Make Digest (renamed Md5Digest) a little more multi-purpose.

--
MOS_MIGRATED_REVID=130986194

8 files changed, 161 insertions, 170 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/actions/ActionCacheChecker.java b/src/main/java/com/google/devtools/build/lib/actions/ActionCacheChecker.java
index b96a9e4111..5b913ad1c3 100644
--- a/src/main/java/com/google/devtools/build/lib/actions/ActionCacheChecker.java
+++ b/src/main/java/com/google/devtools/build/lib/actions/ActionCacheChecker.java
@@ -19,7 +19,7 @@ import com.google.common.collect.Iterables;
 import com.google.devtools.build.lib.actions.ActionAnalysisMetadata.MiddlemanType;
 import com.google.devtools.build.lib.actions.cache.ActionCache;
 import com.google.devtools.build.lib.actions.cache.ActionCache.Entry;
-import com.google.devtools.build.lib.actions.cache.Digest;
+import com.google.devtools.build.lib.actions.cache.DigestUtils;
 import com.google.devtools.build.lib.actions.cache.Metadata;
 import com.google.devtools.build.lib.actions.cache.MetadataHandler;
 import com.google.devtools.build.lib.events.Event;
@@ -108,7 +108,7 @@ public class ActionCacheChecker {
     for (Artifact artifact : artifacts) {
       mdMap.put(artifact.getExecPathString(), metadataHandler.getMetadataMaybe(artifact));
     }
-    return !Digest.fromMetadata(mdMap).equals(entry.getFileDigest());
+    return !DigestUtils.fromMetadata(mdMap).equals(entry.getFileDigest());
   }
 
   private void reportCommand(EventHandler handler, Action action) {
diff --git a/src/main/java/com/google/devtools/build/lib/actions/cache/ActionCache.java b/src/main/java/com/google/devtools/build/lib/actions/cache/ActionCache.java
index b87dd846ab..5dc88cf0ff 100644
--- a/src/main/java/com/google/devtools/build/lib/actions/cache/ActionCache.java
+++ b/src/main/java/com/google/devtools/build/lib/actions/cache/ActionCache.java
@@ -19,7 +19,6 @@ import com.google.common.collect.Lists;
 import com.google.devtools.build.lib.concurrent.ThreadSafety.ThreadCompatible;
 import com.google.devtools.build.lib.util.Preconditions;
 import com.google.devtools.build.lib.vfs.PathFragment;
-
 import java.io.IOException;
 import java.io.PrintStream;
 import java.util.ArrayList;
@@ -28,7 +27,6 @@ import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
-
 import javax.annotation.Nullable;
 
 /**
@@ -73,9 +71,9 @@ public interface ActionCache {
     @Nullable
     // Null iff the corresponding action does not do input discovery.
     private final List<String> files;
-    // If null, digest is non-null and the entry is immutable.
+    // If null, md5Digest is non-null and the entry is immutable.
     private Map<String, Metadata> mdMap;
-    private Digest digest;
+    private Md5Digest md5Digest;
 
     public Entry(String key, boolean discoversInputs) {
       actionKey = key;
@@ -83,10 +81,10 @@ public interface ActionCache {
       mdMap = new HashMap<>();
     }
 
-    public Entry(String key, @Nullable List<String> files, Digest digest) {
+    public Entry(String key, @Nullable List<String> files, Md5Digest md5Digest) {
       actionKey = key;
       this.files = files;
-      this.digest = digest;
+      this.md5Digest = md5Digest;
       mdMap = null;
     }
 
@@ -97,7 +95,7 @@ public interface ActionCache {
     public void addFile(PathFragment relativePath, Metadata md) {
       Preconditions.checkState(mdMap != null);
       Preconditions.checkState(!isCorrupted());
-      Preconditions.checkState(digest == null);
+      Preconditions.checkState(md5Digest == null);
 
       String execPath = relativePath.getPathString();
       if (discoversInputs()) {
@@ -114,17 +112,17 @@ public interface ActionCache {
     }
 
