAccessorTable().getField(field)
+        .setRepeated(this, index, value);
+      return (BuilderType) this;
+    }
+
+    public BuilderType addRepeatedField(final FieldDescriptor field,
+                                        final Object value) {
+      internalGetFieldAccessorTable().getField(field).addRepeated(this, value);
+      return (BuilderType) this;
+    }
+
+    public BuilderType setUnknownFields(
+        final UnknownFieldSet unknownFields) {
+      this.unknownFields = unknownFields;
+      onChanged();
+      return (BuilderType) this;
+    }
+
+    @Override
+    public BuilderType mergeUnknownFields(
+        final UnknownFieldSet unknownFields) {
+      this.unknownFields =
+        UnknownFieldSet.newBuilder(this.unknownFields)
+                       .mergeFrom(unknownFields)
+                       .build();
+      onChanged();
+      return (BuilderType) this;
+    }
+
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    public boolean isInitialized() {
+      for (final FieldDescriptor field : getDescriptorForType().getFields()) {
+        // Check that all required fields are present.
+        if (field.isRequired()) {
+          if (!hasField(field)) {
+            return false;
+          }
+        }
+        // Check that embedded messages are initialized.
+        if (field.getJavaType() == FieldDescriptor.JavaType.MESSAGE) {
+          if (field.isRepeated()) {
+            @SuppressWarnings("unchecked") final
+            List<Message> messageList = (List<Message>) getField(field);
+            for (final Message element : messageList) {
+              if (!element.isInitialized()) {
+                return false;
+              }
+            }
+          } else {
+            if (hasField(field) &&
+                !((Message) getField(field)).isInitialized()) {
+              return false;
+            }
+          }
+        }
+      }
+      return true;
+    }
+
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    public final UnknownFieldSet getUnknownFields() {
+      return unknownFields;
+    }
+
+    /**
+     * Called by subclasses to parse an unknown field.
+     * @return {@code true} unless the tag is an end-group tag.
+     */
+    protected boolean parseUnknownField(
+        final CodedInputStream input,
+        final UnknownFieldSet.Builder unknownFields,
+        final ExtensionRegistryLite extensionRegistry,
+        final int tag) throws IOException {
+      return unknownFields.mergeFieldFrom(tag, input);
+    }
+
+    /**
+     * Implementation of {@link BuilderParent} for giving to our children. This
+     * small inner class makes it so we don't publicly expose the BuilderParent
+     * methods.
+     */
+    private class BuilderParentImpl implements BuilderParent {
+
+      //@Override (Java 1.6 override semantics, but we must support 1.5)
+      public void markDirty() {
+        onChanged();
+      }
+    }
+
+    /**
+     * Gets the {@link BuilderParent} for giving to our children.
+     * @return The builder parent for our children.
+     */
+    protected BuilderParent getParentForChildren() {
+      if (meAsParent == null) {
+        meAsParent = new BuilderParentImpl();
+      }
+      return meAsParent;
+    }
+
+    /**
+     * Called when a the builder or one of its nested children has changed
+     * and any parent should be notified of its invalidation.
+     */
+    protected final void onChanged() {
+      if (isClean && builderParent != null) {
+        builderParent.markDirty();
+
+        // Don't keep dispatching invalidations until build is called again.
+        isClean = false;
+      }
+    }
+
+    /**
+     * Gets the map field with the given field number. This method should be
+     * overridden in the generated message class if the message contains map
+     * fields.
+     *
+     * Unlike other field types, reflection support for map fields can't be
+     * implemented based on generated public API because we need to access a
+     * map field as a list in reflection API but the generated API only allows
+     * us to access it as a map. This method returns the underlying map field
+     * directly and thus enables us to access the map field as a list.
+     */
+    @SuppressWarnings({"unused", "rawtypes"})
+    protected MapField internalGetMapField(int fieldNumber) {
+      // Note that we can't use descriptor names here because this method will
+      // be called when descriptor is being initialized.
+      throw new RuntimeException(
+          "No map fields found in " + getClass().getName());
+    }
+
+    /** Like {@link internalGetMapField} but return a mutable version. */
+    @SuppressWarnings({"unused", "rawtypes"})
+    protected MapField internalGetMutableMapField(int fieldNumber) {
+      // Note that we can't use descriptor names here because this method will
+      // be called when descriptor is being initialized.
+      throw new RuntimeException(
+          "No map fields found in " + getClass().getName());
+    }
+  }
+
+  // =================================================================
+  // Extensions-related stuff
+
+  public interface ExtendableMessageOrBuilder<
+      MessageType extends ExtendableMessage> extends MessageOrBuilder {
+    // Re-define for return type covariance.
+    Message getDefaultInstanceForType();
+
+    /** Check if a singular extension is present. */
+    <Type> boolean hasExtension(
+        ExtensionLite<MessageType, Type> extension);
+
+    /** Get the number of elements in a repeated extension. */
+    <Type> int getExtensionCount(
+        ExtensionLite<MessageType, List<Type>> extension);
+
+    /** Get the value of an extension. */
+    <Type> Type getExtension(
+        ExtensionLite<MessageType, Type> extension);
+
+    /** Get one element of a repeated extension. */
+    <Type> Type getExtension(
+        ExtensionLite<MessageType, List<Type>> extension,
+        int index);
+  }
+
+  /**
+   * Generated message classes for message types that contain extension ranges
+   * subclass this.
+   *
+   * <p>This class implements type-safe accessors for extensions.  They
+   * implement all the same operations that you can do with normal fields --
+   * e.g. "has", "get", and "getCount" -- but for extensions.  The extensions
+   * are identified using instances of the class {@link GeneratedExtension};
+   * the protocol compiler generates a static instance of this class for every
+   * extension in its input.  Through the magic of generics, all is made
+   * type-safe.
+   *
+   * <p>For example, imagine you have the {@code .proto} file:
+   *
+   * <pre>
+   * option java_class = "MyProto";
+   *
+   * message Foo {
+   *   extensions 1000 to max;
+   * }
+   *
+   * extend Foo {
+   *   optional int32 bar;
+   * }
+   * </pre>
+   *
+   * <p>Then you might write code like:
+   *
+   * <pre>
+   * MyProto.Foo foo = getFoo();
+   * int i = foo.getExtension(MyProto.bar);
+   * </pre>
+   *
+   * <p>See also {@link ExtendableBuilder}.
+   */
+  public abstract static class ExtendableMessage<
+        MessageType extends ExtendableMessage>
+      extends GeneratedMessage
+      implements ExtendableMessageOrBuilder<MessageType> {
+
+    private final FieldSet<FieldDescriptor> extensions;
+
+    protected ExtendableMessage() {
+      this.extensions = FieldSet.newFieldSet();
+    }
+
+    protected ExtendableMessage(
+        ExtendableBuilder<MessageType, ?> builder) {
+      super(builder);
+      this.extensions = builder.buildExtensions();
+    }
+
+    private void verifyExtensionContainingType(
+        final Extension<MessageType, ?> extension) {
+      if (extension.getDescriptor().getContainingType() !=
+          getDescriptorForType()) {
+        // This can only happen if someone uses unchecked operations.
+        throw new IllegalArgumentException(
+          "Extension is for type \"" +
+          extension.getDescriptor().getContainingType().getFullName() +
+          "\" which does not match message type \"" +
+          getDescriptorForType().getFullName() + "\".");
+      }
+    }
+
+    /** Check if a singular extension is present. */
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    public final <Type> boolean hasExtension(
+        final ExtensionLite<MessageType, Type> extensionLite) {
+      Extension<MessageType, Type> extension = checkNotLite(extensionLite);
+
+      verifyExtensionContainingType(extension);
+      return extensions.hasField(extension.getDescriptor());
+    }
+
+    /** Get the number of elements in a repeated extension. */
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    public final <Type> int getExtensionCount(
+        final ExtensionLite<MessageType, List<Type>> extensionLite) {
+      Extension<MessageType, List<Type>> extension = checkNotLite(extensionLite);
+
+      verifyExtensionContainingType(extension);
+      final FieldDescriptor descriptor = extension.getDescriptor();
+      return extensions.getRepeatedFieldCount(descriptor);
+    }
+
+    /** Get the value of an extension. */
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    @SuppressWarnings("unchecked")
+    public final <Type> Type getExtension(
+        final ExtensionLite<MessageType, Type> extensionLite) {
+      Extension<MessageType, Type> extension = checkNotLite(extensionLite);
+
+      verifyExtensionContainingType(extension);
+      FieldDescriptor descriptor = extension.getDescriptor();
+      final Object value = extensions.getField(descriptor);
+      if (value == null) {
+        if (descriptor.isRepeated()) {
+          return (Type) Collections.emptyList();
+        } else if (descriptor.getJavaType() ==
+                   FieldDescriptor.JavaType.MESSAGE) {
+          return (Type) extension.getMessageDefaultInstance();
+        } else {
+          return (Type) extension.fromReflectionType(
+              descriptor.getDefaultValue());
+        }
+      } else {
+        return (Type) extension.fromReflectionType(value);
+      }
+    }
+
+    /** Get one element of a repeated extension. */
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    @SuppressWarnings("unchecked")
+    public final <Type> Type getExtension(
+        final ExtensionLite<MessageType, List<Type>> extensionLite,
+        final int index) {
+      Extension<MessageType, List<Type>> extension = checkNotLite(extensionLite);
+
+      verifyExtensionContainingType(extension);
+      FieldDescriptor descriptor = extension.getDescriptor();
+      return (Type) extension.singularFromReflectionType(
+          extensions.getRepeatedField(descriptor, index));
+    }
+
+    /** Called by subclasses to check if all extensions are initialized. */
+    protected boolean extensionsAreInitialized() {
+      return extensions.isInitialized();
+    }
+
+    @Override
+    public boolean isInitialized() {
+      return super.isInitialized() && extensionsAreInitialized();
+    }
+
+    @Override
+    protected boolean parseUnknownField(
+        CodedInputStream input,
+        UnknownFieldSet.Builder unknownFields,
+        ExtensionRegistryLite extensionRegistry,
+        int tag) throws IOException {
+      return MessageReflection.mergeFieldFrom(
+          input, unknownFields, extensionRegistry, getDescriptorForType(),
+          new MessageReflection.ExtensionAdapter(extensions), tag);
+    }
+
+
+    /**
+     * Used by parsing constructors in generated classes.
+     */
+    @Override
+    protected void makeExtensionsImmutable() {
+      extensions.makeImmutable();
+    }
+
+    /**
+     * Used by subclasses to serialize extensions.  Extension ranges may be
+     * interleaved with field numbers, but we must write them in canonical
+     * (sorted by field number) order.  ExtensionWriter helps us write
+     * individual ranges of extensions at once.
+     */
+    protected class ExtensionWriter {
+      // Imagine how much simpler this code would be if Java iterators had
+      // a way to get the next element without advancing the iterator.
+
+      private final Iterator<Map.Entry<FieldDescriptor, Object>> iter =
+        extensions.iterator();
+      private Map.Entry<FieldDescriptor, Object> next;
+      private final boolean messageSetWireFormat;
+
+      private ExtensionWriter(final boolean messageSetWireFormat) {
+        if (iter.hasNext()) {
+          next = iter.next();
+        }
+        this.messageSetWireFormat = messageSetWireFormat;
+      }
+
+      public void writeUntil(final int end, final CodedOutputStream output)
+                             throws IOException {
+        while (next != null && next.getKey().getNumber() < end) {
+          FieldDescriptor descriptor = next.getKey();
+          if (messageSetWireFormat && descriptor.getLiteJavaType() ==
+                  WireFormat.JavaType.MESSAGE &&
+              !descriptor.isRepeated()) {
+            if (next instanceof LazyField.LazyEntry<?>) {
+              output.writeRawMessageSetExtension(descriptor.getNumber(),
+                  ((LazyField.LazyEntry<?>) next).getField().toByteString());
+            } else {
+              output.writeMessageSetExtension(descriptor.getNumber(),
+                                              (Message) next.getValue());
+            }
+          } else {
+            // TODO(xiangl): Taken care of following code, it may cause
+            // problem when we use LazyField for normal fields/extensions.
+            // Due to the optional field can be duplicated at the end of
+            // serialized bytes, which will make the serialized size change
+            // after lazy field parsed. So when we use LazyField globally,
+            // we need to change the following write method to write cached
+            // bytes directly rather than write the parsed message.
+            FieldSet.writeField(descriptor, next.getValue(), output);
+          }
+          if (iter.hasNext()) {
+            next = iter.next();
+          } else {
+            next = null;
+          }
+        }
+      }
+    }
+
+    protected ExtensionWriter newExtensionWriter() {
+      return new ExtensionWriter(false);
+    }
+    protected ExtensionWriter newMessageSetExtensionWriter() {
+      return new ExtensionWriter(true);
+    }
+
+    /** Called by subclasses to compute the size of extensions. */
+    protected int extensionsSerializedSize() {
+      return extensions.getSerializedSize();
+    }
+    protected int extensionsSerializedSizeAsMessageSet() {
+      return extensions.getMessageSetSerializedSize();
+    }
+
+    // ---------------------------------------------------------------
+    // Reflection
+
+    protected Map<FieldDescriptor, Object> getExtensionFields() {
+      return extensions.getAllFields();
+    }
+
+    @Override
+    public Map<FieldDescriptor, Object> getAllFields() {
+      final Map<FieldDescriptor, Object> result =
+          super.getAllFieldsMutable(/* getBytesForString = */ false);
+      result.putAll(getExtensionFields());
+      return Collections.unmodifiableMap(result);
+    }
+
+    @Override
+    public Map<FieldDescriptor, Object> getAllFieldsRaw() {
+      final Map<FieldDescriptor, Object> result =
+          super.getAllFieldsMutable(/* getBytesForString = */ false);
+      result.putAll(getExtensionFields());
+      return Collections.unmodifiableMap(result);
+    }
+
+    @Override
+    public boolean hasField(final FieldDescriptor field) {
+      if (field.isExtension()) {
+        verifyContainingType(field);
+        return extensions.hasField(field);
+      } else {
+        return super.hasField(field);
+      }
+    }
+
+    @Override
+    public Object getField(final FieldDescriptor field) {
+      if (field.isExtension()) {
+        verifyContainingType(field);
+        final Object value = extensions.getField(field);
+        if (value == null) {
+          if (field.getJavaType() == FieldDescriptor.JavaType.MESSAGE) {
+            // Lacking an ExtensionRegistry, we have no way to determine the
+            // extension's real type, so we return a DynamicMessage.
+            return DynamicMessage.getDefaultInstance(field.getMessageType());
+          } else {
+            return field.getDefaultValue();
+          }
+        } else {
+          return value;
+        }
+      } else {
+        return super.getField(field);
+      }
+    }
+
+    @Override
+    public int getRepeatedFieldCount(final FieldDescriptor field) {
+      if (field.isExtension()) {
+        verifyContainingType(field);
+        return extensions.getRepeatedFieldCount(field);
+      } else {
+        return super.getRepeatedFieldCount(field);
+      }
+    }
+
+    @Override
+    public Object getRepeatedField(final FieldDescriptor field,
+                                   final int index) {
+      if (field.isExtension()) {
+        verifyContainingType(field);
+        return extensions.getRepeatedField(field, index);
+      } else {
+        return super.getRepeatedField(field, index);
+      }
+    }
+
+    private void verifyContainingType(final FieldDescriptor field) {
+      if (field.getContainingType() != getDescriptorForType()) {
+        throw new IllegalArgumentException(
+          "FieldDescriptor does not match message type.");
+      }
+    }
+  }
+
+  /**
+   * Generated message builders for message types that contain extension ranges
+   * subclass this.
+   *
+   * <p>This class implements type-safe accessors for extensions.  They
+   * implement all the same operations that you can do with normal fields --
+   * e.g. "get", "set", and "add" -- but for extensions.  The extensions are
+   * identified using instances of the class {@link GeneratedExtension}; the
+   * protocol compiler generates a static instance of this class for every
+   * extension in its input.  Through the magic of generics, all is made
+   * type-safe.
+   *
+   * <p>For example, imagine you have the {@code .proto} file:
+   *
+   * <pre>
+   * option java_class = "MyProto";
+   *
+   * message Foo {
+   *   extensions 1000 to max;
+   * }
+   *
+   * extend Foo {
+   *   optional int32 bar;
+   * }
+   * </pre>
+   *
+   * <p>Then you might write code like:
+   *
+   * <pre>
+   * MyProto.Foo foo =
+   *   MyProto.Foo.newBuilder()
+   *     .setExtension(MyProto.bar, 123)
+   *     .build();
+   * </pre>
+   *
+   * <p>See also {@link ExtendableMessage}.
+   */
+  @SuppressWarnings("unchecked")
+  public abstract static class ExtendableBuilder<
+        MessageType extends ExtendableMessage,
+        BuilderType extends ExtendableBuilder>
+      extends Builder<BuilderType>
+      implements ExtendableMessageOrBuilder<MessageType> {
+
+    private FieldSet<FieldDescriptor> extensions = FieldSet.emptySet();
+
+    protected ExtendableBuilder() {}
+
+    protected ExtendableBuilder(
+        BuilderParent parent) {
+      super(parent);
+    }
+
+    // For immutable message conversion.
+    void internalSetExtensionSet(FieldSet<FieldDescriptor> extensions) {
+      this.extensions = extensions;
+    }
+
+    @Override
+    public BuilderType clear() {
+      extensions = FieldSet.emptySet();
+      return super.clear();
+    }
+
+    // This is implemented here only to work around an apparent bug in the
+    // Java compiler and/or build system.  See bug #1898463.  The mere presence
+    // of this clone() implementation makes it go away.
+    @Override
+    public BuilderType clone() {
+      return super.clone();
+    }
+
+    private void ensureExtensionsIsMutable() {
+      if (extensions.isImmutable()) {
+        extensions = extensions.clone();
+      }
+    }
+
+    private void verifyExtensionContainingType(
+        final Extension<MessageType, ?> extension) {
+      if (extension.getDescriptor().getContainingType() !=
+          getDescriptorForType()) {
+        // This can only happen if someone uses unchecked operations.
+        throw new IllegalArgumentException(
+          "Extension is for type \"" +
+          extension.getDescriptor().getContainingType().getFullName() +
+          "\" which does not match message type \"" +
+          getDescriptorForType().getFullName() + "\".");
+      }
+    }
+
+    /** Check if a singular extension is present. */
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    public final <Type> boolean hasExtension(
+        final ExtensionLite<MessageType, Type> extensionLite) {
+      Extension<MessageType, Type> extension = checkNotLite(extensionLite);
+
+      verifyExtensionContainingType(extension);
+      return extensions.hasField(extension.getDescriptor());
+    }
+
+    /** Get the number of elements in a repeated extension. */
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    public final <Type> int getExtensionCount(
+        final ExtensionLite<MessageType, List<Type>> extensionLite) {
+      Extension<MessageType, List<Type>> extension = checkNotLite(extensionLite);
+
+      verifyExtensionContainingType(extension);
+      final FieldDescriptor descriptor = extension.getDescriptor();
+      return extensions.getRepeatedFieldCount(descriptor);
+    }
+
+    /** Get the value of an extension. */
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    public final <Type> Type getExtension(
+        final ExtensionLite<MessageType, Type> extensionLite) {
+      Extension<MessageType, Type> extension = checkNotLite(extensionLite);
+
+      verifyExtensionContainingType(extension);
+      FieldDescriptor descriptor = extension.getDescriptor();
+      final Object value = extensions.getField(descriptor);
+      if (value == null) {
+        if (descriptor.isRepeated()) {
+          return (Type) Collections.emptyList();
+        } else if (descriptor.getJavaType() ==
+                   FieldDescriptor.JavaType.MESSAGE) {
+          return (Type) extension.getMessageDefaultInstance();
+        } else {
+          return (Type) extension.fromReflectionType(
+              descriptor.getDefaultValue());
+        }
+      } else {
+        return (Type) extension.fromReflectionType(value);
+      }
+    }
+
+    /** Get one element of a repeated extension. */
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    public final <Type> Type getExtension(
+        final ExtensionLite<MessageType, List<Type>> extensionLite,
+        final int index) {
+      Extension<MessageType, List<Type>> extension = checkNotLite(extensionLite);
+
+      verifyExtensionContainingType(extension);
+      FieldDescriptor descriptor = extension.getDescriptor();
+      return (Type) extension.singularFromReflectionType(
+          extensions.getRepeatedField(descriptor, index));
+    }
+
+    /** Set the value of an extension. */
+    public final <Type> BuilderType setExtension(
+        final ExtensionLite<MessageType, Type> extensionLite,
+        final Type value) {
+      Extension<MessageType, Type> extension = checkNotLite(extensionLite);
+
+      verifyExtensionContainingType(extension);
+      ensureExtensionsIsMutable();
+      final FieldDescriptor descriptor = extension.getDescriptor();
+      extensions.setField(descriptor, extension.toReflectionType(value));
+      onChanged();
+      return (BuilderType) this;
+    }
+
+    /** Set the value of one element of a repeated extension. */
+    public final <Type> BuilderType setExtension(
+        final ExtensionLite<MessageType, List<Type>> extensionLite,
+        final int index, final Type value) {
+      Extension<MessageType, List<Type>> extension = checkNotLite(extensionLite);
+
+      verifyExtensionContainingType(extension);
+      ensureExtensionsIsMutable();
+      final FieldDescriptor descriptor = extension.getDescriptor();
+      extensions.setRepeatedField(
+        descriptor, index,
+        extension.singularToReflectionType(value));
+      onChanged();
+      return (BuilderType) this;
+    }
+
+    /** Append a value to a repeated extension. */
+    public final <Type> BuilderType addExtension(
+        final ExtensionLite<MessageType, List<Type>> extensionLite,
+        final Type value) {
+      Extension<MessageType, List<Type>> extension = checkNotLite(extensionLite);
+
+      verifyExtensionContainingType(extension);
+      ensureExtensionsIsMutable();
+      final FieldDescriptor descriptor = extension.getDescriptor();
+      extensions.addRepeatedField(
+          descriptor, extension.singularToReflectionType(value));
+      onChanged();
+      return (BuilderType) this;
+    }
+
+    /** Clear an extension. */
+    public final <Type> BuilderType clearExtension(
+        final ExtensionLite<MessageType, ?> extensionLite) {
+      Extension<MessageType, ?> extension = checkNotLite(extensionLite);
+
+      verifyExtensionContainingType(extension);
+      ensureExtensionsIsMutable();
+      extensions.clearField(extension.getDescriptor());
+      onChanged();
+      return (BuilderType) this;
+    }
+
+    /** Called by subclasses to check if all extensions are initialized. */
+    protected boolean extensionsAreInitialized() {
+      return extensions.isInitialized();
+    }
+
+    /**
+     * Called by the build code path to create a copy of the extensions for
+     * building the message.
+     */
+    private FieldSet<FieldDescriptor> buildExtensions() {
+      extensions.makeImmutable();
+      return extensions;
+    }
+
+    @Override
+    public boolean isInitialized() {
+      return super.isInitialized() && extensionsAreInitialized();
+    }
+
+    /**
+     * Called by subclasses to parse an unknown field or an extension.
+     * @return {@code true} unless the tag is an end-group tag.
+     */
+    @Override
+    protected boolean parseUnknownField(
+        final CodedInputStream input,
+        final UnknownFieldSet.Builder unknownFields,
+        final ExtensionRegistryLite extensionRegistry,
+        final int tag) throws IOException {
+      return MessageReflection.mergeFieldFrom(
+          input, unknownFields, extensionRegistry, getDescriptorForType(),
+          new MessageReflection.BuilderAdapter(this), tag);
+    }
+
+    // ---------------------------------------------------------------
+    // Reflection
+
+    @Override
+    public Map<FieldDescriptor, Object> getAllFields() {
+      final Map<FieldDescriptor, Object> result = super.getAllFieldsMutable();
+      result.putAll(extensions.getAllFields());
+      return Collections.unmodifiableMap(result);
+    }
+
+    @Override
+    public Object getField(final FieldDescriptor field) {
+      if (field.isExtension()) {
+        verifyContainingType(field);
+        final Object value = extensions.getField(field);
+        if (value == null) {
+          if (field.getJavaType() == FieldDescriptor.JavaType.MESSAGE) {
+            // Lacking an ExtensionRegistry, we have no way to determine the
+            // extension's real type, so we return a DynamicMessage.
+            return DynamicMessage.getDefaultInstance(field.getMessageType());
+          } else {
+            return field.getDefaultValue();
+          }
+        } else {
+          return value;
+        }
+      } else {
+        return super.getField(field);
+      }
+    }
+
+    @Override
+    public int getRepeatedFieldCount(final FieldDescriptor field) {
+      if (field.isExtension()) {
+        verifyContainingType(field);
+        return extensions.getRepeatedFieldCount(field);
+      } else {
+        return super.getRepeatedFieldCount(field);
+      }
+    }
+
+    @Override
+    public Object getRepeatedField(final FieldDescriptor field,
+                                   final int index) {
+      if (field.isExtension()) {
+        verifyContainingType(field);
+        return extensions.getRepeatedField(field, index);
+      } else {
+        return super.getRepeatedField(field, index);
+      }
+    }
+
+    @Override
+    public boolean hasField(final FieldDescriptor field) {
+      if (field.isExtension()) {
+        verifyContainingType(field);
+        return extensions.hasField(field);
+      } else {
+        return super.hasField(field);
+      }
+    }
+
+    @Override
+    public BuilderType setField(final FieldDescriptor field,
+                                final Object value) {
+      if (field.isExtension()) {
+        verifyContainingType(field);
+        ensureExtensionsIsMutable();
+        extensions.setField(field, value);
+        onChanged();
+        return (BuilderType) this;
+      } else {
+        return super.setField(field, value);
+      }
+    }
+
+    @Override
+    public BuilderType clearField(final FieldDescriptor field) {
+      if (field.isExtension()) {
+        verifyContainingType(field);
+        ensureExtensionsIsMutable();
+        extensions.clearField(field);
+        onChanged();
+        return (BuilderType) this;
+      } else {
+        return super.clearField(field);
+      }
+    }
+
+    @Override
+    public BuilderType setRepeatedField(final FieldDescriptor field,
+                                        final int index, final Object value) {
+      if (field.isExtension()) {
+        verifyContainingType(field);
+        ensureExtensionsIsMutable();
+        extensions.setRepeatedField(field, index, value);
+        onChanged();
+        return (BuilderType) this;
+      } else {
+        return super.setRepeatedField(field, index, value);
+      }
+    }
+
+    @Override
+    public BuilderType addRepeatedField(final FieldDescriptor field,
+                                        final Object value) {
+      if (field.isExtension()) {
+        verifyContainingType(field);
+        ensureExtensionsIsMutable();
+        extensions.addRepeatedField(field, value);
+        onChanged();
+        return (BuilderType) this;
+      } else {
+        return super.addRepeatedField(field, value);
+      }
+    }
+
+    protected final void mergeExtensionFields(final ExtendableMessage other) {
+      ensureExtensionsIsMutable();
+      extensions.mergeFrom(other.extensions);
+      onChanged();
+    }
+
+    private void verifyContainingType(final FieldDescriptor field) {
+      if (field.getContainingType() != getDescriptorForType()) {
+        throw new IllegalArgumentException(
+          "FieldDescriptor does not match message type.");
+      }
+    }
+  }
+
+  // -----------------------------------------------------------------
+
+  /**
+   * Gets the descriptor for an extension. The implementation depends on whether
+   * the extension is scoped in the top level of a file or scoped in a Message.
+   */
+  static interface ExtensionDescriptorRetriever {
+    FieldDescriptor getDescriptor();
+  }
+
+  /** For use by generated code only. */
+  public static <ContainingType extends Message, Type>
+      GeneratedExtension<ContainingType, Type>
+      newMessageScopedGeneratedExtension(final Message scope,
+                                         final int descriptorIndex,
+                                         final Class singularType,
+                                         final Message defaultInstance) {
+    // For extensions scoped within a Message, we use the Message to resolve
+    // the outer class's descriptor, from which the extension descriptor is
+    // obtained.
+    return new GeneratedExtension<ContainingType, Type>(
+        new CachedDescriptorRetriever() {
+          //@Override (Java 1.6 override semantics, but we must support 1.5)
+          public FieldDescriptor loadDescriptor() {
+            return scope.getDescriptorForType().getExtensions()
+                .get(descriptorIndex);
+          }
+        },
+        singularType,
+        defaultInstance,
+        Extension.ExtensionType.IMMUTABLE);
+  }
+
+  /** For use by generated code only. */
+  public static <ContainingType extends Message, Type>
+     GeneratedExtension<ContainingType, Type>
+     newFileScopedGeneratedExtension(final Class singularType,
+                                     final Message defaultInstance) {
+    // For extensions scoped within a file, we rely on the outer class's
+    // static initializer to call internalInit() on the extension when the
+    // descriptor is available.
+    return new GeneratedExtension<ContainingType, Type>(
+        null,  // ExtensionDescriptorRetriever is initialized in internalInit();
+        singularType,
+        defaultInstance,
+        Extension.ExtensionType.IMMUTABLE);
+  }
+
+  private abstract static class CachedDescriptorRetriever
+      implements ExtensionDescriptorRetriever {
+    private volatile FieldDescriptor descriptor;
+    protected abstract FieldDescriptor loadDescriptor();
+
+    public FieldDescriptor getDescriptor() {
+      if (descriptor == null) {
+        synchronized (this) {
+          if (descriptor == null) {
+            descriptor = loadDescriptor();
+          }
+        }
+      }
+      return descriptor;
+    }
+  }
+
+  /**
+   * Used in proto1 generated code only.
+   *
+   * After enabling bridge, we can define proto2 extensions (the extended type
+   * is a proto2 mutable message) in a proto1 .proto file. For these extensions
+   * we should generate proto2 GeneratedExtensions.
+   */
+  public static <ContainingType extends Message, Type>
+      GeneratedExtension<ContainingType, Type>
+      newMessageScopedGeneratedExtension(
+          final Message scope, final String name,
+          final Class singularType, final Message defaultInstance) {
+    // For extensions scoped within a Message, we use the Message to resolve
+    // the outer class's descriptor, from which the extension descriptor is
+    // obtained.
+    return new GeneratedExtension<ContainingType, Type>(
+        new CachedDescriptorRetriever() {
+          protected FieldDescriptor loadDescriptor() {
+            return scope.getDescriptorForType().findFieldByName(name);
+          }
+        },
+        singularType,
+        defaultInstance,
+        Extension.ExtensionType.MUTABLE);
+  }
+
+  /**
+   * Used in proto1 generated code only.
+   *
+   * After enabling bridge, we can define proto2 extensions (the extended type
+   * is a proto2 mutable message) in a proto1 .proto file. For these extensions
+   * we should generate proto2 GeneratedExtensions.
+   */
+  public static <ContainingType extends Message, Type>
+     GeneratedExtension<ContainingType, Type>
+     newFileScopedGeneratedExtension(
+         final Class singularType, final Message defaultInstance,
+         final String descriptorOuterClass, final String extensionName) {
+    // For extensions scoped within a file, we load the descriptor outer
+    // class and rely on it to get the FileDescriptor which then can be
+    // used to obtain the extension's FieldDescriptor.
+    return new GeneratedExtension<ContainingType, Type>(
+        new CachedDescriptorRetriever() {
+          protected FieldDescriptor loadDescriptor() {
+            try {
+              Class clazz =
+                  singularType.getClassLoader().loadClass(descriptorOuterClass);
+              FileDescriptor file =
+                  (FileDescriptor) clazz.getField("descriptor").get(null);
+              return file.findExtensionByName(extensionName);
+            } catch (Exception e) {
+              throw new RuntimeException(
+                  "Cannot load descriptors: " + descriptorOuterClass +
+                  " is not a valid descriptor class name", e);
+            }
+          }
+        },
+        singularType,
+        defaultInstance,
+        Extension.ExtensionType.MUTABLE);
+  }
+
+  /**
+   * Type used to represent generated extensions.  The protocol compiler
+   * generates a static singleton instance of this class for each extension.
+   *
+   * <p>For example, imagine you have the {@code .proto} file:
+   *
+   * <pre>
+   * option java_class = "MyProto";
+   *
+   * message Foo {
+   *   extensions 1000 to max;
+   * }
+   *
+   * extend Foo {
+   *   optional int32 bar;
+   * }
+   * </pre>
+   *
+   * <p>Then, {@code MyProto.Foo.bar} has type
+   * {@code GeneratedExtension<MyProto.Foo, Integer>}.
+   *
+   * <p>In general, users should ignore the details of this type, and simply use
+   * these static singletons as parameters to the extension accessors defined
+   * in {@link ExtendableMessage} and {@link ExtendableBuilder}.
+   */
+  public static class GeneratedExtension<
+      ContainingType extends Message, Type> extends
+      Extension<ContainingType, Type> {
+    // TODO(kenton):  Find ways to avoid using Java reflection within this
+    //   class.  Also try to avoid suppressing unchecked warnings.
+
+    // We can't always initialize the descriptor of a GeneratedExtension when
+    // we first construct it due to initialization order difficulties (namely,
+    // the descriptor may not have been constructed yet, since it is often
+    // constructed by the initializer of a separate module).
+    //
+    // In the case of nested extensions, we initialize the
+    // ExtensionDescriptorRetriever with an instance that uses the scoping
+    // Message's default instance to retrieve the extension's descriptor.
+    //
+    // In the case of non-nested extensions, we initialize the
+    // ExtensionDescriptorRetriever to null and rely on the outer class's static
+    // initializer to call internalInit() after the descriptor has been parsed.
+    GeneratedExtension(ExtensionDescriptorRetriever descriptorRetriever,
+        Class singularType,
+        Message messageDefaultInstance,
+        ExtensionType extensionType) {
+      if (Message.class.isAssignableFrom(singularType) &&
+          !singularType.isInstance(messageDefaultInstance)) {
+        throw new IllegalArgumentException(
+            "Bad messageDefaultInstance for " + singularType.getName());
+      }
+      this.descriptorRetriever = descriptorRetriever;
+      this.singularType = singularType;
+      this.messageDefaultInstance = messageDefaultInstance;
+
+      if (ProtocolMessageEnum.class.isAssignableFrom(singularType)) {
+        this.enumValueOf = getMethodOrDie(singularType, "valueOf",
+                                          EnumValueDescriptor.class);
+        this.enumGetValueDescriptor =
+            getMethodOrDie(singularType, "getValueDescriptor");
+      } else {
+        this.enumValueOf = null;
+        this.enumGetValueDescriptor = null;
+      }
+      this.extensionType = extensionType;
+    }
+
+    /** For use by generated code only. */
+    public void internalInit(final FieldDescriptor descriptor) {
+      if (descriptorRetriever != null) {
+        throw new IllegalStateException("Already initialized.");
+      }
+      descriptorRetriever = new ExtensionDescriptorRetriever() {
+          //@Override (Java 1.6 override semantics, but we must support 1.5)
+          public FieldDescriptor getDescriptor() {
+            return descriptor;
+          }
+        };
+    }
+
+    private ExtensionDescriptorRetriever descriptorRetriever;
+    private final Class singularType;
+    private final Message messageDefaultInstance;
+    private final Method enumValueOf;
+    private final Method enumGetValueDescriptor;
+    private final ExtensionType extensionType;
+
+    public FieldDescriptor getDescriptor() {
+      if (descriptorRetriever == null) {
+        throw new IllegalStateException(
+            "getDescriptor() called before internalInit()");
+      }
+      return descriptorRetriever.getDescriptor();
+    }
+
+    /**
+     * If the extension is an embedded message or group, returns the default
+     * instance of the message.
+     */
+    public Message getMessageDefaultInstance() {
+      return messageDefaultInstance;
+    }
+
+    protected ExtensionType getExtensionType() {
+      return extensionType;
+    }
+
+    /**
+     * Convert from the type used by the reflection accessors to the type used
+     * by native accessors.  E.g., for enums, the reflection accessors use
+     * EnumValueDescriptors but the native accessors use the generated enum
+     * type.
+     */
+    // @Override
+    @SuppressWarnings("unchecked")
+    protected Object fromReflectionType(final Object value) {
+      FieldDescriptor descriptor = getDescriptor();
+      if (descriptor.isRepeated()) {
+        if (descriptor.getJavaType() == FieldDescriptor.JavaType.MESSAGE ||
+            descriptor.getJavaType() == FieldDescriptor.JavaType.ENUM) {
+          // Must convert the whole list.
+          final List result = new ArrayList();
+          for (final Object element : (List) value) {
+            result.add(singularFromReflectionType(element));
+          }
+          return result;
+        } else {
+          return value;
+        }
+      } else {
+        return singularFromReflectionType(value);
+      }
+    }
+
+    /**
+     * Like {@link #fromReflectionType(Object)}, but if the type is a repeated
+     * type, this converts a single element.
+     */
+    // @Override
+    protected Object singularFromReflectionType(final Object value) {
+      FieldDescriptor descriptor = getDescriptor();
+      switch (descriptor.getJavaType()) {
+        case MESSAGE:
+          if (singularType.isInstance(value)) {
+            return value;
+          } else {
+            return messageDefaultInstance.newBuilderForType()
+                .mergeFrom((Message) value).build();
+          }
+        case ENUM:
+          return invokeOrDie(enumValueOf, null, (EnumValueDescriptor) value);
+        default:
+          return value;
+      }
+    }
+
+    /**
+     * Convert from the type used by the native accessors to the type used
+     * by reflection accessors.  E.g., for enums, the reflection accessors use
+     * EnumValueDescriptors but the native accessors use the generated enum
+     * type.
+     */
+    // @Override
+    @SuppressWarnings("unchecked")
+    protected Object toReflectionType(final Object value) {
+      FieldDescriptor descriptor = getDescriptor();
+      if (descriptor.isRepeated()) {
+        if (descriptor.getJavaType() == FieldDescriptor.JavaType.ENUM) {
+          // Must convert the whole list.
+          final List result = new ArrayList();
+          for (final Object element : (List) value) {
+            result.add(singularToReflectionType(element));
+          }
+          return result;
+        } else {
+          return value;
+        }
+      } else {
+        return singularToReflectionType(value);
+      }
+    }
+
+    /**
+     * Like {@link #toReflectionType(Object)}, but if the type is a repeated
+     * type, this converts a single element.
+     */
+    // @Override
+    protected Object singularToReflectionType(final Object value) {
+      FieldDescriptor descriptor = getDescriptor();
+      switch (descriptor.getJavaType()) {
+        case ENUM:
+          return invokeOrDie(enumGetValueDescriptor, value);
+        default:
+          return value;
+      }
+    }
+
+    // @Override
+    public int getNumber() {
+      return getDescriptor().getNumber();
+    }
+
+    // @Override
+    public WireFormat.FieldType getLiteType() {
+      return getDescriptor().getLiteType();
+    }
+
+    // @Override
+    public boolean isRepeated() {
+      return getDescriptor().isRepeated();
+    }
+
+    // @Override
+    @SuppressWarnings("unchecked")
+    public Type getDefaultValue() {
+      if (isRepeated()) {
+        return (Type) Collections.emptyList();
+      }
+      if (getDescriptor().getJavaType() == FieldDescriptor.JavaType.MESSAGE) {
+        return (Type) messageDefaultInstance;
+      }
+      return (Type) singularFromReflectionType(
+          getDescriptor().getDefaultValue());
+    }
+  }
+
+  // =================================================================
+
+  /** Calls Class.getMethod and throws a RuntimeException if it fails. */
+  @SuppressWarnings("unchecked")
+  private static Method getMethodOrDie(
+      final Class clazz, final String name, final Class... params) {
+    try {
+      return clazz.getMethod(name, params);
+    } catch (NoSuchMethodException e) {
+      throw new RuntimeException(
+        "Generated message class \"" + clazz.getName() +
+        "\" missing method \"" + name + "\".", e);
+    }
+  }
+
+  /** Calls invoke and throws a RuntimeException if it fails. */
+  private static Object invokeOrDie(
+      final Method method, final Object object, final Object... params) {
+    try {
+      return method.invoke(object, params);
+    } catch (IllegalAccessException e) {
+      throw new RuntimeException(
+        "Couldn't use Java reflection to implement protocol message " +
+        "reflection.", e);
+    } catch (InvocationTargetException e) {
+      final Throwable cause = e.getCause();
+      if (cause instanceof RuntimeException) {
+        throw (RuntimeException) cause;
+      } else if (cause instanceof Error) {
+        throw (Error) cause;
+      } else {
+        throw new RuntimeException(
+          "Unexpected exception thrown by generated accessor method.", cause);
+      }
+    }
+  }
+
+  /**
+   * Gets the map field with the given field number. This method should be
+   * overridden in the generated message class if the message contains map
+   * fields.
+   *
+   * Unlike other field types, reflection support for map fields can't be
+   * implemented based on generated public API because we need to access a
+   * map field as a list in reflection API but the generated API only allows
+   * us to access it as a map. This method returns the underlying map field
+   * directly and thus enables us to access the map field as a list.
+   */
+  @SuppressWarnings({"rawtypes", "unused"})
+  protected MapField internalGetMapField(int fieldNumber) {
+    // Note that we can't use descriptor names here because this method will
+    // be called when descriptor is being initialized.
+    throw new RuntimeException(
+        "No map fields found in " + getClass().getName());
+  }
+
+  /**
+   * Users should ignore this class.  This class provides the implementation
+   * with access to the fields of a message object using Java reflection.
+   */
+  public static final class FieldAccessorTable {
+
+    /**
+     * Construct a FieldAccessorTable for a particular message class.  Only
+     * one FieldAccessorTable should ever be constructed per class.
+     *
+     * @param descriptor     The type's descriptor.
+     * @param camelCaseNames The camelcase names of all fields in the message.
+     *                       These are used to derive the accessor method names.
+     * @param messageClass   The message type.
+     * @param builderClass   The builder type.
+     */
+    public FieldAccessorTable(
+        final Descriptor descriptor,
+        final String[] camelCaseNames,
+        final Class<? extends GeneratedMessage> messageClass,
+        final Class<? extends Builder> builderClass) {
+      this(descriptor, camelCaseNames);
+      ensureFieldAccessorsInitialized(messageClass, builderClass);
+    }
+
+    /**
+     * Construct a FieldAccessorTable for a particular message class without
+     * initializing FieldAccessors.
+     */
+    public FieldAccessorTable(
+        final Descriptor descriptor,
+        final String[] camelCaseNames) {
+      this.descriptor = descriptor;
+      this.camelCaseNames = camelCaseNames;
+      fields = new FieldAccessor[descriptor.getFields().size()];
+      oneofs = new OneofAccessor[descriptor.getOneofs().size()];
+      initialized = false;
+    }
+
+    private boolean isMapFieldEnabled(FieldDescriptor field) {
+      boolean result = true;
+      return result;
+    }
+
+    /**
+     * Ensures the field accessors are initialized. This method is thread-safe.
+     *
+     * @param messageClass   The message type.
+     * @param builderClass   The builder type.
+     * @return this
+     */
+    public FieldAccessorTable ensureFieldAccessorsInitialized(
+        Class<? extends GeneratedMessage> messageClass,
+        Class<? extends Builder> builderClass) {
+      if (initialized) { return this; }
+      synchronized (this) {
+        if (initialized) { return this; }
+        int fieldsSize = fields.length;
+        for (int i = 0; i < fieldsSize; i++) {
+          FieldDescriptor field = descriptor.getFields().get(i);
+          String containingOneofCamelCaseName = null;
+          if (field.getContainingOneof() != null) {
+            containingOneofCamelCaseName =
+                camelCaseNames[fieldsSize + field.getContainingOneof().getIndex()];
+          }
+          if (field.isRepeated()) {
+            if (field.getJavaType() == FieldDescriptor.JavaType.MESSAGE) {
+              if (field.isMapField() && isMapFieldEnabled(field)) {
+                fields[i] = new MapFieldAccessor(
+                    field, camelCaseNames[i], messageClass, builderClass);
+              } else {
+                fields[i] = new RepeatedMessageFieldAccessor(
+                    field, camelCaseNames[i], messageClass, builderClass);
+              }
+            } else if (field.getJavaType() == FieldDescriptor.JavaType.ENUM) {
+              fields[i] = new RepeatedEnumFieldAccessor(
+                  field, camelCaseNames[i], messageClass, builderClass);
+            } else {
+              fields[i] = new RepeatedFieldAccessor(
+                  field, camelCaseNames[i], messageClass, builderClass);
+            }
+          } else {
+            if (field.getJavaType() == FieldDescriptor.JavaType.MESSAGE) {
+              fields[i] = new SingularMessageFieldAccessor(
+                  field, camelCaseNames[i], messageClass, builderClass,
+                  containingOneofCamelCaseName);
+            } else if (field.getJavaType() == FieldDescriptor.JavaType.ENUM) {
+              fields[i] = new SingularEnumFieldAccessor(
+                  field, camelCaseNames[i], messageClass, builderClass,
+                  containingOneofCamelCaseName);
+            } else if (field.getJavaType() == FieldDescriptor.JavaType.STRING) {
+              fields[i] = new SingularStringFieldAccessor(
+                  field, camelCaseNames[i], messageClass, builderClass,
+                  containingOneofCamelCaseName);
+            } else {
+              fields[i] = new SingularFieldAccessor(
+                  field, camelCaseNames[i], messageClass, builderClass,
+                  containingOneofCamelCaseName);
+            }
+          }
+        }
+
+        int oneofsSize = oneofs.length;
+        for (int i = 0; i < oneofsSize; i++) {
+          oneofs[i] = new OneofAccessor(
+              descriptor, camelCaseNames[i + fieldsSize],
+              messageClass, builderClass);
+        }
+        initialized = true;
+        camelCaseNames = null;
+        return this;
+      }
+    }
+
+    private final Descriptor descriptor;
+    private final FieldAccessor[] fields;
+    private String[] camelCaseNames;
+    private final OneofAccessor[] oneofs;
+    private volatile boolean initialized;
+
+    /** Get the FieldAccessor for a particular field. */
+    private FieldAccessor getField(final FieldDescriptor field) {
+      if (field.getContainingType() != descriptor) {
+        throw new IllegalArgumentException(
+          "FieldDescriptor does not match message type.");
+      } else if (field.isExtension()) {
+        // If this type had extensions, it would subclass ExtendableMessage,
+        // which overrides the reflection interface to handle extensions.
+        throw new IllegalArgumentException(
+          "This type does not have extensions.");
+      }
+      return fields[field.getIndex()];
+    }
+
+    /** Get the OneofAccessor for a particular oneof. */
+    private OneofAccessor getOneof(final OneofDescriptor oneof) {
+      if (oneof.getContainingType() != descriptor) {
+        throw new IllegalArgumentException(
+          "OneofDescriptor does not match message type.");
+      }
+      return oneofs[oneof.getIndex()];
+    }
+
+    /**
+     * Abstract interface that provides access to a single field.  This is
+     * implemented differently depending on the field type and cardinality.
+     */
+    private interface FieldAccessor {
+      Object get(GeneratedMessage message);
+      Object get(GeneratedMessage.Builder builder);
+      Object getRaw(GeneratedMessage message);
+      Object getRaw(GeneratedMessage.Builder builder);
+      void set(Builder builder, Object value);
+      Object getRepeated(GeneratedMessage message, int index);
+      Object getRepeated(GeneratedMessage.Builder builder, int index);
+      Object getRepeatedRaw(GeneratedMessage message, int index);
+      Object getRepeatedRaw(GeneratedMessage.Builder builder, int index);
+      void setRepeated(Builder builder,
+                       int index, Object value);
+      void addRepeated(Builder builder, Object value);
+      boolean has(GeneratedMessage message);
+      boolean has(GeneratedMessage.Builder builder);
+      int getRepeatedCount(GeneratedMessage message);
+      int getRepeatedCount(GeneratedMessage.Builder builder);
+      void clear(Builder builder);
+      Message.Builder newBuilder();
+      Message.Builder getBuilder(GeneratedMessage.Builder builder);
+      Message.Builder getRepeatedBuilder(GeneratedMessage.Builder builder,
+                                         int index);
+    }
+
+    /** OneofAccessor provides access to a single oneof. */
+    private static class OneofAccessor {
+      OneofAccessor(
+          final Descriptor descriptor, final String camelCaseName,
+          final Class<? extends GeneratedMessage> messageClass,
+          final Class<? extends Builder> builderClass) {
+        this.descriptor = descriptor;
+        caseMethod =
+            getMethodOrDie(messageClass, "get" + camelCaseName + "Case");
+        caseMethodBuilder =
+            getMethodOrDie(builderClass, "get" + camelCaseName + "Case");
+        clearMethod = getMethodOrDie(builderClass, "clear" + camelCaseName);
+      }
+
+      private final Descriptor descriptor;
+      private final Method caseMethod;
+      private final Method caseMethodBuilder;
+      private final Method clearMethod;
+
+      public boolean has(final GeneratedMessage message) {
+        if (((Internal.EnumLite) invokeOrDie(caseMethod, message)).getNumber() == 0) {
+          return false;
+        }
+        return true;
+      }
+
+      public boolean has(GeneratedMessage.Builder builder) {
+        if (((Internal.EnumLite) invokeOrDie(caseMethodBuilder, builder)).getNumber() == 0) {
+          return false;
+        }
+        return true;
+      }
+
+      public FieldDescriptor get(final GeneratedMessage message) {
+        int fieldNumber = ((Internal.EnumLite) invokeOrDie(caseMethod, message)).getNumber();
+        if (fieldNumber > 0) {
+          return descriptor.findFieldByNumber(fieldNumber);
+        }
+        return null;
+      }
+
+      public FieldDescriptor get(GeneratedMessage.Builder builder) {
+        int fieldNumber = ((Internal.EnumLite) invokeOrDie(caseMethodBuilder, builder)).getNumber();
+        if (fieldNumber > 0) {
+          return descriptor.findFieldByNumber(fieldNumber);
+        }
+        return null;
+      }
+
+      public void clear(final Builder builder) {
+        invokeOrDie(clearMethod, builder);
+      }
+    }
+
+    private static boolean supportFieldPresence(FileDescriptor file) {
+      return file.getSyntax() == FileDescriptor.Syntax.PROTO2;
+    }
+
+    // ---------------------------------------------------------------
+
+    private static class SingularFieldAccessor implements FieldAccessor {
+      SingularFieldAccessor(
+          final FieldDescriptor descriptor, final String camelCaseName,
+          final Class<? extends GeneratedMessage> messageClass,
+          final Class<? extends Builder> builderClass,
+          final String containingOneofCamelCaseName) {
+        field = descriptor;
+        isOneofField = descriptor.getContainingOneof() != null;
+        hasHasMethod = supportFieldPresence(descriptor.getFile())
+            || (!isOneofField && descriptor.getJavaType() == FieldDescriptor.JavaType.MESSAGE);
+        getMethod = getMethodOrDie(messageClass, "get" + camelCaseName);
+        getMethodBuilder = getMethodOrDie(builderClass, "get" + camelCaseName);
+        type = getMethod.getReturnType();
+        setMethod = getMethodOrDie(builderClass, "set" + camelCaseName, type);
+        hasMethod =
+            hasHasMethod ? getMethodOrDie(messageClass, "has" + camelCaseName) : null;
+        hasMethodBuilder =
+            hasHasMethod ? getMethodOrDie(builderClass, "has" + camelCaseName) : null;
+        clearMethod = getMethodOrDie(builderClass, "clear" + camelCaseName);
+        caseMethod = isOneofField ? getMethodOrDie(
+            messageClass, "get" + containingOneofCamelCaseName + "Case") : null;
+        caseMethodBuilder = isOneofField ? getMethodOrDie(
+            builderClass, "get" + containingOneofCamelCaseName + "Case") : null;
+      }
+
+      // Note:  We use Java reflection to call public methods rather than
+      //   access private fields directly as this avoids runtime security
+      //   checks.
+      protected final Class<?> type;
+      protected final Method getMethod;
+      protected final Method getMethodBuilder;
+      protected final Method setMethod;
+      protected final Method hasMethod;
+      protected final Method hasMethodBuilder;
+      protected final Method clearMethod;
+      protected final Method caseMethod;
+      protected final Method caseMethodBuilder;
+      protected final FieldDescriptor field;
+      protected final boolean isOneofField;
+      protected final boolean hasHasMethod;
+
+      private int getOneofFieldNumber(final GeneratedMessage message) {
+        return ((Internal.EnumLite) invokeOrDie(caseMethod, message)).getNumber();
+      }
+
+      private int getOneofFieldNumber(final GeneratedMessage.Builder builder) {
+        return ((Internal.EnumLite) invokeOrDie(caseMethodBuilder, builder)).getNumber();
+      }
+
+      public Object get(final GeneratedMessage message) {
+        return invokeOrDie(getMethod, message);
+      }
+      public Object get(GeneratedMessage.Builder builder) {
+        return invokeOrDie(getMethodBuilder, builder);
+      }
+      public Object getRaw(final GeneratedMessage message) {
+        return get(message);
+      }
+      public Object getRaw(GeneratedMessage.Builder builder) {
+        return get(builder);
+      }
+      public void set(final Builder builder, final Object value) {
+        invokeOrDie(setMethod, builder, value);
+      }
+      public Object getRepeated(final GeneratedMessage message,
+                                final int index) {
+        throw new UnsupportedOperationException(
+          "getRepeatedField() called on a singular field.");
+      }
+      public Object getRepeatedRaw(final GeneratedMessage message,
+                                final int index) {
+        throw new UnsupportedOperationException(
+          "getRepeatedFieldRaw() called on a singular field.");
+      }
+      public Object getRepeated(GeneratedMessage.Builder builder, int index) {
+        throw new UnsupportedOperationException(
+          "getRepeatedField() called on a singular field.");
+      }
+      public Object getRepeatedRaw(GeneratedMessage.Builder builder,
+          int index) {
+        throw new UnsupportedOperationException(
+          "getRepeatedFieldRaw() called on a singular field.");
+      }
+      public void setRepeated(final Builder builder, final int index,
+          final Object value) {
+        throw new UnsupportedOperationException(
+          "setRepeatedField() called on a singular field.");
+      }
+      public void addRepeated(final Builder builder, final Object value) {
+        throw new UnsupportedOperationException(
+          "addRepeatedField() called on a singular field.");
+      }
+      public boolean has(final GeneratedMessage message) {
+        if (!hasHasMethod) {
+          if (isOneofField) {
+            return getOneofFieldNumber(message) == field.getNumber();
+          }
+          return !get(message).equals(field.getDefaultValue());
+        }
+        return (Boolean) invokeOrDie(hasMethod, message);
+      }
+      public boolean has(GeneratedMessage.Builder builder) {
+        if (!hasHasMethod) {
+          if (isOneofField) {
+            return getOneofFieldNumber(builder) == field.getNumber();
+          }
+          return !get(builder).equals(field.getDefaultValue());
+        }
+        return (Boolean) invokeOrDie(hasMethodBuilder, builder);
+      }
+      public int getRepeatedCount(final GeneratedMessage message) {
+        throw new UnsupportedOperationException(
+          "getRepeatedFieldSize() called on a singular field.");
+      }
+      public int getRepeatedCount(GeneratedMessage.Builder builder) {
+        throw new UnsupportedOperationException(
+          "getRepeatedFieldSize() called on a singular field.");
+      }
+      public void clear(final Builder builder) {
+        invokeOrDie(clearMethod, builder);
+      }
+      public Message.Builder newBuilder() {
+        throw new UnsupportedOperationException(
+          "newBuilderForField() called on a non-Message type.");
+      }
+      public Message.Builder getBuilder(GeneratedMessage.Builder builder) {
+        throw new UnsupportedOperationException(
+          "getFieldBuilder() called on a non-Message type.");
+      }
+      public Message.Builder getRepeatedBuilder(GeneratedMessage.Builder builder,
+          int index) {
+        throw new UnsupportedOperationException(
+          "getRepeatedFieldBuilder() called on a non-Message type.");
+      }
+    }
+
+    private static class RepeatedFieldAccessor implements FieldAccessor {
+      protected final Class type;
+      protected final Method getMethod;
+      protected final Method getMethodBuilder;
+      protected final Method getRepeatedMethod;
+      protected final Method getRepeatedMethodBuilder;
+      protected final Method setRepeatedMethod;
+      protected final Method addRepeatedMethod;
+      protected final Method getCountMethod;
+      protected final Method getCountMethodBuilder;
+      protected final Method clearMethod;
+
+      RepeatedFieldAccessor(
+          final FieldDescriptor descriptor, final String camelCaseName,
+          final Class<? extends GeneratedMessage> messageClass,
+          final Class<? extends Builder> builderClass) {
+        getMethod = getMethodOrDie(messageClass,
+                                   "get" + camelCaseName + "List");
+        getMethodBuilder = getMethodOrDie(builderClass,
+                                   "get" + camelCaseName + "List");
+        getRepeatedMethod =
+            getMethodOrDie(messageClass, "get" + camelCaseName, Integer.TYPE);
+        getRepeatedMethodBuilder =
+            getMethodOrDie(builderClass, "get" + camelCaseName, Integer.TYPE);
+        type = getRepeatedMethod.getReturnType();
+        setRepeatedMethod =
+            getMethodOrDie(builderClass, "set" + camelCaseName,
+                           Integer.TYPE, type);
+        addRepeatedMethod =
+            getMethodOrDie(builderClass, "add" + camelCaseName, type);
+        getCountMethod =
+            getMethodOrDie(messageClass, "get" + camelCaseName + "Count");
+        getCountMethodBuilder =
+            getMethodOrDie(builderClass, "get" + camelCaseName + "Count");
+
+        clearMethod = getMethodOrDie(builderClass, "clear" + camelCaseName);
+      }
+
+      public Object get(final GeneratedMessage message) {
+        return invokeOrDie(getMethod, message);
+      }
+      public Object get(GeneratedMessage.Builder builder) {
+        return invokeOrDie(getMethodBuilder, builder);
+      }
+      public Object getRaw(final GeneratedMessage message) {
+        return get(message);
+      }
+      public Object getRaw(GeneratedMessage.Builder builder) {
+        return get(builder);
+      }
+      public void set(final Builder builder, final Object value) {
+        // Add all the elements individually.  This serves two purposes:
+        // 1) Verifies that each element has the correct type.
+        // 2) Insures that the caller cannot modify the list later on and
+        //    have the modifications be reflected in the message.
+        clear(builder);
+        for (final Object element : (List<?>) value) {
+          addRepeated(builder, element);
+        }
+      }
+      public Object getRepeated(final GeneratedMessage message,
+                                final int index) {
+        return invokeOrDie(getRepeatedMethod, message, index);
+      }
+      public Object getRepeated(GeneratedMessage.Builder builder, int index) {
+        return invokeOrDie(getRepeatedMethodBuilder, builder, index);
+      }
+      public Object getRepeatedRaw(GeneratedMessage message, int index) {
+        return getRepeated(message, index);
+      }
+      public Object getRepeatedRaw(GeneratedMessage.Builder builder,
+          int index) {
+        return getRepeated(builder, index);
+      }
+      public void setRepeated(final Builder builder,
+                              final int index, final Object value) {
+        invokeOrDie(setRepeatedMethod, builder, index, value);
+      }
+      public void addRepeated(final Builder builder, final Object value) {
+        invokeOrDie(addRepeatedMethod, builder, value);
+      }
+      public boolean has(final GeneratedMessage message) {
+        throw new UnsupportedOperationException(
+          "hasField() called on a repeated field.");
+      }
+      public boolean has(GeneratedMessage.Builder builder) {
+        throw new UnsupportedOperationException(
+          "hasField() called on a repeated field.");
+      }
+      public int getRepeatedCount(final GeneratedMessage message) {
+        return (Integer) invokeOrDie(getCountMethod, message);
+      }
+      public int getRepeatedCount(GeneratedMessage.Builder builder) {
+        return (Integer) invokeOrDie(getCountMethodBuilder, builder);
+      }
+      public void clear(final Builder builder) {
+        invokeOrDie(clearMethod, builder);
+      }
+      public Message.Builder newBuilder() {
+        throw new UnsupportedOperationException(
+          "newBuilderForField() called on a non-Message type.");
+      }
+      public Message.Builder getBuilder(GeneratedMessage.Builder builder) {
+        throw new UnsupportedOperationException(
+          "getFieldBuilder() called on a non-Message type.");
+      }
+      public Message.Builder getRepeatedBuilder(GeneratedMessage.Builder builder,
+          int index) {
+        throw new UnsupportedOperationException(
+          "getRepeatedFieldBuilder() called on a non-Message type.");
+      }
+    }
+
+    private static class MapFieldAccessor implements FieldAccessor {
+      MapFieldAccessor(
+          final FieldDescriptor descriptor, final String camelCaseName,
+          final Class<? extends GeneratedMessage> messageClass,
+          final Class<? extends Builder> builderClass) {
+        field = descriptor;
+        Method getDefaultInstanceMethod =
+            getMethodOrDie(messageClass, "getDefaultInstance");
+        MapField defaultMapField = getMapField(
+            (GeneratedMessage) invokeOrDie(getDefaultInstanceMethod, null));
+        mapEntryMessageDefaultInstance =
+            defaultMapField.getMapEntryMessageDefaultInstance();
+      }
+
+      private final FieldDescriptor field;
+      private final Message mapEntryMessageDefaultInstance;
+
+      private MapField<?, ?> getMapField(GeneratedMessage message) {
+        return (MapField<?, ?>) message.internalGetMapField(field.getNumber());
+      }
+
+      private MapField<?, ?> getMapField(GeneratedMessage.Builder builder) {
+        return (MapField<?, ?>) builder.internalGetMapField(field.getNumber());
+      }
+
+      private MapField<?, ?> getMutableMapField(
+          GeneratedMessage.Builder builder) {
+        return (MapField<?, ?>) builder.internalGetMutableMapField(
+            field.getNumber());
+      }
+
+      public Object get(GeneratedMessage message) {
+        List result = new ArrayList();
+        for (int i = 0; i < getRepeatedCount(message); i++) {
+          result.add(getRepeated(message, i));
+        }
+        return Collections.unmodifiableList(result);
+      }
+
+      public Object get(Builder builder) {
+        List result = new ArrayList();
+        for (int i = 0; i < getRepeatedCount(builder); i++) {
+          result.add(getRepeated(builder, i));
+        }
+        return Collections.unmodifiableList(result);
+      }
+
+      public Object getRaw(GeneratedMessage message) {
+        return get(message);
+      }
+
+      public Object getRaw(GeneratedMessage.Builder builder) {
+        return get(builder);
+      }
+
+      public void set(Builder builder, Object value) {
+        clear(builder);
+        for (Object entry : (List) value) {
+          addRepeated(builder, entry);
+        }
+      }
+
+      public Object getRepeated(GeneratedMessage message, int index) {
+        return getMapField(message).getList().get(index);
+      }
+
+      public Object getRepeated(Builder builder, int index) {
+        return getMapField(builder).getList().get(index);
+      }
+
+      public Object getRepeatedRaw(GeneratedMessage message, int index) {
+        return getRepeated(message, index);
+      }
+
+      public Object getRepeatedRaw(Builder builder, int index) {
+        return getRepeated(builder, index);
+      }
+
+      public void setRepeated(Builder builder, int index, Object value) {
+        getMutableMapField(builder).getMutableList().set(index, (Message) value);
+      }
+
+      public void addRepeated(Builder builder, Object value) {
+        getMutableMapField(builder).getMutableList().add((Message) value);
+      }
+
+      public boolean has(GeneratedMessage message) {
+        throw new UnsupportedOperationException(
+            "hasField() is not supported for repeated fields.");
+      }
+
+      public boolean has(Builder builder) {
+        throw new UnsupportedOperationException(
+            "hasField() is not supported for repeated fields.");
+      }
+
+      public int getRepeatedCount(GeneratedMessage message) {
+        return getMapField(message).getList().size();
+      }
+
+      public int getRepeatedCount(Builder builder) {
+        return getMapField(builder).getList().size();
+      }
+
+      public void clear(Builder builder) {
+        getMutableMapField(builder).getMutableList().clear();
+      }
+
+      public com.google.protobuf.Message.Builder newBuilder() {
+        return mapEntryMessageDefaultInstance.newBuilderForType();
+      }
+
+      public com.google.protobuf.Message.Builder getBuilder(Builder builder) {
+        throw new UnsupportedOperationException(
+            "Nested builder not supported for map fields.");
+      }
+
+      public com.google.protobuf.Message.Builder getRepeatedBuilder(
+          Builder builder, int index) {
+        throw new UnsupportedOperationException(
+            "Nested builder not supported for map fields.");
+      }
+    }
+
+    // ---------------------------------------------------------------
+
+    private static final class SingularEnumFieldAccessor
+        extends SingularFieldAccessor {
+      SingularEnumFieldAccessor(
+          final FieldDescriptor descriptor, final String camelCaseName,
+          final Class<? extends GeneratedMessage> messageClass,
+          final Class<? extends Builder> builderClass,
+          final String containingOneofCamelCaseName) {
+        super(descriptor, camelCaseName, messageClass, builderClass, containingOneofCamelCaseName);
+
+        enumDescriptor = descriptor.getEnumType();
+
+        valueOfMethod = getMethodOrDie(type, "valueOf",
+                                       EnumValueDescriptor.class);
+        getValueDescriptorMethod =
+          getMethodOrDie(type, "getValueDescriptor");
+
+        supportUnknownEnumValue = descriptor.getFile().supportsUnknownEnumValue();
+        if (supportUnknownEnumValue) {
+          getValueMethod =
+              getMethodOrDie(messageClass, "get" + camelCaseName + "Value");
+          getValueMethodBuilder =
+              getMethodOrDie(builderClass, "get" + camelCaseName + "Value");
+          setValueMethod =
+              getMethodOrDie(builderClass, "set" + camelCaseName + "Value", int.class);
+        }
+      }
+
+      private EnumDescriptor enumDescriptor;
+
+      private Method valueOfMethod;
+      private Method getValueDescriptorMethod;
+
+      private boolean supportUnknownEnumValue;
+      private Method getValueMethod;
+      private Method getValueMethodBuilder;
+      private Method setValueMethod;
+
+      @Override
+      public Object get(final GeneratedMessage message) {
+        if (supportUnknownEnumValue) {
+          int value = (Integer) invokeOrDie(getValueMethod, message);
+          return enumDescriptor.findValueByNumberCreatingIfUnknown(value);
+        }
+        return invokeOrDie(getValueDescriptorMethod, super.get(message));
+      }
+
+      @Override
+      public Object get(final GeneratedMessage.Builder builder) {
+        if (supportUnknownEnumValue) {
+          int value = (Integer) invokeOrDie(getValueMethodBuilder, builder);
+          return enumDescriptor.findValueByNumberCreatingIfUnknown(value);
+        }
+        return invokeOrDie(getValueDescriptorMethod, super.get(builder));
+      }
+
+      @Override
+      public void set(final Builder builder, final Object value) {
+        if (supportUnknownEnumValue) {
+          invokeOrDie(setValueMethod, builder,
+              ((EnumValueDescriptor) value).getNumber());
+          return;
+        }
+        super.set(builder, invokeOrDie(valueOfMethod, null, value));
+      }
+    }
+
+    private static final class RepeatedEnumFieldAccessor
+        extends RepeatedFieldAccessor {
+      RepeatedEnumFieldAccessor(
+          final FieldDescriptor descriptor, final String camelCaseName,
+          final Class<? extends GeneratedMessage> messageClass,
+          final Class<? extends Builder> builderClass) {
+        super(descriptor, camelCaseName, messageClass, builderClass);
+
+        enumDescriptor = descriptor.getEnumType();
+
+        valueOfMethod = getMethodOrDie(type, "valueOf",
+                                       EnumValueDescriptor.class);
+        getValueDescriptorMethod =
+          getMethodOrDie(type, "getValueDescriptor");
+
+        supportUnknownEnumValue = descriptor.getFile().supportsUnknownEnumValue();
+        if (supportUnknownEnumValue) {
+          getRepeatedValueMethod =
+              getMethodOrDie(messageClass, "get" + camelCaseName + "Value", int.class);
+          getRepeatedValueMethodBuilder =
+              getMethodOrDie(builderClass, "get" + camelCaseName + "Value", int.class);
+          setRepeatedValueMethod =
+              getMethodOrDie(builderClass, "set" + camelCaseName + "Value", int.class, int.class);
+          addRepeatedValueMethod =
+              getMethodOrDie(builderClass, "add" + camelCaseName + "Value", int.class);
+        }
+      }
+      private EnumDescriptor enumDescriptor;
+
+      private final Method valueOfMethod;
+      private final Method getValueDescriptorMethod;
+
+      private boolean supportUnknownEnumValue;
+      private Method getRepeatedValueMethod;
+      private Method getRepeatedValueMethodBuilder;
+      private Method setRepeatedValueMethod;
+      private Method addRepeatedValueMethod;
+
+      @Override
+      @SuppressWarnings("unchecked")
+      public Object get(final GeneratedMessage message) {
+        final List newList = new ArrayList();
+        final int size = getRepeatedCount(message);
+        for (int i = 0; i < size; i++) {
+          newList.add(getRepeated(message, i));
+        }
+        return Collections.unmodifiableList(newList);
+      }
+
+      @Override
+      @SuppressWarnings("unchecked")
+      public Object get(final GeneratedMessage.Builder builder) {
+        final List newList = new ArrayList();
+        final int size = getRepeatedCount(builder);
+        for (int i = 0; i < size; i++) {
+          newList.add(getRepeated(builder, i));
+        }
+        return Collections.unmodifiableList(newList);
+      }
+
+      @Override
+      public Object getRepeated(final GeneratedMessage message,
+                                final int index) {
+        if (supportUnknownEnumValue) {
+          int value = (Integer) invokeOrDie(getRepeatedValueMethod, message, index);
+          return enumDescriptor.findValueByNumberCreatingIfUnknown(value);
+        }
+        return invokeOrDie(getValueDescriptorMethod,
+          super.getRepeated(message, index));
+      }
+      @Override
+      public Object getRepeated(final GeneratedMessage.Builder builder,
+                                final int index) {
+        if (supportUnknownEnumValue) {
+          int value = (Integer) invokeOrDie(getRepeatedValueMethodBuilder, builder, index);
+          return enumDescriptor.findValueByNumberCreatingIfUnknown(value);
+        }
+        return invokeOrDie(getValueDescriptorMethod,
+          super.getRepeated(builder, index));
+      }
+      @Override
+      public void setRepeated(final Builder builder,
+                              final int index, final Object value) {
+        if (supportUnknownEnumValue) {
+          invokeOrDie(setRepeatedValueMethod, builder, index,
+              ((EnumValueDescriptor) value).getNumber());
+          return;
+        }
+        super.setRepeated(builder, index, invokeOrDie(valueOfMethod, null,
+                          value));
+      }
+      @Override
+      public void addRepeated(final Builder builder, final Object value) {
+        if (supportUnknownEnumValue) {
+          invokeOrDie(addRepeatedValueMethod, builder,
+              ((EnumValueDescriptor) value).getNumber());
+          return;
+        }
+        super.addRepeated(builder, invokeOrDie(valueOfMethod, null, value));
+      }
+    }
+
+    // ---------------------------------------------------------------
+
+    /**
+     * Field accessor for string fields.
