170 lines
6.4 KiB
Python
Executable File
170 lines
6.4 KiB
Python
Executable File
# Protocol Buffers - Google's data interchange format
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# Copyright 2008 Google Inc. All rights reserved.
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# http://code.google.com/p/protobuf/
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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 descriptor as descriptor_mod
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from google.protobuf import message
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_FieldDescriptor = descriptor_mod.FieldDescriptor
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if api_implementation.Type() == 'cpp':
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if api_implementation.Version() == 2:
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from google.protobuf.internal.cpp import cpp_message
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_NewMessage = cpp_message.NewMessage
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_InitMessage = cpp_message.InitMessage
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else:
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from google.protobuf.internal import cpp_message
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_NewMessage = cpp_message.NewMessage
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_InitMessage = cpp_message.InitMessage
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else:
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from google.protobuf.internal import python_message
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_NewMessage = python_message.NewMessage
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_InitMessage = python_message.InitMessage
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class GeneratedProtocolMessageType(type):
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"""Metaclass for protocol message classes created at runtime from Descriptors.
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We add implementations for all methods described in the Message class. We
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also create properties to allow getting/setting all fields in the protocol
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message. Finally, we create slots to prevent users from accidentally
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"setting" nonexistent fields in the protocol message, which then wouldn't get
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serialized / deserialized properly.
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The protocol compiler currently uses this metaclass to create protocol
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message classes at runtime. Clients can also manually create their own
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classes at runtime, as in this example:
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mydescriptor = Descriptor(.....)
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class MyProtoClass(Message):
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__metaclass__ = GeneratedProtocolMessageType
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DESCRIPTOR = mydescriptor
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myproto_instance = MyProtoClass()
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myproto.foo_field = 23
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...
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"""
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# Must be consistent with the protocol-compiler code in
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# proto2/compiler/internal/generator.*.
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_DESCRIPTOR_KEY = 'DESCRIPTOR'
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def __new__(cls, name, bases, dictionary):
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"""Custom allocation for runtime-generated class types.
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We override __new__ because this is apparently the only place
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where we can meaningfully set __slots__ on the class we're creating(?).
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(The interplay between metaclasses and slots is not very well-documented).
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Args:
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name: Name of the class (ignored, but required by the
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metaclass protocol).
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bases: Base classes of the class we're constructing.
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(Should be message.Message). We ignore this field, but
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it's required by the metaclass protocol
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dictionary: The class dictionary of the class we're
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constructing. dictionary[_DESCRIPTOR_KEY] must contain
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a Descriptor object describing this protocol message
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type.
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Returns:
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Newly-allocated class.
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"""
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descriptor = dictionary[GeneratedProtocolMessageType._DESCRIPTOR_KEY]
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bases = _NewMessage(bases, descriptor, dictionary)
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superclass = super(GeneratedProtocolMessageType, cls)
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new_class = superclass.__new__(cls, name, bases, dictionary)
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setattr(descriptor, '_concrete_class', new_class)
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return new_class
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def __init__(cls, name, bases, dictionary):
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"""Here we perform the majority of our work on the class.
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We add enum getters, an __init__ method, implementations
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of all Message methods, and properties for all fields
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in the protocol type.
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Args:
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name: Name of the class (ignored, but required by the
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metaclass protocol).
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bases: Base classes of the class we're constructing.
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(Should be message.Message). We ignore this field, but
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it's required by the metaclass protocol
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dictionary: The class dictionary of the class we're
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constructing. dictionary[_DESCRIPTOR_KEY] must contain
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a Descriptor object describing this protocol message
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type.
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"""
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descriptor = dictionary[GeneratedProtocolMessageType._DESCRIPTOR_KEY]
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_InitMessage(descriptor, cls)
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superclass = super(GeneratedProtocolMessageType, cls)
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superclass.__init__(name, bases, dictionary)
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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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class _ResultClass(message.Message):
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__metaclass__ = GeneratedProtocolMessageType
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DESCRIPTOR = descriptor
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new_msg = _ResultClass()
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new_msg.ParseFromString(byte_str)
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return new_msg
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