diff options
Diffstat (limited to 'python/google/protobuf/internal/decoder.py')
| -rwxr-xr-x | python/google/protobuf/internal/decoder.py | 770 |
1 files changed, 601 insertions, 169 deletions
diff --git a/python/google/protobuf/internal/decoder.py b/python/google/protobuf/internal/decoder.py index 83d6fe0..461a30c 100755 --- a/python/google/protobuf/internal/decoder.py +++ b/python/google/protobuf/internal/decoder.py @@ -28,182 +28,614 @@ # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. -"""Class for decoding protocol buffer primitives. - -Contains the logic for decoding every logical protocol field type -from one of the 5 physical wire types. +"""Code for decoding protocol buffer primitives. + +This code is very similar to encoder.py -- read the docs for that module first. + +A "decoder" is a function with the signature: + Decode(buffer, pos, end, message, field_dict) +The arguments are: + buffer: The string containing the encoded message. + pos: The current position in the string. + end: The position in the string where the current message ends. May be + less than len(buffer) if we're reading a sub-message. + message: The message object into which we're parsing. + field_dict: message._fields (avoids a hashtable lookup). +The decoder reads the field and stores it into field_dict, returning the new +buffer position. A decoder for a repeated field may proactively decode all of +the elements of that field, if they appear consecutively. + +Note that decoders may throw any of the following: + IndexError: Indicates a truncated message. + struct.error: Unpacking of a fixed-width field failed. + message.DecodeError: Other errors. + +Decoders are expected to raise an exception if they are called with pos > end. +This allows callers to be lax about bounds checking: it's fineto read past +"end" as long as you are sure that someone else will notice and throw an +exception later on. + +Something up the call stack is expected to catch IndexError and struct.error +and convert them to message.DecodeError. + +Decoders are constructed using decoder constructors with the signature: + MakeDecoder(field_number, is_repeated, is_packed, key, new_default) +The arguments are: + field_number: The field number of the field we want to decode. + is_repeated: Is the field a repeated field? (bool) + is_packed: Is the field a packed field? (bool) + key: The key to use when looking up the field within field_dict. + (This is actually the FieldDescriptor but nothing in this + file should depend on that.) + new_default: A function which takes a message object as a parameter and + returns a new instance of the default value for this field. + (This is called for repeated fields and sub-messages, when an + instance does not already exist.) + +As with encoders, we define a decoder constructor for every type of field. +Then, for every field of every message class we construct an actual decoder. +That decoder goes into a dict indexed by tag, so when we decode a message +we repeatedly read a tag, look up the corresponding decoder, and invoke it. """ -__author__ = 'robinson@google.com (Will Robinson)' +__author__ = 'kenton@google.com (Kenton Varda)' import struct -from google.protobuf import message -from google.protobuf.internal import input_stream +from google.protobuf.internal import encoder from google.protobuf.internal import wire_format +from google.protobuf import message +# This is not for optimization, but rather to avoid conflicts with local +# variables named "message". +_DecodeError = message.DecodeError + + +def _VarintDecoder(mask): + """Return an encoder for a basic varint value (does not include tag). + + Decoded values will be bitwise-anded with the given mask before being + returned, e.g. to limit them to 32 bits. The returned decoder does not + take the usual "end" parameter -- the caller is expected to do bounds checking + after the fact (often the caller can defer such checking until later). The + decoder returns a (value, new_pos) pair. + """ + + local_ord = ord + def DecodeVarint(buffer, pos): + result = 0 + shift = 0 + while 1: + b = local_ord(buffer[pos]) + result |= ((b & 0x7f) << shift) + pos += 1 + if not (b & 0x80): + result &= mask + return (result, pos) + shift += 7 + if shift >= 64: + raise _DecodeError('Too many bytes when decoding varint.') + return DecodeVarint + + +def _SignedVarintDecoder(mask): + """Like _VarintDecoder() but decodes signed values.""" + + local_ord = ord + def DecodeVarint(buffer, pos): + result = 0 + shift = 0 + while 1: + b = local_ord(buffer[pos]) + result |= ((b & 0x7f) << shift) + pos += 1 + if not (b & 0x80): + if result > 0x7fffffffffffffff: + result -= (1 << 64) + result |= ~mask + else: + result &= mask + return (result, pos) + shift += 7 + if shift >= 64: + raise _DecodeError('Too many bytes when decoding varint.') + return DecodeVarint + + +_DecodeVarint = _VarintDecoder((1 << 64) - 1) +_DecodeSignedVarint = _SignedVarintDecoder((1 << 64) - 1) + +# Use these versions for values which must be limited to 32 bits. +_DecodeVarint32 = _VarintDecoder((1 << 32) - 1) +_DecodeSignedVarint32 = _SignedVarintDecoder((1 << 32) - 1) + + +def ReadTag(buffer, pos): + """Read a tag from the buffer, and return a (tag_bytes, new_pos) tuple. + + We return the raw bytes of the tag rather than decoding them. The raw + bytes can then be used to look up the proper decoder. This effectively allows + us to trade some work that would be done in pure-python (decoding a varint) + for work that is done in C (searching for a byte string in a hash table). + In a low-level language it would be much cheaper to decode the varint and + use that, but not in Python. + """ + + start = pos + while ord(buffer[pos]) & 0x80: + pos += 1 + pos += 1 + return (buffer[start:pos], pos) + + +# -------------------------------------------------------------------- + + +def _SimpleDecoder(wire_type, decode_value): + """Return a constructor for a decoder for fields of a particular type. + + Args: + wire_type: The field's wire type. + decode_value: A function which decodes an individual value, e.g. + _DecodeVarint() + """ + + def SpecificDecoder(field_number, is_repeated, is_packed, key, new_default): + if is_packed: + local_DecodeVarint = _DecodeVarint + def DecodePackedField(buffer, pos, end, message, field_dict): + value = field_dict.get(key) + if value is None: + value = field_dict.setdefault(key, new_default(message)) + (endpoint, pos) = local_DecodeVarint(buffer, pos) + endpoint += pos + if endpoint > end: + raise _DecodeError('Truncated message.') + while pos < endpoint: + (element, pos) = decode_value(buffer, pos) + value.append(element) + if pos > endpoint: + del value[-1] # Discard corrupt value. + raise _DecodeError('Packed element was truncated.') + return pos + return DecodePackedField + elif is_repeated: + tag_bytes = encoder.TagBytes(field_number, wire_type) + tag_len = len(tag_bytes) + def DecodeRepeatedField(buffer, pos, end, message, field_dict): + value = field_dict.get(key) + if value is None: + value = field_dict.setdefault(key, new_default(message)) + while 1: + (element, new_pos) = decode_value(buffer, pos) + value.append(element) + # Predict that the next tag is another copy of the same repeated + # field. + pos = new_pos + tag_len + if buffer[new_pos:pos] != tag_bytes or new_pos >= end: + # Prediction failed. Return. + if new_pos > end: + raise _DecodeError('Truncated message.') + return new_pos + return DecodeRepeatedField + else: + def DecodeField(buffer, pos, end, message, field_dict): + (field_dict[key], pos) = decode_value(buffer, pos) + if pos > end: + del field_dict[key] # Discard corrupt value. + raise _DecodeError('Truncated message.') + return pos + return DecodeField + + return SpecificDecoder + + +def _ModifiedDecoder(wire_type, decode_value, modify_value): + """Like SimpleDecoder but additionally invokes modify_value on every value + before storing it. Usually modify_value is ZigZagDecode. + """ + + # Reusing _SimpleDecoder is slightly slower than copying a bunch of code, but + # not enough to make a significant difference. + + def InnerDecode(buffer, pos): + (result, new_pos) = decode_value(buffer, pos) + return (modify_value(result), new_pos) + return _SimpleDecoder(wire_type, InnerDecode) + + +def _StructPackDecoder(wire_type, format): + """Return a constructor for a decoder for a fixed-width field. + + Args: + wire_type: The field's wire type. + format: The format string to pass to struct.unpack(). + """ + + value_size = struct.calcsize(format) + local_unpack = struct.unpack + + # Reusing _SimpleDecoder is slightly slower than copying a bunch of code, but + # not enough to make a significant difference. + + # Note that we