+     *
+     * <p>This class makes getFooBytes() and setFooBytes() available for
+     * reflection API so that reflection based serialize/parse functions can
+     * access the raw bytes of the field to preserve non-UTF8 bytes in the
+     * string.
+     *
+     * <p>This ensures the serialize/parse round-trip safety, which is important
+     * for servers which forward messages.
+     */
+    private static final class SingularStringFieldAccessor
+        extends SingularFieldAccessor {
+      SingularStringFieldAccessor(
+          final FieldDescriptor descriptor, final String camelCaseName,
+          final Class<? extends GeneratedMessage> messageClass,
+          final Class<? extends Builder> builderClass,
+          final String containingOneofCamelCaseName) {
+        super(descriptor, camelCaseName, messageClass, builderClass,
+            containingOneofCamelCaseName);
+        getBytesMethod = getMethodOrDie(messageClass,
+            "get" + camelCaseName + "Bytes");
+        getBytesMethodBuilder = getMethodOrDie(builderClass,
+            "get" + camelCaseName + "Bytes");
+        setBytesMethodBuilder = getMethodOrDie(builderClass,
+            "set" + camelCaseName + "Bytes", ByteString.class);
+      }
+
+      private final Method getBytesMethod;
+      private final Method getBytesMethodBuilder;
+      private final Method setBytesMethodBuilder;
+
+      @Override
+      public Object getRaw(final GeneratedMessage message) {
+        return invokeOrDie(getBytesMethod, message);
+      }
+
+      @Override
+      public Object getRaw(GeneratedMessage.Builder builder) {
+        return invokeOrDie(getBytesMethodBuilder, builder);
+      }
+
+      @Override
+      public void set(GeneratedMessage.Builder builder, Object value) {
+        if (value instanceof ByteString) {
+          invokeOrDie(setBytesMethodBuilder, builder, value);
+        } else {
+          super.set(builder, value);
+        }
+      }
+    }
+
+    // ---------------------------------------------------------------
+
+    private static final class SingularMessageFieldAccessor
+        extends SingularFieldAccessor {
+      SingularMessageFieldAccessor(
+          final FieldDescriptor descriptor, final String camelCaseName,
+          final Class<? extends GeneratedMessage> messageClass,
+          final Class<? extends Builder> builderClass,
+          final String containingOneofCamelCaseName) {
+        super(descriptor, camelCaseName, messageClass, builderClass,
+            containingOneofCamelCaseName);
+
+        newBuilderMethod = getMethodOrDie(type, "newBuilder");
+        getBuilderMethodBuilder =
+            getMethodOrDie(builderClass, "get" + camelCaseName + "Builder");
+      }
+
+      private final Method newBuilderMethod;
+      private final Method getBuilderMethodBuilder;
+
+      private Object coerceType(final Object value) {
+        if (type.isInstance(value)) {
+          return value;
+        } else {
+          // The value is not the exact right message type.  However, if it
+          // is an alternative implementation of the same type -- e.g. a
+          // DynamicMessage -- we should accept it.  In this case we can make
+          // a copy of the message.
+          return ((Message.Builder) invokeOrDie(newBuilderMethod, null))
+                  .mergeFrom((Message) value).buildPartial();
+        }
+      }
+
+      @Override
+      public void set(final Builder builder, final Object value) {
+        super.set(builder, coerceType(value));
+      }
+      @Override
+      public Message.Builder newBuilder() {
+        return (Message.Builder) invokeOrDie(newBuilderMethod, null);
+      }
+      @Override
+      public Message.Builder getBuilder(GeneratedMessage.Builder builder) {
+        return (Message.Builder) invokeOrDie(getBuilderMethodBuilder, builder);
+      }
+    }
+
+    private static final class RepeatedMessageFieldAccessor
+        extends RepeatedFieldAccessor {
+      RepeatedMessageFieldAccessor(
+          final FieldDescriptor descriptor, final String camelCaseName,
+          final Class<? extends GeneratedMessage> messageClass,
+          final Class<? extends Builder> builderClass) {
+        super(descriptor, camelCaseName, messageClass, builderClass);
+
+        newBuilderMethod = getMethodOrDie(type, "newBuilder");
+        getBuilderMethodBuilder = getMethodOrDie(builderClass,
+            "get" + camelCaseName + "Builder", Integer.TYPE);
+      }
+
+      private final Method newBuilderMethod;
+      private final Method getBuilderMethodBuilder;
+
+      private Object coerceType(final Object value) {
+        if (type.isInstance(value)) {
+          return value;
+        } else {
+          // The value is not the exact right message type.  However, if it
+          // is an alternative implementation of the same type -- e.g. a
+          // DynamicMessage -- we should accept it.  In this case we can make
+          // a copy of the message.
+          return ((Message.Builder) invokeOrDie(newBuilderMethod, null))
+                  .mergeFrom((Message) value).build();
+        }
+      }
+
+      @Override
+      public void setRepeated(final Builder builder,
+                              final int index, final Object value) {
+        super.setRepeated(builder, index, coerceType(value));
+      }
+      @Override
+      public void addRepeated(final Builder builder, final Object value) {
+        super.addRepeated(builder, coerceType(value));
+      }
+      @Override
+      public Message.Builder newBuilder() {
+        return (Message.Builder) invokeOrDie(newBuilderMethod, null);
+      }
+      @Override
+      public Message.Builder getRepeatedBuilder(
+          final GeneratedMessage.Builder builder, final int index) {
+        return (Message.Builder) invokeOrDie(
+            getBuilderMethodBuilder, builder, index);
+      }
+    }
+  }
+
+  /**
+   * Replaces this object in the output stream with a serialized form.
+   * Part of Java's serialization magic.  Generated sub-classes must override
+   * this method by calling {@code return super.writeReplace();}
+   * @return a SerializedForm of this message
+   */
+  protected Object writeReplace() throws ObjectStreamException {
+    return new GeneratedMessageLite.SerializedForm(this);
+  }
+
+  /**
+   * Checks that the {@link Extension} is non-Lite and returns it as a
+   * {@link GeneratedExtension}.
+   */
+  private static <MessageType extends ExtendableMessage<MessageType>, T>
+    Extension<MessageType, T> checkNotLite(
+        ExtensionLite<MessageType, T> extension) {
+    if (extension.isLite()) {
+      throw new IllegalArgumentException("Expected non-lite extension.");
+    }
+
+    return (Extension<MessageType, T>) extension;
+  }
+  
+  protected static int computeStringSize(final int fieldNumber, final Object value) {
+    if (value instanceof String) {
+      return CodedOutputStream.computeStringSize(fieldNumber, (String) value);
+    } else {
+      return CodedOutputStream.computeBytesSize(fieldNumber, (ByteString) value);
+    }
+  }
+  
+  protected static int computeStringSizeNoTag(final Object value) {
+    if (value instanceof String) {
+      return CodedOutputStream.computeStringSizeNoTag((String) value);
+    } else {
+      return CodedOutputStream.computeBytesSizeNoTag((ByteString) value);
+    }
+  }
+  
+  protected static void writeString(
+      CodedOutputStream output, final int fieldNumber, final Object value) throws IOException {
+    if (value instanceof String) {
+      output.writeString(fieldNumber, (String) value);
+    } else {
+      output.writeBytes(fieldNumber, (ByteString) value);
+    }
+  }
+  
+  protected static void writeStringNoTag(
+      CodedOutputStream output, final Object value) throws IOException {
+    if (value instanceof String) {
+      output.writeStringNoTag((String) value);
+    } else {
+      output.writeBytesNoTag((ByteString) value);
+    }
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/GeneratedMessageLite.java b/java/core/src/main/java/com/google/protobuf/GeneratedMessageLite.java
new file mode 100644
index 00000000..81e1862c
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/GeneratedMessageLite.java
@@ -0,0 +1,1276 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import com.google.protobuf.Internal.BooleanList;
+import com.google.protobuf.Internal.DoubleList;
+import com.google.protobuf.Internal.FloatList;
+import com.google.protobuf.Internal.IntList;
+import com.google.protobuf.Internal.LongList;
+import com.google.protobuf.Internal.ProtobufList;
+import com.google.protobuf.WireFormat.FieldType;
+
+import java.io.IOException;
+import java.io.ObjectStreamException;
+import java.io.Serializable;
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * Lite version of {@link GeneratedMessage}.
+ *
+ * @author kenton@google.com Kenton Varda
+ */
+public abstract class GeneratedMessageLite<
+    MessageType extends GeneratedMessageLite<MessageType, BuilderType>,
+    BuilderType extends GeneratedMessageLite.Builder<MessageType, BuilderType>> 
+        extends AbstractMessageLite
+        implements Serializable {
+
+  private static final long serialVersionUID = 1L;
+
+  /** For use by generated code only. Lazily initialized to reduce allocations. */
+  protected UnknownFieldSetLite unknownFields = null;
+  
+  /** For use by generated code only.  */
+  protected int memoizedSerializedSize = -1;
+  
+  @SuppressWarnings("unchecked") // Guaranteed by runtime.
+  public final Parser<MessageType> getParserForType() {
+    return (Parser<MessageType>) dynamicMethod(MethodToInvoke.GET_PARSER);
+  }
+
+  @SuppressWarnings("unchecked") // Guaranteed by runtime.
+  public final MessageType getDefaultInstanceForType() {
+    return (MessageType) dynamicMethod(MethodToInvoke.GET_DEFAULT_INSTANCE);
+  }
+
+  @SuppressWarnings("unchecked") // Guaranteed by runtime.
+  public final BuilderType newBuilderForType() {
+    return (BuilderType) dynamicMethod(MethodToInvoke.NEW_BUILDER);
+  }
+
+  // The general strategy for unknown fields is to use an UnknownFieldSetLite that is treated as
+  // mutable during the parsing constructor and immutable after. This allows us to avoid
+  // any unnecessary intermediary allocations while reducing the generated code size.
+
+  /**
+   * Lazily initializes unknown fields.
+   */
+  private final void ensureUnknownFieldsInitialized() {
+    if (unknownFields == null) {
+      unknownFields = UnknownFieldSetLite.newInstance();
+    }
+  }
+  
+  /**
+   * Called by subclasses to parse an unknown field. For use by generated code only.
+   * 
+   * @return {@code true} unless the tag is an end-group tag.
+   */
+  protected boolean parseUnknownField(int tag, CodedInputStream input) throws IOException {
+    // This will avoid the allocation of unknown fields when a group tag is encountered.
+    if (WireFormat.getTagWireType(tag) == WireFormat.WIRETYPE_END_GROUP) {
+      return false;
+    }
+    
+    ensureUnknownFieldsInitialized();
+    return unknownFields.mergeFieldFrom(tag, input);
+  }
+
+  /**
+   * Called by subclasses to parse an unknown field. For use by generated code only.
+   */
+  protected void mergeVarintField(int tag, int value) {
+    ensureUnknownFieldsInitialized();
+    unknownFields.mergeVarintField(tag, value);
+  }
+  
+  /**
+   * Called by subclasses to parse an unknown field. For use by generated code only.
+   */
+  protected void mergeLengthDelimitedField(int fieldNumber, ByteString value) {
+    ensureUnknownFieldsInitialized();
+    unknownFields.mergeLengthDelimitedField(fieldNumber, value);
+  }
+  
+  /**
+   * Called by subclasses to complete parsing. For use by generated code only.
+   */
+  protected void doneParsing() {
+    if (unknownFields == null) {
+      unknownFields = UnknownFieldSetLite.getDefaultInstance();
+    } else {
+      unknownFields.makeImmutable();
+    }
+  }
+
+  public final boolean isInitialized() {
+    return dynamicMethod(MethodToInvoke.IS_INITIALIZED, Boolean.TRUE) != null;
+  }
+
+  public final BuilderType toBuilder() {
+    BuilderType builder = (BuilderType) dynamicMethod(MethodToInvoke.NEW_BUILDER);
+    builder.mergeFrom((MessageType) this);
+    return builder;
+  }
+
+  /**
+   * Defines which method path to invoke in {@link GeneratedMessageLite
+   * #dynamicMethod(MethodToInvoke, Object...)}.
+   * <p>
+   * For use by generated code only.
+   */
+  public static enum MethodToInvoke {
+    IS_INITIALIZED,
+    PARSE_PARTIAL_FROM,
+    MERGE_FROM,
+    MAKE_IMMUTABLE,
+    NEW_INSTANCE,
+    NEW_BUILDER,
+    GET_DEFAULT_INSTANCE,
+    GET_PARSER;
+  }
+
+  /**
+   * A method that implements different types of operations described in {@link MethodToInvoke}.
+   * Theses different kinds of operations are required to implement message-level operations for
+   * builders in the runtime. This method bundles those operations to reduce the generated methods
+   * count.
+   * <ul>
+   * <li>{@code PARSE_PARTIAL_FROM} is parameterized with an {@link CodedInputStream} and
+   * {@link ExtensionRegistryLite}. It consumes the input stream, parsing the contents into the
+   * returned protocol buffer. If parsing throws an {@link InvalidProtocolBufferException}, the
+   * implementation wraps it in a RuntimeException
+   * <li>{@code NEW_INSTANCE} returns a new instance of the protocol buffer
+   * <li>{@code IS_INITIALIZED} is parameterized with a {@code Boolean} detailing whether to
+   * memoize. It returns {@code null} for false and the default instance for true. We optionally
+   * memoize to support the Builder case, where memoization is not desired.
+   * <li>{@code NEW_BUILDER} returns a {@code BuilderType} instance.
+   * <li>{@code MERGE_FROM} is parameterized with a {@code MessageType} and merges the fields from
+   * that instance into this instance.
+   * <li>{@code MAKE_IMMUTABLE} sets all internal fields to an immutable state.
+   * </ul>
+   * This method, plus the implementation of the Builder, enables the Builder class to be proguarded
+   * away entirely on Android.
+   * <p>
+   * For use by generated code only.
+   */
+  protected abstract Object dynamicMethod(MethodToInvoke method, Object arg0, Object arg1);
+
+  /**
+   * Same as {@link #dynamicMethod(MethodToInvoke, Object, Object)} with {@code null} padding.
+   */
+  protected Object dynamicMethod(MethodToInvoke method, Object arg0) {
+    return dynamicMethod(method, arg0, null);
+  }
+
+  /**
+   * Same as {@link #dynamicMethod(MethodToInvoke, Object, Object)} with {@code null} padding.
+   */
+  protected Object dynamicMethod(MethodToInvoke method) {
+    return dynamicMethod(method, null, null);
+  }
+
+  /**
+   * Merge some unknown fields into the {@link UnknownFieldSetLite} for this
+   * message.
+   *
+   * <p>For use by generated code only.
+   */
+  protected final void mergeUnknownFields(UnknownFieldSetLite unknownFields) {
+    this.unknownFields = UnknownFieldSetLite.mutableCopyOf(this.unknownFields, unknownFields);
+  }
+
+  @SuppressWarnings("unchecked")
+  public abstract static class Builder<
+      MessageType extends GeneratedMessageLite<MessageType, BuilderType>,
+      BuilderType extends Builder<MessageType, BuilderType>>
+          extends AbstractMessageLite.Builder<BuilderType> {
+
+    private final MessageType defaultInstance;
+    protected MessageType instance;
+    protected boolean isBuilt;
+
+    protected Builder(MessageType defaultInstance) {
+      this.defaultInstance = defaultInstance;
+      this.instance = (MessageType) defaultInstance.dynamicMethod(MethodToInvoke.NEW_INSTANCE);
+      isBuilt = false;
+    }
+
+    /**
+     * Called before any method that would mutate the builder to ensure that it correctly copies
+     * any state before the write happens to preserve immutability guarantees.
+     */
+    protected void copyOnWrite() {
+      if (isBuilt) {
+        MessageType newInstance = (MessageType) instance.dynamicMethod(MethodToInvoke.NEW_INSTANCE);
+        newInstance.dynamicMethod(MethodToInvoke.MERGE_FROM, instance);
+        instance = newInstance;
+        isBuilt = false;
+      }
+    }
+
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    public final boolean isInitialized() {
+      return GeneratedMessageLite.isInitialized(instance, false /* shouldMemoize */);
+    }
+
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    public final BuilderType clear() {
+      // No need to copy on write since we're dropping the instance anyways.
+      instance = (MessageType) instance.dynamicMethod(MethodToInvoke.NEW_INSTANCE);
+      return (BuilderType) this;
+    }
+
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    public BuilderType clone() {
+      BuilderType builder =
+          (BuilderType) getDefaultInstanceForType().newBuilderForType();
+      builder.mergeFrom(buildPartial());
+      return builder;
+    }
+
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    public MessageType buildPartial() {
+      if (isBuilt) {
+        return instance;
+      }
+      
+      instance.dynamicMethod(MethodToInvoke.MAKE_IMMUTABLE);
+      instance.unknownFields.makeImmutable();
+      
+      isBuilt = true;
+      return instance;
+    }
+
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    public final MessageType build() {
+      MessageType result = buildPartial();
+      if (!result.isInitialized()) {
+        throw newUninitializedMessageException(result);
+      }
+      return result;
+    }
+    
+    /** All subclasses implement this. */
+    public BuilderType mergeFrom(MessageType message) {
+      copyOnWrite();
+      instance.dynamicMethod(MethodToInvoke.MERGE_FROM, message);
+      return (BuilderType) this;
+    }
+    
+    public MessageType getDefaultInstanceForType() {
+      return defaultInstance;
+    }
+    
+    public BuilderType mergeFrom(
+        com.google.protobuf.CodedInputStream input,
+        com.google.protobuf.ExtensionRegistryLite extensionRegistry)
+        throws java.io.IOException {
+      MessageType parsedMessage = null;
+      try {
+        parsedMessage =
+            (MessageType) getDefaultInstanceForType().getParserForType().parsePartialFrom(
+                input, extensionRegistry);
+      } catch (com.google.protobuf.InvalidProtocolBufferException e) {
+        parsedMessage = (MessageType) e.getUnfinishedMessage();
+        throw e;
+      } finally {
+        if (parsedMessage != null) {
+          mergeFrom(parsedMessage);
+        }
+      }
+      return (BuilderType) this;
+    }
+  }
+
+
+  // =================================================================
+  // Extensions-related stuff
+
+  /**
+   * Lite equivalent of {@link com.google.protobuf.GeneratedMessage.ExtendableMessageOrBuilder}.
+   */
+  public interface ExtendableMessageOrBuilder<
+      MessageType extends ExtendableMessage<MessageType, BuilderType>,
+      BuilderType extends ExtendableBuilder<MessageType, BuilderType>>
+          extends MessageLiteOrBuilder {
+
+    /** Check if a singular extension is present. */
+    <Type> boolean hasExtension(
+        ExtensionLite<MessageType, Type> extension);
+
+    /** Get the number of elements in a repeated extension. */
+    <Type> int getExtensionCount(
+        ExtensionLite<MessageType, List<Type>> extension);
+
+    /** Get the value of an extension. */
+    <Type> Type getExtension(ExtensionLite<MessageType, Type> extension);
+
+    /** Get one element of a repeated extension. */
+    <Type> Type getExtension(
+        ExtensionLite<MessageType, List<Type>> extension,
+        int index);
+  }
+
+  /**
+   * Lite equivalent of {@link GeneratedMessage.ExtendableMessage}.
+   */
+  public abstract static class ExtendableMessage<
+        MessageType extends ExtendableMessage<MessageType, BuilderType>,
+        BuilderType extends ExtendableBuilder<MessageType, BuilderType>>
+            extends GeneratedMessageLite<MessageType, BuilderType>
+            implements ExtendableMessageOrBuilder<MessageType, BuilderType> {
+
+    /**
+     * Represents the set of extensions on this message. For use by generated
+     * code only.
+     */
+    protected FieldSet<ExtensionDescriptor> extensions = FieldSet.newFieldSet();
+
+    protected final void mergeExtensionFields(final MessageType other) {
+      if (extensions.isImmutable()) {
+        extensions = extensions.clone();
+      }
+      extensions.mergeFrom(((ExtendableMessage) other).extensions);
+    }
+    
+    /**
+     * Parse an unknown field or an extension. For use by generated code only.
+     * 
+     * <p>For use by generated code only.
+     * 
+     * @return {@code true} unless the tag is an end-group tag.
+     */
+    protected <MessageType extends MessageLite> boolean parseUnknownField(
+        MessageType defaultInstance,
+        CodedInputStream input,
+        ExtensionRegistryLite extensionRegistry,
+        int tag) throws IOException {
+      int wireType = WireFormat.getTagWireType(tag);
+      int fieldNumber = WireFormat.getTagFieldNumber(tag);
+
+      // TODO(dweis): How much bytecode would be saved by not requiring the generated code to
+      //     provide the default instance?
+      GeneratedExtension<MessageType, ?> extension = extensionRegistry.findLiteExtensionByNumber(
+          defaultInstance, fieldNumber);
+
+      boolean unknown = false;
+      boolean packed = false;
+      if (extension == null) {
+        unknown = true;  // Unknown field.
+      } else if (wireType == FieldSet.getWireFormatForFieldType(
+                   extension.descriptor.getLiteType(),
+                   false  /* isPacked */)) {
+        packed = false;  // Normal, unpacked value.
+      } else if (extension.descriptor.isRepeated &&
+                 extension.descriptor.type.isPackable() &&
+                 wireType == FieldSet.getWireFormatForFieldType(
+                   extension.descriptor.getLiteType(),
+                   true  /* isPacked */)) {
+        packed = true;  // Packed value.
+      } else {
+        unknown = true;  // Wrong wire type.
+      }
+
+      if (unknown) {  // Unknown field or wrong wire type.  Skip.
+        return parseUnknownField(tag, input);
+      }
+
+      if (packed) {
+        int length = input.readRawVarint32();
+        int limit = input.pushLimit(length);
+        if (extension.descriptor.getLiteType() == WireFormat.FieldType.ENUM) {
+          while (input.getBytesUntilLimit() > 0) {
+            int rawValue = input.readEnum();
+            Object value =
+                extension.descriptor.getEnumType().findValueByNumber(rawValue);
+            if (value == null) {
+              // If the number isn't recognized as a valid value for this
+              // enum, drop it (don't even add it to unknownFields).
+              return true;
+            }
+            extensions.addRepeatedField(extension.descriptor,
+                                        extension.singularToFieldSetType(value));
+          }
+        } else {
+          while (input.getBytesUntilLimit() > 0) {
+            Object value =
+                FieldSet.readPrimitiveField(input,
+                                            extension.descriptor.getLiteType(),
+                                            /*checkUtf8=*/ false);
+            extensions.addRepeatedField(extension.descriptor, value);
+          }
+        }
+        input.popLimit(limit);
+      } else {
+        Object value;
+        switch (extension.descriptor.getLiteJavaType()) {
+          case MESSAGE: {
+            MessageLite.Builder subBuilder = null;
+            if (!extension.descriptor.isRepeated()) {
+              MessageLite existingValue =
+                  (MessageLite) extensions.getField(extension.descriptor);
+              if (existingValue != null) {
+                subBuilder = existingValue.toBuilder();
+              }
+            }
+            if (subBuilder == null) {
+              subBuilder = extension.getMessageDefaultInstance()
+                  .newBuilderForType();
+            }
+            if (extension.descriptor.getLiteType() ==
+                WireFormat.FieldType.GROUP) {
+              input.readGroup(extension.getNumber(),
+                              subBuilder, extensionRegistry);
+            } else {
+              input.readMessage(subBuilder, extensionRegistry);
+            }
+            value = subBuilder.build();
+            break;
+          }
+          case ENUM:
+            int rawValue = input.readEnum();
+            value = extension.descriptor.getEnumType()
+                             .findValueByNumber(rawValue);
+            // If the number isn't recognized as a valid value for this enum,
+            // write it to unknown fields object.
+            if (value == null) {
+              mergeVarintField(fieldNumber, rawValue);
+              return true;
+            }
+            break;
+          default:
+            value = FieldSet.readPrimitiveField(input,
+                extension.descriptor.getLiteType(),
+                /*checkUtf8=*/ false);
+            break;
+        }
+
+        if (extension.descriptor.isRepeated()) {
+          extensions.addRepeatedField(extension.descriptor,
+                                      extension.singularToFieldSetType(value));
+        } else {
+          extensions.setField(extension.descriptor,
+                              extension.singularToFieldSetType(value));
+        }
+      }
+
+      return true;
+    }
+    
+    private void verifyExtensionContainingType(
+        final GeneratedExtension<MessageType, ?> extension) {
+      if (extension.getContainingTypeDefaultInstance() !=
+          getDefaultInstanceForType()) {
+        // This can only happen if someone uses unchecked operations.
+        throw new IllegalArgumentException(
+          "This extension is for a different message type.  Please make " +
+          "sure that you are not suppressing any generics type warnings.");
+      }
+    }
+
+    /** Check if a singular extension is present. */
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    public final <Type> boolean hasExtension(
+        final ExtensionLite<MessageType, Type> extension) {
+      GeneratedExtension<MessageType, Type> extensionLite =
+          checkIsLite(extension);
+      
+      verifyExtensionContainingType(extensionLite);
+      return extensions.hasField(extensionLite.descriptor);
+    }
+
+    /** Get the number of elements in a repeated extension. */
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    public final <Type> int getExtensionCount(
+        final ExtensionLite<MessageType, List<Type>> extension) {
+      GeneratedExtension<MessageType, List<Type>> extensionLite =
+          checkIsLite(extension);
+      
+      verifyExtensionContainingType(extensionLite);
+      return extensions.getRepeatedFieldCount(extensionLite.descriptor);
+    }
+
+    /** Get the value of an extension. */
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    @SuppressWarnings("unchecked")
+    public final <Type> Type getExtension(
+        final ExtensionLite<MessageType, Type> extension) {
+      GeneratedExtension<MessageType, Type> extensionLite =
+          checkIsLite(extension);
+      
+      verifyExtensionContainingType(extensionLite);
+      final Object value = extensions.getField(extensionLite.descriptor);
+      if (value == null) {
+        return extensionLite.defaultValue;
+      } else {
+        return (Type) extensionLite.fromFieldSetType(value);
+      }
+    }
+
+    /** Get one element of a repeated extension. */
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    @SuppressWarnings("unchecked")
+    public final <Type> Type getExtension(
+        final ExtensionLite<MessageType, List<Type>> extension,
+        final int index) {
+      GeneratedExtension<MessageType, List<Type>> extensionLite =
+          checkIsLite(extension);
+
+      verifyExtensionContainingType(extensionLite);
+      return (Type) extensionLite.singularFromFieldSetType(
+          extensions.getRepeatedField(extensionLite.descriptor, index));
+    }
+
+    /** Called by subclasses to check if all extensions are initialized. */
+    protected boolean extensionsAreInitialized() {
+      return extensions.isInitialized();
+    }
+
+
+    @Override
+    protected final void doneParsing() {
+      super.doneParsing();
+      
+      extensions.makeImmutable();
+    }
+
+    /**
+     * Used by subclasses to serialize extensions.  Extension ranges may be
+     * interleaved with field numbers, but we must write them in canonical
+     * (sorted by field number) order.  ExtensionWriter helps us write
+     * individual ranges of extensions at once.
+     */
+    protected class ExtensionWriter {
+      // Imagine how much simpler this code would be if Java iterators had
+      // a way to get the next element without advancing the iterator.
+
+      private final Iterator<Map.Entry<ExtensionDescriptor, Object>> iter =
+            extensions.iterator();
+      private Map.Entry<ExtensionDescriptor, Object> next;
+      private final boolean messageSetWireFormat;
+
+      private ExtensionWriter(boolean messageSetWireFormat) {
+        if (iter.hasNext()) {
+          next = iter.next();
+        }
+        this.messageSetWireFormat = messageSetWireFormat;
+      }
+
+      public void writeUntil(final int end, final CodedOutputStream output)
+                             throws IOException {
+        while (next != null && next.getKey().getNumber() < end) {
+          ExtensionDescriptor extension = next.getKey();
+          if (messageSetWireFormat && extension.getLiteJavaType() ==
+                  WireFormat.JavaType.MESSAGE &&
+              !extension.isRepeated()) {
+            output.writeMessageSetExtension(extension.getNumber(),
+                                            (MessageLite) next.getValue());
+          } else {
+            FieldSet.writeField(extension, next.getValue(), output);
+          }
+          if (iter.hasNext()) {
+            next = iter.next();
+          } else {
+            next = null;
+          }
+        }
+      }
+    }
+
+    protected ExtensionWriter newExtensionWriter() {
+      return new ExtensionWriter(false);
+    }
+    protected ExtensionWriter newMessageSetExtensionWriter() {
+      return new ExtensionWriter(true);
+    }
+
+    /** Called by subclasses to compute the size of extensions. */
+    protected int extensionsSerializedSize() {
+      return extensions.getSerializedSize();
+    }
+    protected int extensionsSerializedSizeAsMessageSet() {
+      return extensions.getMessageSetSerializedSize();
+    }
+  }
+
+  /**
+   * Lite equivalent of {@link GeneratedMessage.ExtendableBuilder}.
+   */
+  @SuppressWarnings("unchecked")
+  public abstract static class ExtendableBuilder<
+        MessageType extends ExtendableMessage<MessageType, BuilderType>,
+        BuilderType extends ExtendableBuilder<MessageType, BuilderType>>
+      extends Builder<MessageType, BuilderType>
+      implements ExtendableMessageOrBuilder<MessageType, BuilderType> {
+    protected ExtendableBuilder(MessageType defaultInstance) {
+      super(defaultInstance);
+      
+      // TODO(dweis): This is kind of an unnecessary clone since we construct a
+      //     new instance in the parent constructor which makes the extensions
+      //     immutable. This extra allocation shouldn't matter in practice
+      //     though.
+      instance.extensions = instance.extensions.clone();
+    }
+
+    // For immutable message conversion.
+    void internalSetExtensionSet(FieldSet<ExtensionDescriptor> extensions) {
+      copyOnWrite();
+      instance.extensions = extensions;
+    }
+
+    // @Override (Java 1.6 override semantics, but we must support 1.5)
+    protected void copyOnWrite() {
+      if (!isBuilt) {
+        return;
+      }
+      
+      super.copyOnWrite();
+      instance.extensions = instance.extensions.clone();
+    }
+
+    // @Override (Java 1.6 override semantics, but we must support 1.5)
+    public final MessageType buildPartial() {
+      if (isBuilt) {
+        return instance;
+      }
+
+      instance.extensions.makeImmutable();
+      return super.buildPartial();
+    }
+
+    private void verifyExtensionContainingType(
+        final GeneratedExtension<MessageType, ?> extension) {
+      if (extension.getContainingTypeDefaultInstance() !=
+          getDefaultInstanceForType()) {
+        // This can only happen if someone uses unchecked operations.
+        throw new IllegalArgumentException(
+          "This extension is for a different message type.  Please make " +
+          "sure that you are not suppressing any generics type warnings.");
+      }
+    }
+
+    /** Check if a singular extension is present. */
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    public final <Type> boolean hasExtension(
+        final ExtensionLite<MessageType, Type> extension) {
+      return instance.hasExtension(extension);
+    }
+
+    /** Get the number of elements in a repeated extension. */
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    public final <Type> int getExtensionCount(
+        final ExtensionLite<MessageType, List<Type>> extension) {
+      return instance.getExtensionCount(extension);
+    }
+
+    /** Get the value of an extension. */
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    @SuppressWarnings("unchecked")
+    public final <Type> Type getExtension(
+        final ExtensionLite<MessageType, Type> extension) {
+      return instance.getExtension(extension);
+    }
+
+    /** Get one element of a repeated extension. */
+    @SuppressWarnings("unchecked")
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    public final <Type> Type getExtension(
+        final ExtensionLite<MessageType, List<Type>> extension,
+        final int index) {
+      return instance.getExtension(extension, index);
+    }
+
+    // This is implemented here only to work around an apparent bug in the
+    // Java compiler and/or build system.  See bug #1898463.  The mere presence
+    // of this dummy clone() implementation makes it go away.
+    @Override
+    public BuilderType clone() {
+      return super.clone();
+    }
+    
+    /** Set the value of an extension. */
+    public final <Type> BuilderType setExtension(
+        final ExtensionLite<MessageType, Type> extension,
+        final Type value) {
+      GeneratedExtension<MessageType, Type> extensionLite =
+          checkIsLite(extension);
+      
+      verifyExtensionContainingType(extensionLite);
+      copyOnWrite();
+      instance.extensions.setField(extensionLite.descriptor, extensionLite.toFieldSetType(value));
+      return (BuilderType) this;
+    }
+
+    /** Set the value of one element of a repeated extension. */
+    public final <Type> BuilderType setExtension(
+        final ExtensionLite<MessageType, List<Type>> extension,
+        final int index, final Type value) {
+      GeneratedExtension<MessageType, List<Type>> extensionLite =
+          checkIsLite(extension);
+      
+      verifyExtensionContainingType(extensionLite);
+      copyOnWrite();
+      instance.extensions.setRepeatedField(
+          extensionLite.descriptor, index, extensionLite.singularToFieldSetType(value));
+      return (BuilderType) this;
+    }
+
+    /** Append a value to a repeated extension. */
+    public final <Type> BuilderType addExtension(
+        final ExtensionLite<MessageType, List<Type>> extension,
+        final Type value) {
+      GeneratedExtension<MessageType, List<Type>> extensionLite =
+          checkIsLite(extension);
+      
+      verifyExtensionContainingType(extensionLite);
+      copyOnWrite();
+      instance.extensions.addRepeatedField(
+          extensionLite.descriptor, extensionLite.singularToFieldSetType(value));
+      return (BuilderType) this;
+    }
+
+    /** Clear an extension. */
+    public final <Type> BuilderType clearExtension(
+        final ExtensionLite<MessageType, ?> extension) {
+      GeneratedExtension<MessageType, ?> extensionLite = checkIsLite(extension);
+      
+      verifyExtensionContainingType(extensionLite);
+      copyOnWrite();
+      instance.extensions.clearField(extensionLite.descriptor);
+      return (BuilderType) this;
+    }
+  }
+
+  // -----------------------------------------------------------------
+
+  /** For use by generated code only. */
+  public static <ContainingType extends MessageLite, Type>
+      GeneratedExtension<ContainingType, Type>
+          newSingularGeneratedExtension(
+              final ContainingType containingTypeDefaultInstance,
+              final Type defaultValue,
+              final MessageLite messageDefaultInstance,
+              final Internal.EnumLiteMap<?> enumTypeMap,
+              final int number,
+              final WireFormat.FieldType type,
+              final Class singularType) {
+    return new GeneratedExtension<ContainingType, Type>(
+        containingTypeDefaultInstance,
+        defaultValue,
+        messageDefaultInstance,
+        new ExtensionDescriptor(enumTypeMap, number, type,
+                                false /* isRepeated */,
+                                false /* isPacked */),
+        singularType);
+  }
+
+  /** For use by generated code only. */
+  public static <ContainingType extends MessageLite, Type>
+      GeneratedExtension<ContainingType, Type>
+          newRepeatedGeneratedExtension(
+              final ContainingType containingTypeDefaultInstance,
+              final MessageLite messageDefaultInstance,
+              final Internal.EnumLiteMap<?> enumTypeMap,
+              final int number,
+              final WireFormat.FieldType type,
+              final boolean isPacked,
+              final Class singularType) {
+    @SuppressWarnings("unchecked")  // Subclasses ensure Type is a List
+    Type emptyList = (Type) Collections.emptyList();
+    return new GeneratedExtension<ContainingType, Type>(
+        containingTypeDefaultInstance,
+        emptyList,
+        messageDefaultInstance,
+        new ExtensionDescriptor(
+            enumTypeMap, number, type, true /* isRepeated */, isPacked),
+        singularType);
+  }
+
+  static final class ExtensionDescriptor
+      implements FieldSet.FieldDescriptorLite<
+        ExtensionDescriptor> {
+    ExtensionDescriptor(
+        final Internal.EnumLiteMap<?> enumTypeMap,
+        final int number,
+        final WireFormat.FieldType type,
+        final boolean isRepeated,
+        final boolean isPacked) {
+      this.enumTypeMap = enumTypeMap;
+      this.number = number;
+      this.type = type;
+      this.isRepeated = isRepeated;
+      this.isPacked = isPacked;
+    }
+
+    final Internal.EnumLiteMap<?> enumTypeMap;
+    final int number;
+    final WireFormat.FieldType type;
+    final boolean isRepeated;
+    final boolean isPacked;
+
+    public int getNumber() {
+      return number;
+    }
+
+    public WireFormat.FieldType getLiteType() {
+      return type;
+    }
+
+    public WireFormat.JavaType getLiteJavaType() {
+      return type.getJavaType();
+    }
+
+    public boolean isRepeated() {
+      return isRepeated;
+    }
+
+    public boolean isPacked() {
+      return isPacked;
+    }
+
+    public Internal.EnumLiteMap<?> getEnumType() {
+      return enumTypeMap;
+    }
+
+    @SuppressWarnings("unchecked")
+    public MessageLite.Builder internalMergeFrom(
+        MessageLite.Builder to, MessageLite from) {
+      return ((Builder) to).mergeFrom((GeneratedMessageLite) from);
+    }
+
+
+    public int compareTo(ExtensionDescriptor other) {
+      return number - other.number;
+    }
+  }
+
+  // =================================================================
+
+  /** Calls Class.getMethod and throws a RuntimeException if it fails. */
+  @SuppressWarnings("unchecked")
+  static Method getMethodOrDie(Class clazz, String name, Class... params) {
+    try {
+      return clazz.getMethod(name, params);
+    } catch (NoSuchMethodException e) {
+      throw new RuntimeException(
+        "Generated message class \"" + clazz.getName() +
+        "\" missing method \"" + name + "\".", e);
+    }
+  }
+
+  /** Calls invoke and throws a RuntimeException if it fails. */
+  static Object invokeOrDie(Method method, Object object, Object... params) {
+    try {
+      return method.invoke(object, params);
+    } catch (IllegalAccessException e) {
+      throw new RuntimeException(
+        "Couldn't use Java reflection to implement protocol message " +
+        "reflection.", e);
+    } catch (InvocationTargetException e) {
+      final Throwable cause = e.getCause();
+      if (cause instanceof RuntimeException) {
+        throw (RuntimeException) cause;
+      } else if (cause instanceof Error) {
+        throw (Error) cause;
+      } else {
+        throw new RuntimeException(
+          "Unexpected exception thrown by generated accessor method.", cause);
+      }
+    }
+  }
+
+  /**
+   * Lite equivalent to {@link GeneratedMessage.GeneratedExtension}.
+   *
+   * Users should ignore the contents of this class and only use objects of
+   * this type as parameters to extension accessors and ExtensionRegistry.add().
+   */
+  public static class GeneratedExtension<
+      ContainingType extends MessageLite, Type>
+          extends ExtensionLite<ContainingType, Type> {
+
+    /**
+     * Create a new instance with the given parameters.
+     *
+     * The last parameter {@code singularType} is only needed for enum types.
+     * We store integer values for enum types in a {@link ExtendableMessage}
+     * and use Java reflection to convert an integer value back into a concrete
+     * enum object.
+     */
+    GeneratedExtension(
+        final ContainingType containingTypeDefaultInstance,
+        final Type defaultValue,
+        final MessageLite messageDefaultInstance,
+        final ExtensionDescriptor descriptor,
+        final Class singularType) {
+      // Defensive checks to verify the correct initialization order of
+      // GeneratedExtensions and their related GeneratedMessages.
+      if (containingTypeDefaultInstance == null) {
+        throw new IllegalArgumentException(
+            "Null containingTypeDefaultInstance");
+      }
+      if (descriptor.getLiteType() == WireFormat.FieldType.MESSAGE &&
+          messageDefaultInstance == null) {
+        throw new IllegalArgumentException(
+            "Null messageDefaultInstance");
+      }
+      this.containingTypeDefaultInstance = containingTypeDefaultInstance;
+      this.defaultValue = defaultValue;
+      this.messageDefaultInstance = messageDefaultInstance;
+      this.descriptor = descriptor;
+    }
+
+    final ContainingType containingTypeDefaultInstance;
+    final Type defaultValue;
+    final MessageLite messageDefaultInstance;
+    final ExtensionDescriptor descriptor;
+
+    /**
+     * Default instance of the type being extended, used to identify that type.
+     */
+    public ContainingType getContainingTypeDefaultInstance() {
+      return containingTypeDefaultInstance;
+    }
+
+    /** Get the field number. */
+    public int getNumber() {
+      return descriptor.getNumber();
+    }
+
+
+    /**
+     * If the extension is an embedded message or group, returns the default
+     * instance of the message.
+     */
+    public MessageLite getMessageDefaultInstance() {
+      return messageDefaultInstance;
+    }
+
+    @SuppressWarnings("unchecked")
+    Object fromFieldSetType(final Object value) {
+      if (descriptor.isRepeated()) {
+        if (descriptor.getLiteJavaType() == WireFormat.JavaType.ENUM) {
+          final List result = new ArrayList();
+          for (final Object element : (List) value) {
+            result.add(singularFromFieldSetType(element));
+          }
+          return result;
+        } else {
+          return value;
+        }
+      } else {
+        return singularFromFieldSetType(value);
+      }
+    }
+
+    Object singularFromFieldSetType(final Object value) {
+      if (descriptor.getLiteJavaType() == WireFormat.JavaType.ENUM) {
+        return descriptor.enumTypeMap.findValueByNumber((Integer) value);
+      } else {
+        return value;
+      }
+    }
+
+    @SuppressWarnings("unchecked")
+    Object toFieldSetType(final Object value) {
+      if (descriptor.isRepeated()) {
+        if (descriptor.getLiteJavaType() == WireFormat.JavaType.ENUM) {
+          final List result = new ArrayList();
+          for (final Object element : (List) value) {
+            result.add(singularToFieldSetType(element));
+          }
+          return result;
+        } else {
+          return value;
+        }
+      } else {
+        return singularToFieldSetType(value);
+      }
+    }
+
+    Object singularToFieldSetType(final Object value) {
+      if (descriptor.getLiteJavaType() == WireFormat.JavaType.ENUM) {
+        return ((Internal.EnumLite) value).getNumber();
+      } else {
+        return value;
+      }
+    }
+
+    public FieldType getLiteType() {
+      return descriptor.getLiteType();
+    }
+
+    public boolean isRepeated() {
+      return descriptor.isRepeated;
+    }
+
+    public Type getDefaultValue() {
+      return defaultValue;
+    }
+  }
+
+  /**
+   * A serialized (serializable) form of the generated message.  Stores the
+   * message as a class name and a byte array.
+   */
+  static final class SerializedForm implements Serializable {
+    private static final long serialVersionUID = 0L;
+
+    private final String messageClassName;
+    private final byte[] asBytes;
+
+    /**
+     * Creates the serialized form by calling {@link com.google.protobuf.MessageLite#toByteArray}.
+     * @param regularForm the message to serialize
+     */
+    SerializedForm(MessageLite regularForm) {
+      messageClassName = regularForm.getClass().getName();
+      asBytes = regularForm.toByteArray();
+    }
+
+    /**
+     * When read from an ObjectInputStream, this method converts this object
+     * back to the regular form.  Part of Java's serialization magic.
+     * @return a GeneratedMessage of the type that was serialized
+     */
+    @SuppressWarnings("unchecked")
+    protected Object readResolve() throws ObjectStreamException {
+      try {
+        Class<?> messageClass = Class.forName(messageClassName);
+        java.lang.reflect.Field defaultInstanceField =
+            messageClass.getDeclaredField("DEFAULT_INSTANCE");
+        defaultInstanceField.setAccessible(true);
+        MessageLite defaultInstance = (MessageLite) defaultInstanceField.get(null);
+        return defaultInstance.newBuilderForType()
+            .mergeFrom(asBytes)
+            .buildPartial();
+      } catch (ClassNotFoundException e) {
+        throw new RuntimeException("Unable to find proto buffer class: " + messageClassName, e);
+      } catch (NoSuchFieldException e) {
+        throw new RuntimeException("Unable to find DEFAULT_INSTANCE in " + messageClassName, e);
+      } catch (SecurityException e) {
+        throw new RuntimeException("Unable to call DEFAULT_INSTANCE in " + messageClassName, e);
+      } catch (IllegalAccessException e) {
+        throw new RuntimeException("Unable to call parsePartialFrom", e);
+      } catch (InvalidProtocolBufferException e) {
+        throw new RuntimeException("Unable to understand proto buffer", e);
+      }
+    }
+  }
+
+  /**
+   * Replaces this object in the output stream with a serialized form.
+   * Part of Java's serialization magic.  Generated sub-classes must override
+   * this method by calling {@code return super.writeReplace();}
+   * @return a SerializedForm of this message
+   */
+  protected Object writeReplace() throws ObjectStreamException {
+    return new SerializedForm(this);
+  }
+  
+  /**
+   * Checks that the {@link Extension} is Lite and returns it as a
+   * {@link GeneratedExtension}.
+   */
+  private static <
+      MessageType extends ExtendableMessage<MessageType, BuilderType>,
+      BuilderType extends ExtendableBuilder<MessageType, BuilderType>,
+      T>
+    GeneratedExtension<MessageType, T> checkIsLite(
+        ExtensionLite<MessageType, T> extension) {
+    if (!extension.isLite()) {
+      throw new IllegalArgumentException("Expected a lite extension.");
+    }
+    
+    return (GeneratedExtension<MessageType, T>) extension;
+  }
+
+  /**
+   * A static helper method for checking if a message is initialized, optionally memoizing.
+   * <p>
+   * For use by generated code only.
+   */
+  protected static final <T extends GeneratedMessageLite<T, ?>> boolean isInitialized(
+      T message, boolean shouldMemoize) {
+    return message.dynamicMethod(MethodToInvoke.IS_INITIALIZED, shouldMemoize) != null;
+  }
+  
+  protected static final <T extends GeneratedMessageLite<T, ?>> void makeImmutable(T message) {
+    message.dynamicMethod(MethodToInvoke.MAKE_IMMUTABLE);
+  }
+  
+  /**
+   * A static helper method for parsing a partial from input using the extension registry and the
+   * instance.
+   */
+  static <T extends GeneratedMessageLite<T, ?>> T parsePartialFrom(
+      T instance, CodedInputStream input, ExtensionRegistryLite extensionRegistry)
+          throws InvalidProtocolBufferException {
+    try {
+      return (T) instance.dynamicMethod(
+          MethodToInvoke.PARSE_PARTIAL_FROM, input, extensionRegistry);
+    } catch (RuntimeException e) {
+      if (e.getCause() instanceof InvalidProtocolBufferException) {
+        throw (InvalidProtocolBufferException) e.getCause();
+      }
+      throw e;
+    }
+  }
+  
+  /**
+   * A {@link Parser} implementation that delegates to the default instance.
+   * <p>
+   * For use by generated code only.
+   */
+  protected static class DefaultInstanceBasedParser<T extends GeneratedMessageLite<T, ?>>
+      extends AbstractParser<T> {
+    
+    private T defaultInstance;
+    
+    public DefaultInstanceBasedParser(T defaultInstance) {
+      this.defaultInstance = defaultInstance;
+    }
+    
+    @Override
+    public T parsePartialFrom(CodedInputStream input, ExtensionRegistryLite extensionRegistry)
+        throws InvalidProtocolBufferException {
+      return GeneratedMessageLite.parsePartialFrom(defaultInstance, input, extensionRegistry);
+    }
+  }
+  
+  protected static IntList newIntList() {
+    return new IntArrayList();
+  }
+  
+  protected static IntList newIntListWithCapacity(int capacity) {
+    return new IntArrayList(capacity);
+  }
+  
+  protected static IntList newIntList(List<Integer> toCopy) {
+    return new IntArrayList(toCopy);
+  }
+  
+  protected static IntList emptyIntList() {
+    return IntArrayList.emptyList();
+  }
+
+  protected static LongList newLongList() {
+    return new LongArrayList();
+  }
+
+  protected static LongList newLongListWithCapacity(int capacity) {
+    return new LongArrayList(capacity);
+  }
+  
+  protected static LongList newLongList(List<Long> toCopy) {
+    return new LongArrayList(toCopy);
+  }
+  
+  protected static LongList emptyLongList() {
+    return LongArrayList.emptyList();
+  }
+  
+  protected static FloatList newFloatList() {
+    return new FloatArrayList();
+  }
+  
+  protected static FloatList newFloatListWithCapacity(int capacity) {
+    return new FloatArrayList(capacity);
+  }
+  
+  protected static FloatList newFloatList(List<Float> toCopy) {
+    return new FloatArrayList(toCopy);
+  }
+  
+  protected static FloatList emptyFloatList() {
+    return FloatArrayList.emptyList();
+  }
+  
+  protected static DoubleList newDoubleList() {
+    return new DoubleArrayList();
+  }
+  
+  protected static DoubleList newDoubleListWithCapacity(int capacity) {
+    return new DoubleArrayList(capacity);
+  }
+  
+  protected static DoubleList newDoubleList(List<Double> toCopy) {
+    return new DoubleArrayList(toCopy);
+  }
+  
+  protected static DoubleList emptyDoubleList() {
+    return DoubleArrayList.emptyList();
+  }
+  
+  protected static BooleanList newBooleanList() {
+    return new BooleanArrayList();
+  }
+  
+  protected static BooleanList newBooleanListWithCapacity(int capacity) {
+    return new BooleanArrayList(capacity);
+  }
+  
+  protected static BooleanList newBooleanList(List<Boolean> toCopy) {
+    return new BooleanArrayList(toCopy);
+  }
+  
+  protected static BooleanList emptyBooleanList() {
+    return BooleanArrayList.emptyList();
+  }
+  
+  protected static <E> ProtobufList<E> newProtobufList() {
+    return new ProtobufArrayList<E>();
+  }
+  
+  protected static <E> ProtobufList<E> newProtobufList(List<E> toCopy) {
+    return new ProtobufArrayList<E>(toCopy);
+  }
+  
+  protected static <E> ProtobufList<E> newProtobufListWithCapacity(int capacity) {
+    return new ProtobufArrayList<E>(capacity);
+  }
+  
+  protected static <E> ProtobufList<E> emptyProtobufList() {
+    return ProtobufArrayList.emptyList();
+  }
+  
+  protected static LazyStringArrayList emptyLazyStringArrayList() {
+    return LazyStringArrayList.emptyList();
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/IntArrayList.java b/java/core/src/main/java/com/google/protobuf/IntArrayList.java
new file mode 100644
index 00000000..f4e68ed8
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/IntArrayList.java
@@ -0,0 +1,249 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import com.google.protobuf.Internal.IntList;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.List;
+import java.util.RandomAccess;
+
+/**
+ * An implementation of {@link IntList} on top of a primitive array.
+ * 
+ * @author dweis@google.com (Daniel Weis)
+ */
+final class IntArrayList extends AbstractProtobufList<Integer> implements IntList, RandomAccess {
+  
+  private static final int DEFAULT_CAPACITY = 10;
+  
+  private static final IntArrayList EMPTY_LIST = new IntArrayList();
+  static {
+    EMPTY_LIST.makeImmutable();
+  }
+  
+  public static IntArrayList emptyList() {
+    return EMPTY_LIST;
+  }
+  
+  /**
+   * The backing store for the list.
+   */
+  private int[] array;
+  
+  /**
+   * The size of the list distinct from the length of the array. That is, it is the number of
+   * elements set in the list.
+   */
+  private int size;
+
+  /**
+   * Constructs a new mutable {@code IntArrayList} with default capacity.
+   */
+  IntArrayList() {
+    this(DEFAULT_CAPACITY);
+  }
+
+  /**
+   * Constructs a new mutable {@code IntArrayList} with the provided capacity.
+   */
+  IntArrayList(int capacity) {
+    array = new int[capacity];
+    size = 0;
+  }
+
+  /**
+   * Constructs a new mutable {@code IntArrayList} containing the same elements as {@code other}.
+   */
+  IntArrayList(List<Integer> other) {
+    if (other instanceof IntArrayList) {
+      IntArrayList list = (IntArrayList) other;
+      array = list.array.clone();
+      size = list.size;
+    } else {
+      size = other.size();
+      array = new int[size];
+      for (int i = 0; i < size; i++) {
+        array[i] = other.get(i);
+      }
+    }
+  }
+  
+  @Override
+  public Integer get(int index) {
+    return getInt(index);
+  }
+
+  @Override
+  public int getInt(int index) {
+    ensureIndexInRange(index);
+    return array[index];
+  }
+
+  @Override
+  public int size() {
+    return size;
+  }
+
+  @Override
+  public Integer set(int index, Integer element) {
+    return setInt(index, element);
+  }
+
+  @Override
+  public int setInt(int index, int element) {
+    ensureIsMutable();
+    ensureIndexInRange(index);
+    int previousValue = array[index];
+    array[index] = element;
+    return previousValue;
+  }
+
+  @Override
+  public void add(int index, Integer element) {
+    addInt(index, element);
+  }
+
+  /**
+   * Like {@link #add(Integer)} but more efficient in that it doesn't box the element.
+   */
+  @Override
+  public void addInt(int element) {
+    addInt(size, element);
+  }
+
+  /**
+   * Like {@link #add(int, Integer)} but more efficient in that it doesn't box the element.
+   */
+  private void addInt(int index, int element) {
+    ensureIsMutable();
+    if (index < 0 || index > size) {
+      throw new IndexOutOfBoundsException(makeOutOfBoundsExceptionMessage(index));
+    }
+    
+    if (size < array.length) {
+      // Shift everything over to make room
+      System.arraycopy(array, index, array, index + 1, size - index);
+    } else {
+      // Resize to 1.5x the size
+      int length = ((size * 3) / 2) + 1;
+      int[] newArray = new int[length];
+      
+      // Copy the first part directly
+      System.arraycopy(array, 0, newArray, 0, index);
+      
+      // Copy the rest shifted over by one to make room
+      System.arraycopy(array, index, newArray, index + 1, size - index);
+      array = newArray;
+    }
+
+    array[index] = element;
+    size++;
+    modCount++;
+  }
+
+  @Override
+  public boolean addAll(Collection<? extends Integer> collection) {
+    ensureIsMutable();
+    
+    if (collection == null) {
+      throw new NullPointerException();
+    }
+    
+    // We specialize when adding another IntArrayList to avoid boxing elements.
+    if (!(collection instanceof IntArrayList)) {
+      return super.addAll(collection);
+    }
+    
+    IntArrayList list = (IntArrayList) collection;
+    if (list.size == 0) {
+      return false;
+    }
+    
+    int overflow = Integer.MAX_VALUE - size;
+    if (overflow < list.size) {
+      // We can't actually represent a list this large.
+      throw new OutOfMemoryError();
+    }
+    
+    int newSize = size + list.size;
+    if (newSize > array.length) {
+      array = Arrays.copyOf(array, newSize);
+    }
+    
+    System.arraycopy(list.array, 0, array, size, list.size);
+    size = newSize;
+    modCount++;
+    return true;
+  }
+  
+  @Override
+  public boolean remove(Object o) {
+    ensureIsMutable();
+    for (int i = 0; i < size; i++) {
+      if (o.equals(array[i])) {
+        System.arraycopy(array, i + 1, array, i, size - i);
+        size--;
+        modCount++;
+        return true;
+      }
+    }
+    return false;
+  }
+
+  @Override
+  public Integer remove(int index) {
+    ensureIsMutable();
+    ensureIndexInRange(index);
+    int value = array[index];
+    System.arraycopy(array, index + 1, array, index, size - index);
+    size--;
+    modCount++;
+    return value;
+  }
+
+  /**
+   * Ensures that the provided {@code index} is within the range of {@code [0, size]}. Throws an
+   * {@link IndexOutOfBoundsException} if it is not.
+   * 
+   * @param index the index to verify is in range
+   */
+  private void ensureIndexInRange(int index) {
+    if (index < 0 || index >= size) {
+      throw new IndexOutOfBoundsException(makeOutOfBoundsExceptionMessage(index));
+    }
+  }
+
+  private String makeOutOfBoundsExceptionMessage(int index) {
+    return "Index:" + index + ", Size:" + size;
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/Internal.java b/java/core/src/main/java/com/google/protobuf/Internal.java
new file mode 100644
index 00000000..11901998
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/Internal.java
@@ -0,0 +1,677 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import java.io.IOException;
+import java.lang.reflect.Method;
+import java.nio.ByteBuffer;
+import java.nio.charset.Charset;
+import java.util.AbstractList;
+import java.util.AbstractMap;
+import java.util.AbstractSet;
+import java.util.Arrays;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+
+/**
+ * The classes contained within are used internally by the Protocol Buffer
+ * library and generated message implementations. They are public only because
+ * those generated messages do not reside in the {@code protobuf} package.
+ * Others should not use this class directly.
+ *
+ * @author kenton@google.com (Kenton Varda)
+ */
+public class Internal {
+
+  protected static final Charset UTF_8 = Charset.forName("UTF-8");
+  protected static final Charset ISO_8859_1 = Charset.forName("ISO-8859-1");
+
+  /**
+   * Helper called by generated code to construct default values for string
+   * fields.
+   * <p>
+   * The protocol compiler does not actually contain a UTF-8 decoder -- it
+   * just pushes UTF-8-encoded text around without touching it.  The one place
+   * where this presents a problem is when generating Java string literals.
+   * Unicode characters in the string literal would normally need to be encoded
+   * using a Unicode escape sequence, which would require decoding them.
+   * To get around this, protoc instead embeds the UTF-8 bytes into the
+   * generated code and leaves it to the runtime library to decode them.
+   * <p>
+   * It gets worse, though.  If protoc just generated a byte array, like:
+   *   new byte[] {0x12, 0x34, 0x56, 0x78}
+   * Java actually generates *code* which allocates an array and then fills
+   * in each value.  This is much less efficient than just embedding the bytes
+   * directly into the bytecode.  To get around this, we need another
+   * work-around.  String literals are embedded directly, so protoc actually
+   * generates a string literal corresponding to the bytes.  The easiest way
+   * to do this is to use the ISO-8859-1 character set, which corresponds to
+   * the first 256 characters of the Unicode range.  Protoc can then use
+   * good old CEscape to generate the string.
+   * <p>
+   * So we have a string literal which represents a set of bytes which
+   * represents another string.  This function -- stringDefaultValue --
+   * converts from the generated string to the string we actually want.  The
+   * generated code calls this automatically.
+   */
+  public static String stringDefaultValue(String bytes) {
+    return new String(bytes.getBytes(ISO_8859_1), UTF_8);
+  }
+
+  /**
+   * Helper called by generated code to construct default values for bytes
+   * fields.
+   * <p>
+   * This is a lot like {@link #stringDefaultValue}, but for bytes fields.
+   * In this case we only need the second of the two hacks -- allowing us to
+   * embed raw bytes as a string literal with ISO-8859-1 encoding.
+   */
+  public static ByteString bytesDefaultValue(String bytes) {
+    return ByteString.copyFrom(bytes.getBytes(ISO_8859_1));
+  }
+  /**
+   * Helper called by generated code to construct default values for bytes
+   * fields.
+   * <p>
+   * This is like {@link #bytesDefaultValue}, but returns a byte array.
+   */
+  public static byte[] byteArrayDefaultValue(String bytes) {
+    return bytes.getBytes(ISO_8859_1);
+  }
+
+  /**
+   * Helper called by generated code to construct default values for bytes
+   * fields.
+   * <p>
+   * This is like {@link #bytesDefaultValue}, but returns a ByteBuffer.
+   */
+  public static ByteBuffer byteBufferDefaultValue(String bytes) {
+    return ByteBuffer.wrap(byteArrayDefaultValue(bytes));
+  }
+
+  /**
+   * Create a new ByteBuffer and copy all the content of {@code source}
+   * ByteBuffer to the new ByteBuffer. The new ByteBuffer's limit and
+   * capacity will be source.capacity(), and its position will be 0.
+   * Note that the state of {@code source} ByteBuffer won't be changed.
+   */
+  public static ByteBuffer copyByteBuffer(ByteBuffer source) {
+    // Make a duplicate of the source ByteBuffer and read data from the
+    // duplicate. This is to avoid affecting the source ByteBuffer's state.
+    ByteBuffer temp = source.duplicate();
+    // We want to copy all the data in the source ByteBuffer, not just the
+    // remaining bytes.
+    temp.clear();
+    ByteBuffer result = ByteBuffer.allocate(temp.capacity());
+    result.put(temp);
+    result.clear();
+    return result;
+  }
+
+  /**
+   * Helper called by generated code to determine if a byte array is a valid
+   * UTF-8 encoded string such that the original bytes can be converted to
+   * a String object and then back to a byte array round tripping the bytes
+   * without loss.  More precisely, returns {@code true} whenever:
+   * <pre>   {@code
+   * Arrays.equals(byteString.toByteArray(),
+   *     new String(byteString.toByteArray(), "UTF-8").getBytes("UTF-8"))
+   * }</pre>
+   *
+   * <p>This method rejects "overlong" byte sequences, as well as
+   * 3-byte sequences that would map to a surrogate character, in
+   * accordance with the restricted definition of UTF-8 introduced in
+   * Unicode 3.1.  Note that the UTF-8 decoder included in Oracle's
+   * JDK has been modified to also reject "overlong" byte sequences,
+   * but currently (2011) still accepts 3-byte surrogate character
+   * byte sequences.
+   *
+   * <p>See the Unicode Standard,<br>
+   * Table 3-6. <em>UTF-8 Bit Distribution</em>,<br>
+   * Table 3-7. <em>Well Formed UTF-8 Byte Sequences</em>.
+   *
+   * <p>As of 2011-02, this method simply returns the result of {@link
+   * ByteString#isValidUtf8()}.  Calling that method directly is preferred.
+   *
+   * @param byteString the string to check
+   * @return whether the byte array is round trippable
+   */
+  public static boolean isValidUtf8(ByteString byteString) {
+    return byteString.isValidUtf8();
+  }
+
+  /**
+   * Like {@link #isValidUtf8(ByteString)} but for byte arrays.
+   */
+  public static boolean isValidUtf8(byte[] byteArray) {
+    return Utf8.isValidUtf8(byteArray);
+  }
+
+  /**
+   * Helper method to get the UTF-8 bytes of a string.
+   */
+  public static byte[] toByteArray(String value) {
+    return value.getBytes(UTF_8);
+  }
+
+  /**
+   * Helper method to convert a byte array to a string using UTF-8 encoding.
+   */
+  public static String toStringUtf8(byte[] bytes) {
+    return new String(bytes, UTF_8);
+  }
+
+  /**
+   * Interface for an enum value or value descriptor, to be used in FieldSet.
+   * The lite library stores enum values directly in FieldSets but the full
+   * library stores EnumValueDescriptors in order to better support reflection.
+   */
+  public interface EnumLite {
+    int getNumber();
+  }
+
+  /**
+   * Interface for an object which maps integers to {@link EnumLite}s.
+   * {@link Descriptors.EnumDescriptor} implements this interface by mapping
+   * numbers to {@link Descriptors.EnumValueDescriptor}s.  Additionally,
+   * every generated enum type has a static method internalGetValueMap() which
+   * returns an implementation of this type that maps numbers to enum values.
+   */
+  public interface EnumLiteMap<T extends EnumLite> {
+    T findValueByNumber(int number);
+  }
+
+  /**
+   * Helper method for implementing {@link Message#hashCode()} for longs.
+   * @see Long#hashCode()
+   */
+  public static int hashLong(long n) {
+    return (int) (n ^ (n >>> 32));
+  }
+
+  /**
+   * Helper method for implementing {@link Message#hashCode()} for
+   * booleans.
+   * @see Boolean#hashCode()
+   */
+  public static int hashBoolean(boolean b) {
+    return b ? 1231 : 1237;
+  }
+
+  /**
+   * Helper method for implementing {@link Message#hashCode()} for enums.
+   * <p>
+   * This is needed because {@link java.lang.Enum#hashCode()} is final, but we
+   * need to use the field number as the hash code to ensure compatibility
+   * between statically and dynamically generated enum objects.
+   */
+  public static int hashEnum(EnumLite e) {
+    return e.getNumber();
+  }
+
+  /**
+   * Helper method for implementing {@link Message#hashCode()} for
+   * enum lists.
+   */
+  public static int hashEnumList(List<? extends EnumLite> list) {
+    int hash = 1;
+    for (EnumLite e : list) {
+      hash = 31 * hash + hashEnum(e);
+    }
+    return hash;
+  }
+
+  /**
+   * Helper method for implementing {@link Message#equals(Object)} for bytes field.
+   */
+  public static boolean equals(List<byte[]> a, List<byte[]> b) {
+    if (a.size() != b.size()) return false;
+    for (int i = 0; i < a.size(); ++i) {
+      if (!Arrays.equals(a.get(i), b.get(i))) {
+        return false;
+      }
+    }
+    return true;
+  }
+
+  /**
+   * Helper method for implementing {@link Message#hashCode()} for bytes field.
+   */
+  public static int hashCode(List<byte[]> list) {
+    int hash = 1;
+    for (byte[] bytes : list) {
+      hash = 31 * hash + hashCode(bytes);
+    }
+    return hash;
+  }
+
+  /**
+   * Helper method for implementing {@link Message#hashCode()} for bytes field.
+   */
+  public static int hashCode(byte[] bytes) {
+    // The hash code for a byte array should be the same as the hash code for a
+    // ByteString with the same content. This is to ensure that the generated
+    // hashCode() method will return the same value as the pure reflection
+    // based hashCode() method.
+    return LiteralByteString.hashCode(bytes);
+  }
+
+  /**
+   * Helper method for implementing {@link Message#equals(Object)} for bytes
+   * field.
+   */
+  public static boolean equalsByteBuffer(ByteBuffer a, ByteBuffer b) {
+    if (a.capacity() != b.capacity()) {
+      return false;
+    }
+    // ByteBuffer.equals() will only compare the remaining bytes, but we want to
+    // compare all the content.
+    return a.duplicate().clear().equals(b.duplicate().clear());
+  }
+
+  /**
+   * Helper method for implementing {@link Message#equals(Object)} for bytes
+   * field.
+   */
+  public static boolean equalsByteBuffer(
+      List<ByteBuffer> a, List<ByteBuffer> b) {
+    if (a.size() != b.size()) {
+      return false;
+    }
+    for (int i = 0; i < a.size(); ++i) {
+      if (!equalsByteBuffer(a.get(i), b.get(i))) {
+        return false;
+      }
+    }
+    return true;
+  }
+
+  /**
+   * Helper method for implementing {@link Message#hashCode()} for bytes
+   * field.
