Initial Contribution

froofle/protobuf/internal/decoder.py

@@ -0,0 +1,209 @@
+# Protocol Buffers - Google's data interchange format
+# Copyright 2008 Google Inc.  All rights reserved.
+# http://code.google.com/p/protobuf/
+#
+# 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.
+
+"""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 froofle.protobuf import message
+from froofle.protobuf.internal import input_stream
+from froofle.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.ReadBytes(4)
+    return struct.unpack('f', serialized)[0]
+
+  def ReadDouble(self):
+    """Reads and returns an 8-byte floating-point number."""
+    serialized = self._stream.ReadBytes(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."""
+    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.