122 lines
4.5 KiB
Python
122 lines
4.5 KiB
Python
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# Protocol Buffers - Google's data interchange format
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# Copyright 2008 Google Inc. All rights reserved.
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# https://developers.google.com/protocol-buffers/
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#
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# Redistribution and use in source and binary forms, with or without
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# modification, are permitted provided that the following conditions are
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# met:
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#
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# * Redistributions of source code must retain the above copyright
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# notice, this list of conditions and the following disclaimer.
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# * Redistributions in binary form must reproduce the above
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# copyright notice, this list of conditions and the following disclaimer
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# in the documentation and/or other materials provided with the
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# distribution.
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# * Neither the name of Google Inc. nor the names of its
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# contributors may be used to endorse or promote products derived from
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# this software without specific prior written permission.
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#
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# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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# This code is meant to work on Python 2.4 and above only.
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"""Contains a metaclass and helper functions used to create
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protocol message classes from Descriptor objects at runtime.
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Recall that a metaclass is the "type" of a class.
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(A class is to a metaclass what an instance is to a class.)
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In this case, we use the GeneratedProtocolMessageType metaclass
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to inject all the useful functionality into the classes
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output by the protocol compiler at compile-time.
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The upshot of all this is that the real implementation
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details for ALL pure-Python protocol buffers are *here in
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this file*.
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"""
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__author__ = 'robinson@google.com (Will Robinson)'
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from google.protobuf.internal import api_implementation
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from google.protobuf import message
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if api_implementation.Type() == 'cpp':
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from google.protobuf.pyext import cpp_message as message_impl
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else:
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from google.protobuf.internal import python_message as message_impl
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# The type of all Message classes.
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# Part of the public interface, but normally only used by message factories.
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GeneratedProtocolMessageType = message_impl.GeneratedProtocolMessageType
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MESSAGE_CLASS_CACHE = {}
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def ParseMessage(descriptor, byte_str):
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"""Generate a new Message instance from this Descriptor and a byte string.
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Args:
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descriptor: Protobuf Descriptor object
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byte_str: Serialized protocol buffer byte string
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Returns:
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Newly created protobuf Message object.
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"""
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result_class = MakeClass(descriptor)
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new_msg = result_class()
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new_msg.ParseFromString(byte_str)
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return new_msg
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def MakeClass(descriptor):
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"""Construct a class object for a protobuf described by descriptor.
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Composite descriptors are handled by defining the new class as a member of the
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parent class, recursing as deep as necessary.
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This is the dynamic equivalent to:
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class Parent(message.Message):
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__metaclass__ = GeneratedProtocolMessageType
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DESCRIPTOR = descriptor
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class Child(message.Message):
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__metaclass__ = GeneratedProtocolMessageType
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DESCRIPTOR = descriptor.nested_types[0]
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Sample usage:
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file_descriptor = descriptor_pb2.FileDescriptorProto()
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file_descriptor.ParseFromString(proto2_string)
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msg_descriptor = descriptor.MakeDescriptor(file_descriptor.message_type[0])
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msg_class = reflection.MakeClass(msg_descriptor)
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msg = msg_class()
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Args:
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descriptor: A descriptor.Descriptor object describing the protobuf.
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Returns:
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The Message class object described by the descriptor.
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"""
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if descriptor in MESSAGE_CLASS_CACHE:
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return MESSAGE_CLASS_CACHE[descriptor]
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attributes = {}
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for name, nested_type in list(descriptor.nested_types_by_name.items()):
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attributes[name] = MakeClass(nested_type)
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attributes[GeneratedProtocolMessageType._DESCRIPTOR_KEY] = descriptor
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result = GeneratedProtocolMessageType(
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str(descriptor.name), (message.Message,), attributes)
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MESSAGE_CLASS_CACHE[descriptor] = result
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return result
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