+   */
+  public static int hashCodeByteBuffer(List<ByteBuffer> list) {
+    int hash = 1;
+    for (ByteBuffer bytes : list) {
+      hash = 31 * hash + hashCodeByteBuffer(bytes);
+    }
+    return hash;
+  }
+
+  private static final int DEFAULT_BUFFER_SIZE = 4096;
+
+  /**
+   * Helper method for implementing {@link Message#hashCode()} for bytes
+   * field.
+   */
+  public static int hashCodeByteBuffer(ByteBuffer bytes) {
+    if (bytes.hasArray()) {
+      // Fast path.
+      int h = LiteralByteString.hashCode(bytes.capacity(), bytes.array(),
+          bytes.arrayOffset(), bytes.capacity());
+      return h == 0 ? 1 : h;
+    } else {
+      // Read the data into a temporary byte array before calculating the
+      // hash value.
+      final int bufferSize = bytes.capacity() > DEFAULT_BUFFER_SIZE
+          ? DEFAULT_BUFFER_SIZE : bytes.capacity();
+      final byte[] buffer = new byte[bufferSize];
+      final ByteBuffer duplicated = bytes.duplicate();
+      duplicated.clear();
+      int h = bytes.capacity();
+      while (duplicated.remaining() > 0) {
+        final int length = duplicated.remaining() <= bufferSize ?
+            duplicated.remaining() : bufferSize;
+        duplicated.get(buffer, 0, length);
+        h = LiteralByteString.hashCode(h, buffer, 0, length);
+      }
+      return h == 0 ? 1 : h;
+    }
+  }
+
+  @SuppressWarnings("unchecked")
+  public static <T extends MessageLite> T getDefaultInstance(Class<T> clazz) {
+    try {
+      Method method = clazz.getMethod("getDefaultInstance");
+      return (T) method.invoke(method);
+    } catch (Exception e) {
+      throw new RuntimeException(
+          "Failed to get default instance for " + clazz, e);
+    }
+  }
+
+  /**
+   * An empty byte array constant used in generated code.
+   */
+  public static final byte[] EMPTY_BYTE_ARRAY = new byte[0];
+
+  /**
+   * An empty byte array constant used in generated code.
+   */
+  public static final ByteBuffer EMPTY_BYTE_BUFFER =
+      ByteBuffer.wrap(EMPTY_BYTE_ARRAY);
+
+  /** An empty coded input stream constant used in generated code. */
+  public static final CodedInputStream EMPTY_CODED_INPUT_STREAM =
+      CodedInputStream.newInstance(EMPTY_BYTE_ARRAY);
+
+
+  /**
+   * Provides an immutable view of {@code List<T>} around a {@code List<F>}.
+   *
+   * Protobuf internal. Used in protobuf generated code only.
+   */
+  public static class ListAdapter<F, T> extends AbstractList<T> {
+    /**
+     * Convert individual elements of the List from F to T.
+     */
+    public interface Converter<F, T> {
+      T convert(F from);
+    }
+
+    private final List<F> fromList;
+    private final Converter<F, T> converter;
+
+    public ListAdapter(List<F> fromList, Converter<F, T> converter) {
+      this.fromList = fromList;
+      this.converter = converter;
+    }
+
+    @Override
+    public T get(int index) {
+      return converter.convert(fromList.get(index));
+    }
+
+    @Override
+    public int size() {
+      return fromList.size();
+    }
+  }
+
+  /**
+   * Wrap around a {@code Map<K, RealValue>} and provide a {@code Map<K, V>}
+   * interface.
+   */
+  public static class MapAdapter<K, V, RealValue> extends AbstractMap<K, V> {
+    /**
+     * An interface used to convert between two types.
+     */
+    public interface Converter<A, B> {
+      B doForward(A object);
+      A doBackward(B object);
+    }
+
+    public static <T extends EnumLite> Converter<Integer, T> newEnumConverter(
+        final EnumLiteMap<T> enumMap, final T unrecognizedValue) {
+      return new Converter<Integer, T>() {
+        public T doForward(Integer value) {
+          T result = enumMap.findValueByNumber(value);
+          return result == null ? unrecognizedValue : result;
+        }
+        public Integer doBackward(T value) {
+          return value.getNumber();
+        }
+      };
+    }
+
+    private final Map<K, RealValue> realMap;
+    private final Converter<RealValue, V> valueConverter;
+
+    public MapAdapter(Map<K, RealValue> realMap,
+        Converter<RealValue, V> valueConverter) {
+      this.realMap = realMap;
+      this.valueConverter = valueConverter;
+    }
+
+    @SuppressWarnings("unchecked")
+    @Override
+    public V get(Object key) {
+      RealValue result = realMap.get(key);
+      if (result == null) {
+        return null;
+      }
+      return valueConverter.doForward(result);
+    }
+
+    @Override
+    public V put(K key, V value) {
+      RealValue oldValue = realMap.put(key, valueConverter.doBackward(value));
+      if (oldValue == null) {
+        return null;
+      }
+      return valueConverter.doForward(oldValue);
+    }
+
+    @Override
+    public Set<java.util.Map.Entry<K, V>> entrySet() {
+      return new SetAdapter(realMap.entrySet());
+    }
+
+    private class SetAdapter extends AbstractSet<Map.Entry<K, V>> {
+      private final Set<Map.Entry<K, RealValue>> realSet;
+      public SetAdapter(Set<Map.Entry<K, RealValue>> realSet) {
+        this.realSet = realSet;
+      }
+
+      @Override
+      public Iterator<java.util.Map.Entry<K, V>> iterator() {
+        return new IteratorAdapter(realSet.iterator());
+      }
+
+      @Override
+      public int size() {
+        return realSet.size();
+      }
+    }
+
+    private class IteratorAdapter implements Iterator<Map.Entry<K, V>> {
+      private final Iterator<Map.Entry<K, RealValue>> realIterator;
+
+      public IteratorAdapter(
+          Iterator<Map.Entry<K, RealValue>> realIterator) {
+        this.realIterator = realIterator;
+      }
+
+      @Override
+      public boolean hasNext() {
+        return realIterator.hasNext();
+      }
+
+      @Override
+      public java.util.Map.Entry<K, V> next() {
+        return new EntryAdapter(realIterator.next());
+      }
+
+      @Override
+      public void remove() {
+        realIterator.remove();
+      }
+    }
+
+    private class EntryAdapter implements Map.Entry<K, V> {
+      private final Map.Entry<K, RealValue> realEntry;
+
+      public EntryAdapter(Map.Entry<K, RealValue> realEntry) {
+        this.realEntry = realEntry;
+      }
+
+      @Override
+      public K getKey() {
+        return realEntry.getKey();
+      }
+
+      @Override
+      public V getValue() {
+        return valueConverter.doForward(realEntry.getValue());
+      }
+
+      @Override
+      public V setValue(V value) {
+        RealValue oldValue = realEntry.setValue(
+            valueConverter.doBackward(value));
+        if (oldValue == null) {
+          return null;
+        }
+        return valueConverter.doForward(oldValue);
+      }
+    }
+  }
+
+  /**
+   * Extends {@link List} to add the capability to make the list immutable and inspect if it is
+   * modifiable.
+   */
+  public static interface ProtobufList<E> extends List<E> {
+
+    /**
+     * Makes this list immutable. All subsequent modifications will throw an
+     * {@link UnsupportedOperationException}.
+     */
+    void makeImmutable();
+
+    /**
+     * Returns whether this list can be modified via the publicly accessible {@link List} methods.
+     */
+    boolean isModifiable();
+  }
+
+  /**
+   * A {@link java.util.List} implementation that avoids boxing the elements into Integers if
+   * possible. Does not support null elements.
+   */
+  public static interface IntList extends ProtobufList<Integer> {
+
+    /**
+     * Like {@link #get(int)} but more efficient in that it doesn't box the returned value.
+     */
+    int getInt(int index);
+
+    /**
+     * Like {@link #add(Object)} but more efficient in that it doesn't box the element.
+     */
+    void addInt(int element);
+
+    /**
+     * Like {@link #set(int, Object)} but more efficient in that it doesn't box the element.
+     */
+    int setInt(int index, int element);
+  }
+
+  /**
+   * A {@link java.util.List} implementation that avoids boxing the elements into Booleans if
+   * possible. Does not support null elements.
+   */
+  public static interface BooleanList extends ProtobufList<Boolean> {
+
+    /**
+     * Like {@link #get(int)} but more efficient in that it doesn't box the returned value.
+     */
+    boolean getBoolean(int index);
+
+    /**
+     * Like {@link #add(Object)} but more efficient in that it doesn't box the element.
+     */
+    void addBoolean(boolean element);
+
+    /**
+     * Like {@link #set(int, Object)} but more efficient in that it doesn't box the element.
+     */
+    boolean setBoolean(int index, boolean element);
+  }
+
+  /**
+   * A {@link java.util.List} implementation that avoids boxing the elements into Longs if
+   * possible. Does not support null elements.
+   */
+  public static interface LongList extends ProtobufList<Long> {
+
+    /**
+     * Like {@link #get(int)} but more efficient in that it doesn't box the returned value.
+     */
+    long getLong(int index);
+
+    /**
+     * Like {@link #add(Object)} but more efficient in that it doesn't box the element.
+     */
+    void addLong(long element);
+
+    /**
+     * Like {@link #set(int, Object)} but more efficient in that it doesn't box the element.
+     */
+    long setLong(int index, long element);
+  }
+
+  /**
+   * A {@link java.util.List} implementation that avoids boxing the elements into Doubles if
+   * possible. Does not support null elements.
+   */
+  public static interface DoubleList extends ProtobufList<Double> {
+
+    /**
+     * Like {@link #get(int)} but more efficient in that it doesn't box the returned value.
+     */
+    double getDouble(int index);
+
+    /**
+     * Like {@link #add(Object)} but more efficient in that it doesn't box the element.
+     */
+    void addDouble(double element);
+
+    /**
+     * Like {@link #set(int, Object)} but more efficient in that it doesn't box the element.
+     */
+    double setDouble(int index, double element);
+  }
+
+  /**
+   * A {@link java.util.List} implementation that avoids boxing the elements into Floats if
+   * possible. Does not support null elements.
+   */
+  public static interface FloatList extends ProtobufList<Float> {
+
+    /**
+     * Like {@link #get(int)} but more efficient in that it doesn't box the returned value.
+     */
+    float getFloat(int index);
+
+    /**
+     * Like {@link #add(Object)} but more efficient in that it doesn't box the element.
+     */
+    void addFloat(float element);
+
+    /**
+     * Like {@link #set(int, Object)} but more efficient in that it doesn't box the element.
+     */
+    float setFloat(int index, float element);
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/InvalidProtocolBufferException.java b/java/core/src/main/java/com/google/protobuf/InvalidProtocolBufferException.java
new file mode 100644
index 00000000..0a761052
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/InvalidProtocolBufferException.java
@@ -0,0 +1,122 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import java.io.IOException;
+
+/**
+ * Thrown when a protocol message being parsed is invalid in some way,
+ * e.g. it contains a malformed varint or a negative byte length.
+ *
+ * @author kenton@google.com Kenton Varda
+ */
+public class InvalidProtocolBufferException extends IOException {
+  private static final long serialVersionUID = -1616151763072450476L;
+  private MessageLite unfinishedMessage = null;
+
+  public InvalidProtocolBufferException(final String description) {
+    super(description);
+  }
+
+  /**
+   * Attaches an unfinished message to the exception to support best-effort
+   * parsing in {@code Parser} interface.
+   *
+   * @return this
+   */
+  public InvalidProtocolBufferException setUnfinishedMessage(
+      MessageLite unfinishedMessage) {
+    this.unfinishedMessage = unfinishedMessage;
+    return this;
+  }
+
+  /**
+   * Returns the unfinished message attached to the exception, or null if
+   * no message is attached.
+   */
+  public MessageLite getUnfinishedMessage() {
+    return unfinishedMessage;
+  }
+
+  static InvalidProtocolBufferException truncatedMessage() {
+    return new InvalidProtocolBufferException(
+      "While parsing a protocol message, the input ended unexpectedly " +
+      "in the middle of a field.  This could mean either that the " +
+      "input has been truncated or that an embedded message " +
+      "misreported its own length.");
+  }
+
+  static InvalidProtocolBufferException negativeSize() {
+    return new InvalidProtocolBufferException(
+      "CodedInputStream encountered an embedded string or message " +
+      "which claimed to have negative size.");
+  }
+
+  static InvalidProtocolBufferException malformedVarint() {
+    return new InvalidProtocolBufferException(
+      "CodedInputStream encountered a malformed varint.");
+  }
+
+  static InvalidProtocolBufferException invalidTag() {
+    return new InvalidProtocolBufferException(
+      "Protocol message contained an invalid tag (zero).");
+  }
+
+  static InvalidProtocolBufferException invalidEndTag() {
+    return new InvalidProtocolBufferException(
+      "Protocol message end-group tag did not match expected tag.");
+  }
+
+  static InvalidProtocolBufferException invalidWireType() {
+    return new InvalidProtocolBufferException(
+      "Protocol message tag had invalid wire type.");
+  }
+
+  static InvalidProtocolBufferException recursionLimitExceeded() {
+    return new InvalidProtocolBufferException(
+      "Protocol message had too many levels of nesting.  May be malicious.  " +
+      "Use CodedInputStream.setRecursionLimit() to increase the depth limit.");
+  }
+
+  static InvalidProtocolBufferException sizeLimitExceeded() {
+    return new InvalidProtocolBufferException(
+      "Protocol message was too large.  May be malicious.  " +
+      "Use CodedInputStream.setSizeLimit() to increase the size limit.");
+  }
+
+  static InvalidProtocolBufferException parseFailure() {
+    return new InvalidProtocolBufferException("Failed to parse the message.");
+  }
+
+  static InvalidProtocolBufferException invalidUtf8() {
+    return new InvalidProtocolBufferException("Protocol message had invalid UTF-8.");
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/LazyField.java b/java/core/src/main/java/com/google/protobuf/LazyField.java
new file mode 100644
index 00000000..5e0a485c
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/LazyField.java
@@ -0,0 +1,154 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import java.util.Iterator;
+import java.util.Map.Entry;
+
+/**
+ * LazyField encapsulates the logic of lazily parsing message fields. It stores
+ * the message in a ByteString initially and then parse it on-demand.
+ *
+ * Most of key methods are implemented in {@link LazyFieldLite} but this class
+ * can contain default instance of the message to provide {@code hashCode()},
+ * {@code equals()} and {@code toString()}.
+ *
+ * @author xiangl@google.com (Xiang Li)
+ */
+public class LazyField extends LazyFieldLite {
+
+  /**
+   * Carry a message's default instance which is used by {@code hashCode()}, {@code equals()} and
+   * {@code toString()}.
+   */
+  private final MessageLite defaultInstance;
+
+  public LazyField(MessageLite defaultInstance,
+      ExtensionRegistryLite extensionRegistry, ByteString bytes) {
+    super(extensionRegistry, bytes);
+
+    this.defaultInstance = defaultInstance;
+  }
+
+  @Override
+  public boolean containsDefaultInstance() {
+    return super.containsDefaultInstance() || value == defaultInstance;
+  }
+
+  public MessageLite getValue() {
+    return getValue(defaultInstance);
+  }
+
+  @Override
+  public int hashCode() {
+    return getValue().hashCode();
+  }
+
+  @Override
+  public boolean equals(Object obj) {
+    return getValue().equals(obj);
+  }
+
+  @Override
+  public String toString() {
+    return getValue().toString();
+  }
+
+  // ====================================================
+
+  /**
+   * LazyEntry and LazyIterator are used to encapsulate the LazyField, when
+   * users iterate all fields from FieldSet.
+   */
+  static class LazyEntry<K> implements Entry<K, Object> {
+    private Entry<K, LazyField> entry;
+
+    private LazyEntry(Entry<K, LazyField> entry) {
+      this.entry = entry;
+    }
+
+    // @Override
+    public K getKey() {
+      return entry.getKey();
+    }
+
+    // @Override
+    public Object getValue() {
+      LazyField field = entry.getValue();
+      if (field == null) {
+        return null;
+      }
+      return field.getValue();
+    }
+
+    public LazyField getField() {
+      return entry.getValue();
+    }
+
+    // @Override
+    public Object setValue(Object value) {
+      if (!(value instanceof MessageLite)) {
+        throw new IllegalArgumentException(
+            "LazyField now only used for MessageSet, "
+            + "and the value of MessageSet must be an instance of MessageLite");
+      }
+      return entry.getValue().setValue((MessageLite) value);
+    }
+  }
+
+  static class LazyIterator<K> implements Iterator<Entry<K, Object>> {
+    private Iterator<Entry<K, Object>> iterator;
+
+    public LazyIterator(Iterator<Entry<K, Object>> iterator) {
+      this.iterator = iterator;
+    }
+
+    // @Override
+    public boolean hasNext() {
+      return iterator.hasNext();
+    }
+
+    @SuppressWarnings("unchecked")
+    // @Override
+    public Entry<K, Object> next() {
+      Entry<K, ?> entry = iterator.next();
+      if (entry.getValue() instanceof LazyField) {
+        return new LazyEntry<K>((Entry<K, LazyField>) entry);
+      }
+      return (Entry<K, Object>) entry;
+    }
+
+    // @Override
+    public void remove() {
+      iterator.remove();
+    }
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/LazyFieldLite.java b/java/core/src/main/java/com/google/protobuf/LazyFieldLite.java
new file mode 100644
index 00000000..eea1fe3c
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/LazyFieldLite.java
@@ -0,0 +1,339 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+/**
+ * LazyFieldLite encapsulates the logic of lazily parsing message fields. It stores
+ * the message in a ByteString initially and then parse it on-demand.
+ *
+ * LazyField is thread-compatible e.g. concurrent read are safe, however,
+ * synchronizations are needed under read/write situations.
+ *
+ * This class is internal implementation detail, so you don't need to use it directly.
+ *
+ * @author xiangl@google.com (Xiang Li)
+ */
+public class LazyFieldLite {
+  private static final ExtensionRegistryLite EMPTY_REGISTRY =
+      ExtensionRegistryLite.getEmptyRegistry();
+
+  /**
+   * A delayed-parsed version of the bytes. When this is non-null then {@code extensionRegistry } is
+   * also non-null and {@code value} and {@code memoizedBytes} are null.
+   */
+  private ByteString delayedBytes;
+
+  /**
+   * An {@code ExtensionRegistryLite} for parsing bytes. It is non-null on a best-effort basis. It
+   * is only guaranteed to be non-null if this message was initialized using bytes and an
+   * {@code ExtensionRegistry}. If it directly had a value set then it will be null, unless it has
+   * been merged with another {@code LazyFieldLite} that had an {@code ExtensionRegistry}.
+   */
+  private ExtensionRegistryLite extensionRegistry;
+
+  /**
+   * The parsed value. When this is non-null then {@code delayedBytes} will be null.
+   */
+  protected volatile MessageLite value;
+
+  /**
+   * The memoized bytes for {@code value}. Will be null when {@code value} is null.
+   */
+  private volatile ByteString memoizedBytes;
+
+  /**
+   * Constructs a LazyFieldLite with bytes that will be parsed lazily.
+   */
+  public LazyFieldLite(ExtensionRegistryLite extensionRegistry, ByteString bytes) {
+    checkArguments(extensionRegistry, bytes);
+    this.extensionRegistry = extensionRegistry;
+    this.delayedBytes = bytes;
+  }
+
+  /**
+   * Constructs a LazyFieldLite with no contents, and no ability to parse extensions.
+   */
+  public LazyFieldLite() {
+  }
+
+  /**
+   * Constructs a LazyFieldLite instance with a value. The LazyFieldLite may not be able to parse
+   * the extensions in the value as it has no ExtensionRegistry.
+   */
+  public static LazyFieldLite fromValue(MessageLite value) {
+    LazyFieldLite lf = new LazyFieldLite();
+    lf.setValue(value);
+    return lf;
+  }
+
+  /**
+   * Determines whether this LazyFieldLite instance represents the default instance of this type.
+   */
+  public boolean containsDefaultInstance() {
+    return memoizedBytes == ByteString.EMPTY
+        || value == null && (delayedBytes == null || delayedBytes == ByteString.EMPTY);
+  }
+
+  /**
+   * Clears the value state of this instance.
+   *
+   * <p>LazyField is not thread-safe for write access. Synchronizations are needed
+   * under read/write situations.
+   */
+  public void clear() {
+    // Don't clear the ExtensionRegistry. It might prove useful later on when merging in another
+    // value, but there is no guarantee that it will contain all extensions that were directly set
+    // on the values that need to be merged.
+    delayedBytes = null;
+    value = null;
+    memoizedBytes = null;
+  }
+
+  /**
+   * Overrides the contents of this LazyField.
+   *
+   * <p>LazyField is not thread-safe for write access. Synchronizations are needed
+   * under read/write situations.
+   */
+  public void set(LazyFieldLite other) {
+    this.delayedBytes = other.delayedBytes;
+    this.value = other.value;
+    this.memoizedBytes = other.memoizedBytes;
+    // If the other LazyFieldLite was created by directly setting the value rather than first by
+    // parsing, then it will not have an extensionRegistry. In this case we hold on to the existing
+    // extensionRegistry, which has no guarantees that it has all the extensions that will be
+    // directly set on the value.
+    if (other.extensionRegistry != null) {
+      this.extensionRegistry = other.extensionRegistry;
+    }
+  }
+
+  /**
+   * Returns message instance. It may do some thread-safe delayed parsing of bytes.
+   *
+   * @param defaultInstance its message's default instance. It's also used to get parser for the
+   * message type.
+   */
+  public MessageLite getValue(MessageLite defaultInstance) {
+    ensureInitialized(defaultInstance);
+    return value;
+  }
+
+  /**
+   * Sets the value of the instance and returns the old value without delay parsing anything.
+   *
+   * <p>LazyField is not thread-safe for write access. Synchronizations are needed
+   * under read/write situations.
+   */
+  public MessageLite setValue(MessageLite value) {
+    MessageLite originalValue = this.value;
+    this.delayedBytes = null;
+    this.memoizedBytes = null;
+    this.value = value;
+    return originalValue;
+  }
+
+  /**
+   * Merges another instance's contents. In some cases may drop some extensions if both fields
+   * contain data. If the other field has an {@code ExtensionRegistry} but this does not, then this
+   * field will copy over that {@code ExtensionRegistry}.
+   *
+   * <p>LazyField is not thread-safe for write access. Synchronizations are needed
+   * under read/write situations.
+   */
+  public void merge(LazyFieldLite other) {
+    if (other.containsDefaultInstance()) {
+      return;
+    }
+
+    if (this.containsDefaultInstance()) {
+      set(other);
+      return;
+    }
+
+    // If the other field has an extension registry but this does not, copy over the other extension
+    // registry.
+    if (this.extensionRegistry == null) {
+      this.extensionRegistry = other.extensionRegistry;
+    }
+
+    // In the case that both of them are not parsed we simply concatenate the bytes to save time. In
+    // the (probably rare) case that they have different extension registries there is a chance that
+    // some of the extensions may be dropped, but the tradeoff of making this operation fast seems
+    // to outway the benefits of combining the extension registries, which is not normally done for
+    // lite protos anyways.
+    if (this.delayedBytes != null && other.delayedBytes != null) {
+      this.delayedBytes = this.delayedBytes.concat(other.delayedBytes);
+      return;
+    }
+
+    // At least one is parsed and both contain data. We won't drop any extensions here directly, but
+    // in the case that the extension registries are not the same then we might in the future if we
+    // need to serialze and parse a message again.
+    if (this.value == null && other.value != null) {
+      setValue(mergeValueAndBytes(other.value, this.delayedBytes, this.extensionRegistry));
+      return;
+    } else if (this.value != null && other.value == null) {
+      setValue(mergeValueAndBytes(this.value, other.delayedBytes, other.extensionRegistry));
+      return;
+    }
+
+    // At this point we have two fully parsed messages. We can't merge directly from one to the
+    // other because only generated builder code contains methods to mergeFrom another parsed
+    // message. We have to serialize one instance and then merge the bytes into the other. This may
+    // drop extensions from one of the messages if one of the values had an extension set on it
+    // directly.
+    //
+    // To mitigate this we prefer serializing a message that has an extension registry, and
+    // therefore a chance that all extensions set on it are in that registry.
+    //
+    // NOTE: The check for other.extensionRegistry not being null must come first because at this
+    // point in time if other.extensionRegistry is not null then this.extensionRegistry will not be
+    // null either.
+    if (other.extensionRegistry != null) {
+      setValue(mergeValueAndBytes(this.value, other.toByteString(), other.extensionRegistry));
+      return;
+    } else if (this.extensionRegistry != null) {
+      setValue(mergeValueAndBytes(other.value, this.toByteString(), this.extensionRegistry));
+      return;
+    } else {
+      // All extensions from the other message will be dropped because we have no registry.
+      setValue(mergeValueAndBytes(this.value, other.toByteString(), EMPTY_REGISTRY));
+      return;
+    }
+  }
+
+  private static MessageLite mergeValueAndBytes(
+      MessageLite value, ByteString otherBytes, ExtensionRegistryLite extensionRegistry) {
+    try {
+      return value.toBuilder().mergeFrom(otherBytes, extensionRegistry).build();
+    } catch (InvalidProtocolBufferException e) {
+      // Nothing is logged and no exceptions are thrown. Clients will be unaware that a proto
+      // was invalid.
+      return value;
+    }
+  }
+
+  /**
+   * Sets this field with bytes to delay-parse.
+   */
+  public void setByteString(ByteString bytes, ExtensionRegistryLite extensionRegistry) {
+    checkArguments(extensionRegistry, bytes);
+    this.delayedBytes = bytes;
+    this.extensionRegistry = extensionRegistry;
+    this.value = null;
+    this.memoizedBytes = null;
+  }
+
+  /**
+   * Due to the optional field can be duplicated at the end of serialized
+   * bytes, which will make the serialized size changed after LazyField
+   * parsed. Be careful when using this method.
+   */
+  public int getSerializedSize() {
+    if (delayedBytes != null) {
+      return delayedBytes.size();
+    } else if (memoizedBytes != null) {
+      return memoizedBytes.size();
+    } else if (value != null) {
+      return value.getSerializedSize();
+    } else {
+      return 0;
+    }
+  }
+
+  /**
+   * Returns a BytesString for this field in a thread-safe way.
+   */
+  public ByteString toByteString() {
+    if (delayedBytes != null) {
+      return delayedBytes;
+    }
+    if (memoizedBytes != null) {
+      return memoizedBytes;
+    }
+    synchronized (this) {
+      if (memoizedBytes != null) {
+        return memoizedBytes;
+      }
+      if (value == null) {
+        memoizedBytes = ByteString.EMPTY;
+      } else {
+        memoizedBytes = value.toByteString();
+      }
+      return memoizedBytes;
+    }
+  }
+
+  /**
+   * Might lazily parse the bytes that were previously passed in. Is thread-safe.
+   */
+  protected void ensureInitialized(MessageLite defaultInstance) {
+    if (value != null) {
+      return;
+    }
+    synchronized (this) {
+      if (value != null) {
+        return;
+      }
+      try {
+        if (delayedBytes != null) {
+          // The extensionRegistry shouldn't be null here since we have delayedBytes.
+          MessageLite parsedValue = defaultInstance.getParserForType()
+              .parseFrom(delayedBytes, extensionRegistry);
+          this.value = parsedValue;
+          this.memoizedBytes = delayedBytes;
+          this.delayedBytes = null;
+        } else {
+          this.value = defaultInstance;
+          this.memoizedBytes = ByteString.EMPTY;
+          this.delayedBytes = null;
+        }
+      } catch (InvalidProtocolBufferException e) {
+        // Nothing is logged and no exceptions are thrown. Clients will be unaware that this proto
+        // was invalid.
+        this.value = defaultInstance;
+        this.memoizedBytes = ByteString.EMPTY;
+        this.delayedBytes = null;
+      }
+    }
+  }
+
+
+  private static void checkArguments(ExtensionRegistryLite extensionRegistry, ByteString bytes) {
+    if (extensionRegistry == null) {
+      throw new NullPointerException("found null ExtensionRegistry");
+    }
+    if (bytes == null) {
+      throw new NullPointerException("found null ByteString");
+    }
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/LazyStringArrayList.java b/java/core/src/main/java/com/google/protobuf/LazyStringArrayList.java
new file mode 100644
index 00000000..c3be3cca
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/LazyStringArrayList.java
@@ -0,0 +1,409 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.AbstractList;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.RandomAccess;
+
+/**
+ * An implementation of {@link LazyStringList} that wraps an ArrayList. Each
+ * element is one of String, ByteString, or byte[]. It caches the last one
+ * requested which is most likely the one needed next. This minimizes memory
+ * usage while satisfying the most common use cases.
+ * <p>
+ * <strong>Note that this implementation is not synchronized.</strong>
+ * If multiple threads access an <tt>ArrayList</tt> instance concurrently,
+ * and at least one of the threads modifies the list structurally, it
+ * <i>must</i> be synchronized externally.  (A structural modification is
+ * any operation that adds or deletes one or more elements, or explicitly
+ * resizes the backing array; merely setting the value of an element is not
+ * a structural modification.)  This is typically accomplished by
+ * synchronizing on some object that naturally encapsulates the list.
+ * <p>
+ * If the implementation is accessed via concurrent reads, this is thread safe.
+ * Conversions are done in a thread safe manner. It's possible that the
+ * conversion may happen more than once if two threads attempt to access the
+ * same element and the modifications were not visible to each other, but this
+ * will not result in any corruption of the list or change in behavior other
+ * than performance.
+ *
+ * @author jonp@google.com (Jon Perlow)
+ */
+public class LazyStringArrayList extends AbstractProtobufList<String>
+    implements LazyStringList, RandomAccess {
+  
+  private static final LazyStringArrayList EMPTY_LIST = new LazyStringArrayList();
+  static {
+    EMPTY_LIST.makeImmutable();
+  }
+  
+  static LazyStringArrayList emptyList() {
+    return EMPTY_LIST;
+  }
+
+  // For compatibility with older runtimes.
+  public static final LazyStringList EMPTY = EMPTY_LIST;
+
+  private final List<Object> list;
+
+  public LazyStringArrayList() {
+    list = new ArrayList<Object>();
+  }
+
+  public LazyStringArrayList(int intialCapacity) {
+    list = new ArrayList<Object>(intialCapacity);
+  }
+
+  public LazyStringArrayList(LazyStringList from) {
+    list = new ArrayList<Object>(from.size());
+    addAll(from);
+  }
+
+  public LazyStringArrayList(List<String> from) {
+    list = new ArrayList<Object>(from);
+  }
+
+  @Override
+  public String get(int index) {
+    Object o = list.get(index);
+    if (o instanceof String) {
+      return (String) o;
+    } else if (o instanceof ByteString) {
+      ByteString bs = (ByteString) o;
+      String s = bs.toStringUtf8();
+      if (bs.isValidUtf8()) {
+        list.set(index, s);
+      }
+      return s;
+    } else {
+      byte[] ba = (byte[]) o;
+      String s = Internal.toStringUtf8(ba);
+      if (Internal.isValidUtf8(ba)) {
+        list.set(index, s);
+      }
+      return s;
+    }
+  }
+
+  @Override
+  public int size() {
+    return list.size();
+  }
+
+  @Override
+  public String set(int index, String s) {
+    ensureIsMutable();
+    Object o = list.set(index, s);
+    return asString(o);
+  }
+
+  @Override
+  public void add(int index, String element) {
+    ensureIsMutable();
+    list.add(index, element);
+    modCount++;
+  }
+  
+  private void add(int index, ByteString element) {
+    ensureIsMutable();
+    list.add(index, element);
+    modCount++;
+  }
+  
+  private void add(int index, byte[] element) {
+    ensureIsMutable();
+    list.add(index, element);
+    modCount++;
+  }
+
+  @Override
+  public boolean addAll(Collection<? extends String> c) {
+    // The default implementation of AbstractCollection.addAll(Collection)
+    // delegates to add(Object). This implementation instead delegates to
+    // addAll(int, Collection), which makes a special case for Collections
+    // which are instances of LazyStringList.
+    return addAll(size(), c);
+  }
+
+  @Override
+  public boolean addAll(int index, Collection<? extends String> c) {
+    ensureIsMutable();
+    // When copying from another LazyStringList, directly copy the underlying
+    // elements rather than forcing each element to be decoded to a String.
+    Collection<?> collection = c instanceof LazyStringList
+        ? ((LazyStringList) c).getUnderlyingElements() : c;
+    boolean ret = list.addAll(index, collection);
+    modCount++;
+    return ret;
+  }
+
+  // @Override
+  public boolean addAllByteString(Collection<? extends ByteString> values) {
+    ensureIsMutable();
+    boolean ret = list.addAll(values);
+    modCount++;
+    return ret;
+  }
+
+  // @Override
+  public boolean addAllByteArray(Collection<byte[]> c) {
+    ensureIsMutable();
+    boolean ret = list.addAll(c);
+    modCount++;
+    return ret;
+  }
+
+  @Override
+  public String remove(int index) {
+    ensureIsMutable();
+    Object o = list.remove(index);
+    modCount++;
+    return asString(o);
+  }
+
+  @Override
+  public void clear() {
+    ensureIsMutable();
+    list.clear();
+    modCount++;
+  }
+
+  // @Override
+  public void add(ByteString element) {
+    ensureIsMutable();
+    list.add(element);
+    modCount++;
+  }
+  
+  // @Override
+  public void add(byte[] element) {
+    ensureIsMutable();
+    list.add(element);
+    modCount++;
+  }
+
+  @Override
+  public Object getRaw(int index) {
+    return list.get(index);
+  }
+  
+  // @Override
+  public ByteString getByteString(int index) {
+    Object o = list.get(index);
+    ByteString b = asByteString(o);
+    if (b != o) {
+      list.set(index, b);
+    }
+    return b;
+  }
+  
+  // @Override
+  public byte[] getByteArray(int index) {
+    Object o = list.get(index);
+    byte[] b = asByteArray(o);
+    if (b != o) {
+      list.set(index, b);
+    }
+    return b;
+  }
+
+  // @Override
+  public void set(int index, ByteString s) {
+    setAndReturn(index, s);
+  }
+  
+  private Object setAndReturn(int index, ByteString s) {
+    ensureIsMutable();
+    return list.set(index, s);
+  }
+
+  // @Override
+  public void set(int index, byte[] s) {
+    setAndReturn(index, s);
+  }
+  
+  private Object setAndReturn(int index, byte[] s) {
+    ensureIsMutable();
+    return list.set(index, s);
+  }
+
+  private static String asString(Object o) {
+    if (o instanceof String) {
+      return (String) o;
+    } else if (o instanceof ByteString) {
+      return ((ByteString) o).toStringUtf8();
+    } else {
+      return Internal.toStringUtf8((byte[]) o);
+    }
+  }
+  
+  private static ByteString asByteString(Object o) {
+    if (o instanceof ByteString) {
+      return (ByteString) o;
+    } else if (o instanceof String) {
+      return ByteString.copyFromUtf8((String) o);
+    } else {
+      return ByteString.copyFrom((byte[]) o);
+    }
+  }
+  
+  private static byte[] asByteArray(Object o) {
+    if (o instanceof byte[]) {
+      return (byte[]) o;
+    } else if (o instanceof String) {
+      return Internal.toByteArray((String) o);
+    } else {
+      return ((ByteString) o).toByteArray();
+    }
+  }
+
+  // @Override
+  public List<?> getUnderlyingElements() {
+    return Collections.unmodifiableList(list);
+  }
+
+  // @Override
+  public void mergeFrom(LazyStringList other) {
+    ensureIsMutable();
+    for (Object o : other.getUnderlyingElements()) {
+      if (o instanceof byte[]) {
+        byte[] b = (byte[]) o;
+        // Byte array's content is mutable so they should be copied rather than
+        // shared when merging from one message to another.
+        list.add(Arrays.copyOf(b, b.length));
+      } else {
+        list.add(o);
+      }
+    }
+  }
+
+  private static class ByteArrayListView extends AbstractList<byte[]>
+      implements RandomAccess {
+    private final LazyStringArrayList list;
+    
+    ByteArrayListView(LazyStringArrayList list) {
+      this.list = list;
+    }
+    
+    @Override
+    public byte[] get(int index) {
+      return list.getByteArray(index);
+    }
+
+    @Override
+    public int size() {
+      return list.size();
+    }
+
+    @Override
+    public byte[] set(int index, byte[] s) {
+      Object o = list.setAndReturn(index, s);
+      modCount++;
+      return asByteArray(o);
+    }
+
+    @Override
+    public void add(int index, byte[] s) {
+      list.add(index, s);
+      modCount++;
+    }
+
+    @Override
+    public byte[] remove(int index) {
+      Object o = list.remove(index);
+      modCount++;
+      return asByteArray(o);
+    }
+  }
+  
+  // @Override
+  public List<byte[]> asByteArrayList() {
+    return new ByteArrayListView(this);
+  }
+
+  private static class ByteStringListView extends AbstractList<ByteString>
+      implements RandomAccess {
+    private final LazyStringArrayList list;
+
+    ByteStringListView(LazyStringArrayList list) {
+      this.list = list;
+    }
+
+    @Override
+    public ByteString get(int index) {
+      return list.getByteString(index);
+    }
+
+    @Override
+    public int size() {
+      return list.size();
+    }
+
+    @Override
+    public ByteString set(int index, ByteString s) {
+      Object o = list.setAndReturn(index, s);
+      modCount++;
+      return asByteString(o);
+    }
+
+    @Override
+    public void add(int index, ByteString s) {
+      list.add(index, s);
+      modCount++;
+    }
+
+    @Override
+    public ByteString remove(int index) {
+      Object o = list.remove(index);
+      modCount++;
+      return asByteString(o);
+    }
+  }
+
+  // @Override
+  public List<ByteString> asByteStringList() {
+    return new ByteStringListView(this);
+  }
+
+  // @Override
+  public LazyStringList getUnmodifiableView() {
+    if (isModifiable()) {
+      return new UnmodifiableLazyStringList(this);
+    }
+    return this;
+  }
+
+}
diff --git a/java/core/src/main/java/com/google/protobuf/LazyStringList.java b/java/core/src/main/java/com/google/protobuf/LazyStringList.java
new file mode 100644
index 00000000..3eeedca1
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/LazyStringList.java
@@ -0,0 +1,174 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import java.util.Collection;
+import java.util.List;
+
+/**
+ * An interface extending {@code List<String>} that also provides access to the
+ * items of the list as UTF8-encoded ByteString or byte[] objects. This is
+ * used by the protocol buffer implementation to support lazily converting bytes
+ * parsed over the wire to String objects until needed and also increases the
+ * efficiency of serialization if the String was never requested as the
+ * ByteString or byte[] is already cached. The ByteString methods are used in
+ * immutable API only and byte[] methods used in mutable API only for they use
+ * different representations for string/bytes fields.
+ *
+ * @author jonp@google.com (Jon Perlow)
+ */
+public interface LazyStringList extends ProtocolStringList {
+
+  /**
+   * Returns the element at the specified position in this list as a ByteString.
+   *
+   * @param index index of the element to return
+   * @return the element at the specified position in this list
+   * @throws IndexOutOfBoundsException if the index is out of range
+   *         ({@code index < 0 || index >= size()})
+   */
+  ByteString getByteString(int index);
+
+  /**
+   * Returns the element at the specified position in this list as an Object
+   * that will either be a String or a ByteString.
+   *
+   * @param index index of the element to return
+   * @return the element at the specified position in this list
+   * @throws IndexOutOfBoundsException if the index is out of range
+   *         ({@code index < 0 || index >= size()})
+   */
+  Object getRaw(int index);
+
+  /**
+   * Returns the element at the specified position in this list as byte[].
+   *
+   * @param index index of the element to return
+   * @return the element at the specified position in this list
+   * @throws IndexOutOfBoundsException if the index is out of range
+   *         ({@code index < 0 || index >= size()})
+   */
+  byte[] getByteArray(int index);
+
+  /**
+   * Appends the specified element to the end of this list (optional
+   * operation).
+   *
+   * @param element element to be appended to this list
+   * @throws UnsupportedOperationException if the <tt>add</tt> operation
+   *         is not supported by this list
+   */
+  void add(ByteString element);
+
+  /**
+   * Appends the specified element to the end of this list (optional
+   * operation).
+   *
+   * @param element element to be appended to this list
+   * @throws UnsupportedOperationException if the <tt>add</tt> operation
+   *         is not supported by this list
+   */
+  void add(byte[] element);
+
+  /**
+   * Replaces the element at the specified position in this list with the
+   * specified element (optional operation).
+   *
+   * @param index index of the element to replace
+   * @param element the element to be stored at the specified position
+   * @throws UnsupportedOperationException if the <tt>set</tt> operation
+   *         is not supported by this list
+   *         IndexOutOfBoundsException if the index is out of range
+   *         ({@code index < 0 || index >= size()})
+   */
+  void set(int index, ByteString element);
+  
+  /**
+   * Replaces the element at the specified position in this list with the
+   * specified element (optional operation).
+   *
+   * @param index index of the element to replace
+   * @param element the element to be stored at the specified position
+   * @throws UnsupportedOperationException if the <tt>set</tt> operation
+   *         is not supported by this list
+   *         IndexOutOfBoundsException if the index is out of range
+   *         ({@code index < 0 || index >= size()})
+   */
+  void set(int index, byte[] element);
+
+  /**
+   * Appends all elements in the specified ByteString collection to the end of
+   * this list.
+   *
+   * @param c collection whose elements are to be added to this list
+   * @return true if this list changed as a result of the call
+   * @throws UnsupportedOperationException if the <tt>addAllByteString</tt>
+   *         operation is not supported by this list
+   */
+  boolean addAllByteString(Collection<? extends ByteString> c);
+
+  /**
+   * Appends all elements in the specified byte[] collection to the end of
+   * this list.
+   *
+   * @param c collection whose elements are to be added to this list
+   * @return true if this list changed as a result of the call
+   * @throws UnsupportedOperationException if the <tt>addAllByteArray</tt>
+   *         operation is not supported by this list
+   */
+  boolean addAllByteArray(Collection<byte[]> c);
+
+  /**
+   * Returns an unmodifiable List of the underlying elements, each of which is
+   * either a {@code String} or its equivalent UTF-8 encoded {@code ByteString}
+   * or byte[]. It is an error for the caller to modify the returned
+   * List, and attempting to do so will result in an
+   * {@link UnsupportedOperationException}.
+   */
+  List<?> getUnderlyingElements();
+
+  /**
+   * Merges all elements from another LazyStringList into this one. This method
+   * differs from {@link #addAll(Collection)} on that underlying byte arrays are
+   * copied instead of reference shared. Immutable API doesn't need to use this
+   * method as byte[] is not used there at all.
+   */
+  void mergeFrom(LazyStringList other);
+
+  /**
+   * Returns a mutable view of this list. Changes to the view will be made into
+   * the original list. This method is used in mutable API only.
+   */
+  List<byte[]> asByteArrayList();
+
+  /** Returns an unmodifiable view of the list. */
+  LazyStringList getUnmodifiableView();
+}
diff --git a/java/core/src/main/java/com/google/protobuf/LiteralByteString.java b/java/core/src/main/java/com/google/protobuf/LiteralByteString.java
new file mode 100644
index 00000000..a18c2792
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/LiteralByteString.java
@@ -0,0 +1,267 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import java.io.ByteArrayInputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.nio.ByteBuffer;
+import java.nio.charset.Charset;
+import java.util.Collections;
+import java.util.List;
+
+/**
+ * This class implements a {@link com.google.protobuf.ByteString} backed by a
+ * single array of bytes, contiguous in memory. It supports substring by
+ * pointing to only a sub-range of the underlying byte array, meaning that a
+ * substring will reference the full byte-array of the string it's made from,
+ * exactly as with {@link String}.
+ *
+ * @author carlanton@google.com (Carl Haverl)
+ */
+class LiteralByteString extends ByteString.LeafByteString {
+  private static final long serialVersionUID = 1L;
+
+  protected final byte[] bytes;
+
+  /**
+   * Creates a {@code LiteralByteString} backed by the given array, without
+   * copying.
+   *
+   * @param bytes array to wrap
+   */
+  LiteralByteString(byte[] bytes) {
+    this.bytes = bytes;
+  }
+
+  @Override
+  public byte byteAt(int index) {
+    // Unlike most methods in this class, this one is a direct implementation
+    // ignoring the potential offset because we need to do range-checking in the
+    // substring case anyway.
+    return bytes[index];
+  }
+
+  @Override
+  public int size() {
+    return bytes.length;
+  }
+
+  // =================================================================
+  // ByteString -> substring
+
+  @Override
+  public final ByteString substring(int beginIndex, int endIndex) {
+    final int length = checkRange(beginIndex, endIndex, size());
+
+    if (length == 0) {
+      return ByteString.EMPTY;
+    }
+
+    return new BoundedByteString(bytes, getOffsetIntoBytes() + beginIndex, length);
+  }
+
+  // =================================================================
+  // ByteString -> byte[]
+
+  @Override
+  protected void copyToInternal(
+      byte[] target, int sourceOffset, int targetOffset, int numberToCopy) {
+    // Optimized form, not for subclasses, since we don't call
+    // getOffsetIntoBytes() or check the 'numberToCopy' parameter.
+    // TODO(nathanmittler): Is not calling getOffsetIntoBytes really saving that much?
+    System.arraycopy(bytes, sourceOffset, target, targetOffset, numberToCopy);
+  }
+
+  @Override
+  public final void copyTo(ByteBuffer target) {
+    target.put(bytes, getOffsetIntoBytes(), size()); // Copies bytes
+  }
+
+  @Override
+  public final ByteBuffer asReadOnlyByteBuffer() {
+    return ByteBuffer.wrap(bytes, getOffsetIntoBytes(), size()).asReadOnlyBuffer();
+  }
+
+  @Override
+  public final List<ByteBuffer> asReadOnlyByteBufferList() {
+    return Collections.singletonList(asReadOnlyByteBuffer());
+  }
+
+  @Override
+  public final void writeTo(OutputStream outputStream) throws IOException {
+    outputStream.write(toByteArray());
+  }
+
+  @Override
+  final void writeToInternal(OutputStream outputStream, int sourceOffset, int numberToWrite)
+      throws IOException {
+    outputStream.write(bytes, getOffsetIntoBytes() + sourceOffset, numberToWrite);
+  }
+
+  @Override
+  protected final String toStringInternal(Charset charset) {
+    return new String(bytes, getOffsetIntoBytes(), size(), charset);
+  }
+
+  // =================================================================
+  // UTF-8 decoding
+
+  @Override
+  public final boolean isValidUtf8() {
+    int offset = getOffsetIntoBytes();
+    return Utf8.isValidUtf8(bytes, offset, offset + size());
+  }
+
+  @Override
+  protected final int partialIsValidUtf8(int state, int offset, int length) {
+    int index = getOffsetIntoBytes() + offset;
+    return Utf8.partialIsValidUtf8(state, bytes, index, index + length);
+  }
+
+  // =================================================================
+  // equals() and hashCode()
+
+  @Override
+  public final boolean equals(Object other) {
+    if (other == this) {
+      return true;
+    }
+    if (!(other instanceof ByteString)) {
+      return false;
+    }
+
+    if (size() != ((ByteString) other).size()) {
+      return false;
+    }
+    if (size() == 0) {
+      return true;
+    }
+
+    if (other instanceof LiteralByteString) {
+      LiteralByteString otherAsLiteral = (LiteralByteString) other;
+      // If we know the hash codes and they are not equal, we know the byte
+      // strings are not equal.
+      int thisHash = peekCachedHashCode();
+      int thatHash = otherAsLiteral.peekCachedHashCode();
+      if (thisHash != 0 && thatHash != 0 && thisHash != thatHash) {
+        return false;
+      }
+
+      return equalsRange((LiteralByteString) other, 0, size());
+    } else {
+      // RopeByteString and NioByteString.
+      return other.equals(this);
+    }
+  }
+
+  /**
+   * Check equality of the substring of given length of this object starting at
+   * zero with another {@code LiteralByteString} substring starting at offset.
+   *
+   * @param other  what to compare a substring in
+   * @param offset offset into other
+   * @param length number of bytes to compare
+   * @return true for equality of substrings, else false.
+   */
+  @Override
+  final boolean equalsRange(ByteString other, int offset, int length) {
+    if (length > other.size()) {
+      throw new IllegalArgumentException("Length too large: " + length + size());
+    }
+    if (offset + length > other.size()) {
+      throw new IllegalArgumentException(
+          "Ran off end of other: " + offset + ", " + length + ", " + other.size());
+    }
+
+    if (other instanceof LiteralByteString) {
+      LiteralByteString lbsOther = (LiteralByteString) other;
+      byte[] thisBytes = bytes;
+      byte[] otherBytes = lbsOther.bytes;
+      int thisLimit = getOffsetIntoBytes() + length;
+      for (
+          int thisIndex = getOffsetIntoBytes(), otherIndex = lbsOther.getOffsetIntoBytes() + offset;
+          (thisIndex < thisLimit); ++thisIndex, ++otherIndex) {
+        if (thisBytes[thisIndex] != otherBytes[otherIndex]) {
+          return false;
+        }
+      }
+      return true;
+    }
+
+    return other.substring(offset, offset + length).equals(substring(0, length));
+  }
+
+  @Override
+  protected final int partialHash(int h, int offset, int length) {
+    return hashCode(h, bytes, getOffsetIntoBytes() + offset, length);
+  }
+
+  static int hashCode(int h, byte[] bytes, int offset, int length) {
+    for (int i = offset; i < offset + length; i++) {
+      h = h * 31 + bytes[i];
+    }
+    return h;
+  }
+
+  static int hashCode(byte[] bytes) {
+    int h = hashCode(bytes.length, bytes, 0, bytes.length);
+    return h == 0 ? 1 : h;
+  }
+
+  // =================================================================
+  // Input stream
+
+  @Override
+  public final InputStream newInput() {
+    return new ByteArrayInputStream(bytes, getOffsetIntoBytes(), size()); // No copy
+  }
+
+  @Override
+  public final CodedInputStream newCodedInput() {
+    // We trust CodedInputStream not to modify the bytes, or to give anyone
+    // else access to them.
+    return CodedInputStream.newInstance(this);
+  }
+
+  // =================================================================
+  // Internal methods
+
+  /**
+   * Offset into {@code bytes[]} to use, non-zero for substrings.
+   *
+   * @return always 0 for this class
+   */
+  protected int getOffsetIntoBytes() {
+    return 0;
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/LongArrayList.java b/java/core/src/main/java/com/google/protobuf/LongArrayList.java
new file mode 100644
index 00000000..ebe62029
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/LongArrayList.java
@@ -0,0 +1,249 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import com.google.protobuf.Internal.LongList;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.List;
+import java.util.RandomAccess;
+
+/**
+ * An implementation of {@link LongList} on top of a primitive array.
+ * 
+ * @author dweis@google.com (Daniel Weis)
+ */
+final class LongArrayList extends AbstractProtobufList<Long> implements LongList, RandomAccess {
+  
+  private static final int DEFAULT_CAPACITY = 10;
+  
+  private static final LongArrayList EMPTY_LIST = new LongArrayList();
+  static {
+    EMPTY_LIST.makeImmutable();
+  }
+  
+  public static LongArrayList emptyList() {
+    return EMPTY_LIST;
+  }
+  
+  /**
+   * The backing store for the list.
+   */
+  private long[] array;
+  
+  /**
+   * The size of the list distinct from the length of the array. That is, it is the number of
+   * elements set in the list.
+   */
+  private int size;
+
+  /**
+   * Constructs a new mutable {@code LongArrayList} with default capacity.
+   */
+  LongArrayList() {
+    this(DEFAULT_CAPACITY);
+  }
+
+  /**
+   * Constructs a new mutable {@code LongArrayList} with the provided capacity.
+   */
+  LongArrayList(int capacity) {
+    array = new long[capacity];
+    size = 0;
+  }
+
+  /**
+   * Constructs a new mutable {@code LongArrayList} containing the same elements as {@code other}.
+   */
+  LongArrayList(List<Long> other) {
+    if (other instanceof LongArrayList) {
+      LongArrayList list = (LongArrayList) other;
+      array = list.array.clone();
+      size = list.size;
+    } else {
+      size = other.size();
+      array = new long[size];
+      for (int i = 0; i < size; i++) {
+        array[i] = other.get(i);
+      }
+    }
+  }
+  
+  @Override
+  public Long get(int index) {
+    return getLong(index);
+  }
+
+  @Override
+  public long getLong(int index) {
+    ensureIndexInRange(index);
+    return array[index];
+  }
+
+  @Override
+  public int size() {
+    return size;
+  }
+
+  @Override
+  public Long set(int index, Long element) {
+    return setLong(index, element);
+  }
+
+  @Override
+  public long setLong(int index, long element) {
+    ensureIsMutable();
+    ensureIndexInRange(index);
+    long previousValue = array[index];
+    array[index] = element;
+    return previousValue;
+  }
+
+  @Override
+  public void add(int index, Long element) {
+    addLong(index, element);
+  }
+
+  /**
+   * Like {@link #add(Long)} but more efficient in that it doesn't box the element.
+   */
+  @Override
+  public void addLong(long element) {
+    addLong(size, element);
+  }
+
+  /**
+   * Like {@link #add(int, Long)} but more efficient in that it doesn't box the element.
+   */
+  private void addLong(int index, long element) {
+    ensureIsMutable();
+    if (index < 0 || index > size) {
+      throw new IndexOutOfBoundsException(makeOutOfBoundsExceptionMessage(index));
+    }
+    
+    if (size < array.length) {
+      // Shift everything over to make room
+      System.arraycopy(array, index, array, index + 1, size - index);
+    } else {
+      // Resize to 1.5x the size
+      int length = ((size * 3) / 2) + 1;
+      long[] newArray = new long[length];
+      
+      // Copy the first part directly
+      System.arraycopy(array, 0, newArray, 0, index);
+      
+      // Copy the rest shifted over by one to make room
+      System.arraycopy(array, index, newArray, index + 1, size - index);
+      array = newArray;
+    }
+
+    array[index] = element;
+    size++;
+    modCount++;
+  }
+
+  @Override
+  public boolean addAll(Collection<? extends Long> collection) {
+    ensureIsMutable();
+    
+    if (collection == null) {
+      throw new NullPointerException();
+    }
+    
+    // We specialize when adding another LongArrayList to avoid boxing elements.
+    if (!(collection instanceof LongArrayList)) {
+      return super.addAll(collection);
+    }
+    
+    LongArrayList list = (LongArrayList) collection;
+    if (list.size == 0) {
+      return false;
+    }
+    
+    int overflow = Integer.MAX_VALUE - size;
+    if (overflow < list.size) {
+      // We can't actually represent a list this large.
+      throw new OutOfMemoryError();
+    }
+    
+    int newSize = size + list.size;
+    if (newSize > array.length) {
+      array = Arrays.copyOf(array, newSize);
+    }
+    
+    System.arraycopy(list.array, 0, array, size, list.size);
+    size = newSize;
+    modCount++;
+    return true;
+  }
+  
+  @Override
+  public boolean remove(Object o) {
+    ensureIsMutable();
+    for (int i = 0; i < size; i++) {
+      if (o.equals(array[i])) {
+        System.arraycopy(array, i + 1, array, i, size - i);
+        size--;
+        modCount++;
+        return true;
+      }
+    }
+    return false;
+  }
+
+  @Override
+  public Long remove(int index) {
+    ensureIsMutable();
+    ensureIndexInRange(index);
+    long value = array[index];
+    System.arraycopy(array, index + 1, array, index, size - index);
+    size--;
+    modCount++;
+    return value;
+  }
+
+  /**
+   * Ensures that the provided {@code index} is within the range of {@code [0, size]}. Throws an
+   * {@link IndexOutOfBoundsException} if it is not.
+   * 
+   * @param index the index to verify is in range
+   */
+  private void ensureIndexInRange(int index) {
+    if (index < 0 || index >= size) {
+      throw new IndexOutOfBoundsException(makeOutOfBoundsExceptionMessage(index));
+    }
+  }
+
+  private String makeOutOfBoundsExceptionMessage(int index) {
+    return "Index:" + index + ", Size:" + size;
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/MapEntry.java b/java/core/src/main/java/com/google/protobuf/MapEntry.java
new file mode 100644
index 00000000..31414bb4
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/MapEntry.java
@@ -0,0 +1,433 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import com.google.protobuf.Descriptors.Descriptor;
+import com.google.protobuf.Descriptors.EnumValueDescriptor;
+import com.google.protobuf.Descriptors.FieldDescriptor;
+
+import java.io.IOException;
+import java.util.Collections;
+import java.util.Map;
+import java.util.TreeMap;
+
+/**
+ * Implements MapEntry messages.
+ * 
+ * In reflection API, map fields will be treated as repeated message fields and
+ * each map entry is accessed as a message. This MapEntry class is used to
+ * represent these map entry messages in reflection API.
+ * 
+ * Protobuf internal. Users shouldn't use this class.
+ */
+public final class MapEntry<K, V> extends AbstractMessage {
+  private static class Metadata<K, V> {
+    public final Descriptor descriptor;  
+    public final MapEntry<K, V> defaultInstance;
+    public final AbstractParser<MapEntry<K, V>> parser;
+    
+    public Metadata(
+        final Descriptor descriptor, final MapEntry<K, V> defaultInstance) {
+      this.descriptor = descriptor;
+      this.defaultInstance = defaultInstance;
+      final Metadata<K, V> thisMetadata = this;
+      this.parser = new AbstractParser<MapEntry<K, V>>() {
+        private final Parser<MapEntryLite<K, V>> dataParser =
+            defaultInstance.data.getParserForType();
+        @Override
+        public MapEntry<K, V> parsePartialFrom(
+            CodedInputStream input, ExtensionRegistryLite extensionRegistry)
+            throws InvalidProtocolBufferException {
+          MapEntryLite<K, V> data =
+              dataParser.parsePartialFrom(input, extensionRegistry);
+          return new MapEntry<K, V>(thisMetadata, data);
+        }
+        
+      };
+    }
+  }
+  
+  private final Metadata<K, V> metadata;
+  private final MapEntryLite<K, V> data;
+  
+  /** Create a default MapEntry instance. */
+  private MapEntry(Descriptor descriptor,
+      WireFormat.FieldType keyType, K defaultKey,
+      WireFormat.FieldType valueType, V defaultValue) {
+    this.data = MapEntryLite.newDefaultInstance(
+        keyType, defaultKey, valueType, defaultValue);
+    this.metadata = new Metadata<K, V>(descriptor, this); 
+  }
+  
+  /** Create a new MapEntry message. */
+  private MapEntry(Metadata<K, V> metadata, MapEntryLite<K, V> data) {
+    this.metadata = metadata;
+    this.data = data;
+  }
+  
+  /**
+   * Create a default MapEntry instance. A default MapEntry instance should be
+   * created only once for each map entry message type. Generated code should
+   * store the created default instance and use it later to create new MapEntry
+   * messages of the same type. 
+   */
+  public static <K, V> MapEntry<K, V> newDefaultInstance(
+      Descriptor descriptor,
+      WireFormat.FieldType keyType, K defaultKey,
+      WireFormat.FieldType valueType, V defaultValue) {
+    return new MapEntry<K, V>(
+        descriptor, keyType, defaultKey, valueType, defaultValue);
+  }
+  
+  public K getKey() {
+    return data.getKey();
+  }
+  
+  public V getValue() {
+    return data.getValue();
+  }
+  
+  @Override
+  public int getSerializedSize() {
+    return data.getSerializedSize();
+  }
+  
+  @Override
+  public void writeTo(CodedOutputStream output) throws IOException {
+    data.writeTo(output);
+  }
+  
+  @Override
+  public boolean isInitialized() {
+    return data.isInitialized();
+  }
+  
+  @Override
+  public Parser<MapEntry<K, V>> getParserForType() {
+    return metadata.parser;
+  }
+
+  @Override
+  public Builder<K, V> newBuilderForType() {
+    return new Builder<K, V>(metadata);
+  }
+  
+  @Override
+  public Builder<K, V> toBuilder() {
+    return new Builder<K, V>(metadata, data);
+  }
+
+  @Override
+  public MapEntry<K, V> getDefaultInstanceForType() {
+    return metadata.defaultInstance;
+  }
+
+  @Override
+  public Descriptor getDescriptorForType() {
+    return metadata.descriptor;
+  }
+
+  @Override
+  public Map<FieldDescriptor, Object> getAllFields() {
+    final TreeMap<FieldDescriptor, Object> result =
+        new TreeMap<FieldDescriptor, Object>();
+    for (final FieldDescriptor field : metadata.descriptor.getFields()) {
+      if (hasField(field)) {
+        result.put(field, getField(field));
+      }
+    }
+    return Collections.unmodifiableMap(result);
+  }
+  
+  private void checkFieldDescriptor(FieldDescriptor field) {
+    if (field.getContainingType() != metadata.descriptor) {
+      throw new RuntimeException(
+          "Wrong FieldDescriptor \"" + field.getFullName()
+          + "\" used in message \"" + metadata.descriptor.getFullName()); 
+    }
+  }
+
+  @Override
+  public boolean hasField(FieldDescriptor field) {
+    checkFieldDescriptor(field);;
+    // A MapEntry always contains two fields.
+    return true;
+  }
+
+  @Override
+  public Object getField(FieldDescriptor field) {
+    checkFieldDescriptor(field);
+    Object result = field.getNumber() == 1 ? getKey() : getValue();
+    // Convert enums to EnumValueDescriptor.
+    if (field.getType() == FieldDescriptor.Type.ENUM) {
+      result = field.getEnumType().findValueByNumberCreatingIfUnknown(
+          (java.lang.Integer) result);
+    }
+    return result;
+  }
+
+  @Override
+  public int getRepeatedFieldCount(FieldDescriptor field) {
+    throw new RuntimeException(
+        "There is no repeated field in a map entry message.");
+  }
+
+  @Override
+  public Object getRepeatedField(FieldDescriptor field, int index) {
+    throw new RuntimeException(
+        "There is no repeated field in a map entry message.");
+  }
+
+  @Override
+  public UnknownFieldSet getUnknownFields() {
+    return UnknownFieldSet.getDefaultInstance();
+  }
+
+  /**
+   * Builder to create {@link MapEntry} messages.
+   */
+  public static class Builder<K, V>
+      extends AbstractMessage.Builder<Builder<K, V>> {
+    private final Metadata<K, V> metadata;
+    private MapEntryLite<K, V> data;
+    private MapEntryLite.Builder<K, V> dataBuilder;
+    
+    private Builder(Metadata<K, V> metadata) {
+      this.metadata = metadata;
+      this.data = metadata.defaultInstance.data;
+      this.dataBuilder = null;
+    }
+    
+    private Builder(Metadata<K, V> metadata, MapEntryLite<K, V> data) {
+      this.metadata = metadata;
+      this.data = data;
+      this.dataBuilder = null;
+    }
+    
+    public K getKey() {
+      return dataBuilder == null ? data.getKey() : dataBuilder.getKey();
+    }
+    
+    public V getValue() {
+      return dataBuilder == null ? data.getValue() : dataBuilder.getValue();
+    }
+    
+    private void ensureMutable() {
+      if (dataBuilder == null) {
+        dataBuilder = data.toBuilder();
+      }
+    }
+    
+    public Builder<K, V> setKey(K key) {
+      ensureMutable();
+      dataBuilder.setKey(key);
+      return this;
+    }
+    
+    public Builder<K, V> clearKey() {
+      ensureMutable();
+      dataBuilder.clearKey();
+      return this;
+    }
+    
+    public Builder<K, V> setValue(V value) {
+      ensureMutable();
+      dataBuilder.setValue(value);
+      return this;
+    }
+    
+    public Builder<K, V> clearValue() {
+      ensureMutable();
+      dataBuilder.clearValue();
+      return this;
+    }
+
+    @Override
+    public MapEntry<K, V> build() {
+      MapEntry<K, V> result = buildPartial();
+      if (!result.isInitialized()) {
+        throw newUninitializedMessageException(result);
+      }
+      return result;
+    }
+
+    @Override
+    public MapEntry<K, V> buildPartial() {
+      if (dataBuilder != null) {
+        data = dataBuilder.buildPartial();
+        dataBuilder = null;
+      }
+      return new MapEntry<K, V>(metadata, data);
+    }
+
+    @Override
+    public Descriptor getDescriptorForType() {
+      return metadata.descriptor;
+    }
+    
+    private void checkFieldDescriptor(FieldDescriptor field) {
+      if (field.getContainingType() != metadata.descriptor) {
+        throw new RuntimeException(
+            "Wrong FieldDescriptor \"" + field.getFullName()
+            + "\" used in message \"" + metadata.descriptor.getFullName()); 
+      }
+    }
+
+    @Override
+    public com.google.protobuf.Message.Builder newBuilderForField(
+        FieldDescriptor field) {
+      checkFieldDescriptor(field);;
+      // This method should be called for message fields and in a MapEntry
+      // message only the value field can possibly be a message field.
+      if (field.getNumber() != 2
+          || field.getJavaType() != FieldDescriptor.JavaType.MESSAGE) {
+        throw new RuntimeException(
+            "\"" + field.getFullName() + "\" is not a message value field.");
+      }
+      return ((Message) data.getValue()).newBuilderForType();
+    }
+
+    @SuppressWarnings("unchecked")
+    @Override
+    public Builder<K, V> setField(FieldDescriptor field, Object value) {
+      checkFieldDescriptor(field);
+      if (field.getNumber() == 1) {
+        setKey((K) value);
+      } else {
+        if (field.getType() == FieldDescriptor.Type.ENUM) {
+          value = ((EnumValueDescriptor) value).getNumber();
+        }
+        setValue((V) value);
+      }
+      return this;
+    }
+
+    @Override
+    public Builder<K, V> clearField(FieldDescriptor field) {
+      checkFieldDescriptor(field);
+      if (field.getNumber() == 1) {
+        clearKey();
+      } else {
+        clearValue();
+      }
+      return this;
+    }
+
+    @Override
+    public Builder<K, V> setRepeatedField(FieldDescriptor field, int index,
+        Object value) {
+      throw new RuntimeException(
+          "There is no repeated field in a map entry message.");
+    }
+
+    @Override
+    public Builder<K, V> addRepeatedField(FieldDescriptor field, Object value) {
+      throw new RuntimeException(
+          "There is no repeated field in a map entry message.");
+    }
+
+    @Override
+    public Builder<K, V> setUnknownFields(UnknownFieldSet unknownFields) {
+      // Unknown fields are discarded for MapEntry message.
+      return this;
+    }
+
+    @Override
+    public MapEntry<K, V> getDefaultInstanceForType() {
+      return metadata.defaultInstance;
+    }
+
+    @Override
+    public boolean isInitialized() {
+      if (dataBuilder != null) {
+        return dataBuilder.isInitialized();
+      } else {
+        return data.isInitialized();
+      }
+    }
+
+    @Override
+    public Map<FieldDescriptor, Object> getAllFields() {
+      final TreeMap<FieldDescriptor, Object> result =
+          new TreeMap<FieldDescriptor, Object>();
+      for (final FieldDescriptor field : metadata.descriptor.getFields()) {
+        if (hasField(field)) {
+          result.put(field, getField(field));
+        }
+      }
+      return Collections.unmodifiableMap(result);
+    }
+
+    @Override
+    public boolean hasField(FieldDescriptor field) {
+      checkFieldDescriptor(field);
+      return true;
+    }
+
+    @Override
+    public Object getField(FieldDescriptor field) {
+      checkFieldDescriptor(field);
+      Object result = field.getNumber() == 1 ? getKey() : getValue();
+      // Convert enums to EnumValueDescriptor.
+      if (field.getType() == FieldDescriptor.Type.ENUM) {
+        result = field.getEnumType().findValueByNumberCreatingIfUnknown(
+            (java.lang.Integer) result);
+      }
+      return result;
+    }
+
+    @Override
+    public int getRepeatedFieldCount(FieldDescriptor field) {
+      throw new RuntimeException(
+          "There is no repeated field in a map entry message.");
+    }
+    
+    @Override
+    public Object getRepeatedField(FieldDescriptor field, int index) {
+      throw new RuntimeException(
+          "There is no repeated field in a map entry message.");
+    }
+    
+    @Override
+    public UnknownFieldSet getUnknownFields() {
+      return UnknownFieldSet.getDefaultInstance();
+    }
+
+    @Override
+    public Builder<K, V> clone() {
+      if (dataBuilder == null) {
+        return new Builder<K, V>(metadata, data);
+      } else {
+        return new Builder<K, V>(metadata, dataBuilder.build());
+      }
+    }
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/MapEntryLite.java b/java/core/src/main/java/com/google/protobuf/MapEntryLite.java
new file mode 100644
index 00000000..bcffa946
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/MapEntryLite.java
@@ -0,0 +1,331 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import java.io.IOException;
+
+/**
+ * Implements the lite version of map entry messages.