     /**
-     * Returns the combined digest of the action's inputs and outputs.
+     * Returns the combined md5Digest of the action's inputs and outputs.
      *
-     * This may compresses the data into a more compact representation, and
-     * makes the object immutable.
+     * <p>This may compresses the data into a more compact representation, and makes the object
+     * immutable.
      */
-    public Digest getFileDigest() {
-      if (digest == null) {
-        digest = Digest.fromMetadata(mdMap);
+    public Md5Digest getFileDigest() {
+      if (md5Digest == null) {
+        md5Digest = DigestUtils.fromMetadata(mdMap);
         mdMap = null;
       }
-      return digest;
+      return md5Digest;
     }
 
     /**
@@ -153,10 +151,10 @@ public interface ActionCache {
       StringBuilder builder = new StringBuilder();
       builder.append("      actionKey = ").append(actionKey).append("\n");
       builder.append("      digestKey = ");
-      if (digest == null) {
-        builder.append(Digest.fromMetadata(mdMap)).append(" (from mdMap)\n");
+      if (md5Digest == null) {
+        builder.append(DigestUtils.fromMetadata(mdMap)).append(" (from mdMap)\n");
       } else {
-        builder.append(digest).append("\n");
+        builder.append(md5Digest).append("\n");
       }
 
       if (discoversInputs()) {
diff --git a/src/main/java/com/google/devtools/build/lib/actions/cache/CompactPersistentActionCache.java b/src/main/java/com/google/devtools/build/lib/actions/cache/CompactPersistentActionCache.java
index 8cbfd7705b..f0b47f857d 100644
--- a/src/main/java/com/google/devtools/build/lib/actions/cache/CompactPersistentActionCache.java
+++ b/src/main/java/com/google/devtools/build/lib/actions/cache/CompactPersistentActionCache.java
@@ -26,7 +26,6 @@ import com.google.devtools.build.lib.util.StringIndexer;
 import com.google.devtools.build.lib.util.VarInt;
 import com.google.devtools.build.lib.vfs.Path;
 import com.google.devtools.build.lib.vfs.UnixGlob;
-
 import java.io.ByteArrayOutputStream;
 import java.io.DataInputStream;
 import java.io.DataOutputStream;
@@ -352,14 +351,18 @@ public class CompactPersistentActionCache implements ActionCache {
       // + 16 bytes for the digest
       // + 5 bytes max for the file list length
       // + 5 bytes max for each file id
-      int maxSize = VarInt.MAX_VARINT_SIZE + actionKeyBytes.length + Digest.MD5_SIZE
-          + VarInt.MAX_VARINT_SIZE + files.size() * VarInt.MAX_VARINT_SIZE;
+      int maxSize =
+          VarInt.MAX_VARINT_SIZE
+              + actionKeyBytes.length
+              + Md5Digest.MD5_SIZE
+              + VarInt.MAX_VARINT_SIZE
+              + files.size() * VarInt.MAX_VARINT_SIZE;
       ByteArrayOutputStream sink = new ByteArrayOutputStream(maxSize);
 
       VarInt.putVarInt(actionKeyBytes.length, sink);
       sink.write(actionKeyBytes);
 
-      entry.getFileDigest().write(sink);
+      DigestUtils.write(entry.getFileDigest(), sink);
 
       VarInt.putVarInt(entry.discoversInputs() ? files.size() : NO_INPUT_DISCOVERY_COUNT, sink);
       for (String file : files) {
@@ -385,7 +388,7 @@ public class CompactPersistentActionCache implements ActionCache {
       source.get(actionKeyBytes);
       String actionKey = new String(actionKeyBytes, ISO_8859_1);
 
-      Digest digest = Digest.read(source);
+      Md5Digest md5Digest = DigestUtils.read(source);
 
