1# Protocol Buffers - Google's data interchange format 2# Copyright 2008 Google Inc. All rights reserved. 3# https://developers.google.com/protocol-buffers/ 4# 5# Redistribution and use in source and binary forms, with or without 6# modification, are permitted provided that the following conditions are 7# met: 8# 9# * Redistributions of source code must retain the above copyright 10# notice, this list of conditions and the following disclaimer. 11# * Redistributions in binary form must reproduce the above 12# copyright notice, this list of conditions and the following disclaimer 13# in the documentation and/or other materials provided with the 14# distribution. 15# * Neither the name of Google Inc. nor the names of its 16# contributors may be used to endorse or promote products derived from 17# this software without specific prior written permission. 18# 19# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 20# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 21# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 22# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 23# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 24# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 25# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 26# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 27# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 28# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 29# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 30 31# This code is meant to work on Python 2.4 and above only. 32 33"""Contains a metaclass and helper functions used to create 34protocol message classes from Descriptor objects at runtime. 35 36Recall that a metaclass is the "type" of a class. 37(A class is to a metaclass what an instance is to a class.) 38 39In this case, we use the GeneratedProtocolMessageType metaclass 40to inject all the useful functionality into the classes 41output by the protocol compiler at compile-time. 42 43The upshot of all this is that the real implementation 44details for ALL pure-Python protocol buffers are *here in 45this file*. 46""" 47 48__author__ = 'robinson@google.com (Will Robinson)' 49 50 51from google.protobuf.internal import api_implementation 52from google.protobuf import message 53 54 55if api_implementation.Type() == 'cpp': 56 from google.protobuf.pyext import cpp_message as message_impl 57else: 58 from google.protobuf.internal import python_message as message_impl 59 60# The type of all Message classes. 61# Part of the public interface, but normally only used by message factories. 62GeneratedProtocolMessageType = message_impl.GeneratedProtocolMessageType 63 64 65def ParseMessage(descriptor, byte_str): 66 """Generate a new Message instance from this Descriptor and a byte string. 67 68 Args: 69 descriptor: Protobuf Descriptor object 70 byte_str: Serialized protocol buffer byte string 71 72 Returns: 73 Newly created protobuf Message object. 74 """ 75 result_class = MakeClass(descriptor) 76 new_msg = result_class() 77 new_msg.ParseFromString(byte_str) 78 return new_msg 79 80 81def MakeClass(descriptor): 82 """Construct a class object for a protobuf described by descriptor. 83 84 Composite descriptors are handled by defining the new class as a member of the 85 parent class, recursing as deep as necessary. 86 This is the dynamic equivalent to: 87 88 class Parent(message.Message): 89 __metaclass__ = GeneratedProtocolMessageType 90 DESCRIPTOR = descriptor 91 class Child(message.Message): 92 __metaclass__ = GeneratedProtocolMessageType 93 DESCRIPTOR = descriptor.nested_types[0] 94 95 Sample usage: 96 file_descriptor = descriptor_pb2.FileDescriptorProto() 97 file_descriptor.ParseFromString(proto2_string) 98 msg_descriptor = descriptor.MakeDescriptor(file_descriptor.message_type[0]) 99 msg_class = reflection.MakeClass(msg_descriptor) 100 msg = msg_class() 101 102 Args: 103 descriptor: A descriptor.Descriptor object describing the protobuf. 104 Returns: 105 The Message class object described by the descriptor. 106 """ 107 attributes = {} 108 for name, nested_type in descriptor.nested_types_by_name.items(): 109 attributes[name] = MakeClass(nested_type) 110 111 attributes[GeneratedProtocolMessageType._DESCRIPTOR_KEY] = descriptor 112 113 return GeneratedProtocolMessageType(str(descriptor.name), (message.Message,), 114 attributes) 115