+ * 
+ * This class serves as an utility class to help do serialization/parsing of
+ * map entries. It's used in generated code and also in the full version
+ * MapEntry message.
+ * 
+ * Protobuf internal. Users shouldn't use.
+ */
+public class MapEntryLite<K, V> extends AbstractMessageLite {
+  private static class Metadata<K, V> {
+    public final MapEntryLite<K, V> defaultInstance;
+    public final WireFormat.FieldType keyType;
+    public final WireFormat.FieldType valueType;
+    public final Parser<MapEntryLite<K, V>> parser;
+    public Metadata(
+        MapEntryLite<K, V> defaultInstance,
+        WireFormat.FieldType keyType,
+        WireFormat.FieldType valueType) {
+      this.defaultInstance = defaultInstance; 
+      this.keyType = keyType;
+      this.valueType = valueType;
+      final Metadata<K, V> finalThis = this;
+      this.parser = new AbstractParser<MapEntryLite<K, V>>() {
+        @Override
+        public MapEntryLite<K, V> parsePartialFrom(
+            CodedInputStream input, ExtensionRegistryLite extensionRegistry)
+            throws InvalidProtocolBufferException {
+          return new MapEntryLite<K, V>(finalThis, input, extensionRegistry);
+        }
+      };
+    }
+  }
+  
+  private static final int KEY_FIELD_NUMBER = 1;
+  private static final int VALUE_FIELD_NUMBER = 2;
+  
+  private final Metadata<K, V> metadata;
+  private final K key;
+  private final V value;
+  
+  /** Creates a default MapEntryLite message instance. */
+  private MapEntryLite(
+      WireFormat.FieldType keyType, K defaultKey,
+      WireFormat.FieldType valueType, V defaultValue) {
+    this.metadata = new Metadata<K, V>(this, keyType, valueType);
+    this.key = defaultKey;
+    this.value = defaultValue;
+  }
+  
+  /** Creates a new MapEntryLite message. */
+  private MapEntryLite(Metadata<K, V> metadata, K key, V value) {
+    this.metadata = metadata;
+    this.key = key;
+    this.value = value;
+  }
+  
+  public K getKey() {
+    return key;
+  }
+  
+  public V getValue() {
+    return value;
+  }
+
+  /**
+   * Creates a default MapEntryLite message instance.
+   * 
+   * This method is used by generated code to create the default instance for
+   * a map entry message. The created default instance should be used to create
+   * new map entry messages of the same type. For each map entry message, only
+   * one default instance should be created. 
+   */
+  public static <K, V> MapEntryLite<K, V> newDefaultInstance(
+      WireFormat.FieldType keyType, K defaultKey,
+      WireFormat.FieldType valueType, V defaultValue) {
+    return new MapEntryLite<K, V>(
+        keyType, defaultKey, valueType, defaultValue);
+  }
+  
+  @Override
+  public void writeTo(CodedOutputStream output) throws IOException {
+    writeField(KEY_FIELD_NUMBER, metadata.keyType, key, output);
+    writeField(VALUE_FIELD_NUMBER, metadata.valueType, value, output);
+  }
+
+  private void writeField(
+      int number, WireFormat.FieldType type, Object value,
+      CodedOutputStream output) throws IOException {
+    output.writeTag(number, type.getWireType());
+    FieldSet.writeElementNoTag(output, type, value);
+  }
+
+  private volatile int cachedSerializedSize = -1;
+  @Override
+  public int getSerializedSize() {
+    if (cachedSerializedSize != -1) {
+      return cachedSerializedSize;
+    }
+    int size = 0;
+    size += getFieldSize(KEY_FIELD_NUMBER, metadata.keyType, key);
+    size += getFieldSize(VALUE_FIELD_NUMBER, metadata.valueType, value);
+    cachedSerializedSize = size;
+    return size;
+  }
+
+  private int getFieldSize(
+      int number, WireFormat.FieldType type, Object value) {
+    return CodedOutputStream.computeTagSize(number)
+        + FieldSet.computeElementSizeNoTag(type, value);
+  }
+  
+  /** Parsing constructor. */
+  private MapEntryLite(
+      Metadata<K, V> metadata,
+      CodedInputStream input,
+      ExtensionRegistryLite extensionRegistry)
+      throws InvalidProtocolBufferException {
+    try {
+      K key = metadata.defaultInstance.key;
+      V value = metadata.defaultInstance.value;
+      while (true) {
+        int tag = input.readTag();
+        if (tag == 0) {
+          break;
+        }
+        if (tag == WireFormat.makeTag(
+                KEY_FIELD_NUMBER, metadata.keyType.getWireType())) {
+          key = mergeField(
+              input, extensionRegistry, metadata.keyType, key);
+        } else if (tag == WireFormat.makeTag(
+                       VALUE_FIELD_NUMBER, metadata.valueType.getWireType())) {
+          value = mergeField(
+              input, extensionRegistry, metadata.valueType, value);
+        } else {
+          if (!input.skipField(tag)) {
+            break;
+          }
+        }
+      }
+      this.metadata = metadata;
+      this.key = key;
+      this.value = value;
+    } catch (InvalidProtocolBufferException e) {
+      throw e.setUnfinishedMessage(this);
+    } catch (IOException e) {
+      throw new InvalidProtocolBufferException(e.getMessage())
+          .setUnfinishedMessage(this);
+    }
+  }
+  
+  @SuppressWarnings("unchecked")
+  private <T> T mergeField(
+      CodedInputStream input, ExtensionRegistryLite extensionRegistry,
+      WireFormat.FieldType type, T value) throws IOException {
+    switch (type) {
+      case MESSAGE:
+        MessageLite.Builder subBuilder = ((MessageLite) value).toBuilder();
+        input.readMessage(subBuilder, extensionRegistry);
+        return (T) subBuilder.buildPartial();
+      case ENUM:
+        return (T) (java.lang.Integer) input.readEnum();
+      case GROUP:
+        throw new RuntimeException("Groups are not allowed in maps.");
+      default:
+        return (T) FieldSet.readPrimitiveField(input, type, true);
+    }
+  }
+
+  @Override
+  public Parser<MapEntryLite<K, V>> getParserForType() {
+    return metadata.parser;
+  }
+
+  @Override
+  public Builder<K, V> newBuilderForType() {
+    return new Builder<K, V>(metadata);
+  }
+
+  @Override
+  public Builder<K, V> toBuilder() {
+    return new Builder<K, V>(metadata, key, value);
+  }
+
+  @Override
+  public MapEntryLite<K, V> getDefaultInstanceForType() {
+    return metadata.defaultInstance;
+  }
+
+  @Override
+  public boolean isInitialized() {
+    if (metadata.valueType.getJavaType() == WireFormat.JavaType.MESSAGE) {
+      return ((MessageLite) value).isInitialized();
+    }
+    return true;
+  }
+
+  /**
+   * Builder used to create {@link MapEntryLite} messages.
+   */
+  public static class Builder<K, V>
+      extends AbstractMessageLite.Builder<Builder<K, V>> {
+    private final Metadata<K, V> metadata;
+    private K key;
+    private V value;
+    
+    private Builder(Metadata<K, V> metadata) {
+      this.metadata = metadata;
+      this.key = metadata.defaultInstance.key;
+      this.value = metadata.defaultInstance.value;
+    }
+    
+    public K getKey() {
+      return key;
+    }
+    
+    public V getValue() {
+      return value;
+    }
+    
+    public Builder<K, V> setKey(K key) {
+      this.key = key;
+      return this;
+    }
+    
+    public Builder<K, V> setValue(V value) {
+      this.value = value;
+      return this;
+    }
+    
+    public Builder<K, V> clearKey() {
+      this.key = metadata.defaultInstance.key;
+      return this;
+    }
+    
+    public Builder<K, V> clearValue() {
+      this.value = metadata.defaultInstance.value;
+      return this;
+    }
+
+    @Override
+    public Builder<K, V> clear() {
+      this.key = metadata.defaultInstance.key;
+      this.value = metadata.defaultInstance.value;
+      return this;
+    }
+
+    @Override
+    public MapEntryLite<K, V> build() {
+      MapEntryLite<K, V> result = buildPartial();
+      if (!result.isInitialized()) {
+        throw newUninitializedMessageException(result);
+      }
+      return result;
+    }
+
+    @Override
+    public MapEntryLite<K, V> buildPartial() {
+      return new MapEntryLite<K, V>(metadata, key, value);
+    }
+
+    @Override
+    public MessageLite getDefaultInstanceForType() {
+      return metadata.defaultInstance;
+    }
+
+    @Override
+    public boolean isInitialized() {
+      if (metadata.valueType.getJavaType() == WireFormat.JavaType.MESSAGE) {
+        return ((MessageLite) value).isInitialized();
+      }
+      return true;
+    }
+
+    private Builder(Metadata<K, V> metadata, K key, V value) {
+      this.metadata = metadata;
+      this.key = key;
+      this.value = value;
+    }
+    
+    @Override
+    public Builder<K, V> clone() {
+      return new Builder<K, V>(metadata, key, value);
+    }
+
+    @Override
+    public Builder<K, V> mergeFrom(
+        CodedInputStream input, ExtensionRegistryLite extensionRegistry)
+        throws IOException {
+      MapEntryLite<K, V> entry =
+          new MapEntryLite<K, V>(metadata, input, extensionRegistry);
+      this.key = entry.key;
+      this.value = entry.value;
+      return this;
+    }
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/MapField.java b/java/core/src/main/java/com/google/protobuf/MapField.java
new file mode 100644
index 00000000..b290993c
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/MapField.java
@@ -0,0 +1,286 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import com.google.protobuf.MapFieldLite.MutatabilityAwareMap;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * Internal representation of map fields in generated messages.
+ * 
+ * This class supports accessing the map field as a {@link Map} to be used in
+ * generated API and also supports accessing the field as a {@link List} to be
+ * used in reflection API. It keeps track of where the data is currently stored
+ * and do necessary conversions between map and list.  
+ * 
+ * This class is a protobuf implementation detail. Users shouldn't use this
+ * class directly.
+ * 
+ * THREAD-SAFETY NOTE: Read-only access is thread-safe. Users can call getMap()
+ * and getList() concurrently in multiple threads. If write-access is needed,
+ * all access must be synchronized.
+ */
+public class MapField<K, V> implements MutabilityOracle {
+  /**
+   * Indicates where the data of this map field is currently stored.
+   * 
+   * MAP: Data is stored in mapData.
+   * LIST: Data is stored in listData.
+   * BOTH: mapData and listData have the same data.
+   *
+   * When the map field is accessed (through generated API or reflection API),
+   * it will shift between these 3 modes:
+   * 
+   *          getMap()   getList()   getMutableMap()   getMutableList()
+   *   MAP      MAP        BOTH          MAP               LIST
+   *   LIST     BOTH       LIST          MAP               LIST
+   *   BOTH     BOTH       BOTH          MAP               LIST
+   *   
+   * As the map field changes its mode, the list/map reference returned in a
+   * previous method call may be invalidated. 
+   */
+  private enum StorageMode {MAP, LIST, BOTH}
+
+  private volatile boolean isMutable;
+  private volatile StorageMode mode;
+  private MutatabilityAwareMap<K, V> mapData;
+  private List<Message> listData;
+  
+  // Convert between a map entry Message and a key-value pair.
+  private static interface Converter<K, V> {
+    Message convertKeyAndValueToMessage(K key, V value);
+    void convertMessageToKeyAndValue(Message message, Map<K, V> map);
+    
+    Message getMessageDefaultInstance();
+  }
+  
+  private static class ImmutableMessageConverter<K, V> implements Converter<K, V> {
+    private final MapEntry<K, V> defaultEntry;
+    public ImmutableMessageConverter(MapEntry<K, V> defaultEntry) {
+      this.defaultEntry = defaultEntry;
+    }
+    
+    public Message convertKeyAndValueToMessage(K key, V value) {
+      return defaultEntry.newBuilderForType().setKey(key).setValue(value).buildPartial();
+    }
+    
+    public void convertMessageToKeyAndValue(Message message, Map<K, V> map) {
+      MapEntry<K, V> entry = (MapEntry<K, V>) message;
+      map.put(entry.getKey(), entry.getValue());
+    }
+
+    public Message getMessageDefaultInstance() {
+      return defaultEntry;
+    }
+  }
+  
+
+  private final Converter<K, V> converter;
+  
+  private MapField(
+      Converter<K, V> converter,
+      StorageMode mode,
+      Map<K, V> mapData) {
+    this.converter = converter;
+    this.isMutable = true;
+    this.mode = mode;
+    this.mapData = new MutatabilityAwareMap<K, V>(this, mapData);
+    this.listData = null;
+  }
+    
+  private MapField(
+      MapEntry<K, V> defaultEntry,
+      StorageMode mode,
+      Map<K, V> mapData) {
+    this(new ImmutableMessageConverter<K, V>(defaultEntry), mode, mapData);
+  }
+  
+  
+  /** Returns an immutable empty MapField. */
+  public static <K, V> MapField<K, V> emptyMapField(
+      MapEntry<K, V> defaultEntry) {
+    return new MapField<K, V>(
+        defaultEntry, StorageMode.MAP, Collections.<K, V>emptyMap());
+  }
+  
+  
+  /** Creates a new mutable empty MapField. */
+  public static <K, V> MapField<K, V> newMapField(MapEntry<K, V> defaultEntry) {
+    return new MapField<K, V>(
+        defaultEntry, StorageMode.MAP, new LinkedHashMap<K, V>());
+  }
+  
+  
+  private Message convertKeyAndValueToMessage(K key, V value) {
+    return converter.convertKeyAndValueToMessage(key, value);
+  }
+  
+  @SuppressWarnings("unchecked")
+  private void convertMessageToKeyAndValue(Message message, Map<K, V> map) {
+    converter.convertMessageToKeyAndValue(message, map);
+  }
+
+  private List<Message> convertMapToList(MutatabilityAwareMap<K, V> mapData) {
+    List<Message> listData = new ArrayList<Message>();
+    for (Map.Entry<K, V> entry : mapData.entrySet()) {
+      listData.add(
+          convertKeyAndValueToMessage(
+              entry.getKey(), entry.getValue()));
+    }
+    return listData;
+  }
+
+  private MutatabilityAwareMap<K, V> convertListToMap(List<Message> listData) {
+    Map<K, V> mapData = new LinkedHashMap<K, V>();
+    for (Message item : listData) {
+      convertMessageToKeyAndValue(item, mapData);
+    }
+    return new MutatabilityAwareMap<K, V>(this, mapData);
+  }
+  
+  /** Returns the content of this MapField as a read-only Map. */
+  public Map<K, V> getMap() {
+    if (mode == StorageMode.LIST) {
+      synchronized (this) {
+        if (mode == StorageMode.LIST) {
+          mapData = convertListToMap(listData);
+          mode = StorageMode.BOTH;
+        }
+      }
+    }
+    return Collections.unmodifiableMap(mapData);
+  }
+  
+  /** Gets a mutable Map view of this MapField. */
+  public Map<K, V> getMutableMap() {
+    if (mode != StorageMode.MAP) {
+      if (mode == StorageMode.LIST) {
+        mapData = convertListToMap(listData);
+      }
+      listData = null;
+      mode = StorageMode.MAP; 
+    }
+    return mapData;
+  }
+  
+  public void mergeFrom(MapField<K, V> other) {
+    getMutableMap().putAll(MapFieldLite.copy(other.getMap()));
+  }
+  
+  public void clear() {
+    mapData = new MutatabilityAwareMap<K, V>(this, new LinkedHashMap<K, V>());
+    mode = StorageMode.MAP;
+  }
+  
+  @SuppressWarnings("unchecked")
+  @Override
+  public boolean equals(Object object) {
+    if (!(object instanceof MapField)) {
+      return false;
+    }
+    MapField<K, V> other = (MapField<K, V>) object;
+    return MapFieldLite.<K, V>equals(getMap(), other.getMap());
+  }
+  
+  @Override
+  public int hashCode() {
+    return MapFieldLite.<K, V>calculateHashCodeForMap(getMap());
+  }
+  
+  /** Returns a deep copy of this MapField. */
+  public MapField<K, V> copy() {
+    return new MapField<K, V>(
+        converter, StorageMode.MAP, MapFieldLite.copy(getMap()));
+  }
+  
+  /** Gets the content of this MapField as a read-only List. */
+  List<Message> getList() {
+    if (mode == StorageMode.MAP) {
+      synchronized (this) {
+        if (mode == StorageMode.MAP) {
+          listData = convertMapToList(mapData);
+          mode = StorageMode.BOTH;
+        }
+      }
+    }
+    return Collections.unmodifiableList(listData);
+  }
+  
+  /** Gets a mutable List view of this MapField. */
+  List<Message> getMutableList() {
+    if (mode != StorageMode.LIST) {
+      if (mode == StorageMode.MAP) {
+        listData = convertMapToList(mapData);
+      }
+      mapData = null;
+      mode = StorageMode.LIST;
+    }
+    return listData;
+  }
+  
+  /**
+   * Gets the default instance of the message stored in the list view of this
+   * map field.
+   */
+  Message getMapEntryMessageDefaultInstance() {
+    return converter.getMessageDefaultInstance();
+  }
+  
+  /**
+   * Makes this list immutable. All subsequent modifications will throw an
+   * {@link UnsupportedOperationException}.
+   */
+  public void makeImmutable() {
+    isMutable = false;
+  }
+  
+  /**
+   * Returns whether this field can be modified.
+   */
+  public boolean isMutable() {
+    return isMutable;
+  }
+  
+  /* (non-Javadoc)
+   * @see com.google.protobuf.MutabilityOracle#ensureMutable()
+   */
+  @Override
+  public void ensureMutable() {
+    if (!isMutable()) {
+      throw new UnsupportedOperationException();
+    }
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/MapFieldLite.java b/java/core/src/main/java/com/google/protobuf/MapFieldLite.java
new file mode 100644
index 00000000..16d3e6d2
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/MapFieldLite.java
@@ -0,0 +1,549 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import com.google.protobuf.Internal.EnumLite;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.Iterator;
+import java.util.LinkedHashMap;
+import java.util.Map;
+import java.util.Set;
+
+/**
+ * Internal representation of map fields in generated lite-runtime messages.
+ * 
+ * This class is a protobuf implementation detail. Users shouldn't use this
+ * class directly.
+ */
+public final class MapFieldLite<K, V> implements MutabilityOracle {
+  private MutatabilityAwareMap<K, V> mapData;
+  private boolean isMutable;
+  
+  private MapFieldLite(Map<K, V> mapData) {
+    this.mapData = new MutatabilityAwareMap<K, V>(this, mapData);
+    this.isMutable = true;
+  }
+  
+  @SuppressWarnings({"rawtypes", "unchecked"})
+  private static final MapFieldLite EMPTY_MAP_FIELD =
+      new MapFieldLite(Collections.emptyMap());
+  static {
+    EMPTY_MAP_FIELD.makeImmutable();
+  }
+  
+  /** Returns an singleton immutable empty MapFieldLite instance. */
+  @SuppressWarnings({"unchecked", "cast"})
+  public static <K, V> MapFieldLite<K, V> emptyMapField() {
+    return (MapFieldLite<K, V>) EMPTY_MAP_FIELD;
+  }
+  
+  /** Creates a new MapFieldLite instance. */
+  public static <K, V> MapFieldLite<K, V> newMapField() {
+    return new MapFieldLite<K, V>(new LinkedHashMap<K, V>());
+  }
+  
+  /** Gets the content of this MapField as a read-only Map. */
+  public Map<K, V> getMap() {
+    return Collections.unmodifiableMap(mapData);
+  }
+  
+  /** Gets a mutable Map view of this MapField. */
+  public Map<K, V> getMutableMap() {
+    return mapData;
+  }
+  
+  public void mergeFrom(MapFieldLite<K, V> other) {
+    mapData.putAll(copy(other.mapData));
+  }
+  
+  public void clear() {
+    mapData.clear();
+  }
+  
+  private static boolean equals(Object a, Object b) {
+    if (a instanceof byte[] && b instanceof byte[]) {
+      return Arrays.equals((byte[]) a, (byte[]) b);
+    }
+    return a.equals(b);
+  }
+  
+  /**
+   * Checks whether two {@link Map}s are equal. We don't use the default equals
+   * method of {@link Map} because it compares by identity not by content for
+   * byte arrays.
+   */
+  static <K, V> boolean equals(Map<K, V> a, Map<K, V> b) {
+    if (a == b) {
+      return true;
+    }
+    if (a.size() != b.size()) {
+      return false;
+    }
+    for (Map.Entry<K, V> entry : a.entrySet()) {
+      if (!b.containsKey(entry.getKey())) {
+        return false;
+      }
+      if (!equals(entry.getValue(), b.get(entry.getKey()))) {
+        return false;
+      }
+    }
+    return true;
+  }
+  
+  /**
+   * Checks whether two map fields are equal.
+   */
+  @SuppressWarnings("unchecked")
+  @Override
+  public boolean equals(Object object) {
+    if (!(object instanceof MapFieldLite)) {
+      return false;
+    }
+    MapFieldLite<K, V> other = (MapFieldLite<K, V>) object;
+    return equals(mapData, other.mapData);
+  }
+  
+  private static int calculateHashCodeForObject(Object a) {
+    if (a instanceof byte[]) {
+      return LiteralByteString.hashCode((byte[]) a);
+    }
+    // Enums should be stored as integers internally.
+    if (a instanceof EnumLite) {
+      throw new UnsupportedOperationException();
+    }
+    return a.hashCode();
+  }
+
+  /**
+   * Calculates the hash code for a {@link Map}. We don't use the default hash
+   * code method of {@link Map} because for byte arrays and protobuf enums it
+   * use {@link Object#hashCode()}.
+   */
+  static <K, V> int calculateHashCodeForMap(Map<K, V> a) {
+    int result = 0;
+    for (Map.Entry<K, V> entry : a.entrySet()) {
+      result += calculateHashCodeForObject(entry.getKey())
+          ^ calculateHashCodeForObject(entry.getValue());
+    }
+    return result;    
+  }
+  
+  @Override
+  public int hashCode() {
+    return calculateHashCodeForMap(mapData);
+  }
+  
+  private static Object copy(Object object) {
+    if (object instanceof byte[]) {
+      byte[] data = (byte[]) object;
+      return Arrays.copyOf(data, data.length);
+    }
+    return object;
+  }
+  
+  /**
+   * Makes a deep copy of a {@link Map}. Immutable objects in the map will be
+   * shared (e.g., integers, strings, immutable messages) and mutable ones will
+   * have a copy (e.g., byte arrays, mutable messages).
+   */
+  @SuppressWarnings("unchecked")
+  static <K, V> Map<K, V> copy(Map<K, V> map) {
+    Map<K, V> result = new LinkedHashMap<K, V>();
+    for (Map.Entry<K, V> entry : map.entrySet()) {
+      result.put(entry.getKey(), (V) copy(entry.getValue()));
+    }
+    return result;
+  }
+  
+  /** Returns a deep copy of this map field. */
+  public MapFieldLite<K, V> copy() {
+    return new MapFieldLite<K, V>(copy(mapData));
+  }
+  
+  /**
+   * Makes this field immutable. All subsequent modifications will throw an
+   * {@link UnsupportedOperationException}.
+   */
+  public void makeImmutable() {
+    isMutable = false;
+  }
+  
+  /**
+   * Returns whether this field can be modified.
+   */
+  public boolean isMutable() {
+    return isMutable;
+  }
+  
+  @Override
+  public void ensureMutable() {
+    if (!isMutable()) {
+      throw new UnsupportedOperationException();
+    }
+  }
+
+  /**
+   * An internal map that checks for mutability before delegating.
+   */
+  static class MutatabilityAwareMap<K, V> implements Map<K, V> {    
+    private final MutabilityOracle mutabilityOracle;
+    private final Map<K, V> delegate;
+    
+    MutatabilityAwareMap(MutabilityOracle mutabilityOracle, Map<K, V> delegate) {
+      this.mutabilityOracle = mutabilityOracle;
+      this.delegate = delegate;
+    }
+
+    @Override
+    public int size() {
+      return delegate.size();
+    }
+
+    @Override
+    public boolean isEmpty() {
+      return delegate.isEmpty();
+    }
+
+    @Override
+    public boolean containsKey(Object key) {
+      return delegate.containsKey(key);
+    }
+
+    @Override
+    public boolean containsValue(Object value) {
+      return delegate.containsValue(value);
+    }
+
+    @Override
+    public V get(Object key) {
+      return delegate.get(key);
+    }
+
+    @Override
+    public V put(K key, V value) {
+      mutabilityOracle.ensureMutable();
+      return delegate.put(key, value);
+    }
+
+    @Override
+    public V remove(Object key) {
+      mutabilityOracle.ensureMutable();
+      return delegate.remove(key);
+    }
+
+    @Override
+    public void putAll(Map<? extends K, ? extends V> m) {
+      mutabilityOracle.ensureMutable();
+      delegate.putAll(m);
+    }
+
+    @Override
+    public void clear() {
+      mutabilityOracle.ensureMutable();
+      delegate.clear();
+    }
+
+    @Override
+    public Set<K> keySet() {
+      return new MutatabilityAwareSet<K>(mutabilityOracle, delegate.keySet());
+    }
+
+    @Override
+    public Collection<V> values() {
+      return new MutatabilityAwareCollection<V>(mutabilityOracle, delegate.values());
+    }
+
+    @Override
+    public Set<java.util.Map.Entry<K, V>> entrySet() {
+      return new MutatabilityAwareSet<Entry<K, V>>(mutabilityOracle, delegate.entrySet());
+    }
+
+    @Override
+    public boolean equals(Object o) {
+      return delegate.equals(o);
+    }
+
+    @Override
+    public int hashCode() {
+      return delegate.hashCode();
+    }
+
+    @Override
+    public String toString() {
+      return delegate.toString();
+    }
+  }
+
+  /**
+   * An internal collection that checks for mutability before delegating.
+   */
+  private static class MutatabilityAwareCollection<E> implements Collection<E> {
+    private final MutabilityOracle mutabilityOracle;
+    private final Collection<E> delegate;
+    
+    MutatabilityAwareCollection(MutabilityOracle mutabilityOracle, Collection<E> delegate) {
+      this.mutabilityOracle = mutabilityOracle;
+      this.delegate = delegate;
+    }
+
+    @Override
+    public int size() {
+      return delegate.size();
+    }
+
+    @Override
+    public boolean isEmpty() {
+      return delegate.isEmpty();
+    }
+
+    @Override
+    public boolean contains(Object o) {
+      return delegate.contains(o);
+    }
+
+    @Override
+    public Iterator<E> iterator() {
+      return new MutatabilityAwareIterator<E>(mutabilityOracle, delegate.iterator());
+    }
+
+    @Override
+    public Object[] toArray() {
+      return delegate.toArray();
+    }
+
+    @Override
+    public <T> T[] toArray(T[] a) {
+      return delegate.toArray(a);
+    }
+
+    @Override
+    public boolean add(E e) {
+      // Unsupported operation in the delegate.
+      throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public boolean remove(Object o) {
+      mutabilityOracle.ensureMutable();
+      return delegate.remove(o);
+    }
+
+    @Override
+    public boolean containsAll(Collection<?> c) {
+      return delegate.containsAll(c);
+    }
+
+    @Override
+    public boolean addAll(Collection<? extends E> c) {
+      // Unsupported operation in the delegate.
+      throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public boolean removeAll(Collection<?> c) {
+      mutabilityOracle.ensureMutable();
+      return delegate.removeAll(c);
+    }
+
+    @Override
+    public boolean retainAll(Collection<?> c) {
+      mutabilityOracle.ensureMutable();
+      return delegate.retainAll(c);
+    }
+
+    @Override
+    public void clear() {
+      mutabilityOracle.ensureMutable();
+      delegate.clear();
+    }
+
+    @Override
+    public boolean equals(Object o) {
+      return delegate.equals(o);
+    }
+
+    @Override
+    public int hashCode() {
+      return delegate.hashCode();
+    }
+    
+    @Override
+    public String toString() {
+      return delegate.toString();
+    }
+  }
+
+  /**
+   * An internal set that checks for mutability before delegating.
+   */
+  private static class MutatabilityAwareSet<E> implements Set<E> {
+    private final MutabilityOracle mutabilityOracle;
+    private final Set<E> delegate;
+    
+    MutatabilityAwareSet(MutabilityOracle mutabilityOracle, Set<E> delegate) {
+      this.mutabilityOracle = mutabilityOracle;
+      this.delegate = delegate;
+    }
+
+    @Override
+    public int size() {
+      return delegate.size();
+    }
+
+    @Override
+    public boolean isEmpty() {
+      return delegate.isEmpty();
+    }
+
+    @Override
+    public boolean contains(Object o) {
+      return delegate.contains(o);
+    }
+
+    @Override
+    public Iterator<E> iterator() {
+      return new MutatabilityAwareIterator<E>(mutabilityOracle, delegate.iterator());
+    }
+
+    @Override
+    public Object[] toArray() {
+      return delegate.toArray();
+    }
+
+    @Override
+    public <T> T[] toArray(T[] a) {
+      return delegate.toArray(a);
+    }
+
+    @Override
+    public boolean add(E e) {
+      mutabilityOracle.ensureMutable();
+      return delegate.add(e);
+    }
+
+    @Override
+    public boolean remove(Object o) {
+      mutabilityOracle.ensureMutable();
+      return delegate.remove(o);
+    }
+
+    @Override
+    public boolean containsAll(Collection<?> c) {
+      return delegate.containsAll(c);
+    }
+
+    @Override
+    public boolean addAll(Collection<? extends E> c) {
+      mutabilityOracle.ensureMutable();
+      return delegate.addAll(c);
+    }
+
+    @Override
+    public boolean retainAll(Collection<?> c) {
+      mutabilityOracle.ensureMutable();
+      return delegate.retainAll(c);
+    }
+
+    @Override
+    public boolean removeAll(Collection<?> c) {
+      mutabilityOracle.ensureMutable();
+      return delegate.removeAll(c);
+    }
+
+    @Override
+    public void clear() {
+      mutabilityOracle.ensureMutable();
+      delegate.clear();
+    }
+
+    @Override
+    public boolean equals(Object o) {
+      return delegate.equals(o);
+    }
+
+    @Override
+    public int hashCode() {
+      return delegate.hashCode();
+    }
+
+    @Override
+    public String toString() {
+      return delegate.toString();
+    }
+  }
+  
+  /**
+   * An internal iterator that checks for mutability before delegating.
+   */
+  private static class MutatabilityAwareIterator<E> implements Iterator<E> {
+    private final MutabilityOracle mutabilityOracle;
+    private final Iterator<E> delegate;
+    
+    MutatabilityAwareIterator(MutabilityOracle mutabilityOracle, Iterator<E> delegate) {
+      this.mutabilityOracle = mutabilityOracle;
+      this.delegate = delegate;
+    }
+
+    @Override
+    public boolean hasNext() {
+      return delegate.hasNext();
+    }
+
+    @Override
+    public E next() {
+      return delegate.next();
+    }
+
+    @Override
+    public void remove() {
+      mutabilityOracle.ensureMutable();
+      delegate.remove();
+    }
+    
+    @Override
+    public boolean equals(Object obj) {
+      return delegate.equals(obj);
+    }
+    
+    @Override
+    public int hashCode() {
+      return delegate.hashCode();
+    }
+
+    @Override
+    public String toString() {
+      return delegate.toString();
+    }
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/Message.java b/java/core/src/main/java/com/google/protobuf/Message.java
new file mode 100644
index 00000000..9516d71f
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/Message.java
@@ -0,0 +1,266 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// TODO(kenton):  Use generics?  E.g. Builder<BuilderType extends Builder>, then
+//   mergeFrom*() could return BuilderType for better type-safety.
+
+package com.google.protobuf;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.Map;
+
+/**
+ * Abstract interface implemented by Protocol Message objects.
+ * <p>
+ * See also {@link MessageLite}, which defines most of the methods that typical
+ * users care about.  {@link Message} adds to it methods that are not available
+ * in the "lite" runtime.  The biggest added features are introspection and
+ * reflection -- i.e., getting descriptors for the message type and accessing
+ * the field values dynamically.
+ *
+ * @author kenton@google.com Kenton Varda
+ */
+public interface Message extends MessageLite, MessageOrBuilder {
+
+  // (From MessageLite, re-declared here only for return type covariance.)
+  Parser<? extends Message> getParserForType();
+
+
+  // -----------------------------------------------------------------
+  // Comparison and hashing
+
+  /**
+   * Compares the specified object with this message for equality.  Returns
+   * {@code true} if the given object is a message of the same type (as
+   * defined by {@code getDescriptorForType()}) and has identical values for
+   * all of its fields.  Subclasses must implement this; inheriting
+   * {@code Object.equals()} is incorrect.
+   *
+   * @param other object to be compared for equality with this message
+   * @return {@code true} if the specified object is equal to this message
+   */
+  @Override
+  boolean equals(Object other);
+
+  /**
+   * Returns the hash code value for this message.  The hash code of a message
+   * should mix the message's type (object identity of the descriptor) with its
+   * contents (known and unknown field values).  Subclasses must implement this;
+   * inheriting {@code Object.hashCode()} is incorrect.
+   *
+   * @return the hash code value for this message
+   * @see Map#hashCode()
+   */
+  @Override
+  int hashCode();
+
+  // -----------------------------------------------------------------
+  // Convenience methods.
+
+  /**
+   * Converts the message to a string in protocol buffer text format. This is
+   * just a trivial wrapper around {@link
+   * TextFormat#printToString(MessageOrBuilder)}.
+   */
+  @Override
+  String toString();
+
+  // =================================================================
+  // Builders
+
+  // (From MessageLite, re-declared here only for return type covariance.)
+  Builder newBuilderForType();
+  Builder toBuilder();
+
+  /**
+   * Abstract interface implemented by Protocol Message builders.
+   */
+  interface Builder extends MessageLite.Builder, MessageOrBuilder {
+    // (From MessageLite.Builder, re-declared here only for return type
+    // covariance.)
+    Builder clear();
+
+    /**
+     * Merge {@code other} into the message being built.  {@code other} must
+     * have the exact same type as {@code this} (i.e.
+     * {@code getDescriptorForType() == other.getDescriptorForType()}).
+     *
+     * Merging occurs as follows.  For each field:<br>
+     * * For singular primitive fields, if the field is set in {@code other},
+     *   then {@code other}'s value overwrites the value in this message.<br>
+     * * For singular message fields, if the field is set in {@code other},
+     *   it is merged into the corresponding sub-message of this message
+     *   using the same merging rules.<br>
+     * * For repeated fields, the elements in {@code other} are concatenated
+     *   with the elements in this message.
+     * * For oneof groups, if the other message has one of the fields set,
+     *   the group of this message is cleared and replaced by the field
+     *   of the other message, so that the oneof constraint is preserved.
+     *
+     * This is equivalent to the {@code Message::MergeFrom} method in C++.
+     */
+    Builder mergeFrom(Message other);
+
+    // (From MessageLite.Builder, re-declared here only for return type
+    // covariance.)
+    Message build();
+    Message buildPartial();
+    Builder clone();
+    Builder mergeFrom(CodedInputStream input) throws IOException;
+    Builder mergeFrom(CodedInputStream input,
+                      ExtensionRegistryLite extensionRegistry)
+                      throws IOException;
+
+    /**
+     * Get the message's type's descriptor.
+     * See {@link Message#getDescriptorForType()}.
+     */
+    Descriptors.Descriptor getDescriptorForType();
+
+    /**
+     * Create a Builder for messages of the appropriate type for the given
+     * field.  Messages built with this can then be passed to setField(),
+     * setRepeatedField(), or addRepeatedField().
+     */
+    Builder newBuilderForField(Descriptors.FieldDescriptor field);
+
+    /**
+     * Get a nested builder instance for the given field.
+     * <p>
+     * Normally, we hold a reference to the immutable message object for the
+     * message type field. Some implementations(the generated message builders),
+     * however, can also hold a reference to the builder object (a nested
+     * builder) for the field.
+     * <p>
+     * If the field is already backed up by a nested builder, the nested builder
+     * will be returned. Otherwise, a new field builder will be created and
+     * returned. The original message field (if exist) will be merged into the
+     * field builder, which will then be nested into its parent builder.
+     * <p>
+     * NOTE: implementations that do not support nested builders will throw
+     * <code>UnsupportedOperationException</code>.
+     */
+    Builder getFieldBuilder(Descriptors.FieldDescriptor field);
+
+    /**
+     * Get a nested builder instance for the given repeated field instance.
+     * <p>
+     * Normally, we hold a reference to the immutable message object for the
+     * message type field. Some implementations(the generated message builders),
+     * however, can also hold a reference to the builder object (a nested
+     * builder) for the field.
+     * <p>
+     * If the field is already backed up by a nested builder, the nested builder
+     * will be returned. Otherwise, a new field builder will be created and
+     * returned. The original message field (if exist) will be merged into the
+     * field builder, which will then be nested into its parent builder.
+     * <p>
+     * NOTE: implementations that do not support nested builders will throw
+     * <code>UnsupportedOperationException</code>.
+     */
+    Builder getRepeatedFieldBuilder(Descriptors.FieldDescriptor field,
+                                    int index);
+
+    /**
+     * Sets a field to the given value.  The value must be of the correct type
+     * for this field, i.e. the same type that
+     * {@link Message#getField(Descriptors.FieldDescriptor)} would return.
+     */
+    Builder setField(Descriptors.FieldDescriptor field, Object value);
+
+    /**
+     * Clears the field.  This is exactly equivalent to calling the generated
+     * "clear" accessor method corresponding to the field.
+     */
+    Builder clearField(Descriptors.FieldDescriptor field);
+
+    /**
+     * Clears the oneof.  This is exactly equivalent to calling the generated
+     * "clear" accessor method corresponding to the oneof.
+     */
+    Builder clearOneof(Descriptors.OneofDescriptor oneof);
+
+    /**
+     * Sets an element of a repeated field to the given value.  The value must
+     * be of the correct type for this field, i.e. the same type that
+     * {@link Message#getRepeatedField(Descriptors.FieldDescriptor,int)} would
+     * return.
+     * @throws IllegalArgumentException The field is not a repeated field, or
+     *           {@code field.getContainingType() != getDescriptorForType()}.
+     */
+    Builder setRepeatedField(Descriptors.FieldDescriptor field,
+                             int index, Object value);
+
+    /**
+     * Like {@code setRepeatedField}, but appends the value as a new element.
+     * @throws IllegalArgumentException The field is not a repeated field, or
+     *           {@code field.getContainingType() != getDescriptorForType()}.
+     */
+    Builder addRepeatedField(Descriptors.FieldDescriptor field, Object value);
+
+    /** Set the {@link UnknownFieldSet} for this message. */
+    Builder setUnknownFields(UnknownFieldSet unknownFields);
+
+    /**
+     * Merge some unknown fields into the {@link UnknownFieldSet} for this
+     * message.
+     */
+    Builder mergeUnknownFields(UnknownFieldSet unknownFields);
+
+    // ---------------------------------------------------------------
+    // Convenience methods.
+
+    // (From MessageLite.Builder, re-declared here only for return type
+    // covariance.)
+    Builder mergeFrom(ByteString data) throws InvalidProtocolBufferException;
+    Builder mergeFrom(ByteString data,
+                      ExtensionRegistryLite extensionRegistry)
+                      throws InvalidProtocolBufferException;
+    Builder mergeFrom(byte[] data) throws InvalidProtocolBufferException;
+    Builder mergeFrom(byte[] data, int off, int len)
+                      throws InvalidProtocolBufferException;
+    Builder mergeFrom(byte[] data,
+                      ExtensionRegistryLite extensionRegistry)
+                      throws InvalidProtocolBufferException;
+    Builder mergeFrom(byte[] data, int off, int len,
+                      ExtensionRegistryLite extensionRegistry)
+                      throws InvalidProtocolBufferException;
+    Builder mergeFrom(InputStream input) throws IOException;
+    Builder mergeFrom(InputStream input,
+                      ExtensionRegistryLite extensionRegistry)
+                      throws IOException;
+    boolean mergeDelimitedFrom(InputStream input)
+                               throws IOException;
+    boolean mergeDelimitedFrom(InputStream input,
+                               ExtensionRegistryLite extensionRegistry)
+                               throws IOException;
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/MessageLite.java b/java/core/src/main/java/com/google/protobuf/MessageLite.java
new file mode 100644
index 00000000..798b7943
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/MessageLite.java
@@ -0,0 +1,320 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// TODO(kenton):  Use generics?  E.g. Builder<BuilderType extends Builder>, then
+//   mergeFrom*() could return BuilderType for better type-safety.
+
+package com.google.protobuf;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+
+/**
+ * Abstract interface implemented by Protocol Message objects.
+ *
+ * <p>This interface is implemented by all protocol message objects.  Non-lite
+ * messages additionally implement the Message interface, which is a subclass
+ * of MessageLite.  Use MessageLite instead when you only need the subset of
+ * features which it supports -- namely, nothing that uses descriptors or
+ * reflection.  You can instruct the protocol compiler to generate classes
+ * which implement only MessageLite, not the full Message interface, by adding
+ * the follow line to the .proto file:
+ * <pre>
+ *   option optimize_for = LITE_RUNTIME;
+ * </pre>
+ *
+ * <p>This is particularly useful on resource-constrained systems where the
+ * full protocol buffers runtime library is too big.
+ *
+ * <p>Note that on non-constrained systems (e.g. servers) when you need to link
+ * in lots of protocol definitions, a better way to reduce total code footprint
+ * is to use {@code optimize_for = CODE_SIZE}.  This will make the generated
+ * code smaller while still supporting all the same features (at the expense of
+ * speed).  {@code optimize_for = LITE_RUNTIME} is best when you only have a
+ * small number of message types linked into your binary, in which case the
+ * size of the protocol buffers runtime itself is the biggest problem.
+ *
+ * @author kenton@google.com Kenton Varda
+ */
+public interface MessageLite extends MessageLiteOrBuilder {
+
+
+  /**
+   * Serializes the message and writes it to {@code output}.  This does not
+   * flush or close the stream.
+   */
+  void writeTo(CodedOutputStream output) throws IOException;
+
+  /**
+   * Get the number of bytes required to encode this message.  The result
+   * is only computed on the first call and memoized after that.
+   */
+  int getSerializedSize();
+
+
+  /**
+   * Gets the parser for a message of the same type as this message.
+   */
+  Parser<? extends MessageLite> getParserForType();
+
+  // -----------------------------------------------------------------
+  // Convenience methods.
+
+  /**
+   * Serializes the message to a {@code ByteString} and returns it. This is
+   * just a trivial wrapper around
+   * {@link #writeTo(CodedOutputStream)}.
+   */
+  ByteString toByteString();
+
+  /**
+   * Serializes the message to a {@code byte} array and returns it.  This is
+   * just a trivial wrapper around
+   * {@link #writeTo(CodedOutputStream)}.
+   */
+  byte[] toByteArray();
+
+  /**
+   * Serializes the message and writes it to {@code output}.  This is just a
+   * trivial wrapper around {@link #writeTo(CodedOutputStream)}.  This does
+   * not flush or close the stream.
+   * <p>
+   * NOTE:  Protocol Buffers are not self-delimiting.  Therefore, if you write
+   * any more data to the stream after the message, you must somehow ensure
+   * that the parser on the receiving end does not interpret this as being
+   * part of the protocol message.  This can be done e.g. by writing the size
+   * of the message before the data, then making sure to limit the input to
+   * that size on the receiving end (e.g. by wrapping the InputStream in one
+   * which limits the input).  Alternatively, just use
+   * {@link #writeDelimitedTo(OutputStream)}.
+   */
+  void writeTo(OutputStream output) throws IOException;
+
+  /**
+   * Like {@link #writeTo(OutputStream)}, but writes the size of the message
+   * as a varint before writing the data.  This allows more data to be written
+   * to the stream after the message without the need to delimit the message
+   * data yourself.  Use {@link Builder#mergeDelimitedFrom(InputStream)} (or
+   * the static method {@code YourMessageType.parseDelimitedFrom(InputStream)})
+   * to parse messages written by this method.
+   */
+  void writeDelimitedTo(OutputStream output) throws IOException;
+
+
+  // =================================================================
+  // Builders
+
+  /**
+   * Constructs a new builder for a message of the same type as this message.
+   */
+  Builder newBuilderForType();
+
+  /**
+   * Constructs a builder initialized with the current message.  Use this to
+   * derive a new message from the current one.
+   */
+  Builder toBuilder();
+
+  /**
+   * Abstract interface implemented by Protocol Message builders.
+   */
+  interface Builder extends MessageLiteOrBuilder, Cloneable {
+    /** Resets all fields to their default values. */
+    Builder clear();
+
+    /**
+     * Constructs the message based on the state of the Builder. Subsequent
+     * changes to the Builder will not affect the returned message.
+     * @throws UninitializedMessageException The message is missing one or more
+     *         required fields (i.e. {@link #isInitialized()} returns false).
+     *         Use {@link #buildPartial()} to bypass this check.
+     */
+    MessageLite build();
+
+    /**
+     * Like {@link #build()}, but does not throw an exception if the message
+     * is missing required fields.  Instead, a partial message is returned.
+     * Subsequent changes to the Builder will not affect the returned message.
+     */
+    MessageLite buildPartial();
+
+    /**
+     * Clones the Builder.
+     * @see Object#clone()
+     */
+    Builder clone();
+
+    /**
+     * Parses a message of this type from the input and merges it with this
+     * message.
+     *
+     * <p>Warning:  This does not verify that all required fields are present in
+     * the input message.  If you call {@link #build()} without setting all
+     * required fields, it will throw an {@link UninitializedMessageException},
+     * which is a {@code RuntimeException} and thus might not be caught.  There
+     * are a few good ways to deal with this:
+     * <ul>
+     *   <li>Call {@link #isInitialized()} to verify that all required fields
+     *       are set before building.
+     *   <li>Use {@code buildPartial()} to build, which ignores missing
+     *       required fields.
+     * </ul>
+     *
+     * <p>Note:  The caller should call
+     * {@link CodedInputStream#checkLastTagWas(int)} after calling this to
+     * verify that the last tag seen was the appropriate end-group tag,
+     * or zero for EOF.
+     */
+    Builder mergeFrom(CodedInputStream input) throws IOException;
+
+    /**
+     * Like {@link Builder#mergeFrom(CodedInputStream)}, but also
+     * parses extensions.  The extensions that you want to be able to parse
+     * must be registered in {@code extensionRegistry}.  Extensions not in
+     * the registry will be treated as unknown fields.
+     */
+    Builder mergeFrom(CodedInputStream input,
+                      ExtensionRegistryLite extensionRegistry)
+                      throws IOException;
+
+    // ---------------------------------------------------------------
+    // Convenience methods.
+
+    /**
+     * Parse {@code data} as a message of this type and merge it with the
+     * message being built.  This is just a small wrapper around
+     * {@link #mergeFrom(CodedInputStream)}.
+     *
+     * @return this
+     */
+    Builder mergeFrom(ByteString data) throws InvalidProtocolBufferException;
+
+    /**
+     * Parse {@code data} as a message of this type and merge it with the
+     * message being built.  This is just a small wrapper around
+     * {@link #mergeFrom(CodedInputStream,ExtensionRegistryLite)}.
+     *
+     * @return this
+     */
+    Builder mergeFrom(ByteString data,
+                      ExtensionRegistryLite extensionRegistry)
+                      throws InvalidProtocolBufferException;
+
+    /**
+     * Parse {@code data} as a message of this type and merge it with the
+     * message being built.  This is just a small wrapper around
+     * {@link #mergeFrom(CodedInputStream)}.
+     *
+     * @return this
+     */
+    Builder mergeFrom(byte[] data) throws InvalidProtocolBufferException;
+
+    /**
+     * Parse {@code data} as a message of this type and merge it with the
+     * message being built.  This is just a small wrapper around
+     * {@link #mergeFrom(CodedInputStream)}.
+     *
+     * @return this
+     */
+    Builder mergeFrom(byte[] data, int off, int len)
+                      throws InvalidProtocolBufferException;
+
+    /**
+     * Parse {@code data} as a message of this type and merge it with the
+     * message being built.  This is just a small wrapper around
+     * {@link #mergeFrom(CodedInputStream,ExtensionRegistryLite)}.
+     *
+     * @return this
+     */
+    Builder mergeFrom(byte[] data,
+                      ExtensionRegistryLite extensionRegistry)
+                      throws InvalidProtocolBufferException;
+
+    /**
+     * Parse {@code data} as a message of this type and merge it with the
+     * message being built.  This is just a small wrapper around
+     * {@link #mergeFrom(CodedInputStream,ExtensionRegistryLite)}.
+     *
+     * @return this
+     */
+    Builder mergeFrom(byte[] data, int off, int len,
+                      ExtensionRegistryLite extensionRegistry)
+                      throws InvalidProtocolBufferException;
+
+    /**
+     * Parse a message of this type from {@code input} and merge it with the
+     * message being built.  This is just a small wrapper around
+     * {@link #mergeFrom(CodedInputStream)}.  Note that this method always
+     * reads the <i>entire</i> input (unless it throws an exception).  If you
+     * want it to stop earlier, you will need to wrap your input in some
+     * wrapper stream that limits reading.  Or, use
+     * {@link MessageLite#writeDelimitedTo(OutputStream)} to write your message
+     * and {@link #mergeDelimitedFrom(InputStream)} to read it.
+     * <p>
+     * Despite usually reading the entire input, this does not close the stream.
+     *
+     * @return this
+     */
+    Builder mergeFrom(InputStream input) throws IOException;
+
+    /**
+     * Parse a message of this type from {@code input} and merge it with the
+     * message being built.  This is just a small wrapper around
+     * {@link #mergeFrom(CodedInputStream,ExtensionRegistryLite)}.
+     *
+     * @return this
+     */
+    Builder mergeFrom(InputStream input,
+                      ExtensionRegistryLite extensionRegistry)
+                      throws IOException;
+
+    /**
+     * Like {@link #mergeFrom(InputStream)}, but does not read until EOF.
+     * Instead, the size of the message (encoded as a varint) is read first,
+     * then the message data.  Use
+     * {@link MessageLite#writeDelimitedTo(OutputStream)} to write messages in
+     * this format.
+     *
+     * @return True if successful, or false if the stream is at EOF when the
+     *         method starts.  Any other error (including reaching EOF during
+     *         parsing) will cause an exception to be thrown.
+     */
+    boolean mergeDelimitedFrom(InputStream input)
+                               throws IOException;
+
+    /**
+     * Like {@link #mergeDelimitedFrom(InputStream)} but supporting extensions.
+     */
+    boolean mergeDelimitedFrom(InputStream input,
+                               ExtensionRegistryLite extensionRegistry)
+                               throws IOException;
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/MessageLiteOrBuilder.java b/java/core/src/main/java/com/google/protobuf/MessageLiteOrBuilder.java
new file mode 100644
index 00000000..818386ce
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/MessageLiteOrBuilder.java
@@ -0,0 +1,60 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+/**
+ * Base interface for methods common to {@link MessageLite}
+ * and {@link MessageLite.Builder} to provide type equivalency.
+ *
+ * @author jonp@google.com (Jon Perlow)
+ */
+public interface MessageLiteOrBuilder {
+  /**
+   * Get an instance of the type with no fields set. Because no fields are set,
+   * all getters for singular fields will return default values and repeated
+   * fields will appear empty.
+   * This may or may not be a singleton.  This differs from the
+   * {@code getDefaultInstance()} method of generated message classes in that
+   * this method is an abstract method of the {@code MessageLite} interface
+   * whereas {@code getDefaultInstance()} is a static method of a specific
+   * class.  They return the same thing.
+   */
+  MessageLite getDefaultInstanceForType();
+
+  /**
+   * Returns true if all required fields in the message and all embedded
+   * messages are set, false otherwise.
+   *
+   * <p>See also: {@link MessageOrBuilder#getInitializationErrorString()}
+   */
+  boolean isInitialized();
+
+}
diff --git a/java/core/src/main/java/com/google/protobuf/MessageLiteToString.java b/java/core/src/main/java/com/google/protobuf/MessageLiteToString.java
new file mode 100644
index 00000000..e69de29b
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/MessageLiteToString.java
diff --git a/java/core/src/main/java/com/google/protobuf/MessageOrBuilder.java b/java/core/src/main/java/com/google/protobuf/MessageOrBuilder.java
new file mode 100644
index 00000000..f0fc4859
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/MessageOrBuilder.java
@@ -0,0 +1,143 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import java.util.List;
+import java.util.Map;
+
+/**
+ * Base interface for methods common to {@link Message} and
+ * {@link Message.Builder} to provide type equivalency.
+ *
+ * @author jonp@google.com (Jon Perlow)
+ */
+public interface MessageOrBuilder extends MessageLiteOrBuilder {
+
+  // (From MessageLite, re-declared here only for return type covariance.)
+  //@Override (Java 1.6 override semantics, but we must support 1.5)
+  Message getDefaultInstanceForType();
+
+  /**
+   * Returns a list of field paths (e.g. "foo.bar.baz") of required fields
+   * which are not set in this message.  You should call
+   * {@link MessageLiteOrBuilder#isInitialized()} first to check if there
+   * are any missing fields, as that method is likely to be much faster
+   * than this one even when the message is fully-initialized.
+   */
+  List<String> findInitializationErrors();
+
+  /**
+   * Returns a comma-delimited list of required fields which are not set
+   * in this message object.  You should call
+   * {@link MessageLiteOrBuilder#isInitialized()} first to check if there
+   * are any missing fields, as that method is likely to be much faster
+   * than this one even when the message is fully-initialized.
+   */
+  String getInitializationErrorString();
+
+  /**
+   * Get the message's type's descriptor.  This differs from the
+   * {@code getDescriptor()} method of generated message classes in that
+   * this method is an abstract method of the {@code Message} interface
+   * whereas {@code getDescriptor()} is a static method of a specific class.
+   * They return the same thing.
+   */
+  Descriptors.Descriptor getDescriptorForType();
+
+  /**
+   * Returns a collection of all the fields in this message which are set
+   * and their corresponding values.  A singular ("required" or "optional")
+   * field is set iff hasField() returns true for that field.  A "repeated"
+   * field is set iff getRepeatedFieldCount() is greater than zero.  The
+   * values are exactly what would be returned by calling
+   * {@link #getField(Descriptors.FieldDescriptor)} for each field.  The map
+   * is guaranteed to be a sorted map, so iterating over it will return fields
+   * in order by field number.
+   * <br>
+   * If this is for a builder, the returned map may or may not reflect future
+   * changes to the builder.  Either way, the returned map is itself
+   * unmodifiable.
+   */
+  Map<Descriptors.FieldDescriptor, Object> getAllFields();
+
+  /**
+   * Returns true if the given oneof is set.
+   * @throws IllegalArgumentException if
+   *           {@code oneof.getContainingType() != getDescriptorForType()}.
+   */
+  boolean hasOneof(Descriptors.OneofDescriptor oneof);
+
+  /**
+   * Obtains the FieldDescriptor if the given oneof is set. Returns null
+   * if no field is set.
+   */
+  Descriptors.FieldDescriptor getOneofFieldDescriptor(
+      Descriptors.OneofDescriptor oneof);
+
+  /**
+   * Returns true if the given field is set.  This is exactly equivalent to
+   * calling the generated "has" accessor method corresponding to the field.
+   * @throws IllegalArgumentException The field is a repeated field, or
+   *           {@code field.getContainingType() != getDescriptorForType()}.
+   */
+  boolean hasField(Descriptors.FieldDescriptor field);
+
+  /**
+   * Obtains the value of the given field, or the default value if it is
+   * not set.  For primitive fields, the boxed primitive value is returned.
+   * For enum fields, the EnumValueDescriptor for the value is returned. For
+   * embedded message fields, the sub-message is returned.  For repeated
+   * fields, a java.util.List is returned.
+   */
+  Object getField(Descriptors.FieldDescriptor field);
+
+  /**
+   * Gets the number of elements of a repeated field.  This is exactly
+   * equivalent to calling the generated "Count" accessor method corresponding
+   * to the field.
+   * @throws IllegalArgumentException The field is not a repeated field, or
+   *           {@code field.getContainingType() != getDescriptorForType()}.
+   */
+  int getRepeatedFieldCount(Descriptors.FieldDescriptor field);
+
+  /**
+   * Gets an element of a repeated field.  For primitive fields, the boxed
+   * primitive value is returned.  For enum fields, the EnumValueDescriptor
+   * for the value is returned. For embedded message fields, the sub-message
+   * is returned.
+   * @throws IllegalArgumentException The field is not a repeated field, or
+   *           {@code field.getContainingType() != getDescriptorForType()}.
+   */
+  Object getRepeatedField(Descriptors.FieldDescriptor field, int index);
+
+  /** Get the {@link UnknownFieldSet} for this message. */
+  UnknownFieldSet getUnknownFields();
+}
diff --git a/java/core/src/main/java/com/google/protobuf/MessageReflection.java b/java/core/src/main/java/com/google/protobuf/MessageReflection.java
new file mode 100644
index 00000000..de4bfd3e
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/MessageReflection.java
@@ -0,0 +1,952 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import com.google.protobuf.Descriptors.FieldDescriptor;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.TreeMap;
+
+/**
+ * Reflection utility methods shared by both mutable and immutable messages.
+ *
+ * @author liujisi@google.com (Pherl Liu)
+ */
+class MessageReflection {
+
+  static void writeMessageTo(
+      Message message,
+      Map<FieldDescriptor, Object> fields,
+      CodedOutputStream output,
+      boolean alwaysWriteRequiredFields)
+      throws IOException {
+    final boolean isMessageSet =
+        message.getDescriptorForType().getOptions().getMessageSetWireFormat();
+    if (alwaysWriteRequiredFields) {
+      fields = new TreeMap<FieldDescriptor, Object>(fields);
+      for (final FieldDescriptor field :
+          message.getDescriptorForType().getFields()) {
+        if (field.isRequired() && !fields.containsKey(field)) {
+          fields.put(field, message.getField(field));
+        }
+      }
+    }
+    for (final Map.Entry<Descriptors.FieldDescriptor, Object> entry :
+        fields.entrySet()) {
+      final Descriptors.FieldDescriptor field = entry.getKey();
+      final Object value = entry.getValue();
+      if (isMessageSet && field.isExtension() &&
+          field.getType() == Descriptors.FieldDescriptor.Type.MESSAGE &&
+          !field.isRepeated()) {
+        output.writeMessageSetExtension(field.getNumber(), (Message) value);
+      } else {
+        FieldSet.writeField(field, value, output);
+      }
+    }
+
+    final UnknownFieldSet unknownFields = message.getUnknownFields();
+    if (isMessageSet) {
+      unknownFields.writeAsMessageSetTo(output);
+    } else {
+      unknownFields.writeTo(output);
+    }
+  }
+
+  static int getSerializedSize(
+      Message message,
+      Map<FieldDescriptor, Object> fields) {
+    int size = 0;
+    final boolean isMessageSet =
+        message.getDescriptorForType().getOptions().getMessageSetWireFormat();
+
+    for (final Map.Entry<Descriptors.FieldDescriptor, Object> entry :
+        fields.entrySet()) {
+      final Descriptors.FieldDescriptor field = entry.getKey();
+      final Object value = entry.getValue();
+      if (isMessageSet && field.isExtension() &&
+          field.getType() == Descriptors.FieldDescriptor.Type.MESSAGE &&
+          !field.isRepeated()) {
+        size += CodedOutputStream.computeMessageSetExtensionSize(
+            field.getNumber(), (Message) value);
+      } else {
+        size += FieldSet.computeFieldSize(field, value);
+      }
+    }
+
+    final UnknownFieldSet unknownFields = message.getUnknownFields();
+    if (isMessageSet) {
+      size += unknownFields.getSerializedSizeAsMessageSet();
+    } else {
+      size += unknownFields.getSerializedSize();
+    }
+    return size;
+  }
+
+  static String delimitWithCommas(List<String> parts) {
+    StringBuilder result = new StringBuilder();
+    for (String part : parts) {
+      if (result.length() > 0) {
+        result.append(", ");
+      }
+      result.append(part);
+    }
+    return result.toString();
+  }
+
+  @SuppressWarnings("unchecked")
+  static boolean isInitialized(MessageOrBuilder message) {
+    // Check that all required fields are present.
+    for (final Descriptors.FieldDescriptor field : message
+        .getDescriptorForType()
+        .getFields()) {
+      if (field.isRequired()) {
+        if (!message.hasField(field)) {
+          return false;
+        }
+      }
+    }
+
+    // Check that embedded messages are initialized.
+    for (final Map.Entry<Descriptors.FieldDescriptor, Object> entry :
+        message.getAllFields().entrySet()) {
+      final Descriptors.FieldDescriptor field = entry.getKey();
+      if (field.getJavaType() == Descriptors.FieldDescriptor.JavaType.MESSAGE) {
+        if (field.isRepeated()) {
+          for (final Message element
+              : (List<Message>) entry.getValue()) {
+            if (!element.isInitialized()) {
+              return false;
+            }
+          }
+        } else {
+          if (!((Message) entry.getValue()).isInitialized()) {
+            return false;
+          }
+        }
+      }
+    }
+
+    return true;
+  }
+
+  private static String subMessagePrefix(final String prefix,
+      final Descriptors.FieldDescriptor field,
+      final int index) {
+    final StringBuilder result = new StringBuilder(prefix);
+    if (field.isExtension()) {
+      result.append('(')
+          .append(field.getFullName())
+          .append(')');
+    } else {
+      result.append(field.getName());
+    }
+    if (index != -1) {
+      result.append('[')
+          .append(index)
+          .append(']');
+    }
+    result.append('.');
+    return result.toString();
+  }
+
+  private static void findMissingFields(final MessageOrBuilder message,
+      final String prefix,
+      final List<String> results) {
+    for (final Descriptors.FieldDescriptor field :
+        message.getDescriptorForType().getFields()) {
+      if (field.isRequired() && !message.hasField(field)) {
+        results.add(prefix + field.getName());
+      }
+    }
+
+    for (final Map.Entry<Descriptors.FieldDescriptor, Object> entry :
+        message.getAllFields().entrySet()) {
+      final Descriptors.FieldDescriptor field = entry.getKey();
+      final Object value = entry.getValue();
+
+      if (field.getJavaType() == Descriptors.FieldDescriptor.JavaType.MESSAGE) {
+        if (field.isRepeated()) {
+          int i = 0;
+          for (final Object element : (List) value) {
+            findMissingFields((MessageOrBuilder) element,
+                subMessagePrefix(prefix, field, i++),
+                results);
+          }
+        } else {
+          if (message.hasField(field)) {
+            findMissingFields((MessageOrBuilder) value,
+                subMessagePrefix(prefix, field, -1),
+                results);
+          }
+        }
+      }
+    }
+  }
+
+  /**
+   * Populates {@code this.missingFields} with the full "path" of each missing
+   * required field in the given message.
+   */
+  static List<String> findMissingFields(
+      final MessageOrBuilder message) {
+    final List<String> results = new ArrayList<String>();
+    findMissingFields(message, "", results);
+    return results;
+  }
+
+  static interface MergeTarget {
+    enum ContainerType {
+      MESSAGE, EXTENSION_SET
+    }
+
+    /**
+     * Returns the descriptor for the target.
+     */
+    public Descriptors.Descriptor getDescriptorForType();
+
+    public ContainerType getContainerType();
+
+    public ExtensionRegistry.ExtensionInfo findExtensionByName(
+        ExtensionRegistry registry, String name);
+
+    public ExtensionRegistry.ExtensionInfo findExtensionByNumber(
+        ExtensionRegistry registry, Descriptors.Descriptor containingType,
+        int fieldNumber);
+
+    /**
+     * Obtains the value of the given field, or the default value if it is not
+     * set.  For primitive fields, the boxed primitive value is returned. For
+     * enum fields, the EnumValueDescriptor for the value is returned. For
+     * embedded message fields, the sub-message is returned.  For repeated
+     * fields, a java.util.List is returned.
+     */
+    public Object getField(Descriptors.FieldDescriptor field);
+
+    /**
+     * Returns true if the given field is set.  This is exactly equivalent to
+     * calling the generated "has" accessor method corresponding to the field.
+     *
+     * @throws IllegalArgumentException The field is a repeated field, or {@code
+     *     field.getContainingType() != getDescriptorForType()}.
+     */
+    boolean hasField(Descriptors.FieldDescriptor field);
+
+    /**
+     * Sets a field to the given value.  The value must be of the correct type
+     * for this field, i.e. the same type that
+     * {@link Message#getField(Descriptors.FieldDescriptor)}
+     * would return.
+     */
+    MergeTarget setField(Descriptors.FieldDescriptor field, Object value);
+
+    /**
+     * Clears the field.  This is exactly equivalent to calling the generated
+     * "clear" accessor method corresponding to the field.
+     */
+    MergeTarget clearField(Descriptors.FieldDescriptor field);
+
+    /**
+     * Sets an element of a repeated field to the given value.  The value must
+     * be of the correct type for this field, i.e. the same type that {@link
+     * Message#getRepeatedField(Descriptors.FieldDescriptor, int)} would return.
+     *
+     * @throws IllegalArgumentException The field is not a repeated field, or
+     *                                  {@code field.getContainingType() !=
+     *                                  getDescriptorForType()}.
+     */
+    MergeTarget setRepeatedField(Descriptors.FieldDescriptor field,
+        int index, Object value);
+
+    /**
+     * Like {@code setRepeatedField}, but appends the value as a new element.
+     *
+     * @throws IllegalArgumentException The field is not a repeated field, or
+     *                                  {@code field.getContainingType() !=
+     *                                  getDescriptorForType()}.
+     */
+    MergeTarget addRepeatedField(Descriptors.FieldDescriptor field,
+        Object value);
+
+    /**
+     * Returns true if the given oneof is set.
+     *
+     * @throws IllegalArgumentException if
+     *           {@code oneof.getContainingType() != getDescriptorForType()}.
+     */
+    boolean hasOneof(Descriptors.OneofDescriptor oneof);
+
+    /**
+     * Clears the oneof.  This is exactly equivalent to calling the generated
+     * "clear" accessor method corresponding to the oneof.
+     */
+    MergeTarget clearOneof(Descriptors.OneofDescriptor oneof);
+
+    /**
+     * Obtains the FieldDescriptor if the given oneof is set. Returns null
+     * if no field is set.
+     */
+    Descriptors.FieldDescriptor getOneofFieldDescriptor(Descriptors.OneofDescriptor oneof);
+
+    /**
+     * Parse the input stream into a sub field group defined based on either
+     * FieldDescriptor or the default instance.
+     */
+    Object parseGroup(CodedInputStream input, ExtensionRegistryLite registry,
+        Descriptors.FieldDescriptor descriptor, Message defaultInstance)
+        throws IOException;
+
+    /**
+     * Parse the input stream into a sub field message defined based on either
+     * FieldDescriptor or the default instance.
+     */
+    Object parseMessage(CodedInputStream input, ExtensionRegistryLite registry,
+        Descriptors.FieldDescriptor descriptor, Message defaultInstance)
+        throws IOException;
+
+    /**
+     * Parse from a ByteString into a sub field message defined based on either
+     * FieldDescriptor or the default instance.  There isn't a varint indicating
+     * the length of the message at the beginning of the input ByteString.
+     */
+    Object parseMessageFromBytes(
+        ByteString bytes, ExtensionRegistryLite registry,
+        Descriptors.FieldDescriptor descriptor, Message defaultInstance)
+        throws IOException;
+
+    /**
+     * Returns the UTF8 validation level for the field.
+     */
+    WireFormat.Utf8Validation getUtf8Validation(Descriptors.FieldDescriptor
+        descriptor);
+
+    /**
+     * Returns a new merge target for a sub-field. When defaultInstance is
+     * provided, it indicates the descriptor is for an extension type, and
+     * implementations should create a new instance from the defaultInstance
+     * prototype directly.
+     */
+    MergeTarget newMergeTargetForField(
+        Descriptors.FieldDescriptor descriptor,
+        Message defaultInstance);
+
+    /**
+     * Finishes the merge and returns the underlying object.