expect someone up-stack to catch struct.error and convert + # it to _DecodeError -- this way we don't have to set up exception- + # handling blocks every time we parse one value. + + def InnerDecode(buffer, pos): + new_pos = pos + value_size + result = local_unpack(format, buffer[pos:new_pos])[0] + return (result, new_pos) + return _SimpleDecoder(wire_type, InnerDecode) + + +# -------------------------------------------------------------------- + + +Int32Decoder = EnumDecoder = _SimpleDecoder( + wire_format.WIRETYPE_VARINT, _DecodeSignedVarint32) + +Int64Decoder = _SimpleDecoder( + wire_format.WIRETYPE_VARINT, _DecodeSignedVarint) + +UInt32Decoder = _SimpleDecoder(wire_format.WIRETYPE_VARINT, _DecodeVarint32) +UInt64Decoder = _SimpleDecoder(wire_format.WIRETYPE_VARINT, _DecodeVarint) + +SInt32Decoder = _ModifiedDecoder( + wire_format.WIRETYPE_VARINT, _DecodeVarint32, wire_format.ZigZagDecode) +SInt64Decoder = _ModifiedDecoder( + wire_format.WIRETYPE_VARINT, _DecodeVarint, wire_format.ZigZagDecode) + +# Note that Python conveniently guarantees that when using the '<' prefix on +# formats, they will also have the same size across all platforms (as opposed +# to without the prefix, where their sizes depend on the C compiler's basic +# type sizes). +Fixed32Decoder = _StructPackDecoder(wire_format.WIRETYPE_FIXED32, '<I') +Fixed64Decoder = _StructPackDecoder(wire_format.WIRETYPE_FIXED64, '<Q') +SFixed32Decoder = _StructPackDecoder(wire_format.WIRETYPE_FIXED32, '<i') +SFixed64Decoder = _StructPackDecoder(wire_format.WIRETYPE_FIXED64, '<q') +FloatDecoder = _StructPackDecoder(wire_format.WIRETYPE_FIXED32, '<f') +DoubleDecoder = _StructPackDecoder(wire_format.WIRETYPE_FIXED64, '<d') + +BoolDecoder = _ModifiedDecoder( + wire_format.WIRETYPE_VARINT, _DecodeVarint, bool) + + +def StringDecoder(field_number, is_repeated, is_packed, key, new_default): + """Returns a decoder for a string field.""" + + local_DecodeVarint = _DecodeVarint + local_unicode = unicode + + assert not is_packed + if is_repeated: + tag_bytes = encoder.TagBytes(field_number, + wire_format.WIRETYPE_LENGTH_DELIMITED) + tag_len = len(tag_bytes) + def DecodeRepeatedField(buffer, pos, end, message, field_dict): + value = field_dict.get(key) + if value is None: + value = field_dict.setdefault(key, new_default(message)) + while 1: + (size, pos) = local_DecodeVarint(buffer, pos) + new_pos = pos + size + if new_pos > end: + raise _DecodeError('Truncated string.') + value.append(local_unicode(buffer[pos:new_pos], 'utf-8')) + # Predict that the next tag is another copy of the same repeated field. + pos = new_pos + tag_len + if buffer[new_pos:pos] != tag_bytes or new_pos == end: + # Prediction failed. Return. + return new_pos + return DecodeRepeatedField + else: + def DecodeField(buffer, pos, end, message, field_dict): + (size, pos) = local_DecodeVarint(buffer, pos) + new_pos = pos + size + if new_pos > end: + raise _DecodeError('Truncated string.') + field_dict[key] = local_unicode(buffer[pos:new_pos], 'utf-8') + return new_pos + return DecodeField + + +def BytesDecoder(field_number, is_repeated, is_packed, key, new_default): + """Returns a decoder for a bytes field.""" + + local_DecodeVarint = _DecodeVarint + + assert not is_packed + if is_repeated: + tag_bytes = encoder.TagBytes(field_number, + wire_format.WIRETYPE_LENGTH_DELIMITED) + tag_len = len(tag_bytes) + def DecodeRepeatedField(buffer, pos, end, message, field_dict): + value = field_dict.get(key) + if value is None: + value = field_dict.setdefault(key, new_default(message)) + while 1: + (size, pos) = local_DecodeVarint(buffer, pos) + new_pos = pos + size + if new_pos > end: + raise _DecodeError('Truncated string.') + value.append(buffer[pos:new_pos]) + # Predict that the next tag is another copy of the same repeated field. + pos = new_pos + tag_len + if buffer[new_pos:pos] != tag_bytes or new_pos == end: + # Prediction failed. Return. + return new_pos + return DecodeRepeatedField + else: + def DecodeField(buffer, pos, end, message, field_dict): + (size, pos) = local_DecodeVarint(buffer, pos) + new_pos = pos + size + if new_pos > end: + raise _DecodeError('Truncated string.') + field_dict[key] = buffer[pos:new_pos] + return new_pos + return DecodeField + + +def GroupDecoder(field_number, is_repeated, is_packed, key, new_default): + """Returns a decoder for a group