       int count = VarInt.getVarInt(source);
       ImmutableList.Builder<String> builder = new ImmutableList.Builder<>();
@@ -400,8 +403,8 @@ public class CompactPersistentActionCache implements ActionCache {
       if (source.remaining() > 0) {
         throw new IOException("serialized entry data has not been fully decoded");
       }
-      return new Entry(actionKey,
-          count == NO_INPUT_DISCOVERY_COUNT ? null : builder.build(), digest);
+      return new Entry(
+          actionKey, count == NO_INPUT_DISCOVERY_COUNT ? null : builder.build(), md5Digest);
     } catch (BufferUnderflowException e) {
       throw new IOException("encoded entry data is incomplete", e);
     }
diff --git a/src/main/java/com/google/devtools/build/lib/actions/cache/Digest.java b/src/main/java/com/google/devtools/build/lib/actions/cache/Digest.java
deleted file mode 100644
index 06989198d2..0000000000
--- a/src/main/java/com/google/devtools/build/lib/actions/cache/Digest.java
+++ /dev/null
@@ -1,138 +0,0 @@
-// Copyright 2014 The Bazel Authors. All rights reserved.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//    http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-package com.google.devtools.build.lib.actions.cache;
-
-import com.google.common.hash.HashCode;
-import com.google.devtools.build.lib.util.Fingerprint;
-import com.google.devtools.build.lib.util.VarInt;
-
-import java.io.IOException;
-import java.io.OutputStream;
-import java.nio.ByteBuffer;
-import java.util.Arrays;
-import java.util.Map;
-
-/**
- * A value class for capturing and comparing MD5-based digests.
- *
- * <p>Note that this class is responsible for digesting file metadata in an
- * order-independent manner. Care must be taken to do this properly. The
- * digest must be a function of the set of (path, metadata) tuples. While the
- * order of these pairs must not matter, it would <b>not</b> be safe to make
- * the digest be a function of the set of paths and the set of metadata.
- *
- * <p>Note that the (path, metadata) tuples must be unique, otherwise the
- * XOR-based approach will fail.
- */
-public class Digest {
-
-  static final int MD5_SIZE = 16;
-
-  private final byte[] digest;
-
-  /**
-   * Construct the digest from the given bytes.
-   * @param digest an MD5 digest. Must be sized properly.
-   */
-  private Digest(byte[] digest) {
-    this.digest = digest;
-  }
-
-  /**
-   * @param source the byte buffer source.
-   * @return the digest from the given buffer.
-   * @throws IOException if the byte buffer is incorrectly formatted.
-   */
-  public static Digest read(ByteBuffer source) throws IOException {
-    int size = VarInt.getVarInt(source);
-    if (size != MD5_SIZE) {
-      throw new IOException("Unexpected digest length: " + size);
-    }
-    byte[] bytes = new byte[size];
-    source.get(bytes);
-    return new Digest(bytes);
-  }
-
-  /**
-   * Write the digest to the output stream.
-   */
-  public void write(OutputStream sink) throws IOException {
-    VarInt.putVarInt(digest.length, sink);
-    sink.write(digest);
-  }
-
-  /**
-   * @param mdMap A collection of (execPath, Metadata) pairs.
-   *              Values may be null.
-   * @return an <b>order-independent</b> digest from the given "set" of
-   *         (path, metadata) pairs.
-   */
-  public static Digest fromMetadata(Map<String, Metadata> mdMap) {
-    byte[] result = new byte[MD5_SIZE];
-    // Profiling showed that MD5 engine instantiation was a hotspot, so create one instance for
-    // this computation to amortize its cost.
-    Fingerprint fp = new Fingerprint();
-    for (Map.Entry<String, Metadata> entry : mdMap.entrySet()) {
-      xorWith(result, getDigest(fp, entry.getKey(), entry.getValue()));
-    }
-    return new Digest(result);
-  }
-
-  /**
-   * @return this Digest as a Metadata with no mtime.
-   */
-  public Metadata asMetadata() {
-    return new Metadata(digest);
-  }
-
-  @Override
-  public int hashCode() {
-    return Arrays.hashCode(digest);
-  }
-
-  @Override
-  public boolean equals(Object obj) {
-    return (obj instanceof Digest) && Arrays.equals(digest, ((Digest) obj).digest);
-  }
-
-  @Override
-  public String toString() {
-    return HashCode.fromBytes(digest).toString();
-  }
-
-  private static byte[] getDigest(Fingerprint fp, String execPath, Metadata md) {
-    fp.addStringLatin1(execPath);
-
-    if (md == null) {
-      // Move along, nothing to see here.
-    } else if (md.digest == null) {
-      // Use the timestamp if the digest is not present, but not both.
-      // Modifying a timestamp while keeping the contents of a file the
-      // same should not cause rebuilds.
-      fp.addLong(md.mtime);
-    } else {
-      fp.addBytes(md.digest);
-    }
-    return fp.digestAndReset();
-  }
-
-  /**
-   * Compute lhs ^= rhs bitwise operation of the arrays.
-   */
-  private static void xorWith(byte[] lhs, byte[] rhs) {
-    for (int i = 0; i < lhs.length; i++) {
-      lhs[i] ^= rhs[i];
-    }
-  }
-}
diff --git a/src/main/java/com/google/devtools/build/lib/actions/cache/DigestUtils.java b/src/main/java/com/google/devtools/build/lib/actions/cache/DigestUtils.java
index c61e943eda..ef4d9dc4d9 100644
--- a/src/main/java/com/google/devtools/build/lib/actions/cache/DigestUtils.java
+++ b/src/main/java/com/google/devtools/build/lib/actions/cache/DigestUtils.java
@@ -17,21 +17,33 @@ import com.google.common.io.BaseEncoding;
 import com.google.devtools.build.lib.profiler.Profiler;
 import com.google.devtools.build.lib.profiler.ProfilerTask;
 import com.google.devtools.build.lib.util.BlazeClock;
+import com.google.devtools.build.lib.util.Fingerprint;
 import com.google.devtools.build.lib.util.LoggingUtil;
 import com.google.devtools.build.lib.util.Preconditions;
+import com.google.devtools.build.lib.util.VarInt;
 import com.google.devtools.build.lib.vfs.Path;
-
 import java.io.IOException;
+import java.io.OutputStream;
+import java.nio.ByteBuffer;
+import java.util.Map;
 import java.util.Objects;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.logging.Level;
-
 import javax.annotation.Nullable;
 
