python/google/protobuf/proto_builder.py

# Protocol Buffers - Google's data interchange format
# Copyright 2008 Google Inc.  All rights reserved.
# https://developers.google.com/protocol-buffers/
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"""Dynamic Protobuf class creator."""

import hashlib
import os

from google.protobuf import descriptor_pb2
from google.protobuf import message_factory


def _GetMessageFromFactory(factory, full_name):
  """Get a proto class from the MessageFactory by name.

  Args:
    factory: a MessageFactory instance.
    full_name: str, the fully qualified name of the proto type.
  Returns:
    a class, for the type identified by full_name.
  Raises:
    KeyError, if the proto is not found in the factory's descriptor pool.
  """
  proto_descriptor = factory.pool.FindMessageTypeByName(full_name)
  proto_cls = factory.GetPrototype(proto_descriptor)
  return proto_cls


def MakeSimpleProtoClass(fields, full_name, pool=None):
  """Create a Protobuf class whose fields are basic types.

  Note: this doesn't validate field names!

  Args:
    fields: dict of {name: field_type} mappings for each field in the proto.
    full_name: str, the fully-qualified name of the proto type.
    pool: optional DescriptorPool instance.
  Returns:
    a class, the new protobuf class with a FileDescriptor.
  """
  factory = message_factory.MessageFactory(pool=pool)
  try:
    proto_cls = _GetMessageFromFactory(factory, full_name)
    return proto_cls
  except KeyError:
    # The factory's DescriptorPool doesn't know about this class yet.
    pass

  # Use a consistent file name that is unlikely to conflict with any imported
  # proto files.
  fields_hash = hashlib.sha1()
  for f_name, f_type in sorted(fields.items()):
    fields_hash.update(f_name.encode('utf8'))
    fields_hash.update(str(f_type).encode('utf8'))
  proto_file_name = fields_hash.hexdigest() + '.proto'

  package, name = full_name.rsplit('.', 1)
  file_proto = descriptor_pb2.FileDescriptorProto()
  file_proto.name = os.path.join(package.replace('.', '/'), proto_file_name)
  file_proto.package = package
  desc_proto = file_proto.message_type.add()
  desc_proto.name = name
  for f_number, (f_name, f_type) in enumerate(sorted(fields.items()), 1):
    field_proto = desc_proto.field.add()
    field_proto.name = f_name
    field_proto.number = f_number
    field_proto.label = descriptor_pb2.FieldDescriptorProto.LABEL_OPTIONAL
    field_proto.type = f_type

  factory.pool.Add(file_proto)
  return _GetMessageFromFactory(factory, full_name)