field.""" + + end_tag_bytes = encoder.TagBytes(field_number, + wire_format.WIRETYPE_END_GROUP) + end_tag_len = len(end_tag_bytes) + + assert not is_packed + if is_repeated: + tag_bytes = encoder.TagBytes(field_number, + wire_format.WIRETYPE_START_GROUP) + tag_len = len(tag_bytes) + def DecodeRepeatedField(buffer, pos, end, message, field_dict): + value = field_dict.get(key) + if value is None: + value = field_dict.setdefault(key, new_default(message)) + while 1: + value = field_dict.get(key) + if value is None: + value = field_dict.setdefault(key, new_default(message)) + # Read sub-message. + pos = value.add()._InternalParse(buffer, pos, end) + # Read end tag. + new_pos = pos+end_tag_len + if buffer[pos:new_pos] != end_tag_bytes or new_pos > end: + raise _DecodeError('Missing group end tag.') + # Predict that the next tag is another copy of the same repeated field. + pos = new_pos + tag_len + if buffer[new_pos:pos] != tag_bytes or new_pos == end: + # Prediction failed. Return. + return new_pos + return DecodeRepeatedField + else: + def DecodeField(buffer, pos, end, message, field_dict): + value = field_dict.get(key) + if value is None: + value = field_dict.setdefault(key, new_default(message)) + # Read sub-message. + pos = value._InternalParse(buffer, pos, end) + # Read end tag. + new_pos = pos+end_tag_len + if buffer[pos:new_pos] != end_tag_bytes or new_pos > end: + raise _DecodeError('Missing group end tag.') + return new_pos + return DecodeField + + +def MessageDecoder(field_number, is_repeated, is_packed, key, new_default): + """Returns a decoder for a message field.""" + + local_DecodeVarint = _DecodeVarint + + assert not is_packed + if is_repeated: + tag_bytes = encoder.TagBytes(field_number, + wire_format.WIRETYPE_LENGTH_DELIMITED) + tag_len = len(tag_bytes) + def DecodeRepeatedField(buffer, pos, end, message, field_dict): + value = field_dict.get(key) + if value is None: + value = field_dict.setdefault(key, new_default(message)) + while 1: + value = field_dict.get(key) + if value is None: + value = field_dict.setdefault(key, new_default(message)) + # Read length. + (size, pos) = local_DecodeVarint(buffer, pos) + new_pos = pos + size + if new_pos > end: + raise _DecodeError('Truncated message.') + # Read sub-message. + if value.add()._InternalParse(buffer, pos, new_pos) != new_pos: + # The only reason _InternalParse would return early is if it + # encountered an end-group tag. + raise _DecodeError('Unexpected end-group tag.') + # Predict that the next tag is another copy of the same repeated field. + pos = new_pos + tag_len + if buffer[new_pos:pos] != tag_bytes or new_pos == end: + # Prediction failed. Return. + return new_pos + return DecodeRepeatedField + else: + def DecodeField(buffer, pos, end, message, field_dict): + value = field_dict.get(key) + if value is None: + value = field_dict.setdefault(key, new_default(message)) + # Read length. + (size, pos) = local_DecodeVarint(buffer, pos) + new_pos = pos + size + if new_pos > end: + raise _DecodeError('Truncated message.') + # Read sub-message. + if value._InternalParse(buffer, pos, new_pos) != new_pos: + # The only reason _InternalParse would return early is if it encountered + # an end-group tag. + raise _DecodeError('Unexpected end-group tag.') + return new_pos + return DecodeField + + +# -------------------------------------------------------------------- + +MESSAGE_SET_ITEM_TAG = encoder.TagBytes(1, wire_format.WIRETYPE_START_GROUP) + +def MessageSetItemDecoder(extensions_by_number): + """Returns a decoder for a MessageSet item. + + The parameter is the _extensions_by_number map for the message class. + + The message set message looks like this: + message MessageSet { + repeated group Item = 1 { + required int32 type_id = 2; + required string message = 3; + } + } + """ + + type_id_tag_bytes = encoder.TagBytes(2, wire_format.WIRETYPE_VARINT) + message_tag_bytes = encoder.TagBytes(3, wire_format.WIRETYPE_LENGTH_DELIMITED) + item_end_tag_bytes = encoder.TagBytes(1, wire_format.WIRETYPE_END_GROUP) + + local_ReadTag = ReadTag + local_DecodeVarint = _DecodeVarint + local_SkipField = SkipField + + def DecodeItem(buffer, pos, end, message, field_dict): + type_id = -1 + message_start = -1 + message_end = -1 + + # Technically, type_id and message can appear in any order, so we need + # a little loop here. + while 1: + (tag_bytes, pos) = local_ReadTag(buffer, pos) + if tag_bytes == type_id_tag_bytes: + (type_id, pos) = local_DecodeVarint(buffer, pos) + elif tag_bytes == message_tag_bytes: + (size, message_start) = local_DecodeVarint(buffer, pos) + pos = message_end = message_start + size + elif tag_bytes == item_end_tag_bytes: + break + else: + pos = SkipField(buffer, pos, end, tag_bytes) + if pos == -1: + raise _DecodeError('Missing group end tag.') + + if pos > end: + raise _DecodeError('Truncated message.') + + if type_id == -1: + raise _DecodeError('MessageSet item missing type_id.') + if message_start == -1: + raise _DecodeError('MessageSet item missing message.') + + extension = extensions_by_number.get(type_id) + if extension is not None: + value = field_dict.get(extension) + if value is None: + value = field_dict.setdefault( + extension, extension.message_type._concrete_class()) + if value._InternalParse(buffer, message_start,message_end) != message_end: + # The only reason _InternalParse would return early is if it encountered + # an end-group tag. + raise _DecodeError('Unexpected end-group tag.') + + return pos + + return DecodeItem + +# -------------------------------------------------------------------- +# Optimization is not as heavy here because calls to SkipField() are rare, +# except for handling end-group tags. + +def _SkipVarint(buffer, pos, end): + """Skip a varint value. Returns the new position.""" + + while ord(buffer[pos]) & 0x80: + pos += 1 + pos += 1 + if pos > end: + raise _DecodeError('Truncated message.') + return pos + +def _SkipFixed64(buffer, pos, end): + """Skip a fixed64 value. Returns the new position.""" + + pos += 8 + if pos > end: + raise _DecodeError('Truncated message.') + return pos + +def _SkipLengthDelimited(buffer, pos, end): + """Skip a length-delimited value. Returns the new position.""" + + (size, pos) = _DecodeVarint(buffer, pos) + pos += size + if pos > end: + raise _DecodeError('Truncated message.') + return pos + +def _SkipGroup(buffer, pos, end): + """Skip sub-group. Returns the new position.""" + + while 1: + (tag_bytes, pos) = ReadTag(buffer, pos) + new_pos = SkipField(buffer, pos, end, tag_bytes) + if new_pos == -1: + return pos + pos = new_pos + +def _EndGroup(buffer, pos, end): + """Skipping an END_GROUP tag returns -1 to tell the parent loop to break.""" + + return -1 + +def _SkipFixed32(buffer, pos, end): + """Skip a fixed32 value. Returns the new position.""" + + pos += 4 + if pos > end: + raise _DecodeError('Truncated message.') + return pos + +def _RaiseInvalidWireType(buffer, pos, end): + """Skip function for unknown wire types. Raises an exception.""" + + raise _DecodeError('Tag had invalid wire type.') + +def _FieldSkipper(): + """Constructs the SkipField function.""" + + WIRETYPE_TO_SKIPPER = [ + _SkipVarint, + _SkipFixed64, + _SkipLengthDelimited, + _SkipGroup, + _EndGroup, + _SkipFixed32, + _RaiseInvalidWireType, + _RaiseInvalidWireType, + ] + + wiretype_mask = wire_format.TAG_TYPE_MASK + local_ord = ord + + def SkipField(buffer, pos, end, tag_bytes): + """Skips a field with the specified tag. + + |pos| should point to the byte immediately after the tag. + + Returns: + The new position (after the tag value), or -1 if the tag is an end-group + tag (in which case the calling loop should break). + """ -# 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.""" + # The wire type is always in the first byte since varints are little-endian. + wire_type = local_ord(tag_bytes[0]) & wiretype_mask + return WIRETYPE_TO_SKIPPER[wire_type](buffer, pos, end) - def __init__(self, s): - """Initializes the decoder to read from s. + return SkipField - 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.ReadBytes(4) - return struct.unpack(wire_format.FORMAT_FLOAT_LITTLE_ENDIAN, serialized)[0] - - def ReadDouble(self): - """Reads and returns an 8-byte floating-point number.""" - serialized = self._stream.ReadBytes(8) - return struct.unpack(wire_format.FORMAT_DOUBLE_LITTLE_ENDIAN, 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.""" - bytes = self.ReadBytes() - return unicode(bytes, 'utf-8') - - def ReadBytes(self): - """Reads and returns a length-delimited byte sequence.""" - length = self._stream.ReadVarUInt32() - return self._stream.ReadBytes(length) - - 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. +SkipField = _FieldSkipper() |