+     */
+    Object finish();
+  }
+
+  static class BuilderAdapter implements MergeTarget {
+
+    private final Message.Builder builder;
+
+    public Descriptors.Descriptor getDescriptorForType() {
+      return builder.getDescriptorForType();
+    }
+
+    public BuilderAdapter(Message.Builder builder) {
+      this.builder = builder;
+    }
+
+    public Object getField(Descriptors.FieldDescriptor field) {
+      return builder.getField(field);
+    }
+
+    @Override
+    public boolean hasField(Descriptors.FieldDescriptor field) {
+      return builder.hasField(field);
+    }
+
+    public MergeTarget setField(Descriptors.FieldDescriptor field,
+        Object value) {
+      builder.setField(field, value);
+      return this;
+    }
+
+    public MergeTarget clearField(Descriptors.FieldDescriptor field) {
+      builder.clearField(field);
+      return this;
+    }
+
+    public MergeTarget setRepeatedField(
+        Descriptors.FieldDescriptor field, int index, Object value) {
+      builder.setRepeatedField(field, index, value);
+      return this;
+    }
+
+    public MergeTarget addRepeatedField(
+        Descriptors.FieldDescriptor field, Object value) {
+      builder.addRepeatedField(field, value);
+      return this;
+    }
+
+    @Override
+    public boolean hasOneof(Descriptors.OneofDescriptor oneof) {
+      return builder.hasOneof(oneof);
+    }
+
+    @Override
+    public MergeTarget clearOneof(Descriptors.OneofDescriptor oneof) {
+      builder.clearOneof(oneof);
+      return this;
+    }
+
+    @Override
+    public Descriptors.FieldDescriptor getOneofFieldDescriptor(Descriptors.OneofDescriptor oneof) {
+      return builder.getOneofFieldDescriptor(oneof);
+    }
+
+    public ContainerType getContainerType() {
+      return ContainerType.MESSAGE;
+    }
+
+    public ExtensionRegistry.ExtensionInfo findExtensionByName(
+        ExtensionRegistry registry, String name) {
+      return registry.findImmutableExtensionByName(name);
+    }
+
+    public ExtensionRegistry.ExtensionInfo findExtensionByNumber(
+        ExtensionRegistry registry, Descriptors.Descriptor containingType,
+        int fieldNumber) {
+      return registry.findImmutableExtensionByNumber(containingType,
+          fieldNumber);
+    }
+
+    public Object parseGroup(CodedInputStream input,
+        ExtensionRegistryLite extensionRegistry,
+        Descriptors.FieldDescriptor field, Message defaultInstance)
+        throws IOException {
+      Message.Builder subBuilder;
+      // When default instance is not null. The field is an extension field.
+      if (defaultInstance != null) {
+        subBuilder = defaultInstance.newBuilderForType();
+      } else {
+        subBuilder = builder.newBuilderForField(field);
+      }
+      if (!field.isRepeated()) {
+        Message originalMessage = (Message) getField(field);
+        if (originalMessage != null) {
+          subBuilder.mergeFrom(originalMessage);
+        }
+      }
+      input.readGroup(field.getNumber(), subBuilder, extensionRegistry);
+      return subBuilder.buildPartial();
+    }
+
+    public Object parseMessage(CodedInputStream input,
+        ExtensionRegistryLite extensionRegistry,
+        Descriptors.FieldDescriptor field, Message defaultInstance)
+        throws IOException {
+      Message.Builder subBuilder;
+      // When default instance is not null. The field is an extension field.
+      if (defaultInstance != null) {
+        subBuilder = defaultInstance.newBuilderForType();
+      } else {
+        subBuilder = builder.newBuilderForField(field);
+      }
+      if (!field.isRepeated()) {
+        Message originalMessage = (Message) getField(field);
+        if (originalMessage != null) {
+          subBuilder.mergeFrom(originalMessage);
+        }
+      }
+      input.readMessage(subBuilder, extensionRegistry);
+      return subBuilder.buildPartial();
+    }
+
+    public Object parseMessageFromBytes(ByteString bytes,
+        ExtensionRegistryLite extensionRegistry,
+        Descriptors.FieldDescriptor field, Message defaultInstance)
+        throws IOException {
+      Message.Builder subBuilder;
+      // When default instance is not null. The field is an extension field.
+      if (defaultInstance != null) {
+        subBuilder = defaultInstance.newBuilderForType();
+      } else {
+        subBuilder = builder.newBuilderForField(field);
+      }
+      if (!field.isRepeated()) {
+        Message originalMessage = (Message) getField(field);
+        if (originalMessage != null) {
+          subBuilder.mergeFrom(originalMessage);
+        }
+      }
+      subBuilder.mergeFrom(bytes, extensionRegistry);
+      return subBuilder.buildPartial();
+    }
+
+    public MergeTarget newMergeTargetForField(Descriptors.FieldDescriptor field,
+        Message defaultInstance) {
+      if (defaultInstance != null) {
+        return new BuilderAdapter(
+            defaultInstance.newBuilderForType());
+      } else {
+        return new BuilderAdapter(builder.newBuilderForField(field));
+      }
+    }
+
+    public WireFormat.Utf8Validation
+        getUtf8Validation(Descriptors.FieldDescriptor descriptor) {
+      if (descriptor.needsUtf8Check()) {
+        return WireFormat.Utf8Validation.STRICT;
+      }
+      // TODO(liujisi): support lazy strings for repeated fields.
+      if (!descriptor.isRepeated()
+          && builder instanceof GeneratedMessage.Builder) {
+        return WireFormat.Utf8Validation.LAZY;
+      }
+      return WireFormat.Utf8Validation.LOOSE;
+    }
+
+    public Object finish() {
+      return builder.buildPartial();
+    }
+  }
+
+
+  static class ExtensionAdapter implements MergeTarget {
+
+    private final FieldSet<Descriptors.FieldDescriptor> extensions;
+
+    ExtensionAdapter(FieldSet<Descriptors.FieldDescriptor> extensions) {
+      this.extensions = extensions;
+    }
+
+    public Descriptors.Descriptor getDescriptorForType() {
+      throw new UnsupportedOperationException(
+          "getDescriptorForType() called on FieldSet object");
+    }
+
+    public Object getField(Descriptors.FieldDescriptor field) {
+      return extensions.getField(field);
+    }
+
+    public boolean hasField(Descriptors.FieldDescriptor field) {
+      return extensions.hasField(field);
+    }
+
+    public MergeTarget setField(Descriptors.FieldDescriptor field,
+        Object value) {
+      extensions.setField(field, value);
+      return this;
+    }
+
+    public MergeTarget clearField(Descriptors.FieldDescriptor field) {
+      extensions.clearField(field);
+      return this;
+    }
+
+    public MergeTarget setRepeatedField(
+        Descriptors.FieldDescriptor field, int index, Object value) {
+      extensions.setRepeatedField(field, index, value);
+      return this;
+    }
+
+    public MergeTarget addRepeatedField(
+        Descriptors.FieldDescriptor field, Object value) {
+      extensions.addRepeatedField(field, value);
+      return this;
+    }
+
+    @Override
+    public boolean hasOneof(Descriptors.OneofDescriptor oneof) {
+      return false;
+    }
+
+    @Override
+    public MergeTarget clearOneof(Descriptors.OneofDescriptor oneof) {
+      // Nothing to clear.
+      return this;
+    }
+
+    @Override
+    public Descriptors.FieldDescriptor getOneofFieldDescriptor(Descriptors.OneofDescriptor oneof) {
+      return null;
+    }
+
+    public ContainerType getContainerType() {
+      return ContainerType.EXTENSION_SET;
+    }
+
+    public ExtensionRegistry.ExtensionInfo findExtensionByName(
+        ExtensionRegistry registry, String name) {
+      return registry.findImmutableExtensionByName(name);
+    }
+
+    public ExtensionRegistry.ExtensionInfo findExtensionByNumber(
+        ExtensionRegistry registry, Descriptors.Descriptor containingType,
+        int fieldNumber) {
+      return registry.findImmutableExtensionByNumber(containingType,
+          fieldNumber);
+    }
+
+    public Object parseGroup(CodedInputStream input,
+        ExtensionRegistryLite registry, Descriptors.FieldDescriptor field,
+        Message defaultInstance) throws IOException {
+      Message.Builder subBuilder =
+          defaultInstance.newBuilderForType();
+      if (!field.isRepeated()) {
+        Message originalMessage = (Message) getField(field);
+        if (originalMessage != null) {
+          subBuilder.mergeFrom(originalMessage);
+        }
+      }
+      input.readGroup(field.getNumber(), subBuilder, registry);
+      return subBuilder.buildPartial();
+    }
+
+    public Object parseMessage(CodedInputStream input,
+        ExtensionRegistryLite registry, Descriptors.FieldDescriptor field,
+        Message defaultInstance) throws IOException {
+      Message.Builder subBuilder =
+          defaultInstance.newBuilderForType();
+      if (!field.isRepeated()) {
+        Message originalMessage = (Message) getField(field);
+        if (originalMessage != null) {
+          subBuilder.mergeFrom(originalMessage);
+        }
+      }
+      input.readMessage(subBuilder, registry);
+      return subBuilder.buildPartial();
+    }
+
+    public Object parseMessageFromBytes(ByteString bytes,
+        ExtensionRegistryLite registry, Descriptors.FieldDescriptor field,
+        Message defaultInstance) throws IOException {
+      Message.Builder subBuilder =  defaultInstance.newBuilderForType();
+      if (!field.isRepeated()) {
+        Message originalMessage = (Message) getField(field);
+        if (originalMessage != null) {
+          subBuilder.mergeFrom(originalMessage);
+        }
+      }
+      subBuilder.mergeFrom(bytes, registry);
+      return subBuilder.buildPartial();
+    }
+
+    public MergeTarget newMergeTargetForField(
+        Descriptors.FieldDescriptor descriptor, Message defaultInstance) {
+      throw new UnsupportedOperationException(
+          "newMergeTargetForField() called on FieldSet object");
+    }
+
+    public WireFormat.Utf8Validation
+        getUtf8Validation(Descriptors.FieldDescriptor descriptor) {
+      if (descriptor.needsUtf8Check()) {
+        return WireFormat.Utf8Validation.STRICT;
+      }
+      // TODO(liujisi): support lazy strings for ExtesnsionSet.
+      return WireFormat.Utf8Validation.LOOSE;
+    }
+
+    public Object finish() {
+      throw new UnsupportedOperationException(
+          "finish() called on FieldSet object");
+    }
+  }
+
+  /**
+   * Parses a single field into MergeTarget. The target can be Message.Builder,
+   * FieldSet or MutableMessage.
+   *
+   * Package-private because it is used by GeneratedMessage.ExtendableMessage.
+   *
+   * @param tag The tag, which should have already been read.
+   * @return {@code true} unless the tag is an end-group tag.
+   */
+  static boolean mergeFieldFrom(
+      CodedInputStream input,
+      UnknownFieldSet.Builder unknownFields,
+      ExtensionRegistryLite extensionRegistry,
+      Descriptors.Descriptor type,
+      MergeTarget target,
+      int tag) throws IOException {
+    if (type.getOptions().getMessageSetWireFormat() &&
+        tag == WireFormat.MESSAGE_SET_ITEM_TAG) {
+      mergeMessageSetExtensionFromCodedStream(
+          input, unknownFields, extensionRegistry, type, target);
+      return true;
+    }
+
+    final int wireType = WireFormat.getTagWireType(tag);
+    final int fieldNumber = WireFormat.getTagFieldNumber(tag);
+
+    final Descriptors.FieldDescriptor field;
+    Message defaultInstance = null;
+
+    if (type.isExtensionNumber(fieldNumber)) {
+      // extensionRegistry may be either ExtensionRegistry or
+      // ExtensionRegistryLite.  Since the type we are parsing is a full
+      // message, only a full ExtensionRegistry could possibly contain
+      // extensions of it.  Otherwise we will treat the registry as if it
+      // were empty.
+      if (extensionRegistry instanceof ExtensionRegistry) {
+        final ExtensionRegistry.ExtensionInfo extension =
+            target.findExtensionByNumber((ExtensionRegistry) extensionRegistry,
+                type, fieldNumber);
+        if (extension == null) {
+          field = null;
+        } else {
+          field = extension.descriptor;
+          defaultInstance = extension.defaultInstance;
+          if (defaultInstance == null &&
+              field.getJavaType()
+                  == Descriptors.FieldDescriptor.JavaType.MESSAGE) {
+            throw new IllegalStateException(
+                "Message-typed extension lacked default instance: " +
+                    field.getFullName());
+          }
+        }
+      } else {
+        field = null;
+      }
+    } else if (target.getContainerType() == MergeTarget.ContainerType.MESSAGE) {
+      field = type.findFieldByNumber(fieldNumber);
+    } else {
+      field = null;
+    }
+
+    boolean unknown = false;
+    boolean packed = false;
+    if (field == null) {
+      unknown = true;  // Unknown field.
+    } else if (wireType == FieldSet.getWireFormatForFieldType(
+        field.getLiteType(),
+        false  /* isPacked */)) {
+      packed = false;
+    } else if (field.isPackable() &&
+        wireType == FieldSet.getWireFormatForFieldType(
+            field.getLiteType(),
+            true  /* isPacked */)) {
+      packed = true;
+    } else {
+      unknown = true;  // Unknown wire type.
+    }
+
+    if (unknown) {  // Unknown field or wrong wire type.  Skip.
+      return unknownFields.mergeFieldFrom(tag, input);
+    }
+
+    if (packed) {
+      final int length = input.readRawVarint32();
+      final int limit = input.pushLimit(length);
+      if (field.getLiteType() == WireFormat.FieldType.ENUM) {
+        while (input.getBytesUntilLimit() > 0) {
+          final int rawValue = input.readEnum();
+          if (field.getFile().supportsUnknownEnumValue()) {
+            target.addRepeatedField(field,
+                field.getEnumType().findValueByNumberCreatingIfUnknown(rawValue));
+          } else {
+            final Object value = field.getEnumType().findValueByNumber(rawValue);
+            if (value == null) {
+              // If the number isn't recognized as a valid value for this
+              // enum, drop it (don't even add it to unknownFields).
+              return true;
+            }
+            target.addRepeatedField(field, value);
+          }
+        }
+      } else {
+        while (input.getBytesUntilLimit() > 0) {
+          final Object value = WireFormat.readPrimitiveField(
+              input, field.getLiteType(), target.getUtf8Validation(field));
+          target.addRepeatedField(field, value);
+        }
+      }
+      input.popLimit(limit);
+    } else {
+      final Object value;
+      switch (field.getType()) {
+        case GROUP: {
+          value = target
+              .parseGroup(input, extensionRegistry, field, defaultInstance);
+          break;
+        }
+        case MESSAGE: {
+          value = target
+              .parseMessage(input, extensionRegistry, field, defaultInstance);
+          break;
+        }
+        case ENUM:
+          final int rawValue = input.readEnum();
+          if (field.getFile().supportsUnknownEnumValue()) {
+            value = field.getEnumType().findValueByNumberCreatingIfUnknown(rawValue);
+          } else {
+            value = field.getEnumType().findValueByNumber(rawValue);
+            // If the number isn't recognized as a valid value for this enum,
+            // drop it.
+            if (value == null) {
+              unknownFields.mergeVarintField(fieldNumber, rawValue);
+              return true;
+            }
+          }
+          break;
+        default:
+          value = WireFormat.readPrimitiveField(
+              input, field.getLiteType(), target.getUtf8Validation(field));
+          break;
+      }
+
+      if (field.isRepeated()) {
+        target.addRepeatedField(field, value);
+      } else {
+        target.setField(field, value);
+      }
+    }
+
+    return true;
+  }
+
+  /**
+   * Called by {@code #mergeFieldFrom()} to parse a MessageSet extension into
+   * MergeTarget.
+   */
+  private static void mergeMessageSetExtensionFromCodedStream(
+      CodedInputStream input,
+      UnknownFieldSet.Builder unknownFields,
+      ExtensionRegistryLite extensionRegistry,
+      Descriptors.Descriptor type,
+      MergeTarget target) throws IOException {
+
+    // The wire format for MessageSet is:
+    //   message MessageSet {
+    //     repeated group Item = 1 {
+    //       required int32 typeId = 2;
+    //       required bytes message = 3;
+    //     }
+    //   }
+    // "typeId" is the extension's field number.  The extension can only be
+    // a message type, where "message" contains the encoded bytes of that
+    // message.
+    //
+    // In practice, we will probably never see a MessageSet item in which
+    // the message appears before the type ID, or where either field does not
+    // appear exactly once.  However, in theory such cases are valid, so we
+    // should be prepared to accept them.
+
+    int typeId = 0;
+    ByteString rawBytes = null; // If we encounter "message" before "typeId"
+    ExtensionRegistry.ExtensionInfo extension = null;
+
+    // Read bytes from input, if we get it's type first then parse it eagerly,
+    // otherwise we store the raw bytes in a local variable.
+    while (true) {
+      final int tag = input.readTag();
+      if (tag == 0) {
+        break;
+      }
+
+      if (tag == WireFormat.MESSAGE_SET_TYPE_ID_TAG) {
+        typeId = input.readUInt32();
+        if (typeId != 0) {
+          // extensionRegistry may be either ExtensionRegistry or
+          // ExtensionRegistryLite. Since the type we are parsing is a full
+          // message, only a full ExtensionRegistry could possibly contain
+          // extensions of it. Otherwise we will treat the registry as if it
+          // were empty.
+          if (extensionRegistry instanceof ExtensionRegistry) {
+            extension = target.findExtensionByNumber(
+                (ExtensionRegistry) extensionRegistry, type, typeId);
+          }
+        }
+
+      } else if (tag == WireFormat.MESSAGE_SET_MESSAGE_TAG) {
+        if (typeId != 0) {
+          if (extension != null &&
+              ExtensionRegistryLite.isEagerlyParseMessageSets()) {
+            // We already know the type, so we can parse directly from the
+            // input with no copying.  Hooray!
+            eagerlyMergeMessageSetExtension(
+                input, extension, extensionRegistry, target);
+            rawBytes = null;
+            continue;
+          }
+        }
+        // We haven't seen a type ID yet or we want parse message lazily.
+        rawBytes = input.readBytes();
+
+      } else { // Unknown tag. Skip it.
+        if (!input.skipField(tag)) {
+          break; // End of group
+        }
+      }
+    }
+    input.checkLastTagWas(WireFormat.MESSAGE_SET_ITEM_END_TAG);
+
+    // Process the raw bytes.
+    if (rawBytes != null && typeId != 0) { // Zero is not a valid type ID.
+      if (extension != null) { // We known the type
+        mergeMessageSetExtensionFromBytes(
+            rawBytes, extension, extensionRegistry, target);
+      } else { // We don't know how to parse this. Ignore it.
+        if (rawBytes != null) {
+          unknownFields.mergeField(typeId, UnknownFieldSet.Field.newBuilder()
+              .addLengthDelimited(rawBytes).build());
+        }
+      }
+    }
+  }
+
+  private static void mergeMessageSetExtensionFromBytes(
+      ByteString rawBytes,
+      ExtensionRegistry.ExtensionInfo extension,
+      ExtensionRegistryLite extensionRegistry,
+      MergeTarget target) throws IOException {
+
+    Descriptors.FieldDescriptor field = extension.descriptor;
+    boolean hasOriginalValue = target.hasField(field);
+
+    if (hasOriginalValue || ExtensionRegistryLite.isEagerlyParseMessageSets()) {
+      // If the field already exists, we just parse the field.
+      Object value = target.parseMessageFromBytes(
+          rawBytes, extensionRegistry,field, extension.defaultInstance);
+      target.setField(field, value);
+    } else {
+      // Use LazyField to load MessageSet lazily.
+      LazyField lazyField = new LazyField(
+          extension.defaultInstance, extensionRegistry, rawBytes);
+      target.setField(field, lazyField);
+    }
+  }
+
+  private static void eagerlyMergeMessageSetExtension(
+      CodedInputStream input,
+      ExtensionRegistry.ExtensionInfo extension,
+      ExtensionRegistryLite extensionRegistry,
+      MergeTarget target) throws IOException {
+    Descriptors.FieldDescriptor field = extension.descriptor;
+    Object value = target.parseMessage(input, extensionRegistry, field,
+                                       extension.defaultInstance);
+    target.setField(field, value);
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/MutabilityOracle.java b/java/core/src/main/java/com/google/protobuf/MutabilityOracle.java
new file mode 100644
index 00000000..82b723c9
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/MutabilityOracle.java
@@ -0,0 +1,48 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+/**
+ * Verifies that an object is mutable, throwing if not.
+ */
+interface MutabilityOracle {
+  static final MutabilityOracle IMMUTABLE = new MutabilityOracle() {
+    @Override
+    public void ensureMutable() {
+      throw new UnsupportedOperationException();
+    }
+  };
+
+  /**
+   * Throws an {@link UnsupportedOperationException} if not mutable.
+   */
+  void ensureMutable();
+}
diff --git a/java/core/src/main/java/com/google/protobuf/NioByteString.java b/java/core/src/main/java/com/google/protobuf/NioByteString.java
new file mode 100644
index 00000000..f71e41b2
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/NioByteString.java
@@ -0,0 +1,309 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InvalidObjectException;
+import java.io.ObjectInputStream;
+import java.io.OutputStream;
+import java.nio.ByteBuffer;
+import java.nio.InvalidMarkException;
+import java.nio.channels.Channels;
+import java.nio.charset.Charset;
+import java.util.Collections;
+import java.util.List;
+
+/**
+ * A {@link ByteString} that wraps around a {@link ByteBuffer}.
+ */
+final class NioByteString extends ByteString.LeafByteString {
+  private final ByteBuffer buffer;
+
+  NioByteString(ByteBuffer buffer) {
+    if (buffer == null) {
+      throw new NullPointerException("buffer");
+    }
+
+    this.buffer = buffer.slice();
+  }
+
+  // =================================================================
+  // Serializable
+
+  /**
+   * Magic method that lets us override serialization behavior.
+   */
+  private Object writeReplace() {
+    return ByteString.copyFrom(buffer.slice());
+  }
+
+  /**
+   * Magic method that lets us override deserialization behavior.
+   */
+  private void readObject(@SuppressWarnings("unused") ObjectInputStream in) throws IOException {
+    throw new InvalidObjectException("NioByteString instances are not to be serialized directly");
+  }
+
+  // =================================================================
+
+  @Override
+  public byte byteAt(int index) {
+    try {
+      return buffer.get(index);
+    } catch (ArrayIndexOutOfBoundsException e) {
+      throw e;
+    } catch (IndexOutOfBoundsException e) {
+      throw new ArrayIndexOutOfBoundsException(e.getMessage());
+    }
+  }
+
+  @Override
+  public int size() {
+    return buffer.remaining();
+  }
+
+  @Override
+  public ByteString substring(int beginIndex, int endIndex) {
+    try {
+      ByteBuffer slice = slice(beginIndex, endIndex);
+      return new NioByteString(slice);
+    } catch (ArrayIndexOutOfBoundsException e) {
+      throw e;
+    } catch (IndexOutOfBoundsException e) {
+      throw new ArrayIndexOutOfBoundsException(e.getMessage());
+    }
+  }
+
+  @Override
+  protected void copyToInternal(
+      byte[] target, int sourceOffset, int targetOffset, int numberToCopy) {
+    ByteBuffer slice = buffer.slice();
+    slice.position(sourceOffset);
+    slice.get(target, targetOffset, numberToCopy);
+  }
+
+  @Override
+  public void copyTo(ByteBuffer target) {
+    target.put(buffer.slice());
+  }
+
+  @Override
+  public void writeTo(OutputStream out) throws IOException {
+    writeToInternal(out, buffer.position(), buffer.remaining());
+  }
+
+  @Override
+  boolean equalsRange(ByteString other, int offset, int length) {
+    return substring(0, length).equals(other.substring(offset, offset + length));
+  }
+
+  @Override
+  void writeToInternal(OutputStream out, int sourceOffset, int numberToWrite) throws IOException {
+    if (buffer.hasArray()) {
+      // Optimized write for array-backed buffers.
+      // Note that we're taking the risk that a malicious OutputStream could modify the array.
+      int bufferOffset = buffer.arrayOffset() + buffer.position() + sourceOffset;
+      out.write(buffer.array(), bufferOffset, numberToWrite);
+      return;
+    }
+
+    // Slow path
+    if (out instanceof FileOutputStream || numberToWrite >= 8192) {
+      // Use a channel to write out the ByteBuffer.
+      Channels.newChannel(out).write(slice(sourceOffset, sourceOffset + numberToWrite));
+    } else {
+      // Just copy the data to an array and write it.
+      out.write(toByteArray());
+    }
+  }
+
+  @Override
+  public ByteBuffer asReadOnlyByteBuffer() {
+    return buffer.asReadOnlyBuffer();
+  }
+
+  @Override
+  public List<ByteBuffer> asReadOnlyByteBufferList() {
+    return Collections.singletonList(asReadOnlyByteBuffer());
+  }
+
+  @Override
+  protected String toStringInternal(Charset charset) {
+    byte[] bytes;
+    int offset;
+    if (buffer.hasArray()) {
+      bytes = buffer.array();
+      offset = buffer.arrayOffset() + buffer.position();
+    } else {
+      bytes = toByteArray();
+      offset = 0;
+    }
+    return new String(bytes, offset, size(), charset);
+  }
+
+  @Override
+  public boolean isValidUtf8() {
+    // TODO(nathanmittler): add a ByteBuffer fork for Utf8.isValidUtf8 to avoid the copy
+    byte[] bytes;
+    int startIndex;
+    if (buffer.hasArray()) {
+      bytes = buffer.array();
+      startIndex = buffer.arrayOffset() + buffer.position();
+    } else {
+      bytes = toByteArray();
+      startIndex = 0;
+    }
+    return Utf8.isValidUtf8(bytes, startIndex, startIndex + size());
+  }
+
+  @Override
+  protected int partialIsValidUtf8(int state, int offset, int length) {
+    // TODO(nathanmittler): TODO add a ByteBuffer fork for Utf8.partialIsValidUtf8 to avoid the copy
+    byte[] bytes;
+    int startIndex;
+    if (buffer.hasArray()) {
+      bytes = buffer.array();
+      startIndex = buffer.arrayOffset() + buffer.position();
+    } else {
+      bytes = toByteArray();
+      startIndex = 0;
+    }
+    return Utf8.partialIsValidUtf8(state, bytes, startIndex, startIndex + size());
+  }
+
+  @Override
+  public boolean equals(Object other) {
+    if (other == this) {
+      return true;
+    }
+    if (!(other instanceof ByteString)) {
+      return false;
+    }
+    ByteString otherString = ((ByteString) other);
+    if (size() != otherString.size()) {
+      return false;
+    }
+    if (size() == 0) {
+      return true;
+    }
+    if (other instanceof NioByteString) {
+      return buffer.equals(((NioByteString) other).buffer);
+    }
+    if (other instanceof RopeByteString) {
+      return other.equals(this);
+    }
+    return buffer.equals(otherString.asReadOnlyByteBuffer());
+  }
+
+  @Override
+  protected int partialHash(int h, int offset, int length) {
+    for (int i = offset; i < offset + length; i++) {
+      h = h * 31 + buffer.get(i);
+    }
+    return h;
+  }
+
+  @Override
+  public InputStream newInput() {
+    return new InputStream() {
+      private final ByteBuffer buf = buffer.slice();
+
+      @Override
+      public void mark(int readlimit) {
+        buf.mark();
+      }
+
+      @Override
+      public boolean markSupported() {
+        return true;
+      }
+
+      @Override
+      public void reset() throws IOException {
+        try {
+          buf.reset();
+        } catch (InvalidMarkException e) {
+          throw new IOException(e);
+        }
+      }
+
+      @Override
+      public int available() throws IOException {
+        return buf.remaining();
+      }
+
+      @Override
+      public int read() throws IOException {
+        if (!buf.hasRemaining()) {
+          return -1;
+        }
+        return buf.get() & 0xFF;
+      }
+
+      @Override
+      public int read(byte[] bytes, int off, int len) throws IOException {
+        if (!buf.hasRemaining()) {
+          return -1;
+        }
+
+        len = Math.min(len, buf.remaining());
+        buf.get(bytes, off, len);
+        return len;
+      }
+    };
+  }
+
+  @Override
+  public CodedInputStream newCodedInput() {
+    return CodedInputStream.newInstance(buffer);
+  }
+
+  /**
+   * Creates a slice of a range of this buffer.
+   *
+   * @param beginIndex the beginning index of the slice (inclusive).
+   * @param endIndex the end index of the slice (exclusive).
+   * @return the requested slice.
+   */
+  private ByteBuffer slice(int beginIndex, int endIndex) {
+    if (beginIndex < buffer.position() || endIndex > buffer.limit() || beginIndex > endIndex) {
+      throw new IllegalArgumentException(
+          String.format("Invalid indices [%d, %d]", beginIndex, endIndex));
+    }
+
+    ByteBuffer slice = buffer.slice();
+    slice.position(beginIndex - buffer.position());
+    slice.limit(endIndex - buffer.position());
+    return slice;
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/Parser.java b/java/core/src/main/java/com/google/protobuf/Parser.java
new file mode 100644
index 00000000..227c02b7
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/Parser.java
@@ -0,0 +1,261 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import java.io.InputStream;
+
+/**
+ * Abstract interface for parsing Protocol Messages.
+ *
+ * The implementation should be stateless and thread-safe.
+ *
+ * @author liujisi@google.com (Pherl Liu)
+ */
+public interface Parser<MessageType> {
+  /**
+   * Parses a message of {@code MessageType} from the input.
+   *
+   * <p>Note:  The caller should call
+   * {@link CodedInputStream#checkLastTagWas(int)} after calling this to
+   * verify that the last tag seen was the appropriate end-group tag,
+   * or zero for EOF.
+   */
+  public MessageType parseFrom(CodedInputStream input)
+      throws InvalidProtocolBufferException;
+
+  /**
+   * Like {@link #parseFrom(CodedInputStream)}, but also parses extensions.
+   * The extensions that you want to be able to parse must be registered in
+   * {@code extensionRegistry}. Extensions not in the registry will be treated
+   * as unknown fields.
+   */
+  public MessageType parseFrom(CodedInputStream input,
+                               ExtensionRegistryLite extensionRegistry)
+      throws InvalidProtocolBufferException;
+
+  /**
+   * Like {@link #parseFrom(CodedInputStream)}, but does not throw an
+   * exception if the message is missing required fields. Instead, a partial
+   * message is returned.
+   */
+  public MessageType parsePartialFrom(CodedInputStream input)
+      throws InvalidProtocolBufferException;
+
+  /**
+   * Like {@link #parseFrom(CodedInputStream input, ExtensionRegistryLite)},
+   * but does not throw an exception if the message is missing required fields.
+   * Instead, a partial message is returned.
+   */
+  public MessageType parsePartialFrom(CodedInputStream input,
+                                      ExtensionRegistryLite extensionRegistry)
+      throws InvalidProtocolBufferException;
+
+  // ---------------------------------------------------------------
+  // Convenience methods.
+
+  /**
+   * Parses {@code data} as a message of {@code MessageType}.
+   * This is just a small wrapper around {@link #parseFrom(CodedInputStream)}.
+   */
+  public MessageType parseFrom(ByteString data)
+      throws InvalidProtocolBufferException;
+
+  /**
+   * Parses {@code data} as a message of {@code MessageType}.
+   * This is just a small wrapper around
+   * {@link #parseFrom(CodedInputStream, ExtensionRegistryLite)}.
+   */
+  public MessageType parseFrom(ByteString data,
+                               ExtensionRegistryLite extensionRegistry)
+      throws InvalidProtocolBufferException;
+
+  /**
+   * Like {@link #parseFrom(ByteString)}, but does not throw an
+   * exception if the message is missing required fields. Instead, a partial
+   * message is returned.
+   */
+  public MessageType parsePartialFrom(ByteString data)
+      throws InvalidProtocolBufferException;
+
+  /**
+   * Like {@link #parseFrom(ByteString, ExtensionRegistryLite)},
+   * but does not throw an exception if the message is missing required fields.
+   * Instead, a partial message is returned.
+   */
+  public MessageType parsePartialFrom(ByteString data,
+                                      ExtensionRegistryLite extensionRegistry)
+      throws InvalidProtocolBufferException;
+
+  /**
+   * Parses {@code data} as a message of {@code MessageType}.
+   * This is just a small wrapper around {@link #parseFrom(CodedInputStream)}.
+   */
+  public MessageType parseFrom(byte[] data, int off, int len)
+      throws InvalidProtocolBufferException;
+
+  /**
+   * Parses {@code data} as a message of {@code MessageType}.
+   * This is just a small wrapper around
+   * {@link #parseFrom(CodedInputStream, ExtensionRegistryLite)}.
+   */
+  public MessageType parseFrom(byte[] data, int off, int len,
+                               ExtensionRegistryLite extensionRegistry)
+      throws InvalidProtocolBufferException;
+
+  /**
+   * Parses {@code data} as a message of {@code MessageType}.
+   * This is just a small wrapper around {@link #parseFrom(CodedInputStream)}.
+   */
+  public MessageType parseFrom(byte[] data)
+      throws InvalidProtocolBufferException;
+
+  /**
+   * Parses {@code data} as a message of {@code MessageType}.
+   * This is just a small wrapper around
+   * {@link #parseFrom(CodedInputStream, ExtensionRegistryLite)}.
+   */
+  public MessageType parseFrom(byte[] data,
+                               ExtensionRegistryLite extensionRegistry)
+      throws InvalidProtocolBufferException;
+
+  /**
+   * Like {@link #parseFrom(byte[], int, int)}, but does not throw an
+   * exception if the message is missing required fields. Instead, a partial
+   * message is returned.
+   */
+  public MessageType parsePartialFrom(byte[] data, int off, int len)
+      throws InvalidProtocolBufferException;
+
+  /**
+   * Like {@link #parseFrom(ByteString, ExtensionRegistryLite)},
+   * but does not throw an exception if the message is missing required fields.
+   * Instead, a partial message is returned.
+   */
+  public MessageType parsePartialFrom(byte[] data, int off, int len,
+                                      ExtensionRegistryLite extensionRegistry)
+      throws InvalidProtocolBufferException;
+
+  /**
+   * Like {@link #parseFrom(byte[])}, but does not throw an
+   * exception if the message is missing required fields. Instead, a partial
+   * message is returned.
+   */
+  public MessageType parsePartialFrom(byte[] data)
+      throws InvalidProtocolBufferException;
+
+  /**
+   * Like {@link #parseFrom(byte[], ExtensionRegistryLite)},
+   * but does not throw an exception if the message is missing required fields.
+   * Instead, a partial message is returned.
+   */
+  public MessageType parsePartialFrom(byte[] data,
+                                      ExtensionRegistryLite extensionRegistry)
+      throws InvalidProtocolBufferException;
+
+  /**
+   * Parse a message of {@code MessageType} from {@code input}.
+   * This is just a small wrapper around {@link #parseFrom(CodedInputStream)}.
+   * Note that this method always reads the <i>entire</i> input (unless it
+   * throws an exception).  If you want it to stop earlier, you will need to
+   * wrap your input in some wrapper stream that limits reading.  Or, use
+   * {@link MessageLite#writeDelimitedTo(java.io.OutputStream)} to write your
+   * message and {@link #parseDelimitedFrom(InputStream)} to read it.
+   * <p>
+   * Despite usually reading the entire input, this does not close the stream.
+   */
+  public MessageType parseFrom(InputStream input)
+      throws InvalidProtocolBufferException;
+
+  /**
+   * Parses a message of {@code MessageType} from {@code input}.
+   * This is just a small wrapper around
+   * {@link #parseFrom(CodedInputStream, ExtensionRegistryLite)}.
+   */
+  public MessageType parseFrom(InputStream input,
+                               ExtensionRegistryLite extensionRegistry)
+      throws InvalidProtocolBufferException;
+
+  /**
+   * Like {@link #parseFrom(InputStream)}, but does not throw an
+   * exception if the message is missing required fields. Instead, a partial
+   * message is returned.
+   */
+  public MessageType parsePartialFrom(InputStream input)
+      throws InvalidProtocolBufferException;
+
+  /**
+   * Like {@link #parseFrom(InputStream, ExtensionRegistryLite)},
+   * but does not throw an exception if the message is missing required fields.
+   * Instead, a partial message is returned.
+   */
+  public MessageType parsePartialFrom(InputStream input,
+                                      ExtensionRegistryLite extensionRegistry)
+      throws InvalidProtocolBufferException;
+
+  /**
+   * Like {@link #parseFrom(InputStream)}, but does not read util EOF.
+   * Instead, the size of message (encoded as a varint) is read first,
+   * then the message data. Use
+   * {@link MessageLite#writeDelimitedTo(java.io.OutputStream)} to write
+   * messages in this format.
+   *
+   * @return Parsed message if successful, or null if the stream is at EOF when
+   *         the method starts. Any other error (including reaching EOF during
+   *         parsing) will cause an exception to be thrown.
+   */
+  public MessageType parseDelimitedFrom(InputStream input)
+      throws InvalidProtocolBufferException;
+
+  /**
+   * Like {@link #parseDelimitedFrom(InputStream)} but supporting extensions.
+   */
+  public MessageType parseDelimitedFrom(InputStream input,
+                                        ExtensionRegistryLite extensionRegistry)
+      throws InvalidProtocolBufferException;
+
+  /**
+   * Like {@link #parseDelimitedFrom(InputStream)}, but does not throw an
+   * exception if the message is missing required fields. Instead, a partial
+   * message is returned.
+   */
+  public MessageType parsePartialDelimitedFrom(InputStream input)
+      throws InvalidProtocolBufferException;
+
+  /**
+   * Like {@link #parseDelimitedFrom(InputStream, ExtensionRegistryLite)},
+   * but does not throw an exception if the message is missing required fields.
+   * Instead, a partial message is returned.
+   */
+  public MessageType parsePartialDelimitedFrom(
+      InputStream input,
+      ExtensionRegistryLite extensionRegistry)
+      throws InvalidProtocolBufferException;
+}
diff --git a/java/core/src/main/java/com/google/protobuf/ProtobufArrayList.java b/java/core/src/main/java/com/google/protobuf/ProtobufArrayList.java
new file mode 100644
index 00000000..d2f82ac5
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/ProtobufArrayList.java
@@ -0,0 +1,99 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import com.google.protobuf.Internal.ProtobufList;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Implements {@link ProtobufList} for non-primitive and {@link String} types.
+ */
+class ProtobufArrayList<E> extends AbstractProtobufList<E> {
+
+  private static final ProtobufArrayList<Object> EMPTY_LIST = new ProtobufArrayList<Object>();
+  static {
+    EMPTY_LIST.makeImmutable();
+  }
+  
+  @SuppressWarnings("unchecked") // Guaranteed safe by runtime.
+  public static <E> ProtobufArrayList<E> emptyList() {
+    return (ProtobufArrayList<E>) EMPTY_LIST;
+  }
+  
+  private final List<E> list;
+  
+  ProtobufArrayList() {
+    list = new ArrayList<E>();
+  }
+  
+  ProtobufArrayList(List<E> toCopy) {
+    list = new ArrayList<E>(toCopy);
+  }
+  
+  ProtobufArrayList(int capacity) {
+    list = new ArrayList<E>(capacity);
+  }
+  
+  @Override
+  public void add(int index, E element) {
+    ensureIsMutable();
+    list.add(index, element);
+    modCount++;
+  }
+
+  @Override
+  public E get(int index) {
+    return list.get(index);
+  }
+  
+  @Override
+  public E remove(int index) {
+    ensureIsMutable();
+    E toReturn = list.remove(index);
+    modCount++;
+    return toReturn;
+  }
+  
+  @Override
+  public E set(int index, E element) {
+    ensureIsMutable();
+    E toReturn = list.set(index, element);
+    modCount++;
+    return toReturn;
+  }
+
+  @Override
+  public int size() {
+    return list.size();
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/ProtocolMessageEnum.java b/java/core/src/main/java/com/google/protobuf/ProtocolMessageEnum.java
new file mode 100644
index 00000000..0c8df989
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/ProtocolMessageEnum.java
@@ -0,0 +1,58 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import com.google.protobuf.Descriptors.EnumDescriptor;
+import com.google.protobuf.Descriptors.EnumValueDescriptor;
+
+/**
+ * Interface of useful methods added to all enums generated by the protocol
+ * compiler.
+ */
+public interface ProtocolMessageEnum extends Internal.EnumLite {
+
+  /**
+   * Return the value's numeric value as defined in the .proto file.
+   */
+  int getNumber();
+
+  /**
+   * Return the value's descriptor, which contains information such as
+   * value name, number, and type.
+   */
+  EnumValueDescriptor getValueDescriptor();
+
+  /**
+   * Return the enum type's descriptor, which contains information
+   * about each defined value, etc.
+   */
+  EnumDescriptor getDescriptorForType();
+}
diff --git a/java/core/src/main/java/com/google/protobuf/ProtocolStringList.java b/java/core/src/main/java/com/google/protobuf/ProtocolStringList.java
new file mode 100644
index 00000000..d553b41e
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/ProtocolStringList.java
@@ -0,0 +1,48 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import java.util.List;
+
+/**
+ * An interface extending {@code List<String>} used for repeated string fields
+ * to provide optional access to the data as a list of ByteStrings. The
+ * underlying implementation stores values as either ByteStrings or Strings
+ * (see {@link LazyStringArrayList}) depending on how the value was initialized
+ * or last read, and it is often more efficient to deal with lists of
+ * ByteStrings when handling protos that have been deserialized from bytes.
+ */
+public interface ProtocolStringList extends List<String> {
+
+  /** Returns a view of the data as a list of ByteStrings. */
+  List<ByteString> asByteStringList();
+
+}
diff --git a/java/core/src/main/java/com/google/protobuf/RepeatedFieldBuilder.java b/java/core/src/main/java/com/google/protobuf/RepeatedFieldBuilder.java
new file mode 100644
index 00000000..f91cdbce
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/RepeatedFieldBuilder.java
@@ -0,0 +1,702 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import java.util.AbstractList;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.List;
+
+/**
+ * {@code RepeatedFieldBuilder} implements a structure that a protocol
+ * message uses to hold a repeated field of other protocol messages. It supports
+ * the classical use case of adding immutable {@link Message}'s to the
+ * repeated field and is highly optimized around this (no extra memory
+ * allocations and sharing of immutable arrays).
+ * <br>
+ * It also supports the additional use case of adding a {@link Message.Builder}
+ * to the repeated field and deferring conversion of that {@code Builder}
+ * to an immutable {@code Message}. In this way, it's possible to maintain
+ * a tree of {@code Builder}'s that acts as a fully read/write data
+ * structure.
+ * <br>
+ * Logically, one can think of a tree of builders as converting the entire tree
+ * to messages when build is called on the root or when any method is called
+ * that desires a Message instead of a Builder. In terms of the implementation,
+ * the {@code SingleFieldBuilder} and {@code RepeatedFieldBuilder}
+ * classes cache messages that were created so that messages only need to be
+ * created when some change occurred in its builder or a builder for one of its
+ * descendants.
+ *
+ * @param <MType> the type of message for the field
+ * @param <BType> the type of builder for the field
+ * @param <IType> the common interface for the message and the builder
+ *
+ * @author jonp@google.com (Jon Perlow)
+ */
+public class RepeatedFieldBuilder
+    <MType extends GeneratedMessage,
+     BType extends GeneratedMessage.Builder,
+     IType extends MessageOrBuilder>
+    implements GeneratedMessage.BuilderParent {
+
+  // Parent to send changes to.
+  private GeneratedMessage.BuilderParent parent;
+
+  // List of messages. Never null. It may be immutable, in which case
+  // isMessagesListMutable will be false. See note below.
+  private List<MType> messages;
+
+  // Whether messages is an mutable array that can be modified.
+  private boolean isMessagesListMutable;
+
+  // List of builders. May be null, in which case, no nested builders were
+  // created. If not null, entries represent the builder for that index.
+  private List<SingleFieldBuilder<MType, BType, IType>> builders;
+
+  // Here are the invariants for messages and builders:
+  // 1. messages is never null and its count corresponds to the number of items
+  //    in the repeated field.
+  // 2. If builders is non-null, messages and builders MUST always
+  //    contain the same number of items.
+  // 3. Entries in either array can be null, but for any index, there MUST be
+  //    either a Message in messages or a builder in builders.
+  // 4. If the builder at an index is non-null, the builder is
+  //    authoritative. This is the case where a Builder was set on the index.
+  //    Any message in the messages array MUST be ignored.
+  // t. If the builder at an index is null, the message in the messages
+  //    list is authoritative. This is the case where a Message (not a Builder)
+  //    was set directly for an index.
+
+  // Indicates that we've built a message and so we are now obligated
+  // to dispatch dirty invalidations. See GeneratedMessage.BuilderListener.
+  private boolean isClean;
+
+  // A view of this builder that exposes a List interface of messages. This is
+  // initialized on demand. This is fully backed by this object and all changes
+  // are reflected in it. Access to any item converts it to a message if it
+  // was a builder.
+  private MessageExternalList<MType, BType, IType> externalMessageList;
+
+  // A view of this builder that exposes a List interface of builders. This is
+  // initialized on demand. This is fully backed by this object and all changes
+  // are reflected in it. Access to any item converts it to a builder if it
+  // was a message.
+  private BuilderExternalList<MType, BType, IType> externalBuilderList;
+
+  // A view of this builder that exposes a List interface of the interface
+  // implemented by messages and builders. This is initialized on demand. This
+  // is fully backed by this object and all changes are reflected in it.
+  // Access to any item returns either a builder or message depending on
+  // what is most efficient.
+  private MessageOrBuilderExternalList<MType, BType, IType>
+      externalMessageOrBuilderList;
+
+  /**
+   * Constructs a new builder with an empty list of messages.
+   *
+   * @param messages the current list of messages
+   * @param isMessagesListMutable Whether the messages list is mutable
+   * @param parent a listener to notify of changes
+   * @param isClean whether the builder is initially marked clean
+   */
+  public RepeatedFieldBuilder(
+      List<MType> messages,
+      boolean isMessagesListMutable,
+      GeneratedMessage.BuilderParent parent,
+      boolean isClean) {
+    this.messages = messages;
+    this.isMessagesListMutable = isMessagesListMutable;
+    this.parent = parent;
+    this.isClean = isClean;
+  }
+
+  public void dispose() {
+    // Null out parent so we stop sending it invalidations.
+    parent = null;
+  }
+
+  /**
+   * Ensures that the list of messages is mutable so it can be updated. If it's
+   * immutable, a copy is made.
+   */
+  private void ensureMutableMessageList() {
+    if (!isMessagesListMutable) {
+      messages = new ArrayList<MType>(messages);
+      isMessagesListMutable = true;
+    }
+  }
+
+  /**
+   * Ensures that the list of builders is not null. If it's null, the list is
+   * created and initialized to be the same size as the messages list with
+   * null entries.
+   */
+  private void ensureBuilders() {
+    if (this.builders == null) {
+      this.builders =
+          new ArrayList<SingleFieldBuilder<MType, BType, IType>>(
+              messages.size());
+      for (int i = 0; i < messages.size(); i++) {
+        builders.add(null);
+      }
+    }
+  }
+
+  /**
+   * Gets the count of items in the list.
+   *
+   * @return the count of items in the list.
+   */
+  public int getCount() {
+    return messages.size();
+  }
+
+  /**
+   * Gets whether the list is empty.
+   *
+   * @return whether the list is empty
+   */
+  public boolean isEmpty() {
+    return messages.isEmpty();
+  }
+
+  /**
+   * Get the message at the specified index. If the message is currently stored
+   * as a {@code Builder}, it is converted to a {@code Message} by
+   * calling {@link Message.Builder#buildPartial} on it.
+   *
+   * @param index the index of the message to get
+   * @return the message for the specified index
+   */
+  public MType getMessage(int index) {
+    return getMessage(index, false);
+  }
+
+  /**
+   * Get the message at the specified index. If the message is currently stored
+   * as a {@code Builder}, it is converted to a {@code Message} by
+   * calling {@link Message.Builder#buildPartial} on it.
+   *
+   * @param index the index of the message to get
+   * @param forBuild this is being called for build so we want to make sure
+   *     we SingleFieldBuilder.build to send dirty invalidations
+   * @return the message for the specified index
+   */
+  private MType getMessage(int index, boolean forBuild) {
+    if (this.builders == null) {
+      // We don't have any builders -- return the current Message.
+      // This is the case where no builder was created, so we MUST have a
+      // Message.
+      return messages.get(index);
+    }
+
+    SingleFieldBuilder<MType, BType, IType> builder = builders.get(index);
+    if (builder == null) {
+      // We don't have a builder -- return the current message.
+      // This is the case where no builder was created for the entry at index,
+      // so we MUST have a message.
+      return messages.get(index);
+
+    } else {
+      return forBuild ? builder.build() : builder.getMessage();
+    }
+  }
+
+  /**
+   * Gets a builder for the specified index. If no builder has been created for
+   * that index, a builder is created on demand by calling
+   * {@link Message#toBuilder}.
+   *
+   * @param index the index of the message to get
+   * @return The builder for that index
+   */
+  public BType getBuilder(int index) {
+    ensureBuilders();
+    SingleFieldBuilder<MType, BType, IType> builder = builders.get(index);
+    if (builder == null) {
+      MType message = messages.get(index);
+      builder = new SingleFieldBuilder<MType, BType, IType>(
+          message, this, isClean);
+      builders.set(index, builder);
+    }
+    return builder.getBuilder();
+  }
+
+  /**
+   * Gets the base class interface for the specified index. This may either be
+   * a builder or a message. It will return whatever is more efficient.
+   *
+   * @param index the index of the message to get
+   * @return the message or builder for the index as the base class interface
+   */
+  @SuppressWarnings("unchecked")
+  public IType getMessageOrBuilder(int index) {
+    if (this.builders == null) {
+      // We don't have any builders -- return the current Message.
+      // This is the case where no builder was created, so we MUST have a
+      // Message.
+      return (IType) messages.get(index);
+    }
+
+    SingleFieldBuilder<MType, BType, IType> builder = builders.get(index);
+    if (builder == null) {
+      // We don't have a builder -- return the current message.
+      // This is the case where no builder was created for the entry at index,
+      // so we MUST have a message.
+      return (IType) messages.get(index);
+
+    } else {
+      return builder.getMessageOrBuilder();
+    }
+  }
+
+  /**
+   * Sets a  message at the specified index replacing the existing item at
+   * that index.
+   *
+   * @param index the index to set.
+   * @param message the message to set
+   * @return the builder
+   */
+  public RepeatedFieldBuilder<MType, BType, IType> setMessage(
+      int index, MType message) {
+    if (message == null) {
+      throw new NullPointerException();
+    }
+    ensureMutableMessageList();
+    messages.set(index, message);
+    if (builders != null) {
+      SingleFieldBuilder<MType, BType, IType> entry =
+          builders.set(index, null);
+      if (entry != null) {
+        entry.dispose();
+      }
+    }
+    onChanged();
+    incrementModCounts();
+    return this;
+  }
+
+  /**
+   * Appends the specified element to the end of this list.
+   *
+   * @param message the message to add
+   * @return the builder
+   */
+  public RepeatedFieldBuilder<MType, BType, IType> addMessage(
+      MType message) {
+    if (message == null) {
+      throw new NullPointerException();
+    }
+    ensureMutableMessageList();
+    messages.add(message);
+    if (builders != null) {
+      builders.add(null);
+    }
+    onChanged();
+    incrementModCounts();
+    return this;
+  }
+
+  /**
+   * Inserts the specified message at the specified position in this list.
+   * Shifts the element currently at that position (if any) and any subsequent
+   * elements to the right (adds one to their indices).
+   *
+   * @param index the index at which to insert the message
+   * @param message the message to add
+   * @return the builder
+   */
+  public RepeatedFieldBuilder<MType, BType, IType> addMessage(
+      int index, MType message) {
+    if (message == null) {
+      throw new NullPointerException();
+    }
+    ensureMutableMessageList();
+    messages.add(index, message);
+    if (builders != null) {
+      builders.add(index, null);
+    }
+    onChanged();
+    incrementModCounts();
+    return this;
+  }
+
+  /**
+   * Appends all of the messages in the specified collection to the end of
+   * this list, in the order that they are returned by the specified
+   * collection's iterator.
+   *
+   * @param values the messages to add
+   * @return the builder
+   */
+  public RepeatedFieldBuilder<MType, BType, IType> addAllMessages(
+      Iterable<? extends MType> values) {
+    for (final MType value : values) {
+      if (value == null) {
+        throw new NullPointerException();
+      }
+    }
+
+    // If we can inspect the size, we can more efficiently add messages.
+    int size = -1;
+    if (values instanceof Collection) {
+      @SuppressWarnings("unchecked") final
+      Collection<MType> collection = (Collection<MType>) values;
+      if (collection.size() == 0) {
+        return this;
+      }
+      size = collection.size();
+    }
+    ensureMutableMessageList();
+
+    if (size >= 0 && messages instanceof ArrayList) {
+      ((ArrayList<MType>) messages)
+          .ensureCapacity(messages.size() + size);
+    }
+
+    for (MType value : values) {
+      addMessage(value);
+    }
+
+    onChanged();
+    incrementModCounts();
+    return this;
+  }
+
+  /**
+   * Appends a new builder to the end of this list and returns the builder.
+   *
+   * @param message the message to add which is the basis of the builder
+   * @return the new builder
+   */
+  public BType addBuilder(MType message) {
+    ensureMutableMessageList();
+    ensureBuilders();
+    SingleFieldBuilder<MType, BType, IType> builder =
+        new SingleFieldBuilder<MType, BType, IType>(
+            message, this, isClean);
+    messages.add(null);
+    builders.add(builder);
+    onChanged();
+    incrementModCounts();
+    return builder.getBuilder();
+  }
+
+  /**
+   * Inserts a new builder at the specified position in this list.
+   * Shifts the element currently at that position (if any) and any subsequent
+   * elements to the right (adds one to their indices).
+   *
+   * @param index the index at which to insert the builder
+   * @param message the message to add which is the basis of the builder
+   * @return the builder
+   */
+  public BType addBuilder(int index, MType message) {
+    ensureMutableMessageList();
+    ensureBuilders();
+    SingleFieldBuilder<MType, BType, IType> builder =
+        new SingleFieldBuilder<MType, BType, IType>(
+            message, this, isClean);
+    messages.add(index, null);
+    builders.add(index, builder);
+    onChanged();
+    incrementModCounts();
+    return builder.getBuilder();
+  }
+
+  /**
+   * Removes the element at the specified position in this list. Shifts any
+   * subsequent elements to the left (subtracts one from their indices).
+   * Returns the element that was removed from the list.
+   *
+   * @param index the index at which to remove the message
+   */
+  public void remove(int index) {
+    ensureMutableMessageList();
+    messages.remove(index);
+    if (builders != null) {
+      SingleFieldBuilder<MType, BType, IType> entry =
+          builders.remove(index);
+      if (entry != null) {
+        entry.dispose();
+      }
+    }
+    onChanged();
+    incrementModCounts();
+  }
+
+  /**
+   * Removes all of the elements from this list.
+   * The list will be empty after this call returns.
+   */
+  public void clear() {
+    messages = Collections.emptyList();
+    isMessagesListMutable = false;
+    if (builders != null) {
+      for (SingleFieldBuilder<MType, BType, IType> entry :
+          builders) {
+        if (entry != null) {
+          entry.dispose();
+        }
+      }
+      builders = null;
+    }
+    onChanged();
+    incrementModCounts();
+  }
+
+  /**
+   * Builds the list of messages from the builder and returns them.
+   *
+   * @return an immutable list of messages
+   */
+  public List<MType> build() {
+    // Now that build has been called, we are required to dispatch
+    // invalidations.
+    isClean = true;
+
+    if (!isMessagesListMutable && builders == null) {
+      // We still have an immutable list and we never created a builder.
+      return messages;
+    }
+
+    boolean allMessagesInSync = true;
+    if (!isMessagesListMutable) {
+      // We still have an immutable list. Let's see if any of them are out
+      // of sync with their builders.
+      for (int i = 0; i < messages.size(); i++) {
+        Message message = messages.get(i);
+        SingleFieldBuilder<MType, BType, IType> builder = builders.get(i);
+        if (builder != null) {
+          if (builder.build() != message) {
+            allMessagesInSync = false;
+            break;
+          }
+        }
+      }
+      if (allMessagesInSync) {
+        // Immutable list is still in sync.
+        return messages;
+      }
+    }
+
+    // Need to make sure messages is up to date
+    ensureMutableMessageList();
+    for (int i = 0; i < messages.size(); i++) {
+      messages.set(i, getMessage(i, true));
+    }
+
+    // We're going to return our list as immutable so we mark that we can
+    // no longer update it.
+    messages = Collections.unmodifiableList(messages);
+    isMessagesListMutable = false;
+    return messages;
+  }
+
+  /**
+   * Gets a view of the builder as a list of messages. The returned list is live
+   * and will reflect any changes to the underlying builder.
+   *
+   * @return the messages in the list
+   */
+  public List<MType> getMessageList() {
+    if (externalMessageList == null) {
+      externalMessageList =
+          new MessageExternalList<MType, BType, IType>(this);
+    }
+    return externalMessageList;
+  }
+
+  /**
+   * Gets a view of the builder as a list of builders. This returned list is
+   * live and will reflect any changes to the underlying builder.
+   *
+   * @return the builders in the list
+   */
+  public List<BType> getBuilderList() {
+    if (externalBuilderList == null) {
+      externalBuilderList =
+          new BuilderExternalList<MType, BType, IType>(this);
+    }
+    return externalBuilderList;
+  }
+
+  /**
+   * Gets a view of the builder as a list of MessageOrBuilders. This returned
+   * list is live and will reflect any changes to the underlying builder.
+   *
+   * @return the builders in the list
+   */
+  public List<IType> getMessageOrBuilderList() {
+    if (externalMessageOrBuilderList == null) {
+      externalMessageOrBuilderList =
+          new MessageOrBuilderExternalList<MType, BType, IType>(this);
+    }
+    return externalMessageOrBuilderList;
+  }
+
+  /**
+   * Called when a the builder or one of its nested children has changed
+   * and any parent should be notified of its invalidation.
+   */
+  private void onChanged() {
+    if (isClean && parent != null) {
+      parent.markDirty();
+
+      // Don't keep dispatching invalidations until build is called again.
+      isClean = false;
+    }
+  }
+
+  //@Override (Java 1.6 override semantics, but we must support 1.5)
+  public void markDirty() {
+    onChanged();
+  }
+
+  /**
+   * Increments the mod counts so that an ConcurrentModificationException can
+   * be thrown if calling code tries to modify the builder while its iterating
+   * the list.
+   */
+  private void incrementModCounts() {
+    if (externalMessageList != null) {
+      externalMessageList.incrementModCount();
+    }
+    if (externalBuilderList != null) {
+      externalBuilderList.incrementModCount();
+    }
+    if (externalMessageOrBuilderList != null) {
+      externalMessageOrBuilderList.incrementModCount();
+    }
+  }
+
+  /**
+   * Provides a live view of the builder as a list of messages.
+   *
+   * @param <MType> the type of message for the field
+   * @param <BType> the type of builder for the field
+   * @param <IType> the common interface for the message and the builder
+   */
+  private static class MessageExternalList<
+      MType extends GeneratedMessage,
+      BType extends GeneratedMessage.Builder,
+      IType extends MessageOrBuilder>
+      extends AbstractList<MType> implements List<MType> {
+
+    RepeatedFieldBuilder<MType, BType, IType> builder;
+
+    MessageExternalList(
+        RepeatedFieldBuilder<MType, BType, IType> builder) {
+      this.builder = builder;
+    }
+
+    public int size() {
+      return this.builder.getCount();
+    }
+
+    public MType get(int index) {
+      return builder.getMessage(index);
+    }
+
+    void incrementModCount() {
+      modCount++;
+    }
+  }
+
+  /**
+   * Provides a live view of the builder as a list of builders.
+   *
+   * @param <MType> the type of message for the field
+   * @param <BType> the type of builder for the field
+   * @param <IType> the common interface for the message and the builder
+   */
+  private static class BuilderExternalList<
+      MType extends GeneratedMessage,
+      BType extends GeneratedMessage.Builder,
+      IType extends MessageOrBuilder>
+      extends AbstractList<BType> implements List<BType> {
+
+    RepeatedFieldBuilder<MType, BType, IType> builder;
+
+    BuilderExternalList(
+        RepeatedFieldBuilder<MType, BType, IType> builder) {
+      this.builder = builder;
+    }
+
+    public int size() {
+      return this.builder.getCount();
+    }
+
+    public BType get(int index) {
+      return builder.getBuilder(index);
+    }
+
+    void incrementModCount() {
+      modCount++;
+    }
+  }
+
+  /**
+   * Provides a live view of the builder as a list of builders.
+   *
+   * @param <MType> the type of message for the field
+   * @param <BType> the type of builder for the field
+   * @param <IType> the common interface for the message and the builder
+   */
+  private static class MessageOrBuilderExternalList<
+      MType extends GeneratedMessage,
+      BType extends GeneratedMessage.Builder,
+      IType extends MessageOrBuilder>
+      extends AbstractList<IType> implements List<IType> {
+
+    RepeatedFieldBuilder<MType, BType, IType> builder;
+
+    MessageOrBuilderExternalList(
+        RepeatedFieldBuilder<MType, BType, IType> builder) {
+      this.builder = builder;
+    }
+
+    public int size() {
+      return this.builder.getCount();
+    }
+
+    public IType get(int index) {
+      return builder.getMessageOrBuilder(index);
+    }
+
+    void incrementModCount() {
+      modCount++;
+    }
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/RopeByteString.java b/java/core/src/main/java/com/google/protobuf/RopeByteString.java
new file mode 100644
index 00000000..6e8eb724
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/RopeByteString.java
@@ -0,0 +1,888 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import java.io.ByteArrayInputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InvalidObjectException;
+import java.io.ObjectInputStream;
+import java.io.OutputStream;
+import java.nio.ByteBuffer;
+import java.nio.charset.Charset;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Iterator;
+import java.util.List;
+import java.util.NoSuchElementException;
+import java.util.Stack;
+
+/**
+ * Class to represent {@code ByteStrings} formed by concatenation of other
+ * ByteStrings, without copying the data in the pieces. The concatenation is
+ * represented as a tree whose leaf nodes are each a {@link LiteralByteString}.
+ *
+ * <p>Most of the operation here is inspired by the now-famous paper <a
+ * href="http://www.cs.ubc.ca/local/reading/proceedings/spe91-95/spe/vol25/issue12/spe986.pdf">
+ * BAP95 </a> Ropes: an Alternative to Strings hans-j. boehm, russ atkinson and
+ * michael plass
+ *
+ * <p>The algorithms described in the paper have been implemented for character
+ * strings in {@code com.google.common.string.Rope} and in the c++ class {@code
+ * cord.cc}.
+ *
+ * <p>Fundamentally the Rope algorithm represents the collection of pieces as a
+ * binary tree. BAP95 uses a Fibonacci bound relating depth to a minimum
+ * sequence length, sequences that are too short relative to their depth cause a
+ * tree rebalance.  More precisely, a tree of depth d is "balanced" in the
+ * terminology of BAP95 if its length is at least F(d+2), where F(n) is the
+ * n-the Fibonacci number. Thus for depths 0, 1, 2, 3, 4, 5,... we have minimum
+ * lengths 1, 2, 3, 5, 8, 13,...
+ *
+ * @author carlanton@google.com (Carl Haverl)
+ */
+final class RopeByteString extends ByteString {
+
+  /**
+   * BAP95. Let Fn be the nth Fibonacci number. A {@link RopeByteString} of
+   * depth n is "balanced", i.e flat enough, if its length is at least Fn+2,
+   * e.g. a "balanced" {@link RopeByteString} of depth 1 must have length at
+   * least 2, of depth 4 must have length >= 8, etc.
+   *
+   * <p>There's nothing special about using the Fibonacci numbers for this, but
+   * they are a reasonable sequence for encapsulating the idea that we are OK
+   * with longer strings being encoded in deeper binary trees.
+   *
+   * <p>For 32-bit integers, this array has length 46.
+   */
+  private static final int[] minLengthByDepth;
+
+  static {
+    // Dynamically generate the list of Fibonacci numbers the first time this
+    // class is accessed.
+    List<Integer> numbers = new ArrayList<Integer>();
+
+    // we skip the first Fibonacci number (1).  So instead of: 1 1 2 3 5 8 ...
+    // we have: 1 2 3 5 8 ...
+    int f1 = 1;
+    int f2 = 1;
+
+    // get all the values until we roll over.
+    while (f2 > 0) {
+      numbers.add(f2);
+      int temp = f1 + f2;
+      f1 = f2;
+      f2 = temp;
+    }
+
+    // we include this here so that we can index this array to [x + 1] in the
+    // loops below.
+    numbers.add(Integer.MAX_VALUE);
+    minLengthByDepth = new int[numbers.size()];
+    for (int i = 0; i < minLengthByDepth.length; i++) {
+      // unbox all the values
+      minLengthByDepth[i] = numbers.get(i);
+    }
+  }
+
+  private final int totalLength;
+  private final ByteString left;
+  private final ByteString right;
+  private final int leftLength;
+  private final int treeDepth;
+
+  /**
+   * Create a new RopeByteString, which can be thought of as a new tree node, by
+   * recording references to the two given strings.
+   *
+   * @param left  string on the left of this node, should have {@code size() >
+   *              0}
+   * @param right string on the right of this node, should have {@code size() >
+   *              0}
+   */
+  private RopeByteString(ByteString left, ByteString right) {
+    this.left = left;
+    this.right = right;
+    leftLength = left.size();
+    totalLength = leftLength + right.size();
+    treeDepth = Math.max(left.getTreeDepth(), right.getTreeDepth()) + 1;
+  }
+
+  /**
+   * Concatenate the given strings while performing various optimizations to
+   * slow the growth rate of tree depth and tree node count. The result is
+   * either a {@link LiteralByteString} or a {@link RopeByteString}
+   * depending on which optimizations, if any, were applied.
+   *
+   * <p>Small pieces of length less than {@link
+   * ByteString#CONCATENATE_BY_COPY_SIZE} may be copied by value here, as in
+   * BAP95.  Large pieces are referenced without copy.
+   *
+   * @param left  string on the left
+   * @param right string on the right
+   * @return concatenation representing the same sequence as the given strings
+   */
+  static ByteString concatenate(ByteString left, ByteString right) {
+    if (right.size() == 0) {
+      return left;
+    }
+
+    if (left.size() == 0) {
+      return right;
+    }
+
+    final int newLength = left.size() + right.size();
+    if (newLength < ByteString.CONCATENATE_BY_COPY_SIZE) {
+      // Optimization from BAP95: For short (leaves in paper, but just short
+      // here) total length, do a copy of data to a new leaf.
+      return concatenateBytes(left, right);
+    }
+
+    if (left instanceof RopeByteString) {
+      final RopeByteString leftRope = (RopeByteString) left;
+      if (leftRope.right.size() + right.size() < CONCATENATE_BY_COPY_SIZE) {
+        // Optimization from BAP95: As an optimization of the case where the
+        // ByteString is constructed by repeated concatenate, recognize the case
+        // where a short string is concatenated to a left-hand node whose
+        // right-hand branch is short.  In the paper this applies to leaves, but
+        // we just look at the length here. This has the advantage of shedding
+        // references to unneeded data when substrings have been taken.
+        //
+        // When we recognize this case, we do a copy of the data and create a
+        // new parent node so that the depth of the result is the same as the
+        // given left tree.
+        ByteString newRight = concatenateBytes(leftRope.right, right);
+        return new RopeByteString(leftRope.left, newRight);
+      }
+
+      if (leftRope.left.getTreeDepth() > leftRope.right.getTreeDepth()
+          && leftRope.getTreeDepth() > right.getTreeDepth()) {
+        // Typically for concatenate-built strings the left-side is deeper than
+        // the right.  This is our final attempt to concatenate without
+        // increasing the tree depth.  We'll redo the the node on the RHS.  This
+        // is yet another optimization for building the string by repeatedly
+        // concatenating on the right.
+        ByteString newRight = new RopeByteString(leftRope.right, right);
+        return new RopeByteString(leftRope.left, newRight);
+      }
+    }
+
+    // Fine, we'll add a node and increase the tree depth--unless we rebalance ;^)
+    int newDepth = Math.max(left.getTreeDepth(), right.getTreeDepth()) + 1;
+    if (newLength >= minLengthByDepth[newDepth]) {
+      // The tree is shallow enough, so don't rebalance
+      return new RopeByteString(left, right);
+    }
+
+    return new Balancer().balance(left, right);
+  }
+
+  /**
+   * Concatenates two strings by copying data values. This is called in a few
+   * cases in order to reduce the growth of the number of tree nodes.
