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Diffstat (limited to 'python/google/protobuf/internal/decoder.py')
| -rwxr-xr-x | python/google/protobuf/internal/decoder.py | 194 |
1 files changed, 194 insertions, 0 deletions
diff --git a/python/google/protobuf/internal/decoder.py b/python/google/protobuf/internal/decoder.py new file mode 100755 index 00000000..b81f04a5 --- /dev/null +++ b/python/google/protobuf/internal/decoder.py @@ -0,0 +1,194 @@ +# Protocol Buffers - Google's data interchange format +# Copyright 2008 Google Inc. +# http://code.google.com/p/protobuf/ +# +# 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. + +"""Class for decoding protocol buffer primitives. + +Contains the logic for decoding every logical protocol field type +from one of the 5 physical wire types. +""" + +__author__ = 'robinson@google.com (Will Robinson)' + +import struct +from google.protobuf import message +from google.protobuf.internal import input_stream +from google.protobuf.internal import wire_format + + + +# Note that much of this code is ported from //net/proto/ProtocolBuffer, and +# that the interface is strongly inspired by WireFormat from the C++ proto2 +# implementation. + + +class Decoder(object): + + """Decodes logical protocol buffer fields from the wire.""" + + def __init__(self, s): + """Initializes the decoder to read from s. + + Args: + s: An immutable sequence of bytes, which must be accessible + via the Python buffer() primitive (i.e., buffer(s)). + """ + self._stream = input_stream.InputStream(s) + + def EndOfStream(self): + """Returns true iff we've reached the end of the bytes we're reading.""" + return self._stream.EndOfStream() + + def Position(self): + """Returns the 0-indexed position in |s|.""" + return self._stream.Position() + + def ReadFieldNumberAndWireType(self): + """Reads a tag from the wire. Returns a (field_number, wire_type) pair.""" + tag_and_type = self.ReadUInt32() + return wire_format.UnpackTag(tag_and_type) + + def SkipBytes(self, bytes): + """Skips the specified number of bytes on the wire.""" + self._stream.SkipBytes(bytes) + + # Note that the Read*() methods below are not exactly symmetrical with the + # corresponding Encoder.Append*() methods. Those Encoder methods first + # encode a tag, but the Read*() methods below assume that the tag has already + # been read, and that the client wishes to read a field of the specified type + # starting at the current position. + + def ReadInt32(self): + """Reads and returns a signed, varint-encoded, 32-bit integer.""" + return self._stream.ReadVarint32() + + def ReadInt64(self): + """Reads and returns a signed, varint-encoded, 64-bit integer.""" + return self._stream.ReadVarint64() + + def ReadUInt32(self): + """Reads and returns an signed, varint-encoded, 32-bit integer.""" + return self._stream.ReadVarUInt32() + + def ReadUInt64(self): + """Reads and returns an signed, varint-encoded,64-bit integer.""" + return self._stream.ReadVarUInt64() + + def ReadSInt32(self): + """Reads and returns a signed, zigzag-encoded, varint-encoded, + 32-bit integer.""" + return wire_format.ZigZagDecode(self._stream.ReadVarUInt32()) + + def ReadSInt64(self): + """Reads and returns a signed, zigzag-encoded, varint-encoded, + 64-bit integer.""" + return wire_format.ZigZagDecode(self._stream.ReadVarUInt64()) + + def ReadFixed32(self): + """Reads and returns an unsigned, fixed-width, 32-bit integer.""" + return self._stream.ReadLittleEndian32() + + def ReadFixed64(self): + """Reads and returns an unsigned, fixed-width, 64-bit integer.""" + return self._stream.ReadLittleEndian64() + + def ReadSFixed32(self): + """Reads and returns a signed, fixed-width, 32-bit integer.""" + value = self._stream.ReadLittleEndian32() + if value >= (1 << 31): + value -= (1 << 32) + return value + + def ReadSFixed64(self): + """Reads and returns a signed, fixed-width, 64-bit integer.""" + value = self._stream.ReadLittleEndian64() + if value >= (1 << 63): + value -= (1 << 64) + return value + + def ReadFloat(self): + """Reads and returns a 4-byte floating-point number.""" + serialized = self._stream.ReadString(4) + return struct.unpack('f', serialized)[0] + + def ReadDouble(self): + """Reads and returns an 8-byte floating-point number.""" + serialized = self._stream.ReadString(8) + return struct.unpack('d', serialized)[0] + + def ReadBool(self): + """Reads and returns a bool.""" + i = self._stream.ReadVarUInt32() + return bool(i) + + def ReadEnum(self): + """Reads and returns an enum value.""" + return self._stream.ReadVarUInt32() + + def ReadString(self): + """Reads and returns a length-delimited string.""" + length = self._stream.ReadVarUInt32() + return self._stream.ReadString(length) + + def ReadBytes(self): + """Reads and returns a length-delimited byte sequence.""" + return self.ReadString() + + def ReadMessageInto(self, msg): + """Calls msg.MergeFromString() to merge + length-delimited serialized message data into |msg|. + + REQUIRES: The decoder must be positioned at the serialized "length" + prefix to a length-delmiited serialized message. + + POSTCONDITION: The decoder is positioned just after the + serialized message, and we have merged those serialized + contents into |msg|. + """ + length = self._stream.ReadVarUInt32() + sub_buffer = self._stream.GetSubBuffer(length) + num_bytes_used = msg.MergeFromString(sub_buffer) + if num_bytes_used != length: + raise message.DecodeError( + 'Submessage told to deserialize from %d-byte encoding, ' + 'but used only %d bytes' % (length, num_bytes_used)) + self._stream.SkipBytes(num_bytes_used) + + def ReadGroupInto(self, expected_field_number, group): + """Calls group.MergeFromString() to merge + END_GROUP-delimited serialized message data into |group|. + We'll raise an exception if we don't find an END_GROUP + tag immediately after the serialized message contents. + + REQUIRES: The decoder is positioned just after the START_GROUP + tag for this group. + + POSTCONDITION: The decoder is positioned just after the + END_GROUP tag for this group, and we have merged + the contents of the group into |group|. + """ + sub_buffer = self._stream.GetSubBuffer() # No a priori length limit. + num_bytes_used = group.MergeFromString(sub_buffer) + if num_bytes_used < 0: + raise message.DecodeError('Group message reported negative bytes read.') + self._stream.SkipBytes(num_bytes_used) + field_number, field_type = self.ReadFieldNumberAndWireType() + if field_type != wire_format.WIRETYPE_END_GROUP: + raise message.DecodeError('Group message did not end with an END_GROUP.') + if field_number != expected_field_number: + raise message.DecodeError('END_GROUP tag had field ' + 'number %d, was expecting field number %d' % ( + field_number, expected_field_number)) + # We're now positioned just after the END_GROUP tag. Perfect. |