1# Protocol Buffers - Google's data interchange format
2# Copyright 2008 Google Inc.  All rights reserved.
3# https://developers.google.com/protocol-buffers/
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30
31"""Provides a factory class for generating dynamic messages.
32
33The easiest way to use this class is if you have access to the FileDescriptor
34protos containing the messages you want to create you can just do the following:
35
36message_classes = message_factory.GetMessages(iterable_of_file_descriptors)
37my_proto_instance = message_classes['some.proto.package.MessageName']()
38"""
39
40__author__ = 'matthewtoia@google.com (Matt Toia)'
41
42from google.protobuf.internal import api_implementation
43from google.protobuf import descriptor_pool
44from google.protobuf import message
45
46if api_implementation.Type() == 'cpp':
47  from google.protobuf.pyext import cpp_message as message_impl
48else:
49  from google.protobuf.internal import python_message as message_impl
50
51
52# The type of all Message classes.
53_GENERATED_PROTOCOL_MESSAGE_TYPE = message_impl.GeneratedProtocolMessageType
54
55
56class MessageFactory(object):
57  """Factory for creating Proto2 messages from descriptors in a pool."""
58
59  def __init__(self, pool=None):
60    """Initializes a new factory."""
61    self.pool = pool or descriptor_pool.DescriptorPool()
62
63    # local cache of all classes built from protobuf descriptors
64    self._classes = {}
65
66  def GetPrototype(self, descriptor):
67    """Builds a proto2 message class based on the passed in descriptor.
68
69    Passing a descriptor with a fully qualified name matching a previous
70    invocation will cause the same class to be returned.
71
72    Args:
73      descriptor: The descriptor to build from.
74
75    Returns:
76      A class describing the passed in descriptor.
77    """
78    if descriptor not in self._classes:
79      descriptor_name = descriptor.name
80      if str is bytes:  # PY2
81        descriptor_name = descriptor.name.encode('ascii', 'ignore')
82      result_class = _GENERATED_PROTOCOL_MESSAGE_TYPE(
83          descriptor_name,
84          (message.Message,),
85          {'DESCRIPTOR': descriptor, '__module__': None})
86      # If module not set, it wrongly points to message_factory module.
87      self._classes[descriptor] = result_class
88      for field in descriptor.fields:
89        if field.message_type:
90          self.GetPrototype(field.message_type)
91      for extension in result_class.DESCRIPTOR.extensions:
92        if extension.containing_type not in self._classes:
93          self.GetPrototype(extension.containing_type)
94        extended_class = self._classes[extension.containing_type]
95        extended_class.RegisterExtension(extension)
96    return self._classes[descriptor]
97
98  def GetMessages(self, files):
99    """Gets all the messages from a specified file.
100
101    This will find and resolve dependencies, failing if the descriptor
102    pool cannot satisfy them.
103
104    Args:
105      files: The file names to extract messages from.
106
107    Returns:
108      A dictionary mapping proto names to the message classes. This will include
109      any dependent messages as well as any messages defined in the same file as
110      a specified message.
111    """
112    result = {}
113    for file_name in files:
114      file_desc = self.pool.FindFileByName(file_name)
115      for desc in file_desc.message_types_by_name.values():
116        result[desc.full_name] = self.GetPrototype(desc)
117
118      # While the extension FieldDescriptors are created by the descriptor pool,
119      # the python classes created in the factory need them to be registered
120      # explicitly, which is done below.
121      #
122      # The call to RegisterExtension will specifically check if the
123      # extension was already registered on the object and either
124      # ignore the registration if the original was the same, or raise
125      # an error if they were different.
126
127      for extension in file_desc.extensions_by_name.values():
128        if extension.containing_type not in self._classes:
129          self.GetPrototype(extension.containing_type)
130        extended_class = self._classes[extension.containing_type]
131        extended_class.RegisterExtension(extension)
132    return result
133
134
135_FACTORY = MessageFactory()
136
137
138def GetMessages(file_protos):
139  """Builds a dictionary of all the messages available in a set of files.
140
141  Args:
142    file_protos: Iterable of FileDescriptorProto to build messages out of.
143
144  Returns:
145    A dictionary mapping proto names to the message classes. This will include
146    any dependent messages as well as any messages defined in the same file as
147    a specified message.
148  """
149  # The cpp implementation of the protocol buffer library requires to add the
150  # message in topological order of the dependency graph.
151  file_by_name = {file_proto.name: file_proto for file_proto in file_protos}
152  def _AddFile(file_proto):
153    for dependency in file_proto.dependency:
154      if dependency in file_by_name:
155        # Remove from elements to be visited, in order to cut cycles.
156        _AddFile(file_by_name.pop(dependency))
157    _FACTORY.pool.Add(file_proto)
158  while file_by_name:
159    _AddFile(file_by_name.popitem()[1])
160  return _FACTORY.GetMessages([file_proto.name for file_proto in file_protos])
161