+   *
+   * @param left  string on the left
+   * @param right string on the right
+   * @return string formed by copying data bytes
+   */
+  private static LiteralByteString concatenateBytes(ByteString left,
+      ByteString right) {
+    int leftSize = left.size();
+    int rightSize = right.size();
+    byte[] bytes = new byte[leftSize + rightSize];
+    left.copyTo(bytes, 0, 0, leftSize);
+    right.copyTo(bytes, 0, leftSize, rightSize);
+    return new LiteralByteString(bytes);  // Constructor wraps bytes
+  }
+
+  /**
+   * Create a new RopeByteString for testing only while bypassing all the
+   * defenses of {@link #concatenate(ByteString, ByteString)}. This allows
+   * testing trees of specific structure. We are also able to insert empty
+   * leaves, though these are dis-allowed, so that we can make sure the
+   * implementation can withstand their presence.
+   *
+   * @param left  string on the left of this node
+   * @param right string on the right of this node
+   * @return an unsafe instance for testing only
+   */
+  static RopeByteString newInstanceForTest(ByteString left, ByteString right) {
+    return new RopeByteString(left, right);
+  }
+
+  /**
+   * Gets the byte at the given index.
+   * Throws {@link ArrayIndexOutOfBoundsException} for backwards-compatibility
+   * reasons although it would more properly be {@link
+   * IndexOutOfBoundsException}.
+   *
+   * @param index index of byte
+   * @return the value
+   * @throws ArrayIndexOutOfBoundsException {@code index} is < 0 or >= size
+   */
+  @Override
+  public byte byteAt(int index) {
+    checkIndex(index, totalLength);
+
+    // Find the relevant piece by recursive descent
+    if (index < leftLength) {
+      return left.byteAt(index);
+    }
+
+    return right.byteAt(index - leftLength);
+  }
+
+  @Override
+  public int size() {
+    return totalLength;
+  }
+
+  // =================================================================
+  // Pieces
+
+  @Override
+  protected int getTreeDepth() {
+    return treeDepth;
+  }
+
+  /**
+   * Determines if the tree is balanced according to BAP95, which means the tree
+   * is flat-enough with respect to the bounds. Note that this definition of
+   * balanced is one where sub-trees of balanced trees are not necessarily
+   * balanced.
+   *
+   * @return true if the tree is balanced
+   */
+  @Override
+  protected boolean isBalanced() {
+    return totalLength >= minLengthByDepth[treeDepth];
+  }
+
+  /**
+   * Takes a substring of this one. This involves recursive descent along the
+   * left and right edges of the substring, and referencing any wholly contained
+   * segments in between. Any leaf nodes entirely uninvolved in the substring
+   * will not be referenced by the substring.
+   *
+   * <p>Substrings of {@code length < 2} should result in at most a single
+   * recursive call chain, terminating at a leaf node. Thus the result will be a
+   * {@link LiteralByteString}. {@link #RopeByteString(ByteString,
+   * ByteString)}.
+   *
+   * @param beginIndex start at this index
+   * @param endIndex   the last character is the one before this index
+   * @return substring leaf node or tree
+   */
+  @Override
+  public ByteString substring(int beginIndex, int endIndex) {
+    final int length = checkRange(beginIndex, endIndex, totalLength);
+
+    if (length == 0) {
+      // Empty substring
+      return ByteString.EMPTY;
+    }
+
+    if (length == totalLength) {
+      // The whole string
+      return this;
+    }
+
+    // Proper substring
+    if (endIndex <= leftLength) {
+      // Substring on the left
+      return left.substring(beginIndex, endIndex);
+    }
+
+    if (beginIndex >= leftLength) {
+      // Substring on the right
+      return right.substring(beginIndex - leftLength, endIndex - leftLength);
+    }
+
+    // Split substring
+    ByteString leftSub = left.substring(beginIndex);
+    ByteString rightSub = right.substring(0, endIndex - leftLength);
+    // Intentionally not rebalancing, since in many cases these two
+    // substrings will already be less deep than the top-level
+    // RopeByteString we're taking a substring of.
+    return new RopeByteString(leftSub, rightSub);
+  }
+
+  // =================================================================
+  // ByteString -> byte[]
+
+  @Override
+  protected void copyToInternal(byte[] target, int sourceOffset,
+      int targetOffset, int numberToCopy) {
+   if (sourceOffset + numberToCopy <= leftLength) {
+      left.copyToInternal(target, sourceOffset, targetOffset, numberToCopy);
+    } else if (sourceOffset >= leftLength) {
+      right.copyToInternal(target, sourceOffset - leftLength, targetOffset,
+          numberToCopy);
+    } else {
+      int leftLength = this.leftLength - sourceOffset;
+      left.copyToInternal(target, sourceOffset, targetOffset, leftLength);
+      right.copyToInternal(target, 0, targetOffset + leftLength,
+          numberToCopy - leftLength);
+    }
+  }
+
+  @Override
+  public void copyTo(ByteBuffer target) {
+    left.copyTo(target);
+    right.copyTo(target);
+  }
+
+  @Override
+  public ByteBuffer asReadOnlyByteBuffer() {
+    ByteBuffer byteBuffer = ByteBuffer.wrap(toByteArray());
+    return byteBuffer.asReadOnlyBuffer();
+  }
+
+  @Override
+  public List<ByteBuffer> asReadOnlyByteBufferList() {
+    // Walk through the list of LiteralByteString's that make up this
+    // rope, and add each one as a read-only ByteBuffer.
+    List<ByteBuffer> result = new ArrayList<ByteBuffer>();
+    PieceIterator pieces = new PieceIterator(this);
+    while (pieces.hasNext()) {
+      LeafByteString byteString = pieces.next();
+      result.add(byteString.asReadOnlyByteBuffer());
+    }
+    return result;
+  }
+
+  @Override
+  public void writeTo(OutputStream outputStream) throws IOException {
+    left.writeTo(outputStream);
+    right.writeTo(outputStream);
+  }
+
+  @Override
+  void writeToInternal(OutputStream out, int sourceOffset,
+      int numberToWrite) throws IOException {
+    if (sourceOffset + numberToWrite <= leftLength) {
+      left.writeToInternal(out, sourceOffset, numberToWrite);
+    } else if (sourceOffset >= leftLength) {
+      right.writeToInternal(out, sourceOffset - leftLength, numberToWrite);
+    } else {
+      int numberToWriteInLeft = leftLength - sourceOffset;
+      left.writeToInternal(out, sourceOffset, numberToWriteInLeft);
+      right.writeToInternal(out, 0, numberToWrite - numberToWriteInLeft);
+    }
+  }
+
+  @Override
+  protected String toStringInternal(Charset charset) {
+    return new String(toByteArray(), charset);
+  }
+
+  // =================================================================
+  // UTF-8 decoding
+
+  @Override
+  public boolean isValidUtf8() {
+    int leftPartial = left.partialIsValidUtf8(Utf8.COMPLETE, 0, leftLength);
+    int state = right.partialIsValidUtf8(leftPartial, 0, right.size());
+    return state == Utf8.COMPLETE;
+  }
+
+  @Override
+  protected int partialIsValidUtf8(int state, int offset, int length) {
+    int toIndex = offset + length;
+    if (toIndex <= leftLength) {
+      return left.partialIsValidUtf8(state, offset, length);
+    } else if (offset >= leftLength) {
+      return right.partialIsValidUtf8(state, offset - leftLength, length);
+    } else {
+      int leftLength = this.leftLength - offset;
+      int leftPartial = left.partialIsValidUtf8(state, offset, leftLength);
+      return right.partialIsValidUtf8(leftPartial, 0, length - leftLength);
+    }
+  }
+
+  // =================================================================
+  // equals() and hashCode()
+
+  @Override
+  public boolean equals(Object other) {
+    if (other == this) {
+      return true;
+    }
+    if (!(other instanceof ByteString)) {
+      return false;
+    }
+
+    ByteString otherByteString = (ByteString) other;
+    if (totalLength != otherByteString.size()) {
+      return false;
+    }
+    if (totalLength == 0) {
+      return true;
+    }
+
+    // You don't really want to be calling equals on long strings, but since
+    // we cache the hashCode, we effectively cache inequality. We use the cached
+    // hashCode if it's already computed.  It's arguable we should compute the
+    // hashCode here, and if we're going to be testing a bunch of byteStrings,
+    // it might even make sense.
+    int thisHash = peekCachedHashCode();
+    int thatHash = otherByteString.peekCachedHashCode();
+    if (thisHash != 0 && thatHash != 0 && thisHash != thatHash) {
+      return false;
+    }
+
+    return equalsFragments(otherByteString);
+  }
+
+  /**
+   * Determines if this string is equal to another of the same length by
+   * iterating over the leaf nodes. On each step of the iteration, the
+   * overlapping segments of the leaves are compared.
+   *
+   * @param other string of the same length as this one
+   * @return true if the values of this string equals the value of the given
+   *         one
+   */
+  private boolean equalsFragments(ByteString other) {
+    int thisOffset = 0;
+    Iterator<LeafByteString> thisIter = new PieceIterator(this);
+    LeafByteString thisString = thisIter.next();
+
+    int thatOffset = 0;
+    Iterator<LeafByteString> thatIter = new PieceIterator(other);
+    LeafByteString thatString = thatIter.next();
+
+    int pos = 0;
+    while (true) {
+      int thisRemaining = thisString.size() - thisOffset;
+      int thatRemaining = thatString.size() - thatOffset;
+      int bytesToCompare = Math.min(thisRemaining, thatRemaining);
+
+      // At least one of the offsets will be zero
+      boolean stillEqual = (thisOffset == 0)
+          ? thisString.equalsRange(thatString, thatOffset, bytesToCompare)
+          : thatString.equalsRange(thisString, thisOffset, bytesToCompare);
+      if (!stillEqual) {
+        return false;
+      }
+
+      pos += bytesToCompare;
+      if (pos >= totalLength) {
+        if (pos == totalLength) {
+          return true;
+        }
+        throw new IllegalStateException();
+      }
+      // We always get to the end of at least one of the pieces
+      if (bytesToCompare == thisRemaining) { // If reached end of this
+        thisOffset = 0;
+        thisString = thisIter.next();
+      } else {
+        thisOffset += bytesToCompare;
+      }
+      if (bytesToCompare == thatRemaining) { // If reached end of that
+        thatOffset = 0;
+        thatString = thatIter.next();
+      } else {
+        thatOffset += bytesToCompare;
+      }
+    }
+  }
+
+  @Override
+  protected int partialHash(int h, int offset, int length) {
+    int toIndex = offset + length;
+    if (toIndex <= leftLength) {
+      return left.partialHash(h, offset, length);
+    } else if (offset >= leftLength) {
+      return right.partialHash(h, offset - leftLength, length);
+    } else {
+      int leftLength = this.leftLength - offset;
+      int leftPartial = left.partialHash(h, offset, leftLength);
+      return right.partialHash(leftPartial, 0, length - leftLength);
+    }
+  }
+
+  // =================================================================
+  // Input stream
+
+  @Override
+  public CodedInputStream newCodedInput() {
+    return CodedInputStream.newInstance(new RopeInputStream());
+  }
+
+  @Override
+  public InputStream newInput() {
+    return new RopeInputStream();
+  }
+
+  /**
+   * This class implements the balancing algorithm of BAP95. In the paper the
+   * authors use an array to keep track of pieces, while here we use a stack.
+   * The tree is balanced by traversing subtrees in left to right order, and the
+   * stack always contains the part of the string we've traversed so far.
+   *
+   * <p>One surprising aspect of the algorithm is the result of balancing is not
+   * necessarily balanced, though it is nearly balanced.  For details, see
+   * BAP95.
+   */
+  private static class Balancer {
+    // Stack containing the part of the string, starting from the left, that
+    // we've already traversed.  The final string should be the equivalent of
+    // concatenating the strings on the stack from bottom to top.
+    private final Stack<ByteString> prefixesStack = new Stack<ByteString>();
+
+    private ByteString balance(ByteString left, ByteString right) {
+      doBalance(left);
+      doBalance(right);
+
+      // Sweep stack to gather the result
+      ByteString partialString = prefixesStack.pop();
+      while (!prefixesStack.isEmpty()) {
+        ByteString newLeft = prefixesStack.pop();
+        partialString = new RopeByteString(newLeft, partialString);
+      }
+      // We should end up with a RopeByteString since at a minimum we will
+      // create one from concatenating left and right
+      return partialString;
+    }
+
+    private void doBalance(ByteString root) {
+      // BAP95: Insert balanced subtrees whole. This means the result might not
+      // be balanced, leading to repeated rebalancings on concatenate. However,
+      // these rebalancings are shallow due to ignoring balanced subtrees, and
+      // relatively few calls to insert() result.
+      if (root.isBalanced()) {
+        insert(root);
+      } else if (root instanceof RopeByteString) {
+        RopeByteString rbs = (RopeByteString) root;
+        doBalance(rbs.left);
+        doBalance(rbs.right);
+      } else {
+        throw new IllegalArgumentException(
+            "Has a new type of ByteString been created? Found " +
+                root.getClass());
+      }
+    }
+
+    /**
+     * Push a string on the balance stack (BAP95).  BAP95 uses an array and
+     * calls the elements in the array 'bins'.  We instead use a stack, so the
+     * 'bins' of lengths are represented by differences between the elements of
+     * minLengthByDepth.
+     *
+     * <p>If the length bin for our string, and all shorter length bins, are
+     * empty, we just push it on the stack.  Otherwise, we need to start
+     * concatenating, putting the given string in the "middle" and continuing
+     * until we land in an empty length bin that matches the length of our
+     * concatenation.
+     *
+     * @param byteString string to place on the balance stack
+     */
+    private void insert(ByteString byteString) {
+      int depthBin = getDepthBinForLength(byteString.size());
+      int binEnd = minLengthByDepth[depthBin + 1];
+
+      // BAP95: Concatenate all trees occupying bins representing the length of
+      // our new piece or of shorter pieces, to the extent that is possible.
+      // The goal is to clear the bin which our piece belongs in, but that may
+      // not be entirely possible if there aren't enough longer bins occupied.
+      if (prefixesStack.isEmpty() || prefixesStack.peek().size() >= binEnd) {
+        prefixesStack.push(byteString);
+      } else {
+        int binStart = minLengthByDepth[depthBin];
+
+        // Concatenate the subtrees of shorter length
+        ByteString newTree = prefixesStack.pop();
+        while (!prefixesStack.isEmpty()
+            && prefixesStack.peek().size() < binStart) {
+          ByteString left = prefixesStack.pop();
+          newTree = new RopeByteString(left, newTree);
+        }
+
+        // Concatenate the given string
+        newTree = new RopeByteString(newTree, byteString);
+
+        // Continue concatenating until we land in an empty bin
+        while (!prefixesStack.isEmpty()) {
+          depthBin = getDepthBinForLength(newTree.size());
+          binEnd = minLengthByDepth[depthBin + 1];
+          if (prefixesStack.peek().size() < binEnd) {
+            ByteString left = prefixesStack.pop();
+            newTree = new RopeByteString(left, newTree);
+          } else {
+            break;
+          }
+        }
+        prefixesStack.push(newTree);
+      }
+    }
+
+    private int getDepthBinForLength(int length) {
+      int depth = Arrays.binarySearch(minLengthByDepth, length);
+      if (depth < 0) {
+        // It wasn't an exact match, so convert to the index of the containing
+        // fragment, which is one less even than the insertion point.
+        int insertionPoint = -(depth + 1);
+        depth = insertionPoint - 1;
+      }
+
+      return depth;
+    }
+  }
+
+  /**
+   * This class is a continuable tree traversal, which keeps the state
+   * information which would exist on the stack in a recursive traversal instead
+   * on a stack of "Bread Crumbs". The maximum depth of the stack in this
+   * iterator is the same as the depth of the tree being traversed.
+   *
+   * <p>This iterator is used to implement
+   * {@link RopeByteString#equalsFragments(ByteString)}.
+   */
+  private static class PieceIterator implements Iterator<LeafByteString> {
+
+    private final Stack<RopeByteString> breadCrumbs =
+        new Stack<RopeByteString>();
+    private LeafByteString next;
+
+    private PieceIterator(ByteString root) {
+      next = getLeafByLeft(root);
+    }
+
+    private LeafByteString getLeafByLeft(ByteString root) {
+      ByteString pos = root;
+      while (pos instanceof RopeByteString) {
+        RopeByteString rbs = (RopeByteString) pos;
+        breadCrumbs.push(rbs);
+        pos = rbs.left;
+      }
+      return (LeafByteString) pos;
+    }
+
+    private LeafByteString getNextNonEmptyLeaf() {
+      while (true) {
+        // Almost always, we go through this loop exactly once.  However, if
+        // we discover an empty string in the rope, we toss it and try again.
+        if (breadCrumbs.isEmpty()) {
+          return null;
+        } else {
+          LeafByteString result = getLeafByLeft(breadCrumbs.pop().right);
+          if (!result.isEmpty()) {
+            return result;
+          }
+        }
+      }
+    }
+
+    @Override
+    public boolean hasNext() {
+      return next != null;
+    }
+
+    /**
+     * Returns the next item and advances one {@code LiteralByteString}.
+     *
+     * @return next non-empty LiteralByteString or {@code null}
+     */
+    @Override
+    public LeafByteString next() {
+      if (next == null) {
+        throw new NoSuchElementException();
+      }
+      LeafByteString result = next;
+      next = getNextNonEmptyLeaf();
+      return result;
+    }
+
+    @Override
+    public void remove() {
+      throw new UnsupportedOperationException();
+    }
+  }
+
+  // =================================================================
+  // Serializable
+
+  private static final long serialVersionUID = 1L;
+
+  Object writeReplace() {
+    return new LiteralByteString(toByteArray());
+  }
+
+  private void readObject(@SuppressWarnings("unused") ObjectInputStream in) throws IOException {
+    throw new InvalidObjectException(
+        "RopeByteStream instances are not to be serialized directly");
+  }
+
+  /**
+   * This class is the {@link RopeByteString} equivalent for
+   * {@link ByteArrayInputStream}.
+   */
+  private class RopeInputStream extends InputStream {
+    // Iterates through the pieces of the rope
+    private PieceIterator pieceIterator;
+    // The current piece
+    private LeafByteString currentPiece;
+    // The size of the current piece
+    private int currentPieceSize;
+    // The index of the next byte to read in the current piece
+    private int currentPieceIndex;
+    // The offset of the start of the current piece in the rope byte string
+    private int currentPieceOffsetInRope;
+    // Offset in the buffer at which user called mark();
+    private int mark;
+
+    public RopeInputStream() {
+      initialize();
+    }
+
+    @Override
+    public int read(byte b[], int offset, int length)  {
+      if (b == null) {
+        throw new NullPointerException();
+      } else if (offset < 0 || length < 0 || length > b.length - offset) {
+        throw new IndexOutOfBoundsException();
+      }
+      return readSkipInternal(b, offset, length);
+    }
+
+    @Override
+    public long skip(long length) {
+      if (length < 0) {
+        throw new IndexOutOfBoundsException();
+      } else if (length > Integer.MAX_VALUE) {
+        length = Integer.MAX_VALUE;
+      }
+      return readSkipInternal(null, 0, (int) length);
+    }
+
+    /**
+     * Internal implementation of read and skip.  If b != null, then read the
+     * next {@code length} bytes into the buffer {@code b} at
+     * offset {@code offset}.  If b == null, then skip the next {@code length}
+     * bytes.
+     * <p>
+     * This method assumes that all error checking has already happened.
+     * <p>
+     * Returns the actual number of bytes read or skipped.
+     */
+    private int readSkipInternal(byte b[], int offset, int length)  {
+      int bytesRemaining = length;
+      while (bytesRemaining > 0) {
+        advanceIfCurrentPieceFullyRead();
+        if (currentPiece == null) {
+          if (bytesRemaining == length) {
+             // We didn't manage to read anything
+             return -1;
+           }
+          break;
+        } else {
+          // Copy the bytes from this piece.
+          int currentPieceRemaining = currentPieceSize - currentPieceIndex;
+          int count = Math.min(currentPieceRemaining, bytesRemaining);
+          if (b != null) {
+            currentPiece.copyTo(b, currentPieceIndex, offset, count);
+            offset += count;
+          }
+          currentPieceIndex += count;
+          bytesRemaining -= count;
+        }
+      }
+       // Return the number of bytes read.
+      return length - bytesRemaining;
+    }
+
+    @Override
+    public int read() throws IOException {
+      advanceIfCurrentPieceFullyRead();
+      if (currentPiece == null) {
+        return -1;
+      } else {
+        return currentPiece.byteAt(currentPieceIndex++) & 0xFF;
+      }
+    }
+
+    @Override
+    public int available() throws IOException {
+      int bytesRead = currentPieceOffsetInRope + currentPieceIndex;
+      return RopeByteString.this.size() - bytesRead;
+    }
+
+    @Override
+    public boolean markSupported() {
+      return true;
+    }
+
+    @Override
+    public void mark(int readAheadLimit) {
+      // Set the mark to our position in the byte string
+      mark = currentPieceOffsetInRope + currentPieceIndex;
+    }
+
+    @Override
+    public synchronized void reset() {
+      // Just reinitialize and skip the specified number of bytes.
+      initialize();
+      readSkipInternal(null, 0, mark);
+    }
+
+    /** Common initialization code used by both the constructor and reset() */
+    private void initialize() {
+      pieceIterator = new PieceIterator(RopeByteString.this);
+      currentPiece = pieceIterator.next();
+      currentPieceSize = currentPiece.size();
+      currentPieceIndex = 0;
+      currentPieceOffsetInRope = 0;
+    }
+
+    /**
+     * Skips to the next piece if we have read all the data in the current
+     * piece.  Sets currentPiece to null if we have reached the end of the
+     * input.
+     */
+    private void advanceIfCurrentPieceFullyRead() {
+      if (currentPiece != null && currentPieceIndex == currentPieceSize) {
+        // Generally, we can only go through this loop at most once, since
+        // empty strings can't end up in a rope.  But better to test.
+        currentPieceOffsetInRope += currentPieceSize;
+        currentPieceIndex = 0;
+        if (pieceIterator.hasNext()) {
+          currentPiece = pieceIterator.next();
+          currentPieceSize = currentPiece.size();
+        } else {
+          currentPiece = null;
+          currentPieceSize = 0;
+        }
+      }
+    }
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/RpcCallback.java b/java/core/src/main/java/com/google/protobuf/RpcCallback.java
new file mode 100644
index 00000000..10752968
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/RpcCallback.java
@@ -0,0 +1,47 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+/**
+ * Interface for an RPC callback, normally called when an RPC completes.
+ * {@code ParameterType} is normally the method's response message type.
+ *
+ * <p>Starting with version 2.3.0, RPC implementations should not try to build
+ * on this, but should instead provide code generator plugins which generate
+ * code specific to the particular RPC implementation.  This way the generated
+ * code can be more appropriate for the implementation in use and can avoid
+ * unnecessary layers of indirection.
+ *
+ * @author kenton@google.com Kenton Varda
+ */
+public interface RpcCallback<ParameterType> {
+  void run(ParameterType parameter);
+}
diff --git a/java/core/src/main/java/com/google/protobuf/RpcChannel.java b/java/core/src/main/java/com/google/protobuf/RpcChannel.java
new file mode 100644
index 00000000..f272f4ad
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/RpcChannel.java
@@ -0,0 +1,71 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+/**
+ * <p>Abstract interface for an RPC channel.  An {@code RpcChannel} represents a
+ * communication line to a {@link Service} which can be used to call that
+ * {@link Service}'s methods.  The {@link Service} may be running on another
+ * machine.  Normally, you should not call an {@code RpcChannel} directly, but
+ * instead construct a stub {@link Service} wrapping it.  Example:
+ *
+ * <pre>
+ *   RpcChannel channel = rpcImpl.newChannel("remotehost.example.com:1234");
+ *   RpcController controller = rpcImpl.newController();
+ *   MyService service = MyService.newStub(channel);
+ *   service.myMethod(controller, request, callback);
+ * </pre>
+ *
+ * <p>Starting with version 2.3.0, RPC implementations should not try to build
+ * on this, but should instead provide code generator plugins which generate
+ * code specific to the particular RPC implementation.  This way the generated
+ * code can be more appropriate for the implementation in use and can avoid
+ * unnecessary layers of indirection.
+ *
+ * @author kenton@google.com Kenton Varda
+ */
+public interface RpcChannel {
+  /**
+   * Call the given method of the remote service.  This method is similar to
+   * {@code Service.callMethod()} with one important difference:  the caller
+   * decides the types of the {@code Message} objects, not the callee.  The
+   * request may be of any type as long as
+   * {@code request.getDescriptor() == method.getInputType()}.
+   * The response passed to the callback will be of the same type as
+   * {@code responsePrototype} (which must have
+   * {@code getDescriptor() == method.getOutputType()}).
+   */
+  void callMethod(Descriptors.MethodDescriptor method,
+                  RpcController controller,
+                  Message request,
+                  Message responsePrototype,
+                  RpcCallback<Message> done);
+}
diff --git a/java/core/src/main/java/com/google/protobuf/RpcController.java b/java/core/src/main/java/com/google/protobuf/RpcController.java
new file mode 100644
index 00000000..a92dd7be
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/RpcController.java
@@ -0,0 +1,118 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+/**
+ * <p>An {@code RpcController} mediates a single method call.  The primary
+ * purpose of the controller is to provide a way to manipulate settings
+ * specific to the RPC implementation and to find out about RPC-level errors.
+ *
+ * <p>Starting with version 2.3.0, RPC implementations should not try to build
+ * on this, but should instead provide code generator plugins which generate
+ * code specific to the particular RPC implementation.  This way the generated
+ * code can be more appropriate for the implementation in use and can avoid
+ * unnecessary layers of indirection.
+ *
+ * <p>The methods provided by the {@code RpcController} interface are intended
+ * to be a "least common denominator" set of features which we expect all
+ * implementations to support.  Specific implementations may provide more
+ * advanced features (e.g. deadline propagation).
+ *
+ * @author kenton@google.com Kenton Varda
+ */
+public interface RpcController {
+  // -----------------------------------------------------------------
+  // These calls may be made from the client side only.  Their results
+  // are undefined on the server side (may throw RuntimeExceptions).
+
+  /**
+   * Resets the RpcController to its initial state so that it may be reused in
+   * a new call.  This can be called from the client side only.  It must not
+   * be called while an RPC is in progress.
+   */
+  void reset();
+
+  /**
+   * After a call has finished, returns true if the call failed.  The possible
+   * reasons for failure depend on the RPC implementation.  {@code failed()}
+   * most only be called on the client side, and must not be called before a
+   * call has finished.
+   */
+  boolean failed();
+
+  /**
+   * If {@code failed()} is {@code true}, returns a human-readable description
+   * of the error.
+   */
+  String errorText();
+
+  /**
+   * Advises the RPC system that the caller desires that the RPC call be
+   * canceled.  The RPC system may cancel it immediately, may wait awhile and
+   * then cancel it, or may not even cancel the call at all.  If the call is
+   * canceled, the "done" callback will still be called and the RpcController
+   * will indicate that the call failed at that time.
+   */
+  void startCancel();
+
+  // -----------------------------------------------------------------
+  // These calls may be made from the server side only.  Their results
+  // are undefined on the client side (may throw RuntimeExceptions).
+
+  /**
+   * Causes {@code failed()} to return true on the client side.  {@code reason}
+   * will be incorporated into the message returned by {@code errorText()}.
+   * If you find you need to return machine-readable information about
+   * failures, you should incorporate it into your response protocol buffer
+   * and should NOT call {@code setFailed()}.
+   */
+  void setFailed(String reason);
+
+  /**
+   * If {@code true}, indicates that the client canceled the RPC, so the server
+   * may as well give up on replying to it.  This method must be called on the
+   * server side only.  The server should still call the final "done" callback.
+   */
+  boolean isCanceled();
+
+  /**
+   * Asks that the given callback be called when the RPC is canceled.  The
+   * parameter passed to the callback will always be {@code null}.  The
+   * callback will always be called exactly once.  If the RPC completes without
+   * being canceled, the callback will be called after completion.  If the RPC
+   * has already been canceled when NotifyOnCancel() is called, the callback
+   * will be called immediately.
+   *
+   * <p>{@code notifyOnCancel()} must be called no more than once per request.
+   * It must be called on the server side only.
+   */
+  void notifyOnCancel(RpcCallback<Object> callback);
+}
diff --git a/java/core/src/main/java/com/google/protobuf/RpcUtil.java b/java/core/src/main/java/com/google/protobuf/RpcUtil.java
new file mode 100644
index 00000000..694b8d13
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/RpcUtil.java
@@ -0,0 +1,134 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+/**
+ * Grab-bag of utility functions useful when dealing with RPCs.
+ *
+ * @author kenton@google.com Kenton Varda
+ */
+public final class RpcUtil {
+  private RpcUtil() {}
+
+  /**
+   * Take an {@code RpcCallback<Message>} and convert it to an
+   * {@code RpcCallback} accepting a specific message type.  This is always
+   * type-safe (parameter type contravariance).
+   */
+  @SuppressWarnings("unchecked")
+  public static <Type extends Message> RpcCallback<Type>
+  specializeCallback(final RpcCallback<Message> originalCallback) {
+    return (RpcCallback<Type>)originalCallback;
+    // The above cast works, but only due to technical details of the Java
+    // implementation.  A more theoretically correct -- but less efficient --
+    // implementation would be as follows:
+    //   return new RpcCallback<Type>() {
+    //     public void run(Type parameter) {
+    //       originalCallback.run(parameter);
+    //     }
+    //   };
+  }
+
+  /**
+   * Take an {@code RpcCallback} accepting a specific message type and convert
+   * it to an {@code RpcCallback<Message>}.  The generalized callback will
+   * accept any message object which has the same descriptor, and will convert
+   * it to the correct class before calling the original callback.  However,
+   * if the generalized callback is given a message with a different descriptor,
+   * an exception will be thrown.
+   */
+  public static <Type extends Message>
+  RpcCallback<Message> generalizeCallback(
+      final RpcCallback<Type> originalCallback,
+      final Class<Type> originalClass,
+      final Type defaultInstance) {
+    return new RpcCallback<Message>() {
+      public void run(final Message parameter) {
+        Type typedParameter;
+        try {
+          typedParameter = originalClass.cast(parameter);
+        } catch (ClassCastException ignored) {
+          typedParameter = copyAsType(defaultInstance, parameter);
+        }
+        originalCallback.run(typedParameter);
+      }
+    };
+  }
+
+  /**
+   * Creates a new message of type "Type" which is a copy of "source".  "source"
+   * must have the same descriptor but may be a different class (e.g.
+   * DynamicMessage).
+   */
+  @SuppressWarnings("unchecked")
+  private static <Type extends Message> Type copyAsType(
+      final Type typeDefaultInstance, final Message source) {
+    return (Type) typeDefaultInstance
+        .newBuilderForType().mergeFrom(source).build();
+  }
+
+  /**
+   * Creates a callback which can only be called once.  This may be useful for
+   * security, when passing a callback to untrusted code:  most callbacks do
+   * not expect to be called more than once, so doing so may expose bugs if it
+   * is not prevented.
+   */
+  public static <ParameterType>
+    RpcCallback<ParameterType> newOneTimeCallback(
+      final RpcCallback<ParameterType> originalCallback) {
+    return new RpcCallback<ParameterType>() {
+      private boolean alreadyCalled = false;
+
+      public void run(final ParameterType parameter) {
+        synchronized(this) {
+          if (alreadyCalled) {
+            throw new AlreadyCalledException();
+          }
+          alreadyCalled = true;
+        }
+
+        originalCallback.run(parameter);
+      }
+    };
+  }
+
+  /**
+   * Exception thrown when a one-time callback is called more than once.
+   */
+  public static final class AlreadyCalledException extends RuntimeException {
+    private static final long serialVersionUID = 5469741279507848266L;
+
+    public AlreadyCalledException() {
+      super("This RpcCallback was already called and cannot be called " +
+            "multiple times.");
+    }
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/Service.java b/java/core/src/main/java/com/google/protobuf/Service.java
new file mode 100644
index 00000000..ba7b033e
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/Service.java
@@ -0,0 +1,117 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+/**
+ * Abstract base interface for protocol-buffer-based RPC services.  Services
+ * themselves are abstract classes (implemented either by servers or as
+ * stubs), but they subclass this base interface.  The methods of this
+ * interface can be used to call the methods of the service without knowing
+ * its exact type at compile time (analogous to the Message interface).
+ *
+ * <p>Starting with version 2.3.0, RPC implementations should not try to build
+ * on this, but should instead provide code generator plugins which generate
+ * code specific to the particular RPC implementation.  This way the generated
+ * code can be more appropriate for the implementation in use and can avoid
+ * unnecessary layers of indirection.
+ *
+ * @author kenton@google.com Kenton Varda
+ */
+public interface Service {
+  /**
+   * Get the {@code ServiceDescriptor} describing this service and its methods.
+   */
+  Descriptors.ServiceDescriptor getDescriptorForType();
+
+  /**
+   * <p>Call a method of the service specified by MethodDescriptor.  This is
+   * normally implemented as a simple {@code switch()} that calls the standard
+   * definitions of the service's methods.
+   *
+   * <p>Preconditions:
+   * <ul>
+   *   <li>{@code method.getService() == getDescriptorForType()}
+   *   <li>{@code request} is of the exact same class as the object returned by
+   *       {@code getRequestPrototype(method)}.
+   *   <li>{@code controller} is of the correct type for the RPC implementation
+   *       being used by this Service.  For stubs, the "correct type" depends
+   *       on the RpcChannel which the stub is using.  Server-side Service
+   *       implementations are expected to accept whatever type of
+   *       {@code RpcController} the server-side RPC implementation uses.
+   * </ul>
+   *
+   * <p>Postconditions:
+   * <ul>
+   *   <li>{@code done} will be called when the method is complete.  This may be
+   *       before {@code callMethod()} returns or it may be at some point in
+   *       the future.
+   *   <li>The parameter to {@code done} is the response.  It must be of the
+   *       exact same type as would be returned by
+   *       {@code getResponsePrototype(method)}.
+   *   <li>If the RPC failed, the parameter to {@code done} will be
+   *       {@code null}.  Further details about the failure can be found by
+   *       querying {@code controller}.
+   * </ul>
+   */
+  void callMethod(Descriptors.MethodDescriptor method,
+                  RpcController controller,
+                  Message request,
+                  RpcCallback<Message> done);
+
+  /**
+   * <p>{@code callMethod()} requires that the request passed in is of a
+   * particular subclass of {@code Message}.  {@code getRequestPrototype()}
+   * gets the default instances of this type for a given method.  You can then
+   * call {@code Message.newBuilderForType()} on this instance to
+   * construct a builder to build an object which you can then pass to
+   * {@code callMethod()}.
+   *
+   * <p>Example:
+   * <pre>
+   *   MethodDescriptor method =
+   *     service.getDescriptorForType().findMethodByName("Foo");
+   *   Message request =
+   *     stub.getRequestPrototype(method).newBuilderForType()
+   *         .mergeFrom(input).build();
+   *   service.callMethod(method, request, callback);
+   * </pre>
+   */
+  Message getRequestPrototype(Descriptors.MethodDescriptor method);
+
+  /**
+   * Like {@code getRequestPrototype()}, but gets a prototype of the response
+   * message.  {@code getResponsePrototype()} is generally not needed because
+   * the {@code Service} implementation constructs the response message itself,
+   * but it may be useful in some cases to know ahead of time what type of
+   * object will be returned.
+   */
+  Message getResponsePrototype(Descriptors.MethodDescriptor method);
+}
diff --git a/java/core/src/main/java/com/google/protobuf/ServiceException.java b/java/core/src/main/java/com/google/protobuf/ServiceException.java
new file mode 100644
index 00000000..00d57075
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/ServiceException.java
@@ -0,0 +1,52 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+/**
+ * Thrown by blocking RPC methods when a failure occurs.
+ *
+ * @author cpovirk@google.com (Chris Povirk)
+ */
+public class ServiceException extends Exception {
+  private static final long serialVersionUID = -1219262335729891920L;
+
+  public ServiceException(final String message) {
+    super(message);
+  }
+
+  public ServiceException(final Throwable cause) {
+    super(cause);
+  }
+
+  public ServiceException(final String message, final Throwable cause) {
+    super(message, cause);
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/SingleFieldBuilder.java b/java/core/src/main/java/com/google/protobuf/SingleFieldBuilder.java
new file mode 100644
index 00000000..aba65e32
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/SingleFieldBuilder.java
@@ -0,0 +1,241 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+/**
+ * {@code SingleFieldBuilder} implements a structure that a protocol
+ * message uses to hold a single field of another protocol message. It supports
+ * the classical use case of setting an immutable {@link Message} as the value
+ * of the field and is highly optimized around this.
+ * <br>
+ * It also supports the additional use case of setting a {@link Message.Builder}
+ * as the field and deferring conversion of that {@code Builder}
+ * to an immutable {@code Message}. In this way, it's possible to maintain
+ * a tree of {@code Builder}'s that acts as a fully read/write data
+ * structure.
+ * <br>
+ * Logically, one can think of a tree of builders as converting the entire tree
+ * to messages when build is called on the root or when any method is called
+ * that desires a Message instead of a Builder. In terms of the implementation,
+ * the {@code SingleFieldBuilder} and {@code RepeatedFieldBuilder}
+ * classes cache messages that were created so that messages only need to be
+ * created when some change occurred in its builder or a builder for one of its
+ * descendants.
+ *
+ * @param <MType> the type of message for the field
+ * @param <BType> the type of builder for the field
+ * @param <IType> the common interface for the message and the builder
+ *
+ * @author jonp@google.com (Jon Perlow)
+ */
+public class SingleFieldBuilder
+    <MType extends GeneratedMessage,
+     BType extends GeneratedMessage.Builder,
+     IType extends MessageOrBuilder>
+    implements GeneratedMessage.BuilderParent {
+
+  // Parent to send changes to.
+  private GeneratedMessage.BuilderParent parent;
+
+  // Invariant: one of builder or message fields must be non-null.
+
+  // If set, this is the case where we are backed by a builder. In this case,
+  // message field represents a cached message for the builder (or null if
+  // there is no cached message).
+  private BType builder;
+
+  // If builder is non-null, this represents a cached message from the builder.
+  // If builder is null, this is the authoritative message for the field.
+  private MType message;
+
+  // Indicates that we've built a message and so we are now obligated
+  // to dispatch dirty invalidations. See GeneratedMessage.BuilderListener.
+  private boolean isClean;
+
+  public SingleFieldBuilder(
+      MType message,
+      GeneratedMessage.BuilderParent parent,
+      boolean isClean) {
+    if (message == null) {
+      throw new NullPointerException();
+    }
+    this.message = message;
+    this.parent = parent;
+    this.isClean = isClean;
+  }
+
+  public void dispose() {
+    // Null out parent so we stop sending it invalidations.
+    parent = null;
+  }
+
+  /**
+   * Get the message for the field. If the message is currently stored
+   * as a {@code Builder}, it is converted to a {@code Message} by
+   * calling {@link Message.Builder#buildPartial} on it. If no message has
+   * been set, returns the default instance of the message.
+   *
+   * @return the message for the field
+   */
+  @SuppressWarnings("unchecked")
+  public MType getMessage() {
+    if (message == null) {
+      // If message is null, the invariant is that we must be have a builder.
+      message = (MType) builder.buildPartial();
+    }
+    return message;
+  }
+
+  /**
+   * Builds the message and returns it.
+   *
+   * @return the message
+   */
+  public MType build() {
+    // Now that build has been called, we are required to dispatch
+    // invalidations.
+    isClean = true;
+    return getMessage();
+  }
+
+  /**
+   * Gets a builder for the field. If no builder has been created yet, a
+   * builder is created on demand by calling {@link Message#toBuilder}.
+   *
+   * @return The builder for the field
+   */
+  @SuppressWarnings("unchecked")
+  public BType getBuilder() {
+    if (builder == null) {
+      // builder.mergeFrom() on a fresh builder
+      // does not create any sub-objects with independent clean/dirty states,
+      // therefore setting the builder itself to clean without actually calling
+      // build() cannot break any invariants.
+      builder = (BType) message.newBuilderForType(this);
+      builder.mergeFrom(message); // no-op if message is the default message
+      builder.markClean();
+    }
+    return builder;
+  }
+
+  /**
+   * Gets the base class interface for the field. This may either be a builder
+   * or a message. It will return whatever is more efficient.
+   *
+   * @return the message or builder for the field as the base class interface
+   */
+  @SuppressWarnings("unchecked")
+  public IType getMessageOrBuilder() {
+    if (builder != null) {
+      return  (IType) builder;
+    } else {
+      return (IType) message;
+    }
+  }
+
+  /**
+   * Sets a  message for the field replacing any existing value.
+   *
+   * @param message the message to set
+   * @return the builder
+   */
+  public SingleFieldBuilder<MType, BType, IType> setMessage(
+      MType message) {
+    if (message == null) {
+      throw new NullPointerException();
+    }
+    this.message = message;
+    if (builder != null) {
+      builder.dispose();
+      builder = null;
+    }
+    onChanged();
+    return this;
+  }
+
+  /**
+   * Merges the field from another field.
+   *
+   * @param value the value to merge from
+   * @return the builder
+   */
+  public SingleFieldBuilder<MType, BType, IType> mergeFrom(
+      MType value) {
+    if (builder == null && message == message.getDefaultInstanceForType()) {
+      message = value;
+    } else {
+      getBuilder().mergeFrom(value);
+    }
+    onChanged();
+    return this;
+  }
+
+  /**
+   * Clears the value of the field.
+   *
+   * @return the builder
+   */
+  @SuppressWarnings("unchecked")
+  public SingleFieldBuilder<MType, BType, IType> clear() {
+    message = (MType) (message != null ?
+        message.getDefaultInstanceForType() :
+        builder.getDefaultInstanceForType());
+    if (builder != null) {
+      builder.dispose();
+      builder = null;
+    }
+    onChanged();
+    return this;
+  }
+
+  /**
+   * Called when a the builder or one of its nested children has changed
+   * and any parent should be notified of its invalidation.
+   */
+  private void onChanged() {
+    // If builder is null, this is the case where onChanged is being called
+    // from setMessage or clear.
+    if (builder != null) {
+      message = null;
+    }
+    if (isClean && parent != null) {
+      parent.markDirty();
+
+      // Don't keep dispatching invalidations until build is called again.
+      isClean = false;
+    }
+  }
+
+  //@Override (Java 1.6 override semantics, but we must support 1.5)
+  public void markDirty() {
+    onChanged();
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/SmallSortedMap.java b/java/core/src/main/java/com/google/protobuf/SmallSortedMap.java
new file mode 100644
index 00000000..0674d2e2
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/SmallSortedMap.java
@@ -0,0 +1,618 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import java.util.AbstractMap;
+import java.util.AbstractSet;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Iterator;
+import java.util.TreeMap;
+import java.util.List;
+import java.util.Map;
+import java.util.NoSuchElementException;
+import java.util.Set;
+import java.util.SortedMap;
+
+/**
+ * A custom map implementation from FieldDescriptor to Object optimized to
+ * minimize the number of memory allocations for instances with a small number
+ * of mappings. The implementation stores the first {@code k} mappings in an
+ * array for a configurable value of {@code k}, allowing direct access to the
+ * corresponding {@code Entry}s without the need to create an Iterator. The
+ * remaining entries are stored in an overflow map. Iteration over the entries
+ * in the map should be done as follows:
+ *
+ * <pre>   {@code
+ * for (int i = 0; i < fieldMap.getNumArrayEntries(); i++) {
+ *   process(fieldMap.getArrayEntryAt(i));
+ * }
+ * for (Map.Entry<K, V> entry : fieldMap.getOverflowEntries()) {
+ *   process(entry);
+ * }
+ * }</pre>
+ *
+ * The resulting iteration is in order of ascending field tag number. The
+ * object returned by {@link #entrySet()} adheres to the same contract but is
+ * less efficient as it necessarily involves creating an object for iteration.
+ * <p>
+ * The tradeoff for this memory efficiency is that the worst case running time
+ * of the {@code put()} operation is {@code O(k + lg n)}, which happens when
+ * entries are added in descending order. {@code k} should be chosen such that
+ * it covers enough common cases without adversely affecting larger maps. In
+ * practice, the worst case scenario does not happen for extensions because
+ * extension fields are serialized and deserialized in order of ascending tag
+ * number, but the worst case scenario can happen for DynamicMessages.
+ * <p>
+ * The running time for all other operations is similar to that of
+ * {@code TreeMap}.
+ * <p>
+ * Instances are not thread-safe until {@link #makeImmutable()} is called,
+ * after which any modifying operation will result in an
+ * {@link UnsupportedOperationException}.
+ *
+ * @author darick@google.com Darick Tong
+ */
+// This class is final for all intents and purposes because the constructor is
+// private. However, the FieldDescriptor-specific logic is encapsulated in
+// a subclass to aid testability of the core logic.
+class SmallSortedMap<K extends Comparable<K>, V> extends AbstractMap<K, V> {
+
+  /**
+   * Creates a new instance for mapping FieldDescriptors to their values.
+   * The {@link #makeImmutable()} implementation will convert the List values
+   * of any repeated fields to unmodifiable lists.
+   *
+   * @param arraySize The size of the entry array containing the
+   *        lexicographically smallest mappings.
+   */
+  static <FieldDescriptorType extends
+      FieldSet.FieldDescriptorLite<FieldDescriptorType>>
+      SmallSortedMap<FieldDescriptorType, Object> newFieldMap(int arraySize) {
+    return new SmallSortedMap<FieldDescriptorType, Object>(arraySize) {
+      @Override
+      @SuppressWarnings("unchecked")
+      public void makeImmutable() {
+        if (!isImmutable()) {
+          for (int i = 0; i < getNumArrayEntries(); i++) {
+            final Map.Entry<FieldDescriptorType, Object> entry =
+                getArrayEntryAt(i);
+            if (entry.getKey().isRepeated()) {
+              final List value = (List) entry.getValue();
+              entry.setValue(Collections.unmodifiableList(value));
+            }
+          }
+          for (Map.Entry<FieldDescriptorType, Object> entry :
+                   getOverflowEntries()) {
+            if (entry.getKey().isRepeated()) {
+              final List value = (List) entry.getValue();
+              entry.setValue(Collections.unmodifiableList(value));
+            }
+          }
+        }
+        super.makeImmutable();
+      }
+    };
+  }
+
+  /**
+   * Creates a new instance for testing.
+   *
+   * @param arraySize The size of the entry array containing the
+   *        lexicographically smallest mappings.
+   */
+  static <K extends Comparable<K>, V> SmallSortedMap<K, V> newInstanceForTest(
+      int arraySize) {
+    return new SmallSortedMap<K, V>(arraySize);
+  }
+
+  private final int maxArraySize;
+  // The "entry array" is actually a List because generic arrays are not
+  // allowed. ArrayList also nicely handles the entry shifting on inserts and
+  // removes.
+  private List<Entry> entryList;
+  private Map<K, V> overflowEntries;
+  private boolean isImmutable;
+  // The EntrySet is a stateless view of the Map. It's initialized the first
+  // time it is requested and reused henceforth.
+  private volatile EntrySet lazyEntrySet;
+
+  /**
+   * @code arraySize Size of the array in which the lexicographically smallest
+   *       mappings are stored. (i.e. the {@code k} referred to in the class
+   *       documentation).
+   */
+  private SmallSortedMap(int arraySize) {
+    this.maxArraySize = arraySize;
+    this.entryList = Collections.emptyList();
+    this.overflowEntries = Collections.emptyMap();
+  }
+
+  /** Make this map immutable from this point forward. */
+  public void makeImmutable() {
+    if (!isImmutable) {
+      // Note: There's no need to wrap the entryList in an unmodifiableList
+      // because none of the list's accessors are exposed. The iterator() of
+      // overflowEntries, on the other hand, is exposed so it must be made
+      // unmodifiable.
+      overflowEntries = overflowEntries.isEmpty() ?
+          Collections.<K, V>emptyMap() :
+          Collections.unmodifiableMap(overflowEntries);
+      isImmutable = true;
+    }
+  }
+
+  /** @return Whether {@link #makeImmutable()} has been called. */
+  public boolean isImmutable() {
+    return isImmutable;
+  }
+
+  /** @return The number of entries in the entry array. */
+  public int getNumArrayEntries() {
+    return entryList.size();
+  }
+
+  /** @return The array entry at the given {@code index}. */
+  public Map.Entry<K, V> getArrayEntryAt(int index) {
+    return entryList.get(index);
+  }
+
+  /** @return There number of overflow entries. */
+  public int getNumOverflowEntries() {
+    return overflowEntries.size();
+  }
+
+  /** @return An iterable over the overflow entries. */
+  public Iterable<Map.Entry<K, V>> getOverflowEntries() {
+    return overflowEntries.isEmpty() ?
+        EmptySet.<Map.Entry<K, V>>iterable() :
+        overflowEntries.entrySet();
+  }
+
+  @Override
+  public int size() {
+    return entryList.size() + overflowEntries.size();
+  }
+
+  /**
+   * The implementation throws a {@code ClassCastException} if o is not an
+   * object of type {@code K}.
+   *
+   * {@inheritDoc}
+   */
+  @Override
+  public boolean containsKey(Object o) {
+    @SuppressWarnings("unchecked")
+    final K key = (K) o;
+    return binarySearchInArray(key) >= 0 || overflowEntries.containsKey(key);
+  }
+
+  /**
+   * The implementation throws a {@code ClassCastException} if o is not an
+   * object of type {@code K}.
+   *
+   * {@inheritDoc}
+   */
+  @Override
+  public V get(Object o) {
+    @SuppressWarnings("unchecked")
+    final K key = (K) o;
+    final int index = binarySearchInArray(key);
+    if (index >= 0) {
+      return entryList.get(index).getValue();
+    }
+    return overflowEntries.get(key);
+  }
+
+  @Override
+  public V put(K key, V value) {
+    checkMutable();
+    final int index = binarySearchInArray(key);
+    if (index >= 0) {
+      // Replace existing array entry.
+      return entryList.get(index).setValue(value);
+    }
+    ensureEntryArrayMutable();
+    final int insertionPoint = -(index + 1);
+    if (insertionPoint >= maxArraySize) {
+      // Put directly in overflow.
+      return getOverflowEntriesMutable().put(key, value);
+    }
+    // Insert new Entry in array.
+    if (entryList.size() == maxArraySize) {
+      // Shift the last array entry into overflow.
+      final Entry lastEntryInArray = entryList.remove(maxArraySize - 1);
+      getOverflowEntriesMutable().put(lastEntryInArray.getKey(),
+                                      lastEntryInArray.getValue());
+    }
+    entryList.add(insertionPoint, new Entry(key, value));
+    return null;
+  }
+
+  @Override
+  public void clear() {
+    checkMutable();
+    if (!entryList.isEmpty()) {
+      entryList.clear();
+    }
+    if (!overflowEntries.isEmpty()) {
+      overflowEntries.clear();
+    }
+  }
+
+  /**
+   * The implementation throws a {@code ClassCastException} if o is not an
+   * object of type {@code K}.
+   *
+   * {@inheritDoc}
+   */
+  @Override
+  public V remove(Object o) {
+    checkMutable();
+    @SuppressWarnings("unchecked")
+    final K key = (K) o;
+    final int index = binarySearchInArray(key);
+    if (index >= 0) {
+      return removeArrayEntryAt(index);
+    }
+    // overflowEntries might be Collections.unmodifiableMap(), so only
+    // call remove() if it is non-empty.
+    if (overflowEntries.isEmpty()) {
+      return null;
+    } else {
+      return overflowEntries.remove(key);
+    }
+  }
+
+  private V removeArrayEntryAt(int index) {
+    checkMutable();
+    final V removed = entryList.remove(index).getValue();
+    if (!overflowEntries.isEmpty()) {
+      // Shift the first entry in the overflow to be the last entry in the
+      // array.
+      final Iterator<Map.Entry<K, V>> iterator =
+          getOverflowEntriesMutable().entrySet().iterator();
+      entryList.add(new Entry(iterator.next()));
+      iterator.remove();
+    }
+    return removed;
+  }
+
+  /**
+   * @param key The key to find in the entry array.
+   * @return The returned integer position follows the same semantics as the
+   *     value returned by {@link java.util.Arrays#binarySearch()}.
+   */
+  private int binarySearchInArray(K key) {
+    int left = 0;
+    int right = entryList.size() - 1;
+
+    // Optimization: For the common case in which entries are added in
+    // ascending tag order, check the largest element in the array before
+    // doing a full binary search.
+    if (right >= 0) {
+      int cmp = key.compareTo(entryList.get(right).getKey());
+      if (cmp > 0) {
+        return -(right + 2);  // Insert point is after "right".
+      } else if (cmp == 0) {
+        return right;
+      }
+    }
+
+    while (left <= right) {
+      int mid = (left + right) / 2;
+      int cmp = key.compareTo(entryList.get(mid).getKey());
+      if (cmp < 0) {
+        right = mid - 1;
+      } else if (cmp > 0) {
+        left = mid + 1;
+      } else {
+        return mid;
+      }
+    }
+    return -(left + 1);
+  }
+
+  /**
+   * Similar to the AbstractMap implementation of {@code keySet()} and
+   * {@code values()}, the entry set is created the first time this method is
+   * called, and returned in response to all subsequent calls.
+   *
+   * {@inheritDoc}
+   */
+  @Override
+  public Set<Map.Entry<K, V>> entrySet() {
+    if (lazyEntrySet == null) {
+      lazyEntrySet = new EntrySet();
+    }
+    return lazyEntrySet;
+  }
+
+  /**
+   * @throws UnsupportedOperationException if {@link #makeImmutable()} has
+   *         has been called.
+   */
+  private void checkMutable() {
+    if (isImmutable) {
+      throw new UnsupportedOperationException();
+    }
+  }
+
+  /**
+   * @return a {@link SortedMap} to which overflow entries mappings can be
+   *         added or removed.
+   * @throws UnsupportedOperationException if {@link #makeImmutable()} has been
+   *         called.
+   */
+  @SuppressWarnings("unchecked")
+  private SortedMap<K, V> getOverflowEntriesMutable() {
+    checkMutable();
+    if (overflowEntries.isEmpty() && !(overflowEntries instanceof TreeMap)) {
+      overflowEntries = new TreeMap<K, V>();
+    }
+    return (SortedMap<K, V>) overflowEntries;
+  }
+
+  /**
+   * Lazily creates the entry list. Any code that adds to the list must first
+   * call this method.
+   */
+  private void ensureEntryArrayMutable() {
+    checkMutable();
+    if (entryList.isEmpty() && !(entryList instanceof ArrayList)) {
+      entryList = new ArrayList<Entry>(maxArraySize);
+    }
+  }
+
+  /**
+   * Entry implementation that implements Comparable in order to support
+   * binary search within the entry array. Also checks mutability in
+   * {@link #setValue()}.
+   */
+  private class Entry implements Map.Entry<K, V>, Comparable<Entry> {
+
+    private final K key;
+    private V value;
+
+    Entry(Map.Entry<K, V> copy) {
+      this(copy.getKey(), copy.getValue());
+    }
+
+    Entry(K key, V value) {
+      this.key = key;
+      this.value = value;
+    }
+
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    public K getKey() {
+      return key;
+    }
+
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    public V getValue() {
+      return value;
+    }
+
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    public int compareTo(Entry other) {
+      return getKey().compareTo(other.getKey());
+    }
+
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    public V setValue(V newValue) {
+      checkMutable();
+      final V oldValue = this.value;
+      this.value = newValue;
+      return oldValue;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+      if (o == this) {
+        return true;
+      }
+      if (!(o instanceof Map.Entry)) {
+        return false;
+      }
+      @SuppressWarnings("unchecked")
+      Map.Entry<?, ?> other = (Map.Entry<?, ?>) o;
+      return equals(key, other.getKey()) && equals(value, other.getValue());
+    }
+
+    @Override
+    public int hashCode() {
+      return (key == null ? 0 : key.hashCode()) ^
+          (value == null ? 0 : value.hashCode());
+    }
+
+    @Override
+    public String toString() {
+      return key + "=" + value;
+    }
+
+    /** equals() that handles null values. */
+    private boolean equals(Object o1, Object o2) {
+      return o1 == null ? o2 == null : o1.equals(o2);
+    }
+  }
+
+  /**
+   * Stateless view of the entries in the field map.
+   */
+  private class EntrySet extends AbstractSet<Map.Entry<K, V>> {
+
+    @Override
+    public Iterator<Map.Entry<K, V>> iterator() {
+      return new EntryIterator();
+    }
+
+    @Override
+    public int size() {
+      return SmallSortedMap.this.size();
+    }
+
+    /**
+     * Throws a {@link ClassCastException} if o is not of the expected type.
+     *
+     * {@inheritDoc}
+     */
+    @Override
+    public boolean contains(Object o) {
+      @SuppressWarnings("unchecked")
+      final Map.Entry<K, V> entry = (Map.Entry<K, V>) o;
+      final V existing = get(entry.getKey());
+      final V value = entry.getValue();
+      return existing == value ||
+          (existing != null && existing.equals(value));
+    }
+
+    @Override
+    public boolean add(Map.Entry<K, V> entry) {
+      if (!contains(entry)) {
+        put(entry.getKey(), entry.getValue());
+        return true;
+      }
+      return false;
+    }
+
+    /**
+     * Throws a {@link ClassCastException} if o is not of the expected type.
+     *
+     * {@inheritDoc}
+     */
+    @Override
+    public boolean remove(Object o) {
+      @SuppressWarnings("unchecked")
+      final Map.Entry<K, V> entry = (Map.Entry<K, V>) o;
+      if (contains(entry)) {
+        SmallSortedMap.this.remove(entry.getKey());
+        return true;
+      }
+      return false;
+    }
+
+    @Override
+    public void clear() {
+      SmallSortedMap.this.clear();
+    }
+  }
+
+  /**
+   * Iterator implementation that switches from the entry array to the overflow
+   * entries appropriately.
+   */
+  private class EntryIterator implements Iterator<Map.Entry<K, V>> {
+
+    private int pos = -1;
+    private boolean nextCalledBeforeRemove;
+    private Iterator<Map.Entry<K, V>> lazyOverflowIterator;
+
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    public boolean hasNext() {
+      return (pos + 1) < entryList.size() ||
+          getOverflowIterator().hasNext();
+    }
+
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    public Map.Entry<K, V> next() {
+      nextCalledBeforeRemove = true;
+      // Always increment pos so that we know whether the last returned value
+      // was from the array or from overflow.
+      if (++pos < entryList.size()) {
+        return entryList.get(pos);
+      }
+      return getOverflowIterator().next();
+    }
+
+    //@Override (Java 1.6 override semantics, but we must support 1.5)
+    public void remove() {
+      if (!nextCalledBeforeRemove) {
+        throw new IllegalStateException("remove() was called before next()");
+      }
+      nextCalledBeforeRemove = false;
+      checkMutable();
+
+      if (pos < entryList.size()) {
+        removeArrayEntryAt(pos--);
+      } else {
+        getOverflowIterator().remove();
+      }
+    }
+
+    /**
+     * It is important to create the overflow iterator only after the array
+     * entries have been iterated over because the overflow entry set changes
+     * when the client calls remove() on the array entries, which invalidates
+     * any existing iterators.
+     */
+    private Iterator<Map.Entry<K, V>> getOverflowIterator() {
+      if (lazyOverflowIterator == null) {
+        lazyOverflowIterator = overflowEntries.entrySet().iterator();
+      }
+      return lazyOverflowIterator;
+    }
+  }
+
+  /**
+   * Helper class that holds immutable instances of an Iterable/Iterator that
+   * we return when the overflow entries is empty. This eliminates the creation
+   * of an Iterator object when there is nothing to iterate over.
+   */
+  private static class EmptySet {
+
+    private static final Iterator<Object> ITERATOR = new Iterator<Object>() {
+      //@Override (Java 1.6 override semantics, but we must support 1.5)
+      public boolean hasNext() {
+        return false;
+      }
+      //@Override (Java 1.6 override semantics, but we must support 1.5)
+      public Object next() {
+        throw new NoSuchElementException();
+      }
+      //@Override (Java 1.6 override semantics, but we must support 1.5)
+      public void remove() {
+        throw new UnsupportedOperationException();
+      }
+    };
+
+    private static final Iterable<Object> ITERABLE = new Iterable<Object>() {
+      //@Override (Java 1.6 override semantics, but we must support 1.5)
+      public Iterator<Object> iterator() {
+        return ITERATOR;
+      }
+    };
+
+    @SuppressWarnings("unchecked")
+    static <T> Iterable<T> iterable() {
+      return (Iterable<T>) ITERABLE;
+    }
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/TextFormat.java b/java/core/src/main/java/com/google/protobuf/TextFormat.java
new file mode 100644
index 00000000..c99b5285
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/TextFormat.java
@@ -0,0 +1,2065 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import com.google.protobuf.Descriptors.Descriptor;
+import com.google.protobuf.Descriptors.EnumDescriptor;
+import com.google.protobuf.Descriptors.EnumValueDescriptor;
+import com.google.protobuf.Descriptors.FieldDescriptor;
+
+import java.io.IOException;
+import java.math.BigInteger;
+import java.nio.CharBuffer;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Locale;
+import java.util.Map;
+import java.util.logging.Logger;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+/**
+ * Provide text parsing and formatting support for proto2 instances.
+ * The implementation largely follows google/protobuf/text_format.cc.
+ *
+ * @author wenboz@google.com Wenbo Zhu
+ * @author kenton@google.com Kenton Varda
+ */
+public final class TextFormat {
+  private TextFormat() {}
+
+  private static final Logger logger =
+      Logger.getLogger(TextFormat.class.getName());
+
+  private static final Printer DEFAULT_PRINTER = new Printer();
+  private static final Printer SINGLE_LINE_PRINTER =
+      (new Printer()).setSingleLineMode(true);
+  private static final Printer UNICODE_PRINTER =
+      (new Printer()).setEscapeNonAscii(false);
+
+  /**
+   * Outputs a textual representation of the Protocol Message supplied into
+   * the parameter output. (This representation is the new version of the
+   * classic "ProtocolPrinter" output from the original Protocol Buffer system)
+   */
+  public static void print(
+      final MessageOrBuilder message, final Appendable output)
+      throws IOException {
+    DEFAULT_PRINTER.print(message, new TextGenerator(output));
+  }
+
+  /** Outputs a textual representation of {@code fields} to {@code output}. */
+  public static void print(final UnknownFieldSet fields,
+                           final Appendable output)
+                           throws IOException {
+    DEFAULT_PRINTER.printUnknownFields(fields, new TextGenerator(output));
+  }
+
+  /**
+   * Same as {@code print()}, except that non-ASCII characters are not
+   * escaped.
+   */
+  public static void printUnicode(
+      final MessageOrBuilder message, final Appendable output)
+      throws IOException {
+    UNICODE_PRINTER.print(message, new TextGenerator(output));
+  }
+
+  /**
+   * Same as {@code print()}, except that non-ASCII characters are not
+   * escaped.
+   */
+  public static void printUnicode(final UnknownFieldSet fields,
+                                  final Appendable output)
+                                  throws IOException {
+    UNICODE_PRINTER.printUnknownFields(fields, new TextGenerator(output));
+  }
+
+  /**
+   * Generates a human readable form of this message, useful for debugging and
+   * other purposes, with no newline characters.
+   */
+  public static String shortDebugString(final MessageOrBuilder message) {
+    try {
+      final StringBuilder sb = new StringBuilder();
+      SINGLE_LINE_PRINTER.print(message, new TextGenerator(sb));
+      // Single line mode currently might have an extra space at the end.
+      return sb.toString().trim();
+    } catch (IOException e) {
+      throw new IllegalStateException(e);
+    }
+  }
+
+  /**
+   * Generates a human readable form of the field, useful for debugging
+   * and other purposes, with no newline characters.
+   */
+  public static String shortDebugString(final FieldDescriptor field,
+                                        final Object value) {
+    try {
+      final StringBuilder sb = new StringBuilder();
+      SINGLE_LINE_PRINTER.printField(field, value, new TextGenerator(sb));
+      return sb.toString().trim();
+    } catch (IOException e) {
+        throw new IllegalStateException(e);
+    }
+  }
+
+  /**
+   * Generates a human readable form of the unknown fields, useful for debugging
+   * and other purposes, with no newline characters.
+   */
+  public static String shortDebugString(final UnknownFieldSet fields) {
+    try {
+      final StringBuilder sb = new StringBuilder();
+      SINGLE_LINE_PRINTER.printUnknownFields(fields, new TextGenerator(sb));
+      // Single line mode currently might have an extra space at the end.
+      return sb.toString().trim();
+    } catch (IOException e) {
+      throw new IllegalStateException(e);
+    }
+  }
+
+  /**
+   * Like {@code print()}, but writes directly to a {@code String} and
+   * returns it.
+   */
+  public static String printToString(final MessageOrBuilder message) {
+    try {
+      final StringBuilder text = new StringBuilder();
+      print(message, text);
+      return text.toString();
+    } catch (IOException e) {
+      throw new IllegalStateException(e);
+    }
+  }
+
+  /**
+   * Like {@code print()}, but writes directly to a {@code String} and
+   * returns it.
+   */
+  public static String printToString(final UnknownFieldSet fields) {
+    try {
+      final StringBuilder text = new StringBuilder();
+      print(fields, text);
+      return text.toString();
+    } catch (IOException e) {
+      throw new IllegalStateException(e);
+    }
+  }
+
+  /**
+   * Same as {@code printToString()}, except that non-ASCII characters
+   * in string type fields are not escaped in backslash+octals.
+   */
+  public static String printToUnicodeString(final MessageOrBuilder message) {
+    try {
+      final StringBuilder text = new StringBuilder();
+      UNICODE_PRINTER.print(message, new TextGenerator(text));
+      return text.toString();
+    } catch (IOException e) {
+      throw new IllegalStateException(e);
+    }
+  }
+
+  /**
+   * Same as {@code printToString()}, except that non-ASCII characters
+   * in string type fields are not escaped in backslash+octals.
+   */
+  public static String printToUnicodeString(final UnknownFieldSet fields) {
+    try {
+      final StringBuilder text = new StringBuilder();
+      UNICODE_PRINTER.printUnknownFields(fields, new TextGenerator(text));
+      return text.toString();
+    } catch (IOException e) {
+      throw new IllegalStateException(e);
+    }
+  }
+
+  public static void printField(final FieldDescriptor field,
+                                final Object value,
+                                final Appendable output)
+                                throws IOException {
+    DEFAULT_PRINTER.printField(field, value, new TextGenerator(output));
+  }
+
+  public static String printFieldToString(final FieldDescriptor field,
+                                          final Object value) {
+    try {
+      final StringBuilder text = new StringBuilder();
+      printField(field, value, text);
+      return text.toString();
+    } catch (IOException e) {
+      throw new IllegalStateException(e);
+    }
+  }
+
+  /**
+   * Outputs a textual representation of the value of given field value.
+   *
+   * @param field the descriptor of the field
+   * @param value the value of the field
+   * @param output the output to which to append the formatted value
+   * @throws ClassCastException if the value is not appropriate for the
+   *     given field descriptor
+   * @throws IOException if there is an exception writing to the output
+   */
+  public static void printFieldValue(final FieldDescriptor field,
+                                     final Object value,
+                                     final Appendable output)
+                                     throws IOException {
+    DEFAULT_PRINTER.printFieldValue(field, value, new TextGenerator(output));
+  }
+
+  /**
+   * Outputs a textual representation of the value of an unknown field.