 /**
  * Utility class for getting md5 digests of files.
+ *
+ * <p>Note that this class is responsible for digesting file metadata in an order-independent
+ * manner. Care must be taken to do this properly. The digest must be a function of the set of
+ * (path, metadata) tuples. While the order of these pairs must not matter, it would <b>not</b> be
+ * safe to make the digest be a function of the set of paths and the set of metadata.
+ *
+ * <p>Note that the (path, metadata) tuples must be unique, otherwise the XOR-based approach will
+ * fail.
  */
 public class DigestUtils {
+
   // Object to synchronize on when serializing large file reads.
   private static final Object MD5_LOCK = new Object();
   private static final AtomicBoolean MULTI_THREADED_DIGEST = new AtomicBoolean(false);
@@ -122,4 +134,63 @@ public class DigestUtils {
       return getDigestInternal(path);
     }
   }
+
+  /**
+   * @param source the byte buffer source.
+   * @return the digest from the given buffer.
+   * @throws IOException if the byte buffer is incorrectly formatted.
+   */
+  public static Md5Digest read(ByteBuffer source) throws IOException {
+    int size = VarInt.getVarInt(source);
+    if (size != Md5Digest.MD5_SIZE) {
+      throw new IOException("Unexpected digest length: " + size);
+    }
+    byte[] bytes = new byte[size];
+    source.get(bytes);
+    return new Md5Digest(bytes);
+  }
+
+  /** Write the digest to the output stream. */
+  public static void write(Md5Digest digest, OutputStream sink) throws IOException {
+    VarInt.putVarInt(digest.getDigestBytesUnsafe().length, sink);
+    sink.write(digest.getDigestBytesUnsafe());
+  }
+
+  /**
+   * @param mdMap A collection of (execPath, Metadata) pairs. Values may be null.
+   * @return an <b>order-independent</b> digest from the given "set" of (path, metadata) pairs.
+   */
+  public static Md5Digest fromMetadata(Map<String, Metadata> mdMap) {
+    byte[] result = new byte[Md5Digest.MD5_SIZE];
+    // Profiling showed that MD5 engine instantiation was a hotspot, so create one instance for
+    // this computation to amortize its cost.
+    Fingerprint fp = new Fingerprint();
+    for (Map.Entry<String, Metadata> entry : mdMap.entrySet()) {
+      xorWith(result, getDigest(fp, entry.getKey(), entry.getValue()));
+    }
+    return new Md5Digest(result);
+  }
+
+  private static byte[] getDigest(Fingerprint fp, String execPath, Metadata md) {
+    fp.addStringLatin1(execPath);
+
+    if (md == null) {
+      // Move along, nothing to see here.
+    } else if (md.digest == null) {
+      // Use the timestamp if the digest is not present, but not both.
+      // Modifying a timestamp while keeping the contents of a file the
+      // same should not cause rebuilds.
+      fp.addLong(md.mtime);
+    } else {
+      fp.addBytes(md.digest);
+    }
+    return fp.digestAndReset();
+  }
+
+  /** Compute lhs ^= rhs bitwise operation of the arrays. */
+  private static void xorWith(byte[] lhs, byte[] rhs) {
+    for (int i = 0; i < lhs.length; i++) {
+      lhs[i] ^= rhs[i];
+    }
+  }
 }
diff --git a/src/main/java/com/google/devtools/build/lib/actions/cache/Md5Digest.java b/src/main/java/com/google/devtools/build/lib/actions/cache/Md5Digest.java
new file mode 100644
index 0000000000..75441b52e7
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/actions/cache/Md5Digest.java
@@ -0,0 +1,59 @@
+// Copyright 2014 The Bazel Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+package com.google.devtools.build.lib.actions.cache;
+
+import com.google.common.hash.HashCode;
+import com.google.devtools.build.lib.util.Preconditions;
+import java.util.Arrays;
+
+/** A value class for capturing and comparing MD5-based digests. */
+public class Md5Digest {
+
+  static final int MD5_SIZE = 16;
+  private final byte[] digest;
+
+  /**
+   * Construct the digest from the given bytes.
+   *
+   * @param digest an MD5 digest. Must be sized properly.
+   */
+  public Md5Digest(byte[] digest) {
+    Preconditions.checkState(digest.length == MD5_SIZE);
+    this.digest = digest;
+  }
+
+  @Override
+  public int hashCode() {
+    // We are already dealing with the digest so we can just use portion of it as a hash code.
+    return digest[0] + (digest[1] << 8) + (digest[2] << 16) + (digest[3] << 24);
+  }
+
+  @Override
+  public boolean equals(Object obj) {
+    return (obj instanceof Md5Digest) && Arrays.equals(digest, ((Md5Digest) obj).digest);
+  }
+
+  @Override
+  public String toString() {
+    return HashCode.fromBytes(digest).toString();
+  }
+
+  /**
+   * Warning: This is a mutable wrapper and does not necessarily own the underlying byte[]. Don't
+   * modify it unless you are sure about it.
+   */
+  public byte[] getDigestBytesUnsafe() {
+    return digest;
+  }
+}
diff --git a/src/main/java/com/google/devtools/build/lib/actions/cache/Metadata.java b/src/main/java/com/google/devtools/build/lib/actions/cache/Metadata.java
index 21891300b0..316fd234e5 100644
--- a/src/main/java/com/google/devtools/build/lib/actions/cache/Metadata.java
+++ b/src/main/java/com/google/devtools/build/lib/actions/cache/Metadata.java
@@ -18,7 +18,6 @@ import com.google.common.io.BaseEncoding;
 import com.google.devtools.build.lib.concurrent.ThreadSafety.Immutable;
 import com.google.devtools.build.lib.concurrent.ThreadSafety.ThreadSafe;
 import com.google.devtools.build.lib.util.Preconditions;
-
 import java.util.Arrays;
 import java.util.Date;
 
