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# 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.
# This code is meant to work on Python 2.4 and above only.
"""Contains a metaclass and helper functions used to create
protocol message classes from Descriptor objects at runtime.
Recall that a metaclass is the "type" of a class.
(A class is to a metaclass what an instance is to a class.)
In this case, we use the GeneratedProtocolMessageType metaclass
to inject all the useful functionality into the classes
output by the protocol compiler at compile-time.
The upshot of all this is that the real implementation
details for ALL pure-Python protocol buffers are *here in
this file*.
"""
__author__ = 'robinson@google.com (Will Robinson)'
from google.protobuf.internal import api_implementation
from google.protobuf import message
if api_implementation.Type() == 'cpp':
from google.protobuf.pyext import cpp_message as message_impl
else:
from google.protobuf.internal import python_message as message_impl
# The type of all Message classes.
# Part of the public interface, but normally only used by message factories.
GeneratedProtocolMessageType = message_impl.GeneratedProtocolMessageType
MESSAGE_CLASS_CACHE = {}
def ParseMessage(descriptor, byte_str):
"""Generate a new Message instance from this Descriptor and a byte string.
Args:
descriptor: Protobuf Descriptor object
byte_str: Serialized protocol buffer byte string
Returns:
Newly created protobuf Message object.
"""
result_class = MakeClass(descriptor)
new_msg = result_class()
new_msg.ParseFromString(byte_str)
return new_msg
def MakeClass(descriptor):
"""Construct a class object for a protobuf described by descriptor.
Composite descriptors are handled by defining the new class as a member of the
parent class, recursing as deep as necessary.
This is the dynamic equivalent to:
class Parent(message.Message):
__metaclass__ = GeneratedProtocolMessageType
DESCRIPTOR = descriptor
class Child(message.Message):
__metaclass__ = GeneratedProtocolMessageType
DESCRIPTOR = descriptor.nested_types[0]
Sample usage:
file_descriptor = descriptor_pb2.FileDescriptorProto()
file_descriptor.ParseFromString(proto2_string)
msg_descriptor = descriptor.MakeDescriptor(file_descriptor.message_type[0])
msg_class = reflection.MakeClass(msg_descriptor)
msg = msg_class()
Args:
descriptor: A descriptor.Descriptor object describing the protobuf.
Returns:
The Message class object described by the descriptor.
"""
if descriptor in MESSAGE_CLASS_CACHE:
return MESSAGE_CLASS_CACHE[descriptor]
attributes = {}
for name, nested_type in descriptor.nested_types_by_name.items():
attributes[name] = MakeClass(nested_type)
attributes[GeneratedProtocolMessageType._DESCRIPTOR_KEY] = descriptor
result = GeneratedProtocolMessageType(
str(descriptor.name), (message.Message,), attributes)
MESSAGE_CLASS_CACHE[descriptor] = result
return result
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