+   *
+   * @param tag the field's tag number
+   * @param value the value of the field
+   * @param output the output to which to append the formatted value
+   * @throws ClassCastException if the value is not appropriate for the
+   *     given field descriptor
+   * @throws IOException if there is an exception writing to the output
+   */
+  public static void printUnknownFieldValue(final int tag,
+                                            final Object value,
+                                            final Appendable output)
+                                            throws IOException {
+    printUnknownFieldValue(tag, value, new TextGenerator(output));
+  }
+
+  private static void printUnknownFieldValue(final int tag,
+                                             final Object value,
+                                             final TextGenerator generator)
+                                             throws IOException {
+    switch (WireFormat.getTagWireType(tag)) {
+      case WireFormat.WIRETYPE_VARINT:
+        generator.print(unsignedToString((Long) value));
+        break;
+      case WireFormat.WIRETYPE_FIXED32:
+        generator.print(
+            String.format((Locale) null, "0x%08x", (Integer) value));
+        break;
+      case WireFormat.WIRETYPE_FIXED64:
+        generator.print(String.format((Locale) null, "0x%016x", (Long) value));
+        break;
+      case WireFormat.WIRETYPE_LENGTH_DELIMITED:
+        generator.print("\"");
+        generator.print(escapeBytes((ByteString) value));
+        generator.print("\"");
+        break;
+      case WireFormat.WIRETYPE_START_GROUP:
+        DEFAULT_PRINTER.printUnknownFields((UnknownFieldSet) value, generator);
+        break;
+      default:
+        throw new IllegalArgumentException("Bad tag: " + tag);
+    }
+  }
+
+  /** Helper class for converting protobufs to text. */
+  private static final class Printer {
+    /** Whether to omit newlines from the output. */
+    boolean singleLineMode = false;
+
+    /** Whether to escape non ASCII characters with backslash and octal. */
+    boolean escapeNonAscii = true;
+
+    private Printer() {}
+
+    /** Setter of singleLineMode */
+    private Printer setSingleLineMode(boolean singleLineMode) {
+      this.singleLineMode = singleLineMode;
+      return this;
+    }
+
+    /** Setter of escapeNonAscii */
+    private Printer setEscapeNonAscii(boolean escapeNonAscii) {
+      this.escapeNonAscii = escapeNonAscii;
+      return this;
+    }
+
+    private void print(
+        final MessageOrBuilder message, final TextGenerator generator)
+        throws IOException {
+      for (Map.Entry<FieldDescriptor, Object> field
+          : message.getAllFields().entrySet()) {
+        printField(field.getKey(), field.getValue(), generator);
+      }
+      printUnknownFields(message.getUnknownFields(), generator);
+    }
+
+    private void printField(final FieldDescriptor field, final Object value,
+        final TextGenerator generator) throws IOException {
+      if (field.isRepeated()) {
+        // Repeated field.  Print each element.
+        for (Object element : (List<?>) value) {
+          printSingleField(field, element, generator);
+        }
+      } else {
+        printSingleField(field, value, generator);
+      }
+    }
+
+    private void printSingleField(final FieldDescriptor field,
+                                  final Object value,
+                                  final TextGenerator generator)
+                                  throws IOException {
+      if (field.isExtension()) {
+        generator.print("[");
+        // We special-case MessageSet elements for compatibility with proto1.
+        if (field.getContainingType().getOptions().getMessageSetWireFormat()
+            && (field.getType() == FieldDescriptor.Type.MESSAGE)
+            && (field.isOptional())
+            // object equality
+            && (field.getExtensionScope() == field.getMessageType())) {
+          generator.print(field.getMessageType().getFullName());
+        } else {
+          generator.print(field.getFullName());
+        }
+        generator.print("]");
+      } else {
+        if (field.getType() == FieldDescriptor.Type.GROUP) {
+          // Groups must be serialized with their original capitalization.
+          generator.print(field.getMessageType().getName());
+        } else {
+          generator.print(field.getName());
+        }
+      }
+
+      if (field.getJavaType() == FieldDescriptor.JavaType.MESSAGE) {
+        if (singleLineMode) {
+          generator.print(" { ");
+        } else {
+          generator.print(" {\n");
+          generator.indent();
+        }
+      } else {
+        generator.print(": ");
+      }
+
+      printFieldValue(field, value, generator);
+
+      if (field.getJavaType() == FieldDescriptor.JavaType.MESSAGE) {
+        if (singleLineMode) {
+          generator.print("} ");
+        } else {
+          generator.outdent();
+          generator.print("}\n");
+        }
+      } else {
+        if (singleLineMode) {
+          generator.print(" ");
+        } else {
+          generator.print("\n");
+        }
+      }
+    }
+
+    private void printFieldValue(final FieldDescriptor field,
+                                 final Object value,
+                                 final TextGenerator generator)
+                                 throws IOException {
+      switch (field.getType()) {
+        case INT32:
+        case SINT32:
+        case SFIXED32:
+          generator.print(((Integer) value).toString());
+          break;
+
+        case INT64:
+        case SINT64:
+        case SFIXED64:
+          generator.print(((Long) value).toString());
+          break;
+
+        case BOOL:
+          generator.print(((Boolean) value).toString());
+          break;
+
+        case FLOAT:
+          generator.print(((Float) value).toString());
+          break;
+
+        case DOUBLE:
+          generator.print(((Double) value).toString());
+          break;
+
+        case UINT32:
+        case FIXED32:
+          generator.print(unsignedToString((Integer) value));
+          break;
+
+        case UINT64:
+        case FIXED64:
+          generator.print(unsignedToString((Long) value));
+          break;
+
+        case STRING:
+          generator.print("\"");
+          generator.print(escapeNonAscii
+              ? escapeText((String) value)
+              : escapeDoubleQuotesAndBackslashes((String) value)
+                  .replace("\n", "\\n"));
+          generator.print("\"");
+          break;
+
+        case BYTES:
+          generator.print("\"");
+          if (value instanceof ByteString) {
+            generator.print(escapeBytes((ByteString) value));
+          } else {
+            generator.print(escapeBytes((byte[]) value));
+          }
+          generator.print("\"");
+          break;
+
+        case ENUM:
+          generator.print(((EnumValueDescriptor) value).getName());
+          break;
+
+        case MESSAGE:
+        case GROUP:
+          print((Message) value, generator);
+          break;
+      }
+    }
+
+    private void printUnknownFields(final UnknownFieldSet unknownFields,
+                                    final TextGenerator generator)
+                                    throws IOException {
+      for (Map.Entry<Integer, UnknownFieldSet.Field> entry :
+               unknownFields.asMap().entrySet()) {
+        final int number = entry.getKey();
+        final UnknownFieldSet.Field field = entry.getValue();
+        printUnknownField(number, WireFormat.WIRETYPE_VARINT,
+            field.getVarintList(), generator);
+        printUnknownField(number, WireFormat.WIRETYPE_FIXED32,
+            field.getFixed32List(), generator);
+        printUnknownField(number, WireFormat.WIRETYPE_FIXED64,
+            field.getFixed64List(), generator);
+        printUnknownField(number, WireFormat.WIRETYPE_LENGTH_DELIMITED,
+            field.getLengthDelimitedList(), generator);
+        for (final UnknownFieldSet value : field.getGroupList()) {
+          generator.print(entry.getKey().toString());
+          if (singleLineMode) {
+            generator.print(" { ");
+          } else {
+            generator.print(" {\n");
+            generator.indent();
+          }
+          printUnknownFields(value, generator);
+          if (singleLineMode) {
+            generator.print("} ");
+          } else {
+            generator.outdent();
+            generator.print("}\n");
+          }
+        }
+      }
+    }
+
+    private void printUnknownField(final int number,
+                                   final int wireType,
+                                   final List<?> values,
+                                   final TextGenerator generator)
+                                   throws IOException {
+      for (final Object value : values) {
+        generator.print(String.valueOf(number));
+        generator.print(": ");
+        printUnknownFieldValue(wireType, value, generator);
+        generator.print(singleLineMode ? " " : "\n");
+      }
+    }
+  }
+
+  /** Convert an unsigned 32-bit integer to a string. */
+  public static String unsignedToString(final int value) {
+    if (value >= 0) {
+      return Integer.toString(value);
+    } else {
+      return Long.toString(value & 0x00000000FFFFFFFFL);
+    }
+  }
+
+  /** Convert an unsigned 64-bit integer to a string. */
+  public static String unsignedToString(final long value) {
+    if (value >= 0) {
+      return Long.toString(value);
+    } else {
+      // Pull off the most-significant bit so that BigInteger doesn't think
+      // the number is negative, then set it again using setBit().
+      return BigInteger.valueOf(value & 0x7FFFFFFFFFFFFFFFL)
+                       .setBit(63).toString();
+    }
+  }
+
+  /**
+   * An inner class for writing text to the output stream.
+   */
+  private static final class TextGenerator {
+    private final Appendable output;
+    private final StringBuilder indent = new StringBuilder();
+    private boolean atStartOfLine = true;
+
+    private TextGenerator(final Appendable output) {
+      this.output = output;
+    }
+
+    /**
+     * Indent text by two spaces.  After calling Indent(), two spaces will be
+     * inserted at the beginning of each line of text.  Indent() may be called
+     * multiple times to produce deeper indents.
+     */
+    public void indent() {
+      indent.append("  ");
+    }
+
+    /**
+     * Reduces the current indent level by two spaces, or crashes if the indent
+     * level is zero.
+     */
+    public void outdent() {
+      final int length = indent.length();
+      if (length == 0) {
+        throw new IllegalArgumentException(
+            " Outdent() without matching Indent().");
+      }
+      indent.delete(length - 2, length);
+    }
+
+    /**
+     * Print text to the output stream.
+     */
+    public void print(final CharSequence text) throws IOException {
+      final int size = text.length();
+      int pos = 0;
+
+      for (int i = 0; i < size; i++) {
+        if (text.charAt(i) == '\n') {
+          write(text.subSequence(pos, i + 1));
+          pos = i + 1;
+          atStartOfLine = true;
+        }
+      }
+      write(text.subSequence(pos, size));
+    }
+
+    private void write(final CharSequence data) throws IOException {
+      if (data.length() == 0) {
+        return;
+      }
+      if (atStartOfLine) {
+        atStartOfLine = false;
+        output.append(indent);
+      }
+      output.append(data);
+    }
+  }
+
+  // =================================================================
+  // Parsing
+
+  /**
+   * Represents a stream of tokens parsed from a {@code String}.
+   *
+   * <p>The Java standard library provides many classes that you might think
+   * would be useful for implementing this, but aren't.  For example:
+   *
+   * <ul>
+   * <li>{@code java.io.StreamTokenizer}:  This almost does what we want -- or,
+   *   at least, something that would get us close to what we want -- except
+   *   for one fatal flaw:  It automatically un-escapes strings using Java
+   *   escape sequences, which do not include all the escape sequences we
+   *   need to support (e.g. '\x').
+   * <li>{@code java.util.Scanner}:  This seems like a great way at least to
+   *   parse regular expressions out of a stream (so we wouldn't have to load
+   *   the entire input into a single string before parsing).  Sadly,
+   *   {@code Scanner} requires that tokens be delimited with some delimiter.
+   *   Thus, although the text "foo:" should parse to two tokens ("foo" and
+   *   ":"), {@code Scanner} would recognize it only as a single token.
+   *   Furthermore, {@code Scanner} provides no way to inspect the contents
+   *   of delimiters, making it impossible to keep track of line and column
+   *   numbers.
+   * </ul>
+   *
+   * <p>Luckily, Java's regular expression support does manage to be useful to
+   * us.  (Barely:  We need {@code Matcher.usePattern()}, which is new in
+   * Java 1.5.)  So, we can use that, at least.  Unfortunately, this implies
+   * that we need to have the entire input in one contiguous string.
+   */
+  private static final class Tokenizer {
+    private final CharSequence text;
+    private final Matcher matcher;
+    private String currentToken;
+
+    // The character index within this.text at which the current token begins.
+    private int pos = 0;
+
+    // The line and column numbers of the current token.
+    private int line = 0;
+    private int column = 0;
+
+    // The line and column numbers of the previous token (allows throwing
+    // errors *after* consuming).
+    private int previousLine = 0;
+    private int previousColumn = 0;
+
+    // We use possessive quantifiers (*+ and ++) because otherwise the Java
+    // regex matcher has stack overflows on large inputs.
+    private static final Pattern WHITESPACE =
+      Pattern.compile("(\\s|(#.*$))++", Pattern.MULTILINE);
+    private static final Pattern TOKEN = Pattern.compile(
+      "[a-zA-Z_][0-9a-zA-Z_+-]*+|" +                // an identifier
+      "[.]?[0-9+-][0-9a-zA-Z_.+-]*+|" +             // a number
+      "\"([^\"\n\\\\]|\\\\.)*+(\"|\\\\?$)|" +       // a double-quoted string
+      "\'([^\'\n\\\\]|\\\\.)*+(\'|\\\\?$)",         // a single-quoted string
+      Pattern.MULTILINE);
+
+    private static final Pattern DOUBLE_INFINITY = Pattern.compile(
+      "-?inf(inity)?",
+      Pattern.CASE_INSENSITIVE);
+    private static final Pattern FLOAT_INFINITY = Pattern.compile(
+      "-?inf(inity)?f?",
+      Pattern.CASE_INSENSITIVE);
+    private static final Pattern FLOAT_NAN = Pattern.compile(
+      "nanf?",
+      Pattern.CASE_INSENSITIVE);
+
+    /** Construct a tokenizer that parses tokens from the given text. */
+    private Tokenizer(final CharSequence text) {
+      this.text = text;
+      this.matcher = WHITESPACE.matcher(text);
+      skipWhitespace();
+      nextToken();
+    }
+
+    /** Are we at the end of the input? */
+    public boolean atEnd() {
+      return currentToken.length() == 0;
+    }
+
+    /** Advance to the next token. */
+    public void nextToken() {
+      previousLine = line;
+      previousColumn = column;
+
+      // Advance the line counter to the current position.
+      while (pos < matcher.regionStart()) {
+        if (text.charAt(pos) == '\n') {
+          ++line;
+          column = 0;
+        } else {
+          ++column;
+        }
+        ++pos;
+      }
+
+      // Match the next token.
+      if (matcher.regionStart() == matcher.regionEnd()) {
+        // EOF
+        currentToken = "";
+      } else {
+        matcher.usePattern(TOKEN);
+        if (matcher.lookingAt()) {
+          currentToken = matcher.group();
+          matcher.region(matcher.end(), matcher.regionEnd());
+        } else {
+          // Take one character.
+          currentToken = String.valueOf(text.charAt(pos));
+          matcher.region(pos + 1, matcher.regionEnd());
+        }
+
+        skipWhitespace();
+      }
+    }
+
+    /**
+     * Skip over any whitespace so that the matcher region starts at the next
+     * token.
+     */
+    private void skipWhitespace() {
+      matcher.usePattern(WHITESPACE);
+      if (matcher.lookingAt()) {
+        matcher.region(matcher.end(), matcher.regionEnd());
+      }
+    }
+
+    /**
+     * If the next token exactly matches {@code token}, consume it and return
+     * {@code true}.  Otherwise, return {@code false} without doing anything.
+     */
+    public boolean tryConsume(final String token) {
+      if (currentToken.equals(token)) {
+        nextToken();
+        return true;
+      } else {
+        return false;
+      }
+    }
+
+    /**
+     * If the next token exactly matches {@code token}, consume it.  Otherwise,
+     * throw a {@link ParseException}.
+     */
+    public void consume(final String token) throws ParseException {
+      if (!tryConsume(token)) {
+        throw parseException("Expected \"" + token + "\".");
+      }
+    }
+
+    /**
+     * Returns {@code true} if the next token is an integer, but does
+     * not consume it.
+     */
+    public boolean lookingAtInteger() {
+      if (currentToken.length() == 0) {
+        return false;
+      }
+
+      final char c = currentToken.charAt(0);
+      return ('0' <= c && c <= '9')
+          || c == '-' || c == '+';
+    }
+
+    /**
+     * Returns {@code true} if the current token's text is equal to that
+     * specified.
+     */
+    public boolean lookingAt(String text) {
+      return currentToken.equals(text);
+    }
+
+    /**
+     * If the next token is an identifier, consume it and return its value.
+     * Otherwise, throw a {@link ParseException}.
+     */
+    public String consumeIdentifier() throws ParseException {
+      for (int i = 0; i < currentToken.length(); i++) {
+        final char c = currentToken.charAt(i);
+        if (('a' <= c && c <= 'z')
+            || ('A' <= c && c <= 'Z')
+            || ('0' <= c && c <= '9')
+            || (c == '_') || (c == '.')) {
+          // OK
+        } else {
+          throw parseException(
+              "Expected identifier. Found '" + currentToken + "'");
+        }
+      }
+
+      final String result = currentToken;
+      nextToken();
+      return result;
+    }
+
+    /**
+     * If the next token is an identifier, consume it and return {@code true}.
+     * Otherwise, return {@code false} without doing anything.
+     */
+    public boolean tryConsumeIdentifier() {
+      try {
+        consumeIdentifier();
+        return true;
+      } catch (ParseException e) {
+        return false;
+      }
+    }
+
+    /**
+     * If the next token is a 32-bit signed integer, consume it and return its
+     * value.  Otherwise, throw a {@link ParseException}.
+     */
+    public int consumeInt32() throws ParseException {
+      try {
+        final int result = parseInt32(currentToken);
+        nextToken();
+        return result;
+      } catch (NumberFormatException e) {
+        throw integerParseException(e);
+      }
+    }
+
+    /**
+     * If the next token is a 32-bit unsigned integer, consume it and return its
+     * value.  Otherwise, throw a {@link ParseException}.
+     */
+    public int consumeUInt32() throws ParseException {
+      try {
+        final int result = parseUInt32(currentToken);
+        nextToken();
+        return result;
+      } catch (NumberFormatException e) {
+        throw integerParseException(e);
+      }
+    }
+
+    /**
+     * If the next token is a 64-bit signed integer, consume it and return its
+     * value.  Otherwise, throw a {@link ParseException}.
+     */
+    public long consumeInt64() throws ParseException {
+      try {
+        final long result = parseInt64(currentToken);
+        nextToken();
+        return result;
+      } catch (NumberFormatException e) {
+        throw integerParseException(e);
+      }
+    }
+
+    /**
+     * If the next token is a 64-bit signed integer, consume it and return
+     * {@code true}.  Otherwise, return {@code false} without doing anything.
+     */
+    public boolean tryConsumeInt64() {
+      try {
+        consumeInt64();
+        return true;
+      } catch (ParseException e) {
+        return false;
+      }
+    }
+
+    /**
+     * If the next token is a 64-bit unsigned integer, consume it and return its
+     * value.  Otherwise, throw a {@link ParseException}.
+     */
+    public long consumeUInt64() throws ParseException {
+      try {
+        final long result = parseUInt64(currentToken);
+        nextToken();
+        return result;
+      } catch (NumberFormatException e) {
+        throw integerParseException(e);
+      }
+    }
+
+    /**
+     * If the next token is a 64-bit unsigned integer, consume it and return
+     * {@code true}.  Otherwise, return {@code false} without doing anything.
+     */
+    public boolean tryConsumeUInt64() {
+      try {
+        consumeUInt64();
+        return true;
+      } catch (ParseException e) {
+        return false;
+      }
+    }
+
+    /**
+     * If the next token is a double, consume it and return its value.
+     * Otherwise, throw a {@link ParseException}.
+     */
+    public double consumeDouble() throws ParseException {
+      // We need to parse infinity and nan separately because
+      // Double.parseDouble() does not accept "inf", "infinity", or "nan".
+      if (DOUBLE_INFINITY.matcher(currentToken).matches()) {
+        final boolean negative = currentToken.startsWith("-");
+        nextToken();
+        return negative ? Double.NEGATIVE_INFINITY : Double.POSITIVE_INFINITY;
+      }
+      if (currentToken.equalsIgnoreCase("nan")) {
+        nextToken();
+        return Double.NaN;
+      }
+      try {
+        final double result = Double.parseDouble(currentToken);
+        nextToken();
+        return result;
+      } catch (NumberFormatException e) {
+        throw floatParseException(e);
+      }
+    }
+
+    /**
+     * If the next token is a double, consume it and return {@code true}.
+     * Otherwise, return {@code false} without doing anything.
+     */
+    public boolean tryConsumeDouble() {
+      try {
+        consumeDouble();
+        return true;
+      } catch (ParseException e) {
+        return false;
+      }
+    }
+
+    /**
+     * If the next token is a float, consume it and return its value.
+     * Otherwise, throw a {@link ParseException}.
+     */
+    public float consumeFloat() throws ParseException {
+      // We need to parse infinity and nan separately because
+      // Float.parseFloat() does not accept "inf", "infinity", or "nan".
+      if (FLOAT_INFINITY.matcher(currentToken).matches()) {
+        final boolean negative = currentToken.startsWith("-");
+        nextToken();
+        return negative ? Float.NEGATIVE_INFINITY : Float.POSITIVE_INFINITY;
+      }
+      if (FLOAT_NAN.matcher(currentToken).matches()) {
+        nextToken();
+        return Float.NaN;
+      }
+      try {
+        final float result = Float.parseFloat(currentToken);
+        nextToken();
+        return result;
+      } catch (NumberFormatException e) {
+        throw floatParseException(e);
+      }
+    }
+
+    /**
+     * If the next token is a float, consume it and return {@code true}.
+     * Otherwise, return {@code false} without doing anything.
+     */
+    public boolean tryConsumeFloat() {
+      try {
+        consumeFloat();
+        return true;
+      } catch (ParseException e) {
+        return false;
+      }
+    }
+
+    /**
+     * If the next token is a boolean, consume it and return its value.
+     * Otherwise, throw a {@link ParseException}.
+     */
+    public boolean consumeBoolean() throws ParseException {
+      if (currentToken.equals("true")
+          || currentToken.equals("t")
+          || currentToken.equals("1")) {
+        nextToken();
+        return true;
+      } else if (currentToken.equals("false")
+          || currentToken.equals("f")
+          || currentToken.equals("0")) {
+        nextToken();
+        return false;
+      } else {
+        throw parseException("Expected \"true\" or \"false\".");
+      }
+    }
+
+    /**
+     * If the next token is a string, consume it and return its (unescaped)
+     * value.  Otherwise, throw a {@link ParseException}.
+     */
+    public String consumeString() throws ParseException {
+      return consumeByteString().toStringUtf8();
+    }
+
+    /**
+     * If the next token is a string, consume it and return true.  Otherwise,
+     * return false.
+     */
+    public boolean tryConsumeString() {
+      try {
+        consumeString();
+        return true;
+      } catch (ParseException e) {
+        return false;
+      }
+    }
+
+    /**
+     * If the next token is a string, consume it, unescape it as a
+     * {@link ByteString}, and return it.  Otherwise, throw a
+     * {@link ParseException}.
+     */
+    public ByteString consumeByteString() throws ParseException {
+      List<ByteString> list = new ArrayList<ByteString>();
+      consumeByteString(list);
+      while (currentToken.startsWith("'") || currentToken.startsWith("\"")) {
+        consumeByteString(list);
+      }
+      return ByteString.copyFrom(list);
+    }
+
+    /**
+     * Like {@link #consumeByteString()} but adds each token of the string to
+     * the given list.  String literals (whether bytes or text) may come in
+     * multiple adjacent tokens which are automatically concatenated, like in
+     * C or Python.
+     */
+    private void consumeByteString(List<ByteString> list)
+        throws ParseException {
+      final char quote = currentToken.length() > 0
+          ? currentToken.charAt(0)
+          : '\0';
+      if (quote != '\"' && quote != '\'') {
+        throw parseException("Expected string.");
+      }
+
+      if (currentToken.length() < 2
+          || currentToken.charAt(currentToken.length() - 1) != quote) {
+        throw parseException("String missing ending quote.");
+      }
+
+      try {
+        final String escaped =
+            currentToken.substring(1, currentToken.length() - 1);
+        final ByteString result = unescapeBytes(escaped);
+        nextToken();
+        list.add(result);
+      } catch (InvalidEscapeSequenceException e) {
+        throw parseException(e.getMessage());
+      }
+    }
+
+    /**
+     * Returns a {@link ParseException} with the current line and column
+     * numbers in the description, suitable for throwing.
+     */
+    public ParseException parseException(final String description) {
+      // Note:  People generally prefer one-based line and column numbers.
+      return new ParseException(
+        line + 1, column + 1, description);
+    }
+
+    /**
+     * Returns a {@link ParseException} with the line and column numbers of
+     * the previous token in the description, suitable for throwing.
+     */
+    public ParseException parseExceptionPreviousToken(
+        final String description) {
+      // Note:  People generally prefer one-based line and column numbers.
+      return new ParseException(
+        previousLine + 1, previousColumn + 1, description);
+    }
+
+    /**
+     * Constructs an appropriate {@link ParseException} for the given
+     * {@code NumberFormatException} when trying to parse an integer.
+     */
+    private ParseException integerParseException(
+        final NumberFormatException e) {
+      return parseException("Couldn't parse integer: " + e.getMessage());
+    }
+
+    /**
+     * Constructs an appropriate {@link ParseException} for the given
+     * {@code NumberFormatException} when trying to parse a float or double.
+     */
+    private ParseException floatParseException(final NumberFormatException e) {
+      return parseException("Couldn't parse number: " + e.getMessage());
+    }
+    
+    /**
+     * Returns a {@link UnknownFieldParseException} with the line and column
+     * numbers of the previous token in the description, and the unknown field
+     * name, suitable for throwing.
+     */
+    public UnknownFieldParseException unknownFieldParseExceptionPreviousToken(
+        final String unknownField, final String description) {
+      // Note:  People generally prefer one-based line and column numbers.
+      return new UnknownFieldParseException(
+        previousLine + 1, previousColumn + 1, unknownField, description);
+    }
+  }
+
+  /** Thrown when parsing an invalid text format message. */
+  public static class ParseException extends IOException {
+    private static final long serialVersionUID = 3196188060225107702L;
+
+    private final int line;
+    private final int column;
+
+    /** Create a new instance, with -1 as the line and column numbers. */
+    public ParseException(final String message) {
+      this(-1, -1, message);
+    }
+
+    /**
+     * Create a new instance
+     *
+     * @param line the line number where the parse error occurred,
+     * using 1-offset.
+     * @param column the column number where the parser error occurred,
+     * using 1-offset.
+     */
+    public ParseException(final int line, final int column,
+        final String message) {
+      super(Integer.toString(line) + ":" + column + ": " + message);
+      this.line = line;
+      this.column = column;
+    }
+
+    /**
+     * Return the line where the parse exception occurred, or -1 when
+     * none is provided. The value is specified as 1-offset, so the first
+     * line is line 1.
+     */
+    public int getLine() {
+      return line;
+    }
+
+    /**
+     * Return the column where the parse exception occurred, or -1 when
+     * none is provided. The value is specified as 1-offset, so the first
+     * line is line 1.
+     */
+    public int getColumn() {
+      return column;
+    }
+  }
+  
+  /**
+   * Thrown when encountering an unknown field while parsing
+   * a text format message.
+   */
+  public static class UnknownFieldParseException extends ParseException {
+    private final String unknownField;
+
+    /**
+     * Create a new instance, with -1 as the line and column numbers, and an
+     * empty unknown field name.
+     */
+    public UnknownFieldParseException(final String message) {
+      this(-1, -1, "", message);
+    }
+
+    /**
+     * Create a new instance
+     *
+     * @param line the line number where the parse error occurred,
+     * using 1-offset.
+     * @param column the column number where the parser error occurred,
+     * using 1-offset.
+     * @param unknownField the name of the unknown field found while parsing.
+     */
+    public UnknownFieldParseException(final int line, final int column,
+        final String unknownField, final String message) {
+      super(line, column, message);
+      this.unknownField = unknownField;
+    }
+
+    /**
+     * Return the name of the unknown field encountered while parsing the
+     * protocol buffer string.
+     */
+    public String getUnknownField() {
+      return unknownField;
+    }
+  }
+
+  private static final Parser PARSER = Parser.newBuilder().build();
+
+  /**
+   * Return a {@link Parser} instance which can parse text-format
+   * messages. The returned instance is thread-safe.
+   */
+  public static Parser getParser() {
+    return PARSER;
+  }
+
+  /**
+   * Parse a text-format message from {@code input} and merge the contents
+   * into {@code builder}.
+   */
+  public static void merge(final Readable input,
+                           final Message.Builder builder)
+                           throws IOException {
+    PARSER.merge(input, builder);
+  }
+
+  /**
+   * Parse a text-format message from {@code input} and merge the contents
+   * into {@code builder}.
+   */
+  public static void merge(final CharSequence input,
+                           final Message.Builder builder)
+                           throws ParseException {
+    PARSER.merge(input, builder);
+  }
+
+  /**
+   * Parse a text-format message from {@code input} and merge the contents
+   * into {@code builder}.  Extensions will be recognized if they are
+   * registered in {@code extensionRegistry}.
+   */
+  public static void merge(final Readable input,
+                           final ExtensionRegistry extensionRegistry,
+                           final Message.Builder builder)
+                           throws IOException {
+    PARSER.merge(input, extensionRegistry, builder);
+  }
+
+
+  /**
+   * Parse a text-format message from {@code input} and merge the contents
+   * into {@code builder}.  Extensions will be recognized if they are
+   * registered in {@code extensionRegistry}.
+   */
+  public static void merge(final CharSequence input,
+                           final ExtensionRegistry extensionRegistry,
+                           final Message.Builder builder)
+                           throws ParseException {
+    PARSER.merge(input, extensionRegistry, builder);
+  }
+
+
+  /**
+   * Parser for text-format proto2 instances. This class is thread-safe.
+   * The implementation largely follows google/protobuf/text_format.cc.
+   *
+   * <p>Use {@link TextFormat#getParser()} to obtain the default parser, or
+   * {@link Builder} to control the parser behavior.
+   */
+  public static class Parser {
+    /**
+     * Determines if repeated values for non-repeated fields and
+     * oneofs are permitted. For example, given required/optional field "foo"
+     * and a oneof containing "baz" and "qux":
+     * <ul>
+     * <li>"foo: 1 foo: 2"
+     * <li>"baz: 1 qux: 2"
+     * <li>merging "foo: 2" into a proto in which foo is already set, or
+     * <li>merging "qux: 2" into a proto in which baz is already set.
+     * </ul>
+     */
+    public enum SingularOverwritePolicy {
+      /** The last value is retained. */
+      ALLOW_SINGULAR_OVERWRITES,
+      /** An error is issued. */
+      FORBID_SINGULAR_OVERWRITES
+    }
+
+    private final boolean allowUnknownFields;
+    private final SingularOverwritePolicy singularOverwritePolicy;
+
+    private Parser(boolean allowUnknownFields,
+        SingularOverwritePolicy singularOverwritePolicy) {
+      this.allowUnknownFields = allowUnknownFields;
+      this.singularOverwritePolicy = singularOverwritePolicy;
+    }
+
+    /**
+     * Returns a new instance of {@link Builder}.
+     */
+    public static Builder newBuilder() {
+      return new Builder();
+    }
+
+    /**
+     * Builder that can be used to obtain new instances of {@link Parser}.
+     */
+    public static class Builder {
+      private boolean allowUnknownFields = false;
+      private SingularOverwritePolicy singularOverwritePolicy =
+          SingularOverwritePolicy.ALLOW_SINGULAR_OVERWRITES;
+
+
+      /**
+       * Sets parser behavior when a non-repeated field appears more than once.
+       */
+      public Builder setSingularOverwritePolicy(SingularOverwritePolicy p) {
+        this.singularOverwritePolicy = p;
+        return this;
+      }
+
+      public Parser build() {
+        return new Parser(allowUnknownFields, singularOverwritePolicy);
+      }
+    }
+
+    /**
+     * Parse a text-format message from {@code input} and merge the contents
+     * into {@code builder}.
+     */
+    public void merge(final Readable input,
+                      final Message.Builder builder)
+                      throws IOException {
+      merge(input, ExtensionRegistry.getEmptyRegistry(), builder);
+    }
+
+    /**
+     * Parse a text-format message from {@code input} and merge the contents
+     * into {@code builder}.
+     */
+    public void merge(final CharSequence input,
+                      final Message.Builder builder)
+                      throws ParseException {
+      merge(input, ExtensionRegistry.getEmptyRegistry(), builder);
+    }
+
+    /**
+     * Parse a text-format message from {@code input} and merge the contents
+     * into {@code builder}.  Extensions will be recognized if they are
+     * registered in {@code extensionRegistry}.
+     */
+    public void merge(final Readable input,
+                      final ExtensionRegistry extensionRegistry,
+                      final Message.Builder builder)
+                      throws IOException {
+      // Read the entire input to a String then parse that.
+
+      // If StreamTokenizer were not quite so crippled, or if there were a kind
+      // of Reader that could read in chunks that match some particular regex,
+      // or if we wanted to write a custom Reader to tokenize our stream, then
+      // we would not have to read to one big String.  Alas, none of these is
+      // the case.  Oh well.
+
+      merge(toStringBuilder(input), extensionRegistry, builder);
+    }
+
+
+    private static final int BUFFER_SIZE = 4096;
+
+    // TODO(chrisn): See if working around java.io.Reader#read(CharBuffer)
+    // overhead is worthwhile
+    private static StringBuilder toStringBuilder(final Readable input)
+        throws IOException {
+      final StringBuilder text = new StringBuilder();
+      final CharBuffer buffer = CharBuffer.allocate(BUFFER_SIZE);
+      while (true) {
+        final int n = input.read(buffer);
+        if (n == -1) {
+          break;
+        }
+        buffer.flip();
+        text.append(buffer, 0, n);
+      }
+      return text;
+    }
+
+    /**
+     * Parse a text-format message from {@code input} and merge the contents
+     * into {@code builder}.  Extensions will be recognized if they are
+     * registered in {@code extensionRegistry}.
+     */
+    public void merge(final CharSequence input,
+                      final ExtensionRegistry extensionRegistry,
+                      final Message.Builder builder)
+                      throws ParseException {
+      final Tokenizer tokenizer = new Tokenizer(input);
+      MessageReflection.BuilderAdapter target =
+          new MessageReflection.BuilderAdapter(builder);
+
+      while (!tokenizer.atEnd()) {
+        mergeField(tokenizer, extensionRegistry, target);
+      }
+    }
+
+
+    /**
+     * Parse a single field from {@code tokenizer} and merge it into
+     * {@code builder}.
+     */
+    private void mergeField(final Tokenizer tokenizer,
+                            final ExtensionRegistry extensionRegistry,
+                            final MessageReflection.MergeTarget target)
+                            throws ParseException {
+      FieldDescriptor field = null;
+      final Descriptor type = target.getDescriptorForType();
+      ExtensionRegistry.ExtensionInfo extension = null;
+
+      if (tokenizer.tryConsume("[")) {
+        // An extension.
+        final StringBuilder name =
+            new StringBuilder(tokenizer.consumeIdentifier());
+        while (tokenizer.tryConsume(".")) {
+          name.append('.');
+          name.append(tokenizer.consumeIdentifier());
+        }
+
+        extension = target.findExtensionByName(
+            extensionRegistry, name.toString());
+
+        if (extension == null) {
+          if (!allowUnknownFields) {
+            throw tokenizer.parseExceptionPreviousToken(
+              "Extension \"" + name + "\" not found in the ExtensionRegistry.");
+          } else {
+            logger.warning(
+              "Extension \"" + name + "\" not found in the ExtensionRegistry.");
+          }
+        } else {
+          if (extension.descriptor.getContainingType() != type) {
+            throw tokenizer.parseExceptionPreviousToken(
+              "Extension \"" + name + "\" does not extend message type \""
+              + type.getFullName() + "\".");
+          }
+          field = extension.descriptor;
+        }
+
+        tokenizer.consume("]");
+      } else {
+        final String name = tokenizer.consumeIdentifier();
+        field = type.findFieldByName(name);
+
+        // Group names are expected to be capitalized as they appear in the
+        // .proto file, which actually matches their type names, not their field
+        // names.
+        if (field == null) {
+          // Explicitly specify US locale so that this code does not break when
+          // executing in Turkey.
+          final String lowerName = name.toLowerCase(Locale.US);
+          field = type.findFieldByName(lowerName);
+          // If the case-insensitive match worked but the field is NOT a group,
+          if (field != null && field.getType() != FieldDescriptor.Type.GROUP) {
+            field = null;
+          }
+        }
+        // Again, special-case group names as described above.
+        if (field != null && field.getType() == FieldDescriptor.Type.GROUP
+            && !field.getMessageType().getName().equals(name)) {
+          field = null;
+        }
+
+        if (field == null) {
+          if (!allowUnknownFields) {
+            throw tokenizer.unknownFieldParseExceptionPreviousToken(
+              name,
+              "Message type \"" + type.getFullName()
+              + "\" has no field named \"" + name + "\".");
+          } else {
+            logger.warning(
+              "Message type \"" + type.getFullName()
+              + "\" has no field named \"" + name + "\".");
+          }
+        }
+      }
+
+      // Skips unknown fields.
+      if (field == null) {
+        // Try to guess the type of this field.
+        // If this field is not a message, there should be a ":" between the
+        // field name and the field value and also the field value should not
+        // start with "{" or "<" which indicates the beginning of a message body.
+        // If there is no ":" or there is a "{" or "<" after ":", this field has
+        // to be a message or the input is ill-formed.
+        if (tokenizer.tryConsume(":")
+            && !tokenizer.lookingAt("{")
+            && !tokenizer.lookingAt("<")) {
+          skipFieldValue(tokenizer);
+        } else {
+          skipFieldMessage(tokenizer);
+        }
+        return;
+      }
+
+      // Handle potential ':'.
+      if (field.getJavaType() == FieldDescriptor.JavaType.MESSAGE) {
+        tokenizer.tryConsume(":");  // optional
+      } else {
+        tokenizer.consume(":");  // required
+      }
+      // Support specifying repeated field values as a comma-separated list.
+      // Ex."foo: [1, 2, 3]"
+      if (field.isRepeated() && tokenizer.tryConsume("[")) {
+        while (true) {
+          consumeFieldValue(tokenizer, extensionRegistry, target, field, extension);
+          if (tokenizer.tryConsume("]")) {
+            // End of list.
+            break;
+          }
+          tokenizer.consume(",");
+        }
+      } else {
+        consumeFieldValue(tokenizer, extensionRegistry, target, field, extension);
+      }
+
+      // For historical reasons, fields may optionally be separated by commas or
+      // semicolons.
+      if (!tokenizer.tryConsume(";")) {
+        tokenizer.tryConsume(",");
+      }
+    }
+
+    /**
+     * Parse a single field value from {@code tokenizer} and merge it into
+     * {@code builder}.
+     */
+    private void consumeFieldValue(
+        final Tokenizer tokenizer,
+        final ExtensionRegistry extensionRegistry,
+        final MessageReflection.MergeTarget target,
+        final FieldDescriptor field,
+        final ExtensionRegistry.ExtensionInfo extension)
+        throws ParseException {
+      Object value = null;
+
+      if (field.getJavaType() == FieldDescriptor.JavaType.MESSAGE) {
+        final String endToken;
+        if (tokenizer.tryConsume("<")) {
+          endToken = ">";
+        } else {
+          tokenizer.consume("{");
+          endToken = "}";
+        }
+
+        final MessageReflection.MergeTarget subField;
+        subField = target.newMergeTargetForField(field,
+            (extension == null) ? null : extension.defaultInstance);
+
+        while (!tokenizer.tryConsume(endToken)) {
+          if (tokenizer.atEnd()) {
+            throw tokenizer.parseException(
+              "Expected \"" + endToken + "\".");
+          }
+          mergeField(tokenizer, extensionRegistry, subField);
+        }
+
+        value = subField.finish();
+
+      } else {
+        switch (field.getType()) {
+          case INT32:
+          case SINT32:
+          case SFIXED32:
+            value = tokenizer.consumeInt32();
+            break;
+
+          case INT64:
+          case SINT64:
+          case SFIXED64:
+            value = tokenizer.consumeInt64();
+            break;
+
+          case UINT32:
+          case FIXED32:
+            value = tokenizer.consumeUInt32();
+            break;
+
+          case UINT64:
+          case FIXED64:
+            value = tokenizer.consumeUInt64();
+            break;
+
+          case FLOAT:
+            value = tokenizer.consumeFloat();
+            break;
+
+          case DOUBLE:
+            value = tokenizer.consumeDouble();
+            break;
+
+          case BOOL:
+            value = tokenizer.consumeBoolean();
+            break;
+
+          case STRING:
+            value = tokenizer.consumeString();
+            break;
+
+          case BYTES:
+            value = tokenizer.consumeByteString();
+            break;
+
+          case ENUM:
+            final EnumDescriptor enumType = field.getEnumType();
+
+            if (tokenizer.lookingAtInteger()) {
+              final int number = tokenizer.consumeInt32();
+              value = enumType.findValueByNumber(number);
+              if (value == null) {
+                throw tokenizer.parseExceptionPreviousToken(
+                  "Enum type \"" + enumType.getFullName()
+                  + "\" has no value with number " + number + '.');
+              }
+            } else {
+              final String id = tokenizer.consumeIdentifier();
+              value = enumType.findValueByName(id);
+              if (value == null) {
+                throw tokenizer.parseExceptionPreviousToken(
+                  "Enum type \"" + enumType.getFullName()
+                  + "\" has no value named \"" + id + "\".");
+              }
+            }
+
+            break;
+
+          case MESSAGE:
+          case GROUP:
+            throw new RuntimeException("Can't get here.");
+        }
+      }
+
+      if (field.isRepeated()) {
+        target.addRepeatedField(field, value);
+      } else if ((singularOverwritePolicy
+              == SingularOverwritePolicy.FORBID_SINGULAR_OVERWRITES)
+          && target.hasField(field)) {
+        throw tokenizer.parseExceptionPreviousToken("Non-repeated field \""
+            + field.getFullName() + "\" cannot be overwritten.");
+      } else if ((singularOverwritePolicy
+              == SingularOverwritePolicy.FORBID_SINGULAR_OVERWRITES)
+          && field.getContainingOneof() != null
+          && target.hasOneof(field.getContainingOneof())) {
+        Descriptors.OneofDescriptor oneof = field.getContainingOneof();
+        throw tokenizer.parseExceptionPreviousToken("Field \""
+            + field.getFullName() + "\" is specified along with field \""
+            + target.getOneofFieldDescriptor(oneof).getFullName()
+            + "\", another member of oneof \"" + oneof.getName() + "\".");
+      } else {
+        target.setField(field, value);
+      }
+    }
+
+    /**
+     * Skips the next field including the field's name and value.
+     */
+    private void skipField(Tokenizer tokenizer) throws ParseException {
+      if (tokenizer.tryConsume("[")) {
+        // Extension name.
+        do {
+          tokenizer.consumeIdentifier();
+        } while (tokenizer.tryConsume("."));
+        tokenizer.consume("]");
+      } else {
+        tokenizer.consumeIdentifier();
+      }
+
+      // Try to guess the type of this field.
+      // If this field is not a message, there should be a ":" between the
+      // field name and the field value and also the field value should not
+      // start with "{" or "<" which indicates the beginning of a message body.
+      // If there is no ":" or there is a "{" or "<" after ":", this field has
+      // to be a message or the input is ill-formed.
+      if (tokenizer.tryConsume(":")
+          && !tokenizer.lookingAt("<")
+          && !tokenizer.lookingAt("{")) {
+        skipFieldValue(tokenizer);
+      } else {
+        skipFieldMessage(tokenizer);
+      }
+      // For historical reasons, fields may optionally be separated by commas or
+      // semicolons.
+      if (!tokenizer.tryConsume(";")) {
+        tokenizer.tryConsume(",");
+      }
+    }
+
+    /**
+     * Skips the whole body of a message including the beginning delimiter and
+     * the ending delimiter.
+     */
+    private void skipFieldMessage(Tokenizer tokenizer) throws ParseException {
+      final String delimiter;
+      if (tokenizer.tryConsume("<")) {
+        delimiter = ">";
+      } else {
+        tokenizer.consume("{");
+        delimiter = "}";
+      }
+      while (!tokenizer.lookingAt(">") && !tokenizer.lookingAt("}")) {
+        skipField(tokenizer);
+      }
+      tokenizer.consume(delimiter);
+    }
+
+    /**
+     * Skips a field value.
+     */
+    private void skipFieldValue(Tokenizer tokenizer) throws ParseException {
+      if (tokenizer.tryConsumeString()) {
+        while (tokenizer.tryConsumeString()) {}
+        return;
+      }
+      if (!tokenizer.tryConsumeIdentifier()   // includes enum & boolean
+          && !tokenizer.tryConsumeInt64()     // includes int32
+          && !tokenizer.tryConsumeUInt64()    // includes uint32
+          && !tokenizer.tryConsumeDouble()
+          && !tokenizer.tryConsumeFloat()) {
+        throw tokenizer.parseException(
+            "Invalid field value: " + tokenizer.currentToken);
+      }
+    }
+  }
+
+  // =================================================================
+  // Utility functions
+  //
+  // Some of these methods are package-private because Descriptors.java uses
+  // them.
+
+  private interface ByteSequence {
+    int size();
+    byte byteAt(int offset);
+  }
+
+  /**
+   * Escapes bytes in the format used in protocol buffer text format, which
+   * is the same as the format used for C string literals.  All bytes
+   * that are not printable 7-bit ASCII characters are escaped, as well as
+   * backslash, single-quote, and double-quote characters.  Characters for
+   * which no defined short-hand escape sequence is defined will be escaped
+   * using 3-digit octal sequences.
+   */
+  public static String escapeBytes(final ByteSequence input) {
+    final StringBuilder builder = new StringBuilder(input.size());
+    for (int i = 0; i < input.size(); i++) {
+      final byte b = input.byteAt(i);
+      switch (b) {
+        // Java does not recognize \a or \v, apparently.
+        case 0x07: builder.append("\\a"); break;
+        case '\b': builder.append("\\b"); break;
+        case '\f': builder.append("\\f"); break;
+        case '\n': builder.append("\\n"); break;
+        case '\r': builder.append("\\r"); break;
+        case '\t': builder.append("\\t"); break;
+        case 0x0b: builder.append("\\v"); break;
+        case '\\': builder.append("\\\\"); break;
+        case '\'': builder.append("\\\'"); break;
+        case '"' : builder.append("\\\""); break;
+        default:
+          // Only ASCII characters between 0x20 (space) and 0x7e (tilde) are
+          // printable.  Other byte values must be escaped.
+          if (b >= 0x20 && b <= 0x7e) {
+            builder.append((char) b);
+          } else {
+            builder.append('\\');
+            builder.append((char) ('0' + ((b >>> 6) & 3)));
+            builder.append((char) ('0' + ((b >>> 3) & 7)));
+            builder.append((char) ('0' + (b & 7)));
+          }
+          break;
+      }
+    }
+    return builder.toString();
+  }
+
+  /**
+   * Escapes bytes in the format used in protocol buffer text format, which
+   * is the same as the format used for C string literals.  All bytes
+   * that are not printable 7-bit ASCII characters are escaped, as well as
+   * backslash, single-quote, and double-quote characters.  Characters for
+   * which no defined short-hand escape sequence is defined will be escaped
+   * using 3-digit octal sequences.
+   */
+  public static String escapeBytes(final ByteString input) {
+    return escapeBytes(new ByteSequence() {
+      @Override
+      public int size() {
+        return input.size();
+      }
+      @Override
+      public byte byteAt(int offset) {
+        return input.byteAt(offset);
+      }
+    });
+  }
+
+  /**
+   * Like {@link #escapeBytes(ByteString)}, but used for byte array.
+   */
+  public static String escapeBytes(final byte[] input) {
+    return escapeBytes(new ByteSequence() {
+      @Override
+      public int size() {
+        return input.length;
+      }
+      @Override
+      public byte byteAt(int offset) {
+        return input[offset];
+      }
+    });
+  }
+
+  /**
+   * Un-escape a byte sequence as escaped using
+   * {@link #escapeBytes(ByteString)}.  Two-digit hex escapes (starting with
+   * "\x") are also recognized.
+   */
+  public static ByteString unescapeBytes(final CharSequence charString)
+      throws InvalidEscapeSequenceException {
+    // First convert the Java character sequence to UTF-8 bytes.
+    ByteString input = ByteString.copyFromUtf8(charString.toString());
+    // Then unescape certain byte sequences introduced by ASCII '\\'.  The valid
+    // escapes can all be expressed with ASCII characters, so it is safe to
+    // operate on bytes here.
+    //
+    // Unescaping the input byte array will result in a byte sequence that's no
+    // longer than the input.  That's because each escape sequence is between
+    // two and four bytes long and stands for a single byte.
+    final byte[] result = new byte[input.size()];
+    int pos = 0;
+    for (int i = 0; i < input.size(); i++) {
+      byte c = input.byteAt(i);
+      if (c == '\\') {
+        if (i + 1 < input.size()) {
+          ++i;
+          c = input.byteAt(i);
+          if (isOctal(c)) {
+            // Octal escape.
+            int code = digitValue(c);
+            if (i + 1 < input.size() && isOctal(input.byteAt(i + 1))) {
+              ++i;
+              code = code * 8 + digitValue(input.byteAt(i));
+            }
+            if (i + 1 < input.size() && isOctal(input.byteAt(i + 1))) {
+              ++i;
+              code = code * 8 + digitValue(input.byteAt(i));
+            }
+            // TODO: Check that 0 <= code && code <= 0xFF.
+            result[pos++] = (byte) code;
+          } else {
+            switch (c) {
+              case 'a' : result[pos++] = 0x07; break;
+              case 'b' : result[pos++] = '\b'; break;
+              case 'f' : result[pos++] = '\f'; break;
+              case 'n' : result[pos++] = '\n'; break;
+              case 'r' : result[pos++] = '\r'; break;
+              case 't' : result[pos++] = '\t'; break;
+              case 'v' : result[pos++] = 0x0b; break;
+              case '\\': result[pos++] = '\\'; break;
+              case '\'': result[pos++] = '\''; break;
+              case '"' : result[pos++] = '\"'; break;
+
+              case 'x':
+                // hex escape
+                int code = 0;
+                if (i + 1 < input.size() && isHex(input.byteAt(i + 1))) {
+                  ++i;
+                  code = digitValue(input.byteAt(i));
+                } else {
+                  throw new InvalidEscapeSequenceException(
+                      "Invalid escape sequence: '\\x' with no digits");
+                }
+                if (i + 1 < input.size() && isHex(input.byteAt(i + 1))) {
+                  ++i;
+                  code = code * 16 + digitValue(input.byteAt(i));
+                }
+                result[pos++] = (byte) code;
+                break;
+
+              default:
+                throw new InvalidEscapeSequenceException(
+                    "Invalid escape sequence: '\\" + (char) c + '\'');
+            }
+          }
+        } else {
+          throw new InvalidEscapeSequenceException(
+              "Invalid escape sequence: '\\' at end of string.");
+        }
+      } else {
+        result[pos++] = c;
+      }
+    }
+
+    return ByteString.copyFrom(result, 0, pos);
+  }
+
+  /**
+   * Thrown by {@link TextFormat#unescapeBytes} and
+   * {@link TextFormat#unescapeText} when an invalid escape sequence is seen.
+   */
+  public static class InvalidEscapeSequenceException extends IOException {
+    private static final long serialVersionUID = -8164033650142593304L;
+
+    InvalidEscapeSequenceException(final String description) {
+      super(description);
+    }
+  }
+
+  /**
+   * Like {@link #escapeBytes(ByteString)}, but escapes a text string.
+   * Non-ASCII characters are first encoded as UTF-8, then each byte is escaped
+   * individually as a 3-digit octal escape.  Yes, it's weird.
+   */
+  static String escapeText(final String input) {
+    return escapeBytes(ByteString.copyFromUtf8(input));
+  }
+
+  /**
+   * Escape double quotes and backslashes in a String for unicode output of a message.
+   */
+  public static String escapeDoubleQuotesAndBackslashes(final String input) {
+    return input.replace("\\", "\\\\").replace("\"", "\\\"");
+  }
+
+  /**
+   * Un-escape a text string as escaped using {@link #escapeText(String)}.
+   * Two-digit hex escapes (starting with "\x") are also recognized.
+   */
+  static String unescapeText(final String input)
+                             throws InvalidEscapeSequenceException {
+    return unescapeBytes(input).toStringUtf8();
+  }
+
+  /** Is this an octal digit? */
+  private static boolean isOctal(final byte c) {
+    return '0' <= c && c <= '7';
+  }
+
+  /** Is this a hex digit? */
+  private static boolean isHex(final byte c) {
+    return ('0' <= c && c <= '9')
+        || ('a' <= c && c <= 'f')
+        || ('A' <= c && c <= 'F');
+  }
+
+  /**
+   * Interpret a character as a digit (in any base up to 36) and return the
+   * numeric value.  This is like {@code Character.digit()} but we don't accept
+   * non-ASCII digits.
+   */
+  private static int digitValue(final byte c) {
+    if ('0' <= c && c <= '9') {
+      return c - '0';
+    } else if ('a' <= c && c <= 'z') {
+      return c - 'a' + 10;
+    } else {
+      return c - 'A' + 10;
+    }
+  }
+
+  /**
+   * Parse a 32-bit signed integer from the text.  Unlike the Java standard
+   * {@code Integer.parseInt()}, this function recognizes the prefixes "0x"
+   * and "0" to signify hexadecimal and octal numbers, respectively.
+   */
+  static int parseInt32(final String text) throws NumberFormatException {
+    return (int) parseInteger(text, true, false);
+  }
+
+  /**
+   * Parse a 32-bit unsigned integer from the text.  Unlike the Java standard
+   * {@code Integer.parseInt()}, this function recognizes the prefixes "0x"
+   * and "0" to signify hexadecimal and octal numbers, respectively.  The
+   * result is coerced to a (signed) {@code int} when returned since Java has
+   * no unsigned integer type.
+   */
+  static int parseUInt32(final String text) throws NumberFormatException {
+    return (int) parseInteger(text, false, false);
+  }
+
+  /**
+   * Parse a 64-bit signed integer from the text.  Unlike the Java standard
+   * {@code Integer.parseInt()}, this function recognizes the prefixes "0x"
+   * and "0" to signify hexadecimal and octal numbers, respectively.
+   */
+  static long parseInt64(final String text) throws NumberFormatException {
+    return parseInteger(text, true, true);
+  }
+
+  /**
+   * Parse a 64-bit unsigned integer from the text.  Unlike the Java standard
+   * {@code Integer.parseInt()}, this function recognizes the prefixes "0x"
+   * and "0" to signify hexadecimal and octal numbers, respectively.  The
+   * result is coerced to a (signed) {@code long} when returned since Java has
+   * no unsigned long type.
+   */
+  static long parseUInt64(final String text) throws NumberFormatException {
+    return parseInteger(text, false, true);
+  }
+
+  private static long parseInteger(final String text,
+                                   final boolean isSigned,
+                                   final boolean isLong)
+                                   throws NumberFormatException {
+    int pos = 0;
+
+    boolean negative = false;
+    if (text.startsWith("-", pos)) {
+      if (!isSigned) {
+        throw new NumberFormatException("Number must be positive: " + text);
+      }
+      ++pos;
+      negative = true;
+    }
+
+    int radix = 10;
+    if (text.startsWith("0x", pos)) {
+      pos += 2;
+      radix = 16;
+    } else if (text.startsWith("0", pos)) {
+      radix = 8;
+    }
+
+    final String numberText = text.substring(pos);
+
+    long result = 0;
+    if (numberText.length() < 16) {
+      // Can safely assume no overflow.
+      result = Long.parseLong(numberText, radix);
+      if (negative) {
+        result = -result;
+      }
+
+      // Check bounds.
+      // No need to check for 64-bit numbers since they'd have to be 16 chars
+      // or longer to overflow.
+      if (!isLong) {
+        if (isSigned) {
+          if (result > Integer.MAX_VALUE || result < Integer.MIN_VALUE) {
+            throw new NumberFormatException(
+              "Number out of range for 32-bit signed integer: " + text);
+          }
+        } else {
+          if (result >= (1L << 32) || result < 0) {
+            throw new NumberFormatException(
+              "Number out of range for 32-bit unsigned integer: " + text);
+          }
+        }
+      }
+    } else {
+      BigInteger bigValue = new BigInteger(numberText, radix);
+      if (negative) {
+        bigValue = bigValue.negate();
+      }
+
+      // Check bounds.
+      if (!isLong) {
+        if (isSigned) {
+          if (bigValue.bitLength() > 31) {
+            throw new NumberFormatException(
+              "Number out of range for 32-bit signed integer: " + text);
+          }
+        } else {
+          if (bigValue.bitLength() > 32) {
+            throw new NumberFormatException(
+              "Number out of range for 32-bit unsigned integer: " + text);
+          }
+        }
+      } else {
+        if (isSigned) {
+          if (bigValue.bitLength() > 63) {
+            throw new NumberFormatException(
+              "Number out of range for 64-bit signed integer: " + text);
+          }
+        } else {
+          if (bigValue.bitLength() > 64) {
+            throw new NumberFormatException(
+              "Number out of range for 64-bit unsigned integer: " + text);
+          }
+        }
+      }
+
+      result = bigValue.longValue();
+    }
+
+    return result;
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/TextFormatEscaper.java b/java/core/src/main/java/com/google/protobuf/TextFormatEscaper.java
new file mode 100644
index 00000000..e69de29b
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/TextFormatEscaper.java
diff --git a/java/core/src/main/java/com/google/protobuf/UninitializedMessageException.java b/java/core/src/main/java/com/google/protobuf/UninitializedMessageException.java
new file mode 100644
index 00000000..5714c063
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/UninitializedMessageException.java
@@ -0,0 +1,99 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import java.util.Collections;
+import java.util.List;
+
+/**
+ * Thrown when attempting to build a protocol message that is missing required
+ * fields.  This is a {@code RuntimeException} because it normally represents
+ * a programming error:  it happens when some code which constructs a message
+ * fails to set all the fields.  {@code parseFrom()} methods <b>do not</b>
+ * throw this; they throw an {@link InvalidProtocolBufferException} if
+ * required fields are missing, because it is not a programming error to
+ * receive an incomplete message.  In other words,
+ * {@code UninitializedMessageException} should never be thrown by correct
+ * code, but {@code InvalidProtocolBufferException} might be.
+ *
+ * @author kenton@google.com Kenton Varda
+ */
+public class UninitializedMessageException extends RuntimeException {
+  private static final long serialVersionUID = -7466929953374883507L;
+
+  public UninitializedMessageException(final MessageLite message) {
+    super("Message was missing required fields.  (Lite runtime could not " +
+          "determine which fields were missing).");
+    missingFields = null;
+  }
+
+  public UninitializedMessageException(final List<String> missingFields) {
+    super(buildDescription(missingFields));
+    this.missingFields = missingFields;
+  }
+
+  private final List<String> missingFields;
+
+  /**
+   * Get a list of human-readable names of required fields missing from this
+   * message.  Each name is a full path to a field, e.g. "foo.bar[5].baz".
+   * Returns null if the lite runtime was used, since it lacks the ability to
+   * find missing fields.
+   */
+  public List<String> getMissingFields() {
+    return Collections.unmodifiableList(missingFields);
+  }
+
+  /**
+   * Converts this exception to an {@link InvalidProtocolBufferException}.
+   * When a parsed message is missing required fields, this should be thrown
+   * instead of {@code UninitializedMessageException}.
+   */
+  public InvalidProtocolBufferException asInvalidProtocolBufferException() {
+    return new InvalidProtocolBufferException(getMessage());
+  }
+
+  /** Construct the description string for this exception. */
+  private static String buildDescription(final List<String> missingFields) {
+    final StringBuilder description =
+      new StringBuilder("Message missing required fields: ");
+    boolean first = true;
+    for (final String field : missingFields) {
+      if (first) {
+        first = false;
+      } else {
+        description.append(", ");
+      }
+      description.append(field);
+    }
+    return description.toString();
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/UnknownFieldSet.java b/java/core/src/main/java/com/google/protobuf/UnknownFieldSet.java
new file mode 100644
index 00000000..7cd2250e
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/UnknownFieldSet.java
@@ -0,0 +1,1010 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import com.google.protobuf.AbstractMessageLite.Builder.LimitedInputStream;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+import java.util.Map;
+import java.util.TreeMap;
+
+/**
+ * {@code UnknownFieldSet} is used to keep track of fields which were seen when
+ * parsing a protocol message but whose field numbers or types are unrecognized.
+ * This most frequently occurs when new fields are added to a message type
+ * and then messages containing those fields are read by old software that was
+ * compiled before the new types were added.
+ *
+ * <p>Every {@link Message} contains an {@code UnknownFieldSet} (and every
+ * {@link Message.Builder} contains an {@link Builder}).
+ *
+ * <p>Most users will never need to use this class.
+ *
+ * @author kenton@google.com Kenton Varda
+ */
+public final class UnknownFieldSet implements MessageLite {
+  private UnknownFieldSet() {}
+
+  /** Create a new {@link Builder}. */
+  public static Builder newBuilder() {
+    return Builder.create();
+  }
+
+  /**
+   * Create a new {@link Builder} and initialize it to be a copy
+   * of {@code copyFrom}.
+   */
+  public static Builder newBuilder(final UnknownFieldSet copyFrom) {
+    return newBuilder().mergeFrom(copyFrom);
+  }
+
+  /** Get an empty {@code UnknownFieldSet}. */
+  public static UnknownFieldSet getDefaultInstance() {
+    return defaultInstance;
+  }
+  public UnknownFieldSet getDefaultInstanceForType() {
+    return defaultInstance;
+  }
+  private static final UnknownFieldSet defaultInstance =
+    new UnknownFieldSet(Collections.<Integer, Field>emptyMap());
+
+  /**
+   * Construct an {@code UnknownFieldSet} around the given map.  The map is
+   * expected to be immutable.
+   */
+  private UnknownFieldSet(final Map<Integer, Field> fields) {
+    this.fields = fields;
+  }
+  private Map<Integer, Field> fields;
+
+
+  @Override
+  public boolean equals(final Object other) {
+    if (this == other) {
+      return true;
+    }
+    return (other instanceof UnknownFieldSet) &&
+           fields.equals(((UnknownFieldSet) other).fields);
+  }
+
+  @Override
+  public int hashCode() {
+    return fields.hashCode();
+  }
+
+  /** Get a map of fields in the set by number. */
+  public Map<Integer, Field> asMap() {
+    return fields;
+  }
+
+  /** Check if the given field number is present in the set. */
+  public boolean hasField(final int number) {
+    return fields.containsKey(number);
+  }
+
+  /**
+   * Get a field by number.  Returns an empty field if not present.  Never
+   * returns {@code null}.
+   */
+  public Field getField(final int number) {
+    final Field result = fields.get(number);
+    return (result == null) ? Field.getDefaultInstance() : result;
+  }
+
+  /** Serializes the set and writes it to {@code output}. */
+  public void writeTo(final CodedOutputStream output) throws IOException {
+    for (final Map.Entry<Integer, Field> entry : fields.entrySet()) {
+      entry.getValue().writeTo(entry.getKey(), output);
+    }
+  }
+
+  /**
+   * Converts the set to a string in protocol buffer text format. This is
+   * just a trivial wrapper around
+   * {@link TextFormat#printToString(UnknownFieldSet)}.
+   */
+  @Override
+  public String toString() {
+    return TextFormat.printToString(this);
+  }
+
+  /**
+   * Serializes the message to a {@code ByteString} and returns it. This is
+   * just a trivial wrapper around {@link #writeTo(CodedOutputStream)}.
+   */
+  public ByteString toByteString() {
+    try {
+      final ByteString.CodedBuilder out =
+        ByteString.newCodedBuilder(getSerializedSize());
+      writeTo(out.getCodedOutput());
+      return out.build();
+    } catch (final IOException e) {
+      throw new RuntimeException(
+        "Serializing to a ByteString threw an IOException (should " +
+        "never happen).", e);
+    }
+  }
+
+  /**
+   * Serializes the message to a {@code byte} array and returns it.  This is
+   * just a trivial wrapper around {@link #writeTo(CodedOutputStream)}.
+   */
+  public byte[] toByteArray() {
+    try {
+      final byte[] result = new byte[getSerializedSize()];
+      final CodedOutputStream output = CodedOutputStream.newInstance(result);
+      writeTo(output);
+      output.checkNoSpaceLeft();
+      return result;
+    } catch (final IOException e) {
+      throw new RuntimeException(
+        "Serializing to a byte array threw an IOException " +
+        "(should never happen).", e);
+    }
+  }
+
+  /**
+   * Serializes the message and writes it to {@code output}.  This is just a
+   * trivial wrapper around {@link #writeTo(CodedOutputStream)}.
+   */
+  public void writeTo(final OutputStream output) throws IOException {
+    final CodedOutputStream codedOutput = CodedOutputStream.newInstance(output);
+    writeTo(codedOutput);
+    codedOutput.flush();
+  }
+
+  public void writeDelimitedTo(OutputStream output) throws IOException {
+    final CodedOutputStream codedOutput = CodedOutputStream.newInstance(output);
+    codedOutput.writeRawVarint32(getSerializedSize());
+    writeTo(codedOutput);
+    codedOutput.flush();
+  }
+
+  /** Get the number of bytes required to encode this set. */
+  public int getSerializedSize() {
+    int result = 0;
+    for (final Map.Entry<Integer, Field> entry : fields.entrySet()) {
+      result += entry.getValue().getSerializedSize(entry.getKey());
+    }
+    return result;
+  }
+
+  /**
+   * Serializes the set and writes it to {@code output} using
+   * {@code MessageSet} wire format.
+   */
+  public void writeAsMessageSetTo(final CodedOutputStream output)
+      throws IOException {
+    for (final Map.Entry<Integer, Field> entry : fields.entrySet()) {
+      entry.getValue().writeAsMessageSetExtensionTo(
+        entry.getKey(), output);
+    }
+  }
+
+  /**
+   * Get the number of bytes required to encode this set using
+   * {@code MessageSet} wire format.
+   */
+  public int getSerializedSizeAsMessageSet() {
+    int result = 0;
+    for (final Map.Entry<Integer, Field> entry : fields.entrySet()) {
+      result += entry.getValue().getSerializedSizeAsMessageSetExtension(
+        entry.getKey());
+    }
+    return result;
+  }
+
+  public boolean isInitialized() {
+    // UnknownFieldSets do not have required fields, so they are always
+    // initialized.
+    return true;
+  }
+
+  /** Parse an {@code UnknownFieldSet} from the given input stream. */
+  public static UnknownFieldSet parseFrom(final CodedInputStream input)
+                                          throws IOException {
+    return newBuilder().mergeFrom(input).build();
+  }
+
+  /** Parse {@code data} as an {@code UnknownFieldSet} and return it. */
+  public static UnknownFieldSet parseFrom(final ByteString data)
+      throws InvalidProtocolBufferException {
+    return newBuilder().mergeFrom(data).build();
+  }
+
+  /** Parse {@code data} as an {@code UnknownFieldSet} and return it. */
+  public static UnknownFieldSet parseFrom(final byte[] data)
+      throws InvalidProtocolBufferException {
+    return newBuilder().mergeFrom(data).build();
+  }
+
+  /** Parse an {@code UnknownFieldSet} from {@code input} and return it. */
+  public static UnknownFieldSet parseFrom(final InputStream input)
+                                          throws IOException {
+    return newBuilder().mergeFrom(input).build();
+  }
+
+  public Builder newBuilderForType() {
+    return newBuilder();
+  }
+
+  public Builder toBuilder() {
+    return newBuilder().mergeFrom(this);
+  }
+
+  /**
+   * Builder for {@link UnknownFieldSet}s.
+   *
+   * <p>Note that this class maintains {@link Field.Builder}s for all fields
+   * in the set.  Thus, adding one element to an existing {@link Field} does not
+   * require making a copy.  This is important for efficient parsing of
+   * unknown repeated fields.  However, it implies that {@link Field}s cannot
+   * be constructed independently, nor can two {@link UnknownFieldSet}s share
+   * the same {@code Field} object.
+   *
+   * <p>Use {@link UnknownFieldSet#newBuilder()} to construct a {@code Builder}.
+   */
+  public static final class Builder implements MessageLite.Builder {
+    // This constructor should never be called directly (except from 'create').
+    private Builder() {}
+
+    private Map<Integer, Field> fields;
+
+    // Optimization:  We keep around a builder for the last field that was
+    //   modified so that we can efficiently add to it multiple times in a
+    //   row (important when parsing an unknown repeated field).
+    private int lastFieldNumber;
+    private Field.Builder lastField;
+
+    private static Builder create() {
+      Builder builder = new Builder();
+      builder.reinitialize();
+      return builder;
+    }
+
+    /**
+     * Get a field builder for the given field number which includes any
+     * values that already exist.
+     */
+    private Field.Builder getFieldBuilder(final int number) {
+      if (lastField != null) {
+        if (number == lastFieldNumber) {
+          return lastField;
+        }
+        // Note:  addField() will reset lastField and lastFieldNumber.
+        addField(lastFieldNumber, lastField.build());
+      }
+      if (number == 0) {
+        return null;
+      } else {
+        final Field existing = fields.get(number);
+        lastFieldNumber = number;
+        lastField = Field.newBuilder();
+        if (existing != null) {
+          lastField.mergeFrom(existing);
+        }
+        return lastField;
+      }
+    }
+
+    /**
+     * Build the {@link UnknownFieldSet} and return it.
+     *
+     * <p>Once {@code build()} has been called, the {@code Builder} will no
+     * longer be usable.  Calling any method after {@code build()} will result
+     * in undefined behavior and can cause a {@code NullPointerException} to be
+     * thrown.
+     */
+    public UnknownFieldSet build() {
+      getFieldBuilder(0);  // Force lastField to be built.
+      final UnknownFieldSet result;
+      if (fields.isEmpty()) {
+        result = getDefaultInstance();
+      } else {
+        result = new UnknownFieldSet(Collections.unmodifiableMap(fields));
+      }
+      fields = null;
+      return result;
+    }
+
+    public UnknownFieldSet buildPartial() {
+      // No required fields, so this is the same as build().
