python/google/protobuf/message_factory.py

# Protocol Buffers - Google's data interchange format
# Copyright 2008 Google Inc.  All rights reserved.
#
# Use of this source code is governed by a BSD-style
# license that can be found in the LICENSE file or at
# https://developers.google.com/open-source/licenses/bsd
"""Provides a factory class for generating dynamic messages.

The easiest way to use this class is if you have access to the FileDescriptor
protos containing the messages you want to create you can just do the following:

message_classes = message_factory.GetMessages(iterable_of_file_descriptors)
my_proto_instance = message_classes['some.proto.package.MessageName']()

Caution: There are inherent denial of service risks to using this behavior with
untrusted descriptors. See
https://github.com/protocolbuffers/protobuf/security/policy#dynamicmessage-on-untrusted-descriptors
for details.
"""

__author__ = 'matthewtoia@google.com (Matt Toia)'

import warnings

from google.protobuf import descriptor_pool
from google.protobuf import message
from google.protobuf.internal import api_implementation

if api_implementation.Type() == 'python':
  from google.protobuf.internal import python_message as message_impl
else:
  from google.protobuf.pyext import cpp_message as message_impl  # pylint: disable=g-import-not-at-top

# The type of all Message classes.
_GENERATED_PROTOCOL_MESSAGE_TYPE = message_impl.GeneratedProtocolMessageType


def GetMessageClass(descriptor):
  """Obtains a proto2 message class based on the passed in descriptor.

  Passing a descriptor with a fully qualified name matching a previous
  invocation will cause the same class to be returned.

  This is intended to be used only with trusted descriptors. There are inherent
  denial of service risks to using dynamic messages with untrusted descriptors
  which cannot be hardened against. See
  https://github.com/protocolbuffers/protobuf/security/policy#dynamicmessage-on-untrusted-descriptors
  for details.

  Args:
    descriptor: The descriptor to build from.

  Returns:
    A class describing the passed in descriptor.
  """
  concrete_class = getattr(descriptor, '_concrete_class', None)
  if concrete_class:
    return concrete_class
  return _InternalCreateMessageClass(descriptor)


def GetMessageClassesForFiles(files, pool):
  """Gets all the messages from specified files.

  This will find and resolve dependencies, failing if the descriptor
  pool cannot satisfy them.

  This will not return the classes for nested types within those classes, for
  those, use GetMessageClass() on the nested types within their containing
  messages.

  For example, for the message:

  message NestedTypeMessage {
    message NestedType {
      string data = 1;
    }
    NestedType nested = 1;
  }

  NestedTypeMessage will be in the result, but not
  NestedTypeMessage.NestedType.

  Args:
    files: The file names to extract messages from.
    pool: The descriptor pool to find the files including the dependent files.

  Returns:
    A dictionary mapping proto names to the message classes.
  """
  result = {}
  for file_name in files:
    file_desc = pool.FindFileByName(file_name)
    for desc in file_desc.message_types_by_name.values():
      result[desc.full_name] = GetMessageClass(desc)

    # While the extension FieldDescriptors are created by the descriptor pool,
    # the python classes created in the factory need them to be registered
    # explicitly, which is done below.
    #
    # The call to RegisterExtension will specifically check if the
    # extension was already registered on the object and either
    # ignore the registration if the original was the same, or raise
    # an error if they were different.

    for extension in file_desc.extensions_by_name.values():
      _ = GetMessageClass(extension.containing_type)
      if api_implementation.Type() != 'python':
        # TODO: Remove this check here. Duplicate extension
        # register check should be in descriptor_pool.
        if extension is not pool.FindExtensionByNumber(
            extension.containing_type, extension.number
        ):
          raise ValueError('Double registration of Extensions')
      # Recursively load protos for extension field, in order to be able to
      # fully represent the extension. This matches the behavior for regular
      # fields too.
      if extension.message_type:
        GetMessageClass(extension.message_type)
  return result


def _InternalCreateMessageClass(descriptor):
  """Builds a proto2 message class based on the passed in descriptor.

  Args:
    descriptor: The descriptor to build from.

  Returns:
    A class describing the passed in descriptor.
  """
  descriptor_name = descriptor.name
  result_class = _GENERATED_PROTOCOL_MESSAGE_TYPE(
      descriptor_name,
      (message.Message,),
      {
          'DESCRIPTOR': descriptor,
          # If module not set, it wrongly points to message_factory module.
          '__module__': None,
      },
  )
  for field in descriptor.fields:
    if field.message_type:
      GetMessageClass(field.message_type)

  for extension in result_class.DESCRIPTOR.extensions:
    extended_class = GetMessageClass(extension.containing_type)
    if api_implementation.Type() != 'python':
      # TODO: Remove this check here. Duplicate extension
      # register check should be in descriptor_pool.
      pool = extension.containing_type.file.pool
      if extension is not pool.FindExtensionByNumber(
          extension.containing_type, extension.number
      ):
        raise ValueError('Double registration of Extensions')
    if extension.message_type:
      GetMessageClass(extension.message_type)
  return result_class


# Deprecated. Please use GetMessageClass() or GetMessageClassesForFiles()
# method above instead.
class MessageFactory(object):
  """Factory for creating Proto2 messages from descriptors in a pool."""

  def __init__(self, pool=None):
    """Initializes a new factory."""
    self.pool = pool or descriptor_pool.DescriptorPool()


def GetMessages(file_protos, pool=None):
  """Builds a dictionary of all the messages available in a set of files.

  Args:
    file_protos: Iterable of FileDescriptorProto to build messages out of.
    pool: The descriptor pool to add the file protos.

  Returns:
    A dictionary mapping proto names to the message classes. This will include
    any dependent messages as well as any messages defined in the same file as
    a specified message.
  """
  # The cpp implementation of the protocol buffer library requires to add the
  # message in topological order of the dependency graph.
  des_pool = pool or descriptor_pool.DescriptorPool()
  file_by_name = {file_proto.name: file_proto for file_proto in file_protos}

  def _AddFile(file_proto):
    for dependency in file_proto.dependency:
      if dependency in file_by_name:
        # Remove from elements to be visited, in order to cut cycles.
        _AddFile(file_by_name.pop(dependency))
    des_pool.Add(file_proto)

  while file_by_name:
    _AddFile(file_by_name.popitem()[1])
  return GetMessageClassesForFiles(
      [file_proto.name for file_proto in file_protos], des_pool
  )