1 # Protocol Buffers - Google's data interchange format 2 # Copyright 2008 Google Inc. All rights reserved. 3 # http://code.google.com/p/protobuf/ 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 34 protocol message classes from Descriptor objects at runtime. 35 36 Recall that a metaclass is the "type" of a class. 37 (A class is to a metaclass what an instance is to a class.) 38 39 In this case, we use the GeneratedProtocolMessageType metaclass 40 to inject all the useful functionality into the classes 41 output by the protocol compiler at compile-time. 42 43 The upshot of all this is that the real implementation 44 details for ALL pure-Python protocol buffers are *here in 45 this file*. 46 """ 47 48 __author__ = 'robinson (at] google.com (Will Robinson)' 49 50 51 from google.protobuf.internal import api_implementation 52 from google.protobuf import descriptor as descriptor_mod 53 from google.protobuf import message 54 55 _FieldDescriptor = descriptor_mod.FieldDescriptor 56 57 58 if api_implementation.Type() == 'cpp': 59 if api_implementation.Version() == 2: 60 from google.protobuf.internal.cpp import cpp_message 61 _NewMessage = cpp_message.NewMessage 62 _InitMessage = cpp_message.InitMessage 63 else: 64 from google.protobuf.internal import cpp_message 65 _NewMessage = cpp_message.NewMessage 66 _InitMessage = cpp_message.InitMessage 67 else: 68 from google.protobuf.internal import python_message 69 _NewMessage = python_message.NewMessage 70 _InitMessage = python_message.InitMessage 71 72 73 class GeneratedProtocolMessageType(type): 74 75 """Metaclass for protocol message classes created at runtime from Descriptors. 76 77 We add implementations for all methods described in the Message class. We 78 also create properties to allow getting/setting all fields in the protocol 79 message. Finally, we create slots to prevent users from accidentally 80 "setting" nonexistent fields in the protocol message, which then wouldn't get 81 serialized / deserialized properly. 82 83 The protocol compiler currently uses this metaclass to create protocol 84 message classes at runtime. Clients can also manually create their own 85 classes at runtime, as in this example: 86 87 mydescriptor = Descriptor(.....) 88 class MyProtoClass(Message): 89 __metaclass__ = GeneratedProtocolMessageType 90 DESCRIPTOR = mydescriptor 91 myproto_instance = MyProtoClass() 92 myproto.foo_field = 23 93 ... 94 """ 95 96 # Must be consistent with the protocol-compiler code in 97 # proto2/compiler/internal/generator.*. 98 _DESCRIPTOR_KEY = 'DESCRIPTOR' 99 100 def __new__(cls, name, bases, dictionary): 101 """Custom allocation for runtime-generated class types. 102 103 We override __new__ because this is apparently the only place 104 where we can meaningfully set __slots__ on the class we're creating(?). 105 (The interplay between metaclasses and slots is not very well-documented). 106 107 Args: 108 name: Name of the class (ignored, but required by the 109 metaclass protocol). 110 bases: Base classes of the class we're constructing. 111 (Should be message.Message). We ignore this field, but 112 it's required by the metaclass protocol 113 dictionary: The class dictionary of the class we're 114 constructing. dictionary[_DESCRIPTOR_KEY] must contain 115 a Descriptor object describing this protocol message 116 type. 117 118 Returns: 119 Newly-allocated class. 120 """ 121 descriptor = dictionary[GeneratedProtocolMessageType._DESCRIPTOR_KEY] 122 bases = _NewMessage(bases, descriptor, dictionary) 123 superclass = super(GeneratedProtocolMessageType, cls) 124 125 new_class = superclass.__new__(cls, name, bases, dictionary) 126 setattr(descriptor, '_concrete_class', new_class) 127 return new_class 128 129 def __init__(cls, name, bases, dictionary): 130 """Here we perform the majority of our work on the class. 131 We add enum getters, an __init__ method, implementations 132 of all Message methods, and properties for all fields 133 in the protocol type. 134 135 Args: 136 name: Name of the class (ignored, but required by the 137 metaclass protocol). 138 bases: Base classes of the class we're constructing. 139 (Should be message.Message). We ignore this field, but 140 it's required by the metaclass protocol 141 dictionary: The class dictionary of the class we're 142 constructing. dictionary[_DESCRIPTOR_KEY] must contain 143 a Descriptor object describing this protocol message 144 type. 145 """ 146 descriptor = dictionary[GeneratedProtocolMessageType._DESCRIPTOR_KEY] 147 _InitMessage(descriptor, cls) 148 superclass = super(GeneratedProtocolMessageType, cls) 149 superclass.__init__(name, bases, dictionary) 150 151 152 def ParseMessage(descriptor, byte_str): 153 """Generate a new Message instance from this Descriptor and a byte string. 154 155 Args: 156 descriptor: Protobuf Descriptor object 157 byte_str: Serialized protocol buffer byte string 158 159 Returns: 160 Newly created protobuf Message object. 161 """ 162 163 class _ResultClass(message.Message): 164 __metaclass__ = GeneratedProtocolMessageType 165 DESCRIPTOR = descriptor 166 167 new_msg = _ResultClass() 168 new_msg.ParseFromString(byte_str) 169 return new_msg 170