+      return build();
+    }
+
+    @Override
+    public Builder clone() {
+      getFieldBuilder(0);  // Force lastField to be built.
+      return UnknownFieldSet.newBuilder().mergeFrom(
+          new UnknownFieldSet(fields));
+    }
+
+    public UnknownFieldSet getDefaultInstanceForType() {
+      return UnknownFieldSet.getDefaultInstance();
+    }
+
+    private void reinitialize() {
+      fields = Collections.emptyMap();
+      lastFieldNumber = 0;
+      lastField = null;
+    }
+
+    /** Reset the builder to an empty set. */
+    public Builder clear() {
+      reinitialize();
+      return this;
+    }
+    
+    /** Clear fields from the set with a given field number. */
+    public Builder clearField(final int number) {
+      if (number == 0) {
+        throw new IllegalArgumentException("Zero is not a valid field number.");
+      }
+      if (lastField != null && lastFieldNumber == number) {
+        // Discard this.
+        lastField = null;
+        lastFieldNumber = 0;
+      }
+      if (fields.containsKey(number)) {
+        fields.remove(number);
+      }
+      return this;
+    }
+
+    /**
+     * Merge the fields from {@code other} into this set.  If a field number
+     * exists in both sets, {@code other}'s values for that field will be
+     * appended to the values in this set.
+     */
+    public Builder mergeFrom(final UnknownFieldSet other) {
+      if (other != getDefaultInstance()) {
+        for (final Map.Entry<Integer, Field> entry : other.fields.entrySet()) {
+          mergeField(entry.getKey(), entry.getValue());
+        }
+      }
+      return this;
+    }
+
+    /**
+     * Add a field to the {@code UnknownFieldSet}.  If a field with the same
+     * number already exists, the two are merged.
+     */
+    public Builder mergeField(final int number, final Field field) {
+      if (number == 0) {
+        throw new IllegalArgumentException("Zero is not a valid field number.");
+      }
+      if (hasField(number)) {
+        getFieldBuilder(number).mergeFrom(field);
+      } else {
+        // Optimization:  We could call getFieldBuilder(number).mergeFrom(field)
+        // in this case, but that would create a copy of the Field object.
+        // We'd rather reuse the one passed to us, so call addField() instead.
+        addField(number, field);
+      }
+      return this;
+    }
+
+    /**
+     * Convenience method for merging a new field containing a single varint
+     * value.  This is used in particular when an unknown enum value is
+     * encountered.
+     */
+    public Builder mergeVarintField(final int number, final int value) {
+      if (number == 0) {
+        throw new IllegalArgumentException("Zero is not a valid field number.");
+      }
+      getFieldBuilder(number).addVarint(value);
+      return this;
+    }
+
+
+    /**
+     * Convenience method for merging a length-delimited field.
+     *
+     * <p>For use by generated code only.
+     */
+    public Builder mergeLengthDelimitedField(
+        final int number, final ByteString value) {  
+      if (number == 0) {
+        throw new IllegalArgumentException("Zero is not a valid field number.");
+      }
+      getFieldBuilder(number).addLengthDelimited(value);
+      return this;
+    }
+
+    /** Check if the given field number is present in the set. */
+    public boolean hasField(final int number) {
+      if (number == 0) {
+        throw new IllegalArgumentException("Zero is not a valid field number.");
+      }
+      return number == lastFieldNumber || fields.containsKey(number);
+    }
+
+    /**
+     * Add a field to the {@code UnknownFieldSet}.  If a field with the same
+     * number already exists, it is removed.
+     */
+    public Builder addField(final int number, final Field field) {
+      if (number == 0) {
+        throw new IllegalArgumentException("Zero is not a valid field number.");
+      }
+      if (lastField != null && lastFieldNumber == number) {
+        // Discard this.
+        lastField = null;
+        lastFieldNumber = 0;
+      }
+      if (fields.isEmpty()) {
+        fields = new TreeMap<Integer,Field>();
+      }
+      fields.put(number, field);
+      return this;
+    }
+
+    /**
+     * Get all present {@code Field}s as an immutable {@code Map}.  If more
+     * fields are added, the changes may or may not be reflected in this map.
+     */
+    public Map<Integer, Field> asMap() {
+      getFieldBuilder(0);  // Force lastField to be built.
+      return Collections.unmodifiableMap(fields);
+    }
+
+    /**
+     * Parse an entire message from {@code input} and merge its fields into
+     * this set.
+     */
+    public Builder mergeFrom(final CodedInputStream input) throws IOException {
+      while (true) {
+        final int tag = input.readTag();
+        if (tag == 0 || !mergeFieldFrom(tag, input)) {
+          break;
+        }
+      }
+      return this;
+    }
+
+    /**
+     * Parse a single field from {@code input} and merge it into this set.
+     * @param tag The field's tag number, which was already parsed.
+     * @return {@code false} if the tag is an end group tag.
+     */
+    public boolean mergeFieldFrom(final int tag, final CodedInputStream input)
+                                  throws IOException {
+      final int number = WireFormat.getTagFieldNumber(tag);
+      switch (WireFormat.getTagWireType(tag)) {
+        case WireFormat.WIRETYPE_VARINT:
+          getFieldBuilder(number).addVarint(input.readInt64());
+          return true;
+        case WireFormat.WIRETYPE_FIXED64:
+          getFieldBuilder(number).addFixed64(input.readFixed64());
+          return true;
+        case WireFormat.WIRETYPE_LENGTH_DELIMITED:
+          getFieldBuilder(number).addLengthDelimited(input.readBytes());
+          return true;
+        case WireFormat.WIRETYPE_START_GROUP:
+          final Builder subBuilder = newBuilder();
+          input.readGroup(number, subBuilder,
+                          ExtensionRegistry.getEmptyRegistry());
+          getFieldBuilder(number).addGroup(subBuilder.build());
+          return true;
+        case WireFormat.WIRETYPE_END_GROUP:
+          return false;
+        case WireFormat.WIRETYPE_FIXED32:
+          getFieldBuilder(number).addFixed32(input.readFixed32());
+          return true;
+        default:
+          throw InvalidProtocolBufferException.invalidWireType();
+      }
+    }
+
+    /**
+     * Parse {@code data} as an {@code UnknownFieldSet} and merge it with the
+     * set being built.  This is just a small wrapper around
+     * {@link #mergeFrom(CodedInputStream)}.
+     */
+    public Builder mergeFrom(final ByteString data)
+        throws InvalidProtocolBufferException {
+      try {
+        final CodedInputStream input = data.newCodedInput();
+        mergeFrom(input);
+        input.checkLastTagWas(0);
+        return this;
+      } catch (final InvalidProtocolBufferException e) {
+        throw e;
+      } catch (final IOException e) {
+        throw new RuntimeException(
+          "Reading from a ByteString threw an IOException (should " +
+          "never happen).", e);
+      }
+    }
+
+    /**
+     * Parse {@code data} as an {@code UnknownFieldSet} and merge it with the
+     * set being built.  This is just a small wrapper around
+     * {@link #mergeFrom(CodedInputStream)}.
+     */
+    public Builder mergeFrom(final byte[] data)
+        throws InvalidProtocolBufferException {
+      try {
+        final CodedInputStream input = CodedInputStream.newInstance(data);
+        mergeFrom(input);
+        input.checkLastTagWas(0);
+        return this;
+      } catch (final InvalidProtocolBufferException e) {
+        throw e;
+      } catch (final IOException e) {
+        throw new RuntimeException(
+          "Reading from a byte array threw an IOException (should " +
+          "never happen).", e);
+      }
+    }
+
+    /**
+     * Parse an {@code UnknownFieldSet} from {@code input} and merge it with the
+     * set being built.  This is just a small wrapper around
+     * {@link #mergeFrom(CodedInputStream)}.
+     */
+    public Builder mergeFrom(final InputStream input) throws IOException {
+      final CodedInputStream codedInput = CodedInputStream.newInstance(input);
+      mergeFrom(codedInput);
+      codedInput.checkLastTagWas(0);
+      return this;
+    }
+
+    public boolean mergeDelimitedFrom(InputStream input)
+        throws IOException {
+      final int firstByte = input.read();
+      if (firstByte == -1) {
+        return false;
+      }
+      final int size = CodedInputStream.readRawVarint32(firstByte, input);
+      final InputStream limitedInput = new LimitedInputStream(input, size);
+      mergeFrom(limitedInput);
+      return true;
+    }
+
+    public boolean mergeDelimitedFrom(
+        InputStream input,
+        ExtensionRegistryLite extensionRegistry) throws IOException {
+      // UnknownFieldSet has no extensions.
+      return mergeDelimitedFrom(input);
+    }
+
+    public Builder mergeFrom(
+        CodedInputStream input,
+        ExtensionRegistryLite extensionRegistry) throws IOException {
+      // UnknownFieldSet has no extensions.
+      return mergeFrom(input);
+    }
+
+    public Builder mergeFrom(
+        ByteString data,
+        ExtensionRegistryLite extensionRegistry)
+        throws InvalidProtocolBufferException {
+      // UnknownFieldSet has no extensions.
+      return mergeFrom(data);
+    }
+
+    public Builder mergeFrom(byte[] data, int off, int len)
+        throws InvalidProtocolBufferException {
+      try {
+        final CodedInputStream input =
+            CodedInputStream.newInstance(data, off, len);
+        mergeFrom(input);
+        input.checkLastTagWas(0);
+        return this;
+      } catch (InvalidProtocolBufferException e) {
+        throw e;
+      } catch (IOException e) {
+        throw new RuntimeException(
+          "Reading from a byte array threw an IOException (should " +
+          "never happen).", e);
+      }
+    }
+
+    public Builder mergeFrom(
+        byte[] data,
+        ExtensionRegistryLite extensionRegistry)
+        throws InvalidProtocolBufferException {
+      // UnknownFieldSet has no extensions.
+      return mergeFrom(data);
+    }
+
+    public Builder mergeFrom(
+        byte[] data, int off, int len,
+        ExtensionRegistryLite extensionRegistry)
+        throws InvalidProtocolBufferException {
+      // UnknownFieldSet has no extensions.
+      return mergeFrom(data, off, len);
+    }
+
+    public Builder mergeFrom(
+        InputStream input,
+        ExtensionRegistryLite extensionRegistry) throws IOException {
+      // UnknownFieldSet has no extensions.
+      return mergeFrom(input);
+    }
+
+    public boolean isInitialized() {
+      // UnknownFieldSets do not have required fields, so they are always
+      // initialized.
+      return true;
+    }
+  }
+
+  /**
+   * Represents a single field in an {@code UnknownFieldSet}.
+   *
+   * <p>A {@code Field} consists of five lists of values.  The lists correspond
+   * to the five "wire types" used in the protocol buffer binary format.
+   * The wire type of each field can be determined from the encoded form alone,
+   * without knowing the field's declared type.  So, we are able to parse
+   * unknown values at least this far and separate them.  Normally, only one
+   * of the five lists will contain any values, since it is impossible to
+   * define a valid message type that declares two different types for the
+   * same field number.  However, the code is designed to allow for the case
+   * where the same unknown field number is encountered using multiple different
+   * wire types.
+   *
+   * <p>{@code Field} is an immutable class.  To construct one, you must use a
+   * {@link Builder}.
+   *
+   * @see UnknownFieldSet
+   */
+  public static final class Field {
+    private Field() {}
+
+    /** Construct a new {@link Builder}. */
+    public static Builder newBuilder() {
+      return Builder.create();
+    }
+
+    /**
+     * Construct a new {@link Builder} and initialize it to a copy of
+     * {@code copyFrom}.
+     */
+    public static Builder newBuilder(final Field copyFrom) {
+      return newBuilder().mergeFrom(copyFrom);
+    }
+
+    /** Get an empty {@code Field}. */
+    public static Field getDefaultInstance() {
+      return fieldDefaultInstance;
+    }
+    private static final Field fieldDefaultInstance = newBuilder().build();
+
+    /** Get the list of varint values for this field. */
+    public List<Long> getVarintList()               { return varint;          }
+
+    /** Get the list of fixed32 values for this field. */
+    public List<Integer> getFixed32List()           { return fixed32;         }
+
+    /** Get the list of fixed64 values for this field. */
+    public List<Long> getFixed64List()              { return fixed64;         }
+
+    /** Get the list of length-delimited values for this field. */
+    public List<ByteString> getLengthDelimitedList() { return lengthDelimited; }
+
+    /**
+     * Get the list of embedded group values for this field.  These are
+     * represented using {@link UnknownFieldSet}s rather than {@link Message}s
+     * since the group's type is presumably unknown.
+     */
+    public List<UnknownFieldSet> getGroupList()      { return group;           }
+
+    @Override
+    public boolean equals(final Object other) {
+      if (this == other) {
+        return true;
+      }
+      if (!(other instanceof Field)) {
+        return false;
+      }
+      return Arrays.equals(getIdentityArray(),
+          ((Field) other).getIdentityArray());
+    }
+
+    @Override
+    public int hashCode() {
+      return Arrays.hashCode(getIdentityArray());
+    }
+
+    /**
+     * Returns the array of objects to be used to uniquely identify this
+     * {@link Field} instance.
+     */
+    private Object[] getIdentityArray() {
+      return new Object[] {
+          varint,
+          fixed32,
+          fixed64,
+          lengthDelimited,
+          group};
+    }
+
+    /**
+     * Serializes the field, including field number, and writes it to
+     * {@code output}.
+     */
+    public void writeTo(final int fieldNumber, final CodedOutputStream output)
+                        throws IOException {
+      for (final long value : varint) {
+        output.writeUInt64(fieldNumber, value);
+      }
+      for (final int value : fixed32) {
+        output.writeFixed32(fieldNumber, value);
+      }
+      for (final long value : fixed64) {
+        output.writeFixed64(fieldNumber, value);
+      }
+      for (final ByteString value : lengthDelimited) {
+        output.writeBytes(fieldNumber, value);
+      }
+      for (final UnknownFieldSet value : group) {
+        output.writeGroup(fieldNumber, value);
+      }
+    }
+
+    /**
+     * Get the number of bytes required to encode this field, including field
+     * number.
+     */
+    public int getSerializedSize(final int fieldNumber) {
+      int result = 0;
+      for (final long value : varint) {
+        result += CodedOutputStream.computeUInt64Size(fieldNumber, value);
+      }
+      for (final int value : fixed32) {
+        result += CodedOutputStream.computeFixed32Size(fieldNumber, value);
+      }
+      for (final long value : fixed64) {
+        result += CodedOutputStream.computeFixed64Size(fieldNumber, value);
+      }
+      for (final ByteString value : lengthDelimited) {
+        result += CodedOutputStream.computeBytesSize(fieldNumber, value);
+      }
+      for (final UnknownFieldSet value : group) {
+        result += CodedOutputStream.computeGroupSize(fieldNumber, value);
+      }
+      return result;
+    }
+
+    /**
+     * Serializes the field, including field number, and writes it to
+     * {@code output}, using {@code MessageSet} wire format.
+     */
+    public void writeAsMessageSetExtensionTo(
+        final int fieldNumber,
+        final CodedOutputStream output)
+        throws IOException {
+      for (final ByteString value : lengthDelimited) {
+        output.writeRawMessageSetExtension(fieldNumber, value);
+      }
+    }
+
+    /**
+     * Get the number of bytes required to encode this field, including field
+     * number, using {@code MessageSet} wire format.
+     */
+    public int getSerializedSizeAsMessageSetExtension(final int fieldNumber) {
+      int result = 0;
+      for (final ByteString value : lengthDelimited) {
+        result += CodedOutputStream.computeRawMessageSetExtensionSize(
+          fieldNumber, value);
+      }
+      return result;
+    }
+
+    private List<Long> varint;
+    private List<Integer> fixed32;
+    private List<Long> fixed64;
+    private List<ByteString> lengthDelimited;
+    private List<UnknownFieldSet> group;
+
+    /**
+     * Used to build a {@link Field} within an {@link UnknownFieldSet}.
+     *
+     * <p>Use {@link Field#newBuilder()} to construct a {@code Builder}.
+     */
+    public static final class Builder {
+      // This constructor should never be called directly (except from 'create').
+      private Builder() {}
+
+      private static Builder create() {
+        Builder builder = new Builder();
+        builder.result = new Field();
+        return builder;
+      }
+
+      private Field result;
+
+      /**
+       * Build the field.  After {@code build()} has been called, the
+       * {@code Builder} is no longer usable.  Calling any other method will
+       * result in undefined behavior and can cause a
+       * {@code NullPointerException} to be thrown.
+       */
+      public Field build() {
+        if (result.varint == null) {
+          result.varint = Collections.emptyList();
+        } else {
+          result.varint = Collections.unmodifiableList(result.varint);
+        }
+        if (result.fixed32 == null) {
+          result.fixed32 = Collections.emptyList();
+        } else {
+          result.fixed32 = Collections.unmodifiableList(result.fixed32);
+        }
+        if (result.fixed64 == null) {
+          result.fixed64 = Collections.emptyList();
+        } else {
+          result.fixed64 = Collections.unmodifiableList(result.fixed64);
+        }
+        if (result.lengthDelimited == null) {
+          result.lengthDelimited = Collections.emptyList();
+        } else {
+          result.lengthDelimited =
+            Collections.unmodifiableList(result.lengthDelimited);
+        }
+        if (result.group == null) {
+          result.group = Collections.emptyList();
+        } else {
+          result.group = Collections.unmodifiableList(result.group);
+        }
+
+        final Field returnMe = result;
+        result = null;
+        return returnMe;
+      }
+
+      /** Discard the field's contents. */
+      public Builder clear() {
+        result = new Field();
+        return this;
+      }
+
+      /**
+       * Merge the values in {@code other} into this field.  For each list
+       * of values, {@code other}'s values are append to the ones in this
+       * field.
+       */
+      public Builder mergeFrom(final Field other) {
+        if (!other.varint.isEmpty()) {
+          if (result.varint == null) {
+            result.varint = new ArrayList<Long>();
+          }
+          result.varint.addAll(other.varint);
+        }
+        if (!other.fixed32.isEmpty()) {
+          if (result.fixed32 == null) {
+            result.fixed32 = new ArrayList<Integer>();
+          }
+          result.fixed32.addAll(other.fixed32);
+        }
+        if (!other.fixed64.isEmpty()) {
+          if (result.fixed64 == null) {
+            result.fixed64 = new ArrayList<Long>();
+          }
+          result.fixed64.addAll(other.fixed64);
+        }
+        if (!other.lengthDelimited.isEmpty()) {
+          if (result.lengthDelimited == null) {
+            result.lengthDelimited = new ArrayList<ByteString>();
+          }
+          result.lengthDelimited.addAll(other.lengthDelimited);
+        }
+        if (!other.group.isEmpty()) {
+          if (result.group == null) {
+            result.group = new ArrayList<UnknownFieldSet>();
+          }
+          result.group.addAll(other.group);
+        }
+        return this;
+      }
+
+      /** Add a varint value. */
+      public Builder addVarint(final long value) {
+        if (result.varint == null) {
+          result.varint = new ArrayList<Long>();
+        }
+        result.varint.add(value);
+        return this;
+      }
+
+      /** Add a fixed32 value. */
+      public Builder addFixed32(final int value) {
+        if (result.fixed32 == null) {
+          result.fixed32 = new ArrayList<Integer>();
+        }
+        result.fixed32.add(value);
+        return this;
+      }
+
+      /** Add a fixed64 value. */
+      public Builder addFixed64(final long value) {
+        if (result.fixed64 == null) {
+          result.fixed64 = new ArrayList<Long>();
+        }
+        result.fixed64.add(value);
+        return this;
+      }
+
+      /** Add a length-delimited value. */
+      public Builder addLengthDelimited(final ByteString value) {
+        if (result.lengthDelimited == null) {
+          result.lengthDelimited = new ArrayList<ByteString>();
+        }
+        result.lengthDelimited.add(value);
+        return this;
+      }
+
+      /** Add an embedded group. */
+      public Builder addGroup(final UnknownFieldSet value) {
+        if (result.group == null) {
+          result.group = new ArrayList<UnknownFieldSet>();
+        }
+        result.group.add(value);
+        return this;
+      }
+    }
+  }
+
+  /**
+   * Parser to implement MessageLite interface.
+   */
+  public static final class Parser extends AbstractParser<UnknownFieldSet> {
+    public UnknownFieldSet parsePartialFrom(
+        CodedInputStream input, ExtensionRegistryLite extensionRegistry)
+        throws InvalidProtocolBufferException {
+      Builder builder = newBuilder();
+      try {
+        builder.mergeFrom(input);
+      } catch (InvalidProtocolBufferException e) {
+        throw e.setUnfinishedMessage(builder.buildPartial());
+      } catch (IOException e) {
+        throw new InvalidProtocolBufferException(e.getMessage())
+            .setUnfinishedMessage(builder.buildPartial());
+      }
+      return builder.buildPartial();
+    }
+  }
+
+  private static final Parser PARSER = new Parser();
+  public final Parser getParserForType() {
+    return PARSER;
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/UnknownFieldSetLite.java b/java/core/src/main/java/com/google/protobuf/UnknownFieldSetLite.java
new file mode 100644
index 00000000..435ad4d4
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/UnknownFieldSetLite.java
@@ -0,0 +1,458 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import java.io.IOException;
+import java.util.Arrays;
+
+/**
+ * {@code UnknownFieldSetLite} is used to keep track of fields which were seen
+ * when parsing a protocol message but whose field numbers or types are
+ * unrecognized. This most frequently occurs when new fields are added to a
+ * message type and then messages containing those fields are read by old
+ * software that was compiled before the new types were added.
+ *
+ * <p>For use by generated code only.
+ *
+ * @author dweis@google.com (Daniel Weis)
+ */
+public final class UnknownFieldSetLite {
+  
+  // Arbitrarily chosen.
+  // TODO(dweis): Tune this number?
+  private static final int MIN_CAPACITY = 8;
+
+  private static final UnknownFieldSetLite DEFAULT_INSTANCE =
+      new UnknownFieldSetLite(0, new int[0], new Object[0], false /* isMutable */);
+
+  /**
+   * Get an empty {@code UnknownFieldSetLite}.
+   *
+   * <p>For use by generated code only.
+   */
+  public static UnknownFieldSetLite getDefaultInstance() {
+    return DEFAULT_INSTANCE;
+  }
+
+  /**
+   * Returns an empty {@code UnknownFieldSetLite.Builder}.
+   *
+   * <p>For use by generated code only.
+   */
+  public static Builder newBuilder() {
+    return new Builder();
+  }
+  
+  /**
+   * Returns a new mutable instance.
+   */
+  static UnknownFieldSetLite newInstance() {
+    return new UnknownFieldSetLite();
+  }
+
+  /**
+   * Returns a mutable {@code UnknownFieldSetLite} that is the composite of {@code first} and
+   * {@code second}.
+   */
+  static UnknownFieldSetLite mutableCopyOf(UnknownFieldSetLite first, UnknownFieldSetLite second) {
+    int count = first.count + second.count;
+    int[] tags = Arrays.copyOf(first.tags, count);
+    System.arraycopy(second.tags, 0, tags, first.count, second.count);
+    Object[] objects = Arrays.copyOf(first.objects, count);
+    System.arraycopy(second.objects, 0, objects, first.count, second.count);
+    return new UnknownFieldSetLite(count, tags, objects, true /* isMutable */);
+  }
+  
+  /**
+   * The number of elements in the set.
+   */
+  private int count;
+  
+  /**
+   * The tag numbers for the elements in the set.
+   */
+  private int[] tags;
+  
+  /**
+   * The boxed values of the elements in the set.
+   */
+  private Object[] objects;
+  
+  /**
+   * The lazily computed serialized size of the set.
+   */
+  private int memoizedSerializedSize = -1;
+  
+  /**
+   * Indicates that this object is mutable. 
+   */
+  private boolean isMutable;
+
+  /**
+   * Constructs a mutable {@code UnknownFieldSetLite}.
+   */
+  private UnknownFieldSetLite() {
+    this(0, new int[MIN_CAPACITY], new Object[MIN_CAPACITY], true /* isMutable */);
+  }
+  
+  /**
+   * Constructs the {@code UnknownFieldSetLite}.
+   */
+  private UnknownFieldSetLite(int count, int[] tags, Object[] objects, boolean isMutable) {
+    this.count = count;
+    this.tags = tags;
+    this.objects = objects;
+    this.isMutable = isMutable;
+  }
+  
+  /**
+   * Marks this object as immutable.
+   * 
+   * <p>Future calls to methods that attempt to modify this object will throw.
+   */
+  public void makeImmutable() {
+    this.isMutable = false;
+  }
+  
+  /**
+   * Throws an {@link UnsupportedOperationException} if immutable.
+   */
+  void checkMutable() {
+    if (!isMutable) {
+      throw new UnsupportedOperationException(); 
+    }
+  }
+
+  /**
+   * Serializes the set and writes it to {@code output}.
+   *
+   * <p>For use by generated code only.
+   */
+  public void writeTo(CodedOutputStream output) throws IOException {
+    for (int i = 0; i < count; i++) {
+      int tag = tags[i];
+      int fieldNumber = WireFormat.getTagFieldNumber(tag);
+      switch (WireFormat.getTagWireType(tag)) {
+        case WireFormat.WIRETYPE_VARINT:
+          output.writeUInt64(fieldNumber, (Long) objects[i]);
+          break;
+        case WireFormat.WIRETYPE_FIXED32:
+          output.writeFixed32(fieldNumber, (Integer) objects[i]);
+          break;
+        case WireFormat.WIRETYPE_FIXED64:
+          output.writeFixed64(fieldNumber, (Long) objects[i]);
+          break;
+        case WireFormat.WIRETYPE_LENGTH_DELIMITED:
+          output.writeBytes(fieldNumber, (ByteString) objects[i]);
+          break;
+        case WireFormat.WIRETYPE_START_GROUP:
+          output.writeTag(fieldNumber, WireFormat.WIRETYPE_START_GROUP);
+          ((UnknownFieldSetLite) objects[i]).writeTo(output);
+          output.writeTag(fieldNumber, WireFormat.WIRETYPE_END_GROUP);
+          break;
+        default:
+          throw InvalidProtocolBufferException.invalidWireType();
+      }
+    }
+  }
+
+  /**
+   * Get the number of bytes required to encode this set.
+   *
+   * <p>For use by generated code only.
+   */
+  public int getSerializedSize() {
+    int size = memoizedSerializedSize;
+    if (size != -1) {
+      return size;
+    }
+    
+    size = 0;
+    for (int i = 0; i < count; i++) {
+      int tag = tags[i];
+      int fieldNumber = WireFormat.getTagFieldNumber(tag);
+      switch (WireFormat.getTagWireType(tag)) {
+        case WireFormat.WIRETYPE_VARINT:
+          size += CodedOutputStream.computeUInt64Size(fieldNumber, (Long) objects[i]);
+          break;
+        case WireFormat.WIRETYPE_FIXED32:
+          size += CodedOutputStream.computeFixed32Size(fieldNumber, (Integer) objects[i]);
+          break;
+        case WireFormat.WIRETYPE_FIXED64:
+          size += CodedOutputStream.computeFixed64Size(fieldNumber, (Long) objects[i]);
+          break;
+        case WireFormat.WIRETYPE_LENGTH_DELIMITED:
+          size += CodedOutputStream.computeBytesSize(fieldNumber, (ByteString) objects[i]);
+          break;
+        case WireFormat.WIRETYPE_START_GROUP:
+          size +=  CodedOutputStream.computeTagSize(fieldNumber) * 2
+              + ((UnknownFieldSetLite) objects[i]).getSerializedSize();
+          break;
+        default:
+          throw new IllegalStateException(InvalidProtocolBufferException.invalidWireType());
+      }
+    }
+    
+    memoizedSerializedSize = size;
+    
+    return size;
+  }
+
+  @Override
+  public boolean equals(Object obj) {
+    if (this == obj) {
+      return true;
+    }
+
+    if (obj == null) {
+      return false;
+    }
+
+    if (!(obj instanceof UnknownFieldSetLite)) {
+      return false;
+    }
+    
+    UnknownFieldSetLite other = (UnknownFieldSetLite) obj;    
+    if (count != other.count
+        // TODO(dweis): Only have to compare up to count but at worst 2x worse than we need to do.
+        || !Arrays.equals(tags, other.tags)
+        || !Arrays.deepEquals(objects, other.objects)) {
+      return false;
+    }
+
+    return true;
+  }
+
+  @Override
+  public int hashCode() {
+    int hashCode = 17;
+    
+    hashCode = 31 * hashCode + count;
+    hashCode = 31 * hashCode + Arrays.hashCode(tags);
+    hashCode = 31 * hashCode + Arrays.deepHashCode(objects);
+    
+    return hashCode;
+  }
+
+  private void storeField(int tag, Object value) {
+    ensureCapacity();
+    
+    tags[count] = tag;
+    objects[count] = value;
+    count++;
+  }
+  
+  /**
+   * Ensures that our arrays are long enough to store more metadata.
+   */
+  private void ensureCapacity() {
+    if (count == tags.length) {        
+      int increment = count < (MIN_CAPACITY / 2) ? MIN_CAPACITY : count >> 1;
+      int newLength = count + increment;
+        
+      tags = Arrays.copyOf(tags, newLength);
+      objects = Arrays.copyOf(objects, newLength);
+    }
+  }
+  
+  /**
+   * Parse a single field from {@code input} and merge it into this set.
+   *
+   * <p>For use by generated code only.
+   *
+   * @param tag The field's tag number, which was already parsed.
+   * @return {@code false} if the tag is an end group tag.
+   */
+  boolean mergeFieldFrom(final int tag, final CodedInputStream input) throws IOException {
+    checkMutable();
+    final int fieldNumber = WireFormat.getTagFieldNumber(tag);
+    switch (WireFormat.getTagWireType(tag)) {
+      case WireFormat.WIRETYPE_VARINT:
+        storeField(tag, input.readInt64());
+        return true;
+      case WireFormat.WIRETYPE_FIXED32:
+        storeField(tag, input.readFixed32());
+        return true;
+      case WireFormat.WIRETYPE_FIXED64:
+        storeField(tag, input.readFixed64());
+        return true;
+      case WireFormat.WIRETYPE_LENGTH_DELIMITED:
+        storeField(tag, input.readBytes());
+        return true;
+      case WireFormat.WIRETYPE_START_GROUP:
+        final UnknownFieldSetLite subFieldSet = new UnknownFieldSetLite();
+        subFieldSet.mergeFrom(input);
+        input.checkLastTagWas(
+            WireFormat.makeTag(fieldNumber, WireFormat.WIRETYPE_END_GROUP));
+        storeField(tag, subFieldSet);
+        return true;
+      case WireFormat.WIRETYPE_END_GROUP:
+        return false;
+      default:
+        throw InvalidProtocolBufferException.invalidWireType();
+    }
+  }
+
+  /**
+   * Convenience method for merging a new field containing a single varint
+   * value. This is used in particular when an unknown enum value is
+   * encountered.
+   *
+   * <p>For use by generated code only.
+   */
+  UnknownFieldSetLite mergeVarintField(int fieldNumber, int value) {
+    checkMutable();
+    if (fieldNumber == 0) {
+      throw new IllegalArgumentException("Zero is not a valid field number.");
+    }
+
+    storeField(WireFormat.makeTag(fieldNumber, WireFormat.WIRETYPE_VARINT), (long) value);
+    
+    return this;
+  }
+
+  /**
+   * Convenience method for merging a length-delimited field.
+   *
+   * <p>For use by generated code only.
+   */
+  UnknownFieldSetLite mergeLengthDelimitedField(final int fieldNumber, final ByteString value) {  
+    checkMutable();
+    if (fieldNumber == 0) {
+      throw new IllegalArgumentException("Zero is not a valid field number.");
+    }
+
+    storeField(WireFormat.makeTag(fieldNumber, WireFormat.WIRETYPE_LENGTH_DELIMITED), value);
+    
+    return this;
+  }
+  
+  /**
+   * Parse an entire message from {@code input} and merge its fields into
+   * this set.
+   */
+  private UnknownFieldSetLite mergeFrom(final CodedInputStream input) throws IOException {
+    // Ensures initialization in mergeFieldFrom.
+    while (true) {
+      final int tag = input.readTag();
+      if (tag == 0 || !mergeFieldFrom(tag, input)) {
+        break;
+      }
+    }
+    return this;
+  }
+  
+  /**
+   * Builder for {@link UnknownFieldSetLite}s.
+   *
+   * <p>Use {@link UnknownFieldSet#newBuilder()} to construct a {@code Builder}.
+   *
+   * <p>For use by generated code only.
+   */
+  // TODO(dweis): Update the mutable API to no longer need this builder and delete.
+  public static final class Builder {
+
+    private UnknownFieldSetLite set;
+    
+    private Builder() {
+      this.set = null;
+    }
+
+    /**
+     * Ensures internal state is initialized for use.
+     */
+    private void ensureNotBuilt() {
+      if (set == null) {
+        set = new UnknownFieldSetLite();
+      }
+      
+      set.checkMutable();
+    }
+    
+    /**
+     * Parse a single field from {@code input} and merge it into this set.
+     *
+     * <p>For use by generated code only.
+     *
+     * @param tag The field's tag number, which was already parsed.
+     * @return {@code false} if the tag is an end group tag.
+     */
+    boolean mergeFieldFrom(final int tag, final CodedInputStream input) throws IOException {
+      ensureNotBuilt();
+      return set.mergeFieldFrom(tag, input);
+    }
+
+    /**
+     * Convenience method for merging a new field containing a single varint
+     * value. This is used in particular when an unknown enum value is
+     * encountered.
+     *
+     * <p>For use by generated code only.
+     */
+    Builder mergeVarintField(int fieldNumber, int value) {
+      ensureNotBuilt();
+      set.mergeVarintField(fieldNumber, value);
+      return this;
+    }
+    
+    /**
+     * Convenience method for merging a length-delimited field.
+     *
+     * <p>For use by generated code only.
+     */
+    public Builder mergeLengthDelimitedField(final int fieldNumber, final ByteString value) {
+      ensureNotBuilt();  
+      set.mergeLengthDelimitedField(fieldNumber, value);
+      return this;
+    }
+    
+    /**
+     * Build the {@link UnknownFieldSetLite} and return it.
+     *
+     * <p>Once {@code build()} has been called, the {@code Builder} will no
+     * longer be usable.  Calling any method after {@code build()} will result
+     * in undefined behavior and can cause an
+     * {@code UnsupportedOperationException} to be thrown.
+     *
+     * <p>For use by generated code only.
+     */
+    public UnknownFieldSetLite build() {
+      if (set == null) {
+        return DEFAULT_INSTANCE;
+      }
+      
+      set.checkMutable();
+      set.makeImmutable();
+
+      return set;
+    }
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/UnmodifiableLazyStringList.java b/java/core/src/main/java/com/google/protobuf/UnmodifiableLazyStringList.java
new file mode 100644
index 00000000..5257c5a2
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/UnmodifiableLazyStringList.java
@@ -0,0 +1,210 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import java.util.AbstractList;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.Iterator;
+import java.util.List;
+import java.util.ListIterator;
+import java.util.RandomAccess;
+
+/**
+ * An implementation of {@link LazyStringList} that wraps another
+ * {@link LazyStringList} such that it cannot be modified via the wrapper.
+ *
+ * @author jonp@google.com (Jon Perlow)
+ */
+public class UnmodifiableLazyStringList extends AbstractList<String>
+    implements LazyStringList, RandomAccess {
+
+  private final LazyStringList list;
+
+  public UnmodifiableLazyStringList(LazyStringList list) {
+    this.list = list;
+  }
+
+  @Override
+  public String get(int index) {
+    return list.get(index);
+  }
+  
+  @Override
+  public Object getRaw(int index) {
+    return list.getRaw(index);
+  }
+
+  @Override
+  public int size() {
+    return list.size();
+  }
+
+  //@Override (Java 1.6 override semantics, but we must support 1.5)
+  public ByteString getByteString(int index) {
+    return list.getByteString(index);
+  }
+
+  //@Override (Java 1.6 override semantics, but we must support 1.5)
+  public void add(ByteString element) {
+    throw new UnsupportedOperationException();
+  }
+
+  //@Override (Java 1.6 override semantics, but we must support 1.5)
+  public void set(int index, ByteString element) {
+    throw new UnsupportedOperationException();
+  }
+
+  //@Override (Java 1.6 override semantics, but we must support 1.5)
+  public boolean addAllByteString(Collection<? extends ByteString> element) {
+    throw new UnsupportedOperationException();
+  }
+
+  //@Override (Java 1.6 override semantics, but we must support 1.5)
+  public byte[] getByteArray(int index) {
+    return list.getByteArray(index);
+  }
+
+  //@Override (Java 1.6 override semantics, but we must support 1.5)
+  public void add(byte[] element) {
+    throw new UnsupportedOperationException();
+  }
+  
+  //@Override (Java 1.6 override semantics, but we must support 1.5)
+  public void set(int index, byte[] element) {
+    throw new UnsupportedOperationException();
+  }
+
+  //@Override (Java 1.6 override semantics, but we must support 1.5)
+  public boolean addAllByteArray(Collection<byte[]> element) {
+    throw new UnsupportedOperationException();
+  }
+
+  @Override
+  public ListIterator<String> listIterator(final int index) {
+    return new ListIterator<String>() {
+      ListIterator<String> iter = list.listIterator(index);
+
+      //@Override (Java 1.6 override semantics, but we must support 1.5)
+      public boolean hasNext() {
+        return iter.hasNext();
+      }
+
+      //@Override (Java 1.6 override semantics, but we must support 1.5)
+      public String next() {
+        return iter.next();
+      }
+
+      //@Override (Java 1.6 override semantics, but we must support 1.5)
+      public boolean hasPrevious() {
+        return iter.hasPrevious();
+      }
+
+      //@Override (Java 1.6 override semantics, but we must support 1.5)
+      public String previous() {
+        return iter.previous();
+      }
+
+      //@Override (Java 1.6 override semantics, but we must support 1.5)
+      public int nextIndex() {
+        return iter.nextIndex();
+      }
+
+      //@Override (Java 1.6 override semantics, but we must support 1.5)
+      public int previousIndex() {
+        return iter.previousIndex();
+      }
+
+      //@Override (Java 1.6 override semantics, but we must support 1.5)
+      public void remove() {
+        throw new UnsupportedOperationException();
+      }
+
+      //@Override (Java 1.6 override semantics, but we must support 1.5)
+      public void set(String o) {
+        throw new UnsupportedOperationException();
+      }
+
+      //@Override (Java 1.6 override semantics, but we must support 1.5)
+      public void add(String o) {
+        throw new UnsupportedOperationException();
+      }
+    };
+  }
+
+  @Override
+  public Iterator<String> iterator() {
+    return new Iterator<String>() {
+      Iterator<String> iter = list.iterator();
+
+      //@Override (Java 1.6 override semantics, but we must support 1.5)
+      public boolean hasNext() {
+        return iter.hasNext();
+      }
+
+      //@Override (Java 1.6 override semantics, but we must support 1.5)
+      public String next() {
+        return iter.next();
+      }
+
+      //@Override (Java 1.6 override semantics, but we must support 1.5)
+      public void remove() {
+        throw new UnsupportedOperationException();
+      }
+    };
+  }
+
+  //@Override (Java 1.6 override semantics, but we must support 1.5)
+  public List<?> getUnderlyingElements() {
+    // The returned value is already unmodifiable.
+    return list.getUnderlyingElements();
+  }
+
+  //@Override (Java 1.6 override semantics, but we must support 1.5)
+  public void mergeFrom(LazyStringList other) {
+    throw new UnsupportedOperationException();
+  }
+
+  //@Override (Java 1.6 override semantics, but we must support 1.5)
+  public List<byte[]> asByteArrayList() {
+    return Collections.unmodifiableList(list.asByteArrayList());
+  }
+
+  //@Override (Java 1.6 override semantics, but we must support 1.5)
+  public List<ByteString> asByteStringList() {
+    return Collections.unmodifiableList(list.asByteStringList());
+  }
+
+  //@Override (Java 1.6 override semantics, but we must support 1.5)
+  public LazyStringList getUnmodifiableView() {
+    return this;
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/UnsafeByteStrings.java b/java/core/src/main/java/com/google/protobuf/UnsafeByteStrings.java
new file mode 100644
index 00000000..c1997515
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/UnsafeByteStrings.java
@@ -0,0 +1,55 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import java.nio.ByteBuffer;
+
+/**
+ * Provides unsafe factory methods for {@link ByteString} instances.
+ *
+ * <p><strong>DISCLAIMER:</strong> The methods in this class should only be called if it is
+ * guaranteed that the the buffer backing the {@link ByteString} will never change! Mutation of a
+ * {@link ByteString} can lead to unexpected and undesirable consequences in your application,
+ * and will likely be difficult to debug. Proceed with caution!
+ */
+public final class UnsafeByteStrings {
+  private UnsafeByteStrings() {}
+
+  /**
+   * An unsafe operation that returns a {@link ByteString} that is backed by the provided buffer.
+   *
+   * @param buffer the Java NIO buffer to be wrapped.
+   * @return a {@link ByteString} backed by the provided buffer.
+   */
+  public static ByteString unsafeWrap(ByteBuffer buffer) {
+    return new NioByteString(buffer);
+  }
+}
diff --git a/java/core/src/main/java/com/google/protobuf/Utf8.java b/java/core/src/main/java/com/google/protobuf/Utf8.java
new file mode 100644
index 00000000..48c7e9e6
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/Utf8.java
@@ -0,0 +1,481 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+/**
+ * A set of low-level, high-performance static utility methods related
+ * to the UTF-8 character encoding.  This class has no dependencies
+ * outside of the core JDK libraries.
+ *
+ * <p>There are several variants of UTF-8.  The one implemented by
+ * this class is the restricted definition of UTF-8 introduced in
+ * Unicode 3.1, which mandates the rejection of "overlong" byte
+ * sequences as well as rejection of 3-byte surrogate codepoint byte
+ * sequences.  Note that the UTF-8 decoder included in Oracle's JDK
+ * has been modified to also reject "overlong" byte sequences, but (as
+ * of 2011) still accepts 3-byte surrogate codepoint byte sequences.
+ *
+ * <p>The byte sequences considered valid by this class are exactly
+ * those that can be roundtrip converted to Strings and back to bytes
+ * using the UTF-8 charset, without loss: <pre> {@code
+ * Arrays.equals(bytes, new String(bytes, Internal.UTF_8).getBytes(Internal.UTF_8))
+ * }</pre>
+ *
+ * <p>See the Unicode Standard,</br>
+ * Table 3-6. <em>UTF-8 Bit Distribution</em>,</br>
+ * Table 3-7. <em>Well Formed UTF-8 Byte Sequences</em>.
+ *
+ * <p>This class supports decoding of partial byte sequences, so that the
+ * bytes in a complete UTF-8 byte sequences can be stored in multiple
+ * segments.  Methods typically return {@link #MALFORMED} if the partial
+ * byte sequence is definitely not well-formed, {@link #COMPLETE} if it is
+ * well-formed in the absence of additional input, or if the byte sequence
+ * apparently terminated in the middle of a character, an opaque integer
+ * "state" value containing enough information to decode the character when
+ * passed to a subsequent invocation of a partial decoding method.
+ *
+ * @author martinrb@google.com (Martin Buchholz)
+ */
+final class Utf8 {
+  private Utf8() {}
+  
+  /**
+   * Maximum number of bytes per Java UTF-16 char in UTF-8.
+   * @see java.nio.charset.CharsetEncoder#maxBytesPerChar()
+   */
+  static final int MAX_BYTES_PER_CHAR = 3;
+
+  /**
+   * State value indicating that the byte sequence is well-formed and
+   * complete (no further bytes are needed to complete a character).
+   */
+  public static final int COMPLETE = 0;
+
+  /**
+   * State value indicating that the byte sequence is definitely not
+   * well-formed.
+   */
+  public static final int MALFORMED = -1;
+
+  // Other state values include the partial bytes of the incomplete
+  // character to be decoded in the simplest way: we pack the bytes
+  // into the state int in little-endian order.  For example:
+  //
+  // int state = byte1 ^ (byte2 << 8) ^ (byte3 << 16);
+  //
+  // Such a state is unpacked thus (note the ~ operation for byte2 to
+  // undo byte1's sign-extension bits):
+  //
+  // int byte1 = (byte) state;
+  // int byte2 = (byte) ~(state >> 8);
+  // int byte3 = (byte) (state >> 16);
+  //
+  // We cannot store a zero byte in the state because it would be
+  // indistinguishable from the absence of a byte.  But we don't need
+  // to, because partial bytes must always be negative.  When building
+  // a state, we ensure that byte1 is negative and subsequent bytes
+  // are valid trailing bytes.
+
+  /**
+   * Returns {@code true} if the given byte array is a well-formed
+   * UTF-8 byte sequence.
+   *
+   * <p>This is a convenience method, equivalent to a call to {@code
+   * isValidUtf8(bytes, 0, bytes.length)}.
+   */
+  public static boolean isValidUtf8(byte[] bytes) {
+    return isValidUtf8(bytes, 0, bytes.length);
+  }
+
+  /**
+   * Returns {@code true} if the given byte array slice is a
+   * well-formed UTF-8 byte sequence.  The range of bytes to be
+   * checked extends from index {@code index}, inclusive, to {@code
+   * limit}, exclusive.
+   *
+   * <p>This is a convenience method, equivalent to {@code
+   * partialIsValidUtf8(bytes, index, limit) == Utf8.COMPLETE}.
+   */
+  public static boolean isValidUtf8(byte[] bytes, int index, int limit) {
+    return partialIsValidUtf8(bytes, index, limit) == COMPLETE;
+  }
+
+  /**
+   * Tells whether the given byte array slice is a well-formed,
+   * malformed, or incomplete UTF-8 byte sequence.  The range of bytes
+   * to be checked extends from index {@code index}, inclusive, to
+   * {@code limit}, exclusive.
+   *
+   * @param state either {@link Utf8#COMPLETE} (if this is the initial decoding
+   * operation) or the value returned from a call to a partial decoding method
+   * for the previous bytes
+   *
+   * @return {@link #MALFORMED} if the partial byte sequence is
+   * definitely not well-formed, {@link #COMPLETE} if it is well-formed
+   * (no additional input needed), or if the byte sequence is
+   * "incomplete", i.e. apparently terminated in the middle of a character,
+   * an opaque integer "state" value containing enough information to
+   * decode the character when passed to a subsequent invocation of a
+   * partial decoding method.
+   */
+  public static int partialIsValidUtf8(
+      int state, byte[] bytes, int index, int limit) {
+    if (state != COMPLETE) {
+      // The previous decoding operation was incomplete (or malformed).
+      // We look for a well-formed sequence consisting of bytes from
+      // the previous decoding operation (stored in state) together
+      // with bytes from the array slice.
+      //
+      // We expect such "straddler characters" to be rare.
+
+      if (index >= limit) {  // No bytes? No progress.
+        return state;
+      }
+      int byte1 = (byte) state;
+      // byte1 is never ASCII.
+      if (byte1 < (byte) 0xE0) {
+        // two-byte form
+
+        // Simultaneously checks for illegal trailing-byte in
+        // leading position and overlong 2-byte form.
+        if (byte1 < (byte) 0xC2 ||
+            // byte2 trailing-byte test
+            bytes[index++] > (byte) 0xBF) {
+          return MALFORMED;
+        }
+      } else if (byte1 < (byte) 0xF0) {
+        // three-byte form
+
+        // Get byte2 from saved state or array
+        int byte2 = (byte) ~(state >> 8);
+        if (byte2 == 0) {
+          byte2 = bytes[index++];
+          if (index >= limit) {
+            return incompleteStateFor(byte1, byte2);
+          }
+        }
+        if (byte2 > (byte) 0xBF ||
+            // overlong? 5 most significant bits must not all be zero
+            (byte1 == (byte) 0xE0 && byte2 < (byte) 0xA0) ||
+            // illegal surrogate codepoint?
+            (byte1 == (byte) 0xED && byte2 >= (byte) 0xA0) ||
+            // byte3 trailing-byte test
+            bytes[index++] > (byte) 0xBF) {
+          return MALFORMED;
+        }
+      } else {
+        // four-byte form
+
+        // Get byte2 and byte3 from saved state or array
+        int byte2 = (byte) ~(state >> 8);
+        int byte3 = 0;
+        if (byte2 == 0) {
+          byte2 = bytes[index++];
+          if (index >= limit) {
+            return incompleteStateFor(byte1, byte2);
+          }
+        } else {
+          byte3 = (byte) (state >> 16);
+        }
+        if (byte3 == 0) {
+          byte3 = bytes[index++];
+          if (index >= limit) {
+            return incompleteStateFor(byte1, byte2, byte3);
+          }
+        }
+
+        // If we were called with state == MALFORMED, then byte1 is 0xFF,
+        // which never occurs in well-formed UTF-8, and so we will return
+        // MALFORMED again below.
+
+        if (byte2 > (byte) 0xBF ||
+            // Check that 1 <= plane <= 16.  Tricky optimized form of:
+            // if (byte1 > (byte) 0xF4 ||
+            //     byte1 == (byte) 0xF0 && byte2 < (byte) 0x90 ||
+            //     byte1 == (byte) 0xF4 && byte2 > (byte) 0x8F)
+            (((byte1 << 28) + (byte2 - (byte) 0x90)) >> 30) != 0 ||
+            // byte3 trailing-byte test
+            byte3 > (byte) 0xBF ||
+            // byte4 trailing-byte test
+             bytes[index++] > (byte) 0xBF) {
+          return MALFORMED;
+        }
+      }
+    }
+
+    return partialIsValidUtf8(bytes, index, limit);
+  }
+
+  /**
+   * Tells whether the given byte array slice is a well-formed,
+   * malformed, or incomplete UTF-8 byte sequence.  The range of bytes
+   * to be checked extends from index {@code index}, inclusive, to
+   * {@code limit}, exclusive.
+   *
+   * <p>This is a convenience method, equivalent to a call to {@code
+   * partialIsValidUtf8(Utf8.COMPLETE, bytes, index, limit)}.
+   *
+   * @return {@link #MALFORMED} if the partial byte sequence is
+   * definitely not well-formed, {@link #COMPLETE} if it is well-formed
+   * (no additional input needed), or if the byte sequence is
+   * "incomplete", i.e. apparently terminated in the middle of a character,
+   * an opaque integer "state" value containing enough information to
+   * decode the character when passed to a subsequent invocation of a
+   * partial decoding method.
+   */
+  public static int partialIsValidUtf8(
+      byte[] bytes, int index, int limit) {
+    // Optimize for 100% ASCII.
+    // Hotspot loves small simple top-level loops like this.
+    while (index < limit && bytes[index] >= 0) {
+      index++;
+    }
+
+    return (index >= limit) ? COMPLETE :
+        partialIsValidUtf8NonAscii(bytes, index, limit);
+  }
+
+  private static int partialIsValidUtf8NonAscii(
+      byte[] bytes, int index, int limit) {
+    for (;;) {
+      int byte1, byte2;
+
+      // Optimize for interior runs of ASCII bytes.
+      do {
+        if (index >= limit) {
+          return COMPLETE;
+        }
+      } while ((byte1 = bytes[index++]) >= 0);
+
+      if (byte1 < (byte) 0xE0) {
+        // two-byte form
+
+        if (index >= limit) {
+          return byte1;
+        }
+
+        // Simultaneously checks for illegal trailing-byte in
+        // leading position and overlong 2-byte form.
+        if (byte1 < (byte) 0xC2 ||
+            bytes[index++] > (byte) 0xBF) {
+          return MALFORMED;
+        }
+      } else if (byte1 < (byte) 0xF0) {
+        // three-byte form
+
+        if (index >= limit - 1) { // incomplete sequence
+          return incompleteStateFor(bytes, index, limit);
+        }
+        if ((byte2 = bytes[index++]) > (byte) 0xBF ||
+            // overlong? 5 most significant bits must not all be zero
+            (byte1 == (byte) 0xE0 && byte2 < (byte) 0xA0) ||
+            // check for illegal surrogate codepoints
+            (byte1 == (byte) 0xED && byte2 >= (byte) 0xA0) ||
+            // byte3 trailing-byte test
+            bytes[index++] > (byte) 0xBF) {
+          return MALFORMED;
+        }
+      } else {
+        // four-byte form
+
+        if (index >= limit - 2) {  // incomplete sequence
+          return incompleteStateFor(bytes, index, limit);
+        }
+        if ((byte2 = bytes[index++]) > (byte) 0xBF ||
+            // Check that 1 <= plane <= 16.  Tricky optimized form of:
+            // if (byte1 > (byte) 0xF4 ||
+            //     byte1 == (byte) 0xF0 && byte2 < (byte) 0x90 ||
+            //     byte1 == (byte) 0xF4 && byte2 > (byte) 0x8F)
+            (((byte1 << 28) + (byte2 - (byte) 0x90)) >> 30) != 0 ||
+            // byte3 trailing-byte test
+            bytes[index++] > (byte) 0xBF ||
+            // byte4 trailing-byte test
+            bytes[index++] > (byte) 0xBF) {
+          return MALFORMED;
+        }
+      }
+    }
+  }
+
+  private static int incompleteStateFor(int byte1) {
+    return (byte1 > (byte) 0xF4) ?
+        MALFORMED : byte1;
+  }
+
+  private static int incompleteStateFor(int byte1, int byte2) {
+    return (byte1 > (byte) 0xF4 ||
+            byte2 > (byte) 0xBF) ?
+        MALFORMED : byte1 ^ (byte2 << 8);
+  }
+
+  private static int incompleteStateFor(int byte1, int byte2, int byte3) {
+    return (byte1 > (byte) 0xF4 ||
+            byte2 > (byte) 0xBF ||
+            byte3 > (byte) 0xBF) ?
+        MALFORMED : byte1 ^ (byte2 << 8) ^ (byte3 << 16);
+  }
+
+  private static int incompleteStateFor(byte[] bytes, int index, int limit) {
+    int byte1 = bytes[index - 1];
+    switch (limit - index) {
+      case 0: return incompleteStateFor(byte1);
+      case 1: return incompleteStateFor(byte1, bytes[index]);
+      case 2: return incompleteStateFor(byte1, bytes[index], bytes[index + 1]);
+      default: throw new AssertionError();
+    }
+  }
+  
+
+  // These UTF-8 handling methods are copied from Guava's Utf8 class with a modification to throw
+  // a protocol buffer local exception. This exception is then caught in CodedOutputStream so it can
+  // fallback to more lenient behavior.
+  
+  static class UnpairedSurrogateException extends IllegalArgumentException {
+    
+    private UnpairedSurrogateException(int index, int length) {
+      super("Unpaired surrogate at index " + index + " of " + length);
+    }
+  }
+  
+  /**
+   * Returns the number of bytes in the UTF-8-encoded form of {@code sequence}. For a string,
+   * this method is equivalent to {@code string.getBytes(UTF_8).length}, but is more efficient in
+   * both time and space.
+   *
+   * @throws IllegalArgumentException if {@code sequence} contains ill-formed UTF-16 (unpaired
+   *     surrogates)
+   */
+  static int encodedLength(CharSequence sequence) {
+    // Warning to maintainers: this implementation is highly optimized.
+    int utf16Length = sequence.length();
+    int utf8Length = utf16Length;
+    int i = 0;
+
+    // This loop optimizes for pure ASCII.
+    while (i < utf16Length && sequence.charAt(i) < 0x80) {
+      i++;
+    }
+
+    // This loop optimizes for chars less than 0x800.
+    for (; i < utf16Length; i++) {
+      char c = sequence.charAt(i);
+      if (c < 0x800) {
+        utf8Length += ((0x7f - c) >>> 31);  // branch free!
+      } else {
+        utf8Length += encodedLengthGeneral(sequence, i);
+        break;
+      }
+    }
+
+    if (utf8Length < utf16Length) {
+      // Necessary and sufficient condition for overflow because of maximum 3x expansion
+      throw new IllegalArgumentException("UTF-8 length does not fit in int: "
+              + (utf8Length + (1L << 32)));
+    }
+    return utf8Length;
+  }
+
+  private static int encodedLengthGeneral(CharSequence sequence, int start) {
+    int utf16Length = sequence.length();
+    int utf8Length = 0;
+    for (int i = start; i < utf16Length; i++) {
+      char c = sequence.charAt(i);
+      if (c < 0x800) {
+        utf8Length += (0x7f - c) >>> 31; // branch free!
+      } else {
+        utf8Length += 2;
+        // jdk7+: if (Character.isSurrogate(c)) {
+        if (Character.MIN_SURROGATE <= c && c <= Character.MAX_SURROGATE) {
+          // Check that we have a well-formed surrogate pair.
+          int cp = Character.codePointAt(sequence, i);
+          if (cp < Character.MIN_SUPPLEMENTARY_CODE_POINT) {
+            throw new UnpairedSurrogateException(i, utf16Length);
+          }
+          i++;
+        }
+      }
+    }
+    return utf8Length;
+  }
+
+  static int encode(CharSequence sequence, byte[] bytes, int offset, int length) {
+    int utf16Length = sequence.length();
+    int j = offset;
+    int i = 0;
+    int limit = offset + length;
+    // Designed to take advantage of
+    // https://wikis.oracle.com/display/HotSpotInternals/RangeCheckElimination
+    for (char c; i < utf16Length && i + j < limit && (c = sequence.charAt(i)) < 0x80; i++) {
+      bytes[j + i] = (byte) c;
+    }
+    if (i == utf16Length) {
+      return j + utf16Length;
+    }
+    j += i;
+    for (char c; i < utf16Length; i++) {
+      c = sequence.charAt(i);
+      if (c < 0x80 && j < limit) {
+        bytes[j++] = (byte) c;
+      } else if (c < 0x800 && j <= limit - 2) { // 11 bits, two UTF-8 bytes
+        bytes[j++] = (byte) ((0xF << 6) | (c >>> 6));
+        bytes[j++] = (byte) (0x80 | (0x3F & c));
+      } else if ((c < Character.MIN_SURROGATE || Character.MAX_SURROGATE < c) && j <= limit - 3) {
+        // Maximum single-char code point is 0xFFFF, 16 bits, three UTF-8 bytes
+        bytes[j++] = (byte) ((0xF << 5) | (c >>> 12));
+        bytes[j++] = (byte) (0x80 | (0x3F & (c >>> 6)));
+        bytes[j++] = (byte) (0x80 | (0x3F & c));
+      } else if (j <= limit - 4) {
+        // Minimum code point represented by a surrogate pair is 0x10000, 17 bits, four UTF-8 bytes
+        final char low;
+        if (i + 1 == sequence.length()
+                || !Character.isSurrogatePair(c, (low = sequence.charAt(++i)))) {
+          throw new UnpairedSurrogateException((i - 1), utf16Length);
+        }
+        int codePoint = Character.toCodePoint(c, low);
+        bytes[j++] = (byte) ((0xF << 4) | (codePoint >>> 18));
+        bytes[j++] = (byte) (0x80 | (0x3F & (codePoint >>> 12)));
+        bytes[j++] = (byte) (0x80 | (0x3F & (codePoint >>> 6)));
+        bytes[j++] = (byte) (0x80 | (0x3F & codePoint));
+      } else {
+        // If we are surrogates and we're not a surrogate pair, always throw an
+        // IllegalArgumentException instead of an ArrayOutOfBoundsException.
+        if ((Character.MIN_SURROGATE <= c && c <= Character.MAX_SURROGATE)
+            && (i + 1 == sequence.length()
+                || !Character.isSurrogatePair(c, sequence.charAt(i + 1)))) {
+          throw new UnpairedSurrogateException(i, utf16Length);
+        }
+        throw new ArrayIndexOutOfBoundsException("Failed writing " + c + " at index " + j);
+      }
+    }
+    return j;
+  }
+  // End Guava UTF-8 methods.
+}
diff --git a/java/core/src/main/java/com/google/protobuf/WireFormat.java b/java/core/src/main/java/com/google/protobuf/WireFormat.java
new file mode 100644
index 00000000..8dbe1ae3
--- /dev/null
+++ b/java/core/src/main/java/com/google/protobuf/WireFormat.java
@@ -0,0 +1,245 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import java.io.IOException;
+
+/**
+ * This class is used internally by the Protocol Buffer library and generated
+ * message implementations.  It is public only because those generated messages
+ * do not reside in the {@code protobuf} package.  Others should not use this
+ * class directly.
+ *
+ * This class contains constants and helper functions useful for dealing with
+ * the Protocol Buffer wire format.
+ *
+ * @author kenton@google.com Kenton Varda
+ */
+public final class WireFormat {
+  // Do not allow instantiation.
+  private WireFormat() {}
+
+  public static final int WIRETYPE_VARINT           = 0;
+  public static final int WIRETYPE_FIXED64          = 1;
+  public static final int WIRETYPE_LENGTH_DELIMITED = 2;
+  public static final int WIRETYPE_START_GROUP      = 3;
+  public static final int WIRETYPE_END_GROUP        = 4;
+  public static final int WIRETYPE_FIXED32          = 5;
+
+  static final int TAG_TYPE_BITS = 3;
+  static final int TAG_TYPE_MASK = (1 << TAG_TYPE_BITS) - 1;
+
+  /** Given a tag value, determines the wire type (the lower 3 bits). */
+  public static int getTagWireType(final int tag) {
+    return tag & TAG_TYPE_MASK;
+  }
+
+  /** Given a tag value, determines the field number (the upper 29 bits). */
+  public static int getTagFieldNumber(final int tag) {
+    return tag >>> TAG_TYPE_BITS;
+  }
+
+  /** Makes a tag value given a field number and wire type. */
+  static int makeTag(final int fieldNumber, final int wireType) {
+    return (fieldNumber << TAG_TYPE_BITS) | wireType;
+  }
+
+  /**
+   * Lite equivalent to {@link Descriptors.FieldDescriptor.JavaType}.  This is
+   * only here to support the lite runtime and should not be used by users.
+   */
+  public enum JavaType {
+    INT(0),
+    LONG(0L),
+    FLOAT(0F),
+    DOUBLE(0D),
+    BOOLEAN(false),
+    STRING(""),
+    BYTE_STRING(ByteString.EMPTY),
+    ENUM(null),
+    MESSAGE(null);
+
+    JavaType(final Object defaultDefault) {
+      this.defaultDefault = defaultDefault;
+    }
+
+    /**
+     * The default default value for fields of this type, if it's a primitive
+     * type.
+     */
+    Object getDefaultDefault() {
+      return defaultDefault;
+    }
+
+    private final Object defaultDefault;
+  }
+
+  /**
+   * Lite equivalent to {@link Descriptors.FieldDescriptor.Type}.  This is
+   * only here to support the lite runtime and should not be used by users.
+   */
+  public enum FieldType {
+    DOUBLE  (JavaType.DOUBLE     , WIRETYPE_FIXED64         ),
+    FLOAT   (JavaType.FLOAT      , WIRETYPE_FIXED32         ),
+    INT64   (JavaType.LONG       , WIRETYPE_VARINT          ),
+    UINT64  (JavaType.LONG       , WIRETYPE_VARINT          ),
+    INT32   (JavaType.INT        , WIRETYPE_VARINT          ),
+    FIXED64 (JavaType.LONG       , WIRETYPE_FIXED64         ),
+    FIXED32 (JavaType.INT        , WIRETYPE_FIXED32         ),
+    BOOL    (JavaType.BOOLEAN    , WIRETYPE_VARINT          ),
+    STRING  (JavaType.STRING     , WIRETYPE_LENGTH_DELIMITED) {
+      public boolean isPackable() { return false; }
+    },
+    GROUP   (JavaType.MESSAGE    , WIRETYPE_START_GROUP     ) {
+      public boolean isPackable() { return false; }
+    },
+    MESSAGE (JavaType.MESSAGE    , WIRETYPE_LENGTH_DELIMITED) {
+      public boolean isPackable() { return false; }
+    },
+    BYTES   (JavaType.BYTE_STRING, WIRETYPE_LENGTH_DELIMITED) {
+      public boolean isPackable() { return false; }
+    },
+    UINT32  (JavaType.INT        , WIRETYPE_VARINT          ),
+    ENUM    (JavaType.ENUM       , WIRETYPE_VARINT          ),
+    SFIXED32(JavaType.INT        , WIRETYPE_FIXED32         ),
+    SFIXED64(JavaType.LONG       , WIRETYPE_FIXED64         ),
+    SINT32  (JavaType.INT        , WIRETYPE_VARINT          ),
+    SINT64  (JavaType.LONG       , WIRETYPE_VARINT          );
+
+    FieldType(final JavaType javaType, final int wireType) {
+      this.javaType = javaType;
+      this.wireType = wireType;
+    }
+
+    private final JavaType javaType;
+    private final int wireType;
+
+    public JavaType getJavaType() { return javaType; }
+    public int getWireType() { return wireType; }
+
+    public boolean isPackable() { return true; }
+  }
+
+  // Field numbers for fields in MessageSet wire format.
+  static final int MESSAGE_SET_ITEM    = 1;
+  static final int MESSAGE_SET_TYPE_ID = 2;
+  static final int MESSAGE_SET_MESSAGE = 3;
+
+  // Tag numbers.
+  static final int MESSAGE_SET_ITEM_TAG =
+    makeTag(MESSAGE_SET_ITEM, WIRETYPE_START_GROUP);
+  static final int MESSAGE_SET_ITEM_END_TAG =
+    makeTag(MESSAGE_SET_ITEM, WIRETYPE_END_GROUP);
+  static final int MESSAGE_SET_TYPE_ID_TAG =
+    makeTag(MESSAGE_SET_TYPE_ID, WIRETYPE_VARINT);
+  static final int MESSAGE_SET_MESSAGE_TAG =
+    makeTag(MESSAGE_SET_MESSAGE, WIRETYPE_LENGTH_DELIMITED);
+
+  /**
+   * Validation level for handling incoming string field data which potentially
+   * contain non-UTF8 bytes.
+   */
+  enum Utf8Validation {
+    /** Eagerly parses to String; silently accepts invalid UTF8 bytes. */
+    LOOSE {
+      Object readString(CodedInputStream input) throws IOException {
+        return input.readString();
+      }
+    },
+    /** Eagerly parses to String; throws an IOException on invalid bytes. */
+    STRICT {
+      Object readString(CodedInputStream input) throws IOException {
+        return input.readStringRequireUtf8();
+      }
+    },
+    /** Keep data as ByteString; validation/conversion to String is lazy. */
+    LAZY {
+      Object readString(CodedInputStream input) throws IOException {
+        return input.readBytes();
+      }
+    };
+
+    /** Read a string field from the input with the proper UTF8 validation. */
+    abstract Object readString(CodedInputStream input) throws IOException;
+  }
+
+  /**
+   * Read a field of any primitive type for immutable messages from a
+   * CodedInputStream. Enums, groups, and embedded messages are not handled by
+   * this method.
+   *
+   * @param input The stream from which to read.
+   * @param type Declared type of the field.
+   * @param utf8Validation Different string UTF8 validation level for handling
+   *                       string fields.
+   * @return An object representing the field's value, of the exact
+   *         type which would be returned by
+   *         {@link Message#getField(Descriptors.FieldDescriptor)} for
+   *         this field.
+   */
+  static Object readPrimitiveField(
+      CodedInputStream input,
+      FieldType type,
+      Utf8Validation utf8Validation) throws IOException {
+    switch (type) {
+      case DOUBLE  : return input.readDouble  ();
+      case FLOAT   : return input.readFloat   ();
+      case INT64   : return input.readInt64   ();
+      case UINT64  : return input.readUInt64  ();
+      case INT32   : return input.readInt32   ();
+      case FIXED64 : return input.readFixed64 ();
+      case FIXED32 : return input.readFixed32 ();
+      case BOOL    : return input.readBool    ();
+      case BYTES   : return input.readBytes   ();
+      case UINT32  : return input.readUInt32  ();
+      case SFIXED32: return input.readSFixed32();
+      case SFIXED64: return input.readSFixed64();
+      case SINT32  : return input.readSInt32  ();
+      case SINT64  : return input.readSInt64  ();
+
+      case STRING  : return utf8Validation.readString(input);
+      case GROUP:
+        throw new IllegalArgumentException(
+          "readPrimitiveField() cannot handle nested groups.");
+      case MESSAGE:
+        throw new IllegalArgumentException(
+          "readPrimitiveField() cannot handle embedded messages.");
+      case ENUM:
+        // We don't handle enums because we don't know what to do if the
+        // value is not recognized.
+        throw new IllegalArgumentException(
+          "readPrimitiveField() cannot handle enums.");
+    }
+
+    throw new RuntimeException(
+      "There is no way to get here, but the compiler thinks otherwise.");
+  }
+}