diff --git a/src/main/java/com/google/devtools/build/lib/actions/cache/MetadataHandler.java b/src/main/java/com/google/devtools/build/lib/actions/cache/MetadataHandler.java
index 6fcb964840..5e74180014 100644
--- a/src/main/java/com/google/devtools/build/lib/actions/cache/MetadataHandler.java
+++ b/src/main/java/com/google/devtools/build/lib/actions/cache/MetadataHandler.java
@@ -18,7 +18,6 @@ import com.google.devtools.build.lib.actions.Artifact;
 import com.google.devtools.build.lib.actions.Artifact.TreeFileArtifact;
 import com.google.devtools.build.lib.actions.MiddlemanAction;
 import com.google.devtools.build.lib.vfs.FileStatus;
-
 import java.io.IOException;
 
 /** Retrieves {@link Metadata} of {@link Artifact}s, and inserts virtual metadata as well. */
@@ -46,8 +45,8 @@ public interface MetadataHandler {
    */
   Metadata getMetadata(Artifact artifact) throws IOException;
 
-  /** Sets digest for virtual artifacts (e.g. middlemen). {@code digest} must not be null. */
-  void setDigestForVirtualArtifact(Artifact artifact, Digest digest);
+  /** Sets digest for virtual artifacts (e.g. middlemen). {@code md5Digest} must not be null. */
+  void setDigestForVirtualArtifact(Artifact artifact, Md5Digest md5Digest);
 
   /**
    * Registers the given output as contents of a TreeArtifact, without injecting its digest.