# Protocol Buffers - Google's data interchange format
# Copyright 2008 Google Inc. All rights reserved.
# http://code.google.com/p/protobuf/
#
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# met:
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# notice, this list of conditions and the following disclaimer.
# * Redistributions in binary form must reproduce the above
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# in the documentation and/or other materials provided with the
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# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
# This code is meant to work on Python 2.4 and above only.
"""Contains a metaclass and helper functions used to create
protocol message classes from Descriptor objects at runtime.
Recall that a metaclass is the "type" of a class.
(A class is to a metaclass what an instance is to a class.)
In this case, we use the GeneratedProtocolMessageType metaclass
to inject all the useful functionality into the classes
output by the protocol compiler at compile-time.
The upshot of all this is that the real implementation
details for ALL pure-Python protocol buffers are *here in
this file*.
"""
__author__ = 'robinson@google.com (Will Robinson)'
from google.protobuf.internal import api_implementation
from google.protobuf import descriptor as descriptor_mod
_FieldDescriptor = descriptor_mod.FieldDescriptor
if api_implementation.Type() == 'cpp':
from google.protobuf.internal import cpp_message
_NewMessage = cpp_message.NewMessage
_InitMessage = cpp_message.InitMessage
else:
from google.protobuf.internal import python_message
_NewMessage = python_message.NewMessage
_InitMessage = python_message.InitMessage
class GeneratedProtocolMessageType(type):
"""Metaclass for protocol message classes created at runtime from Descriptors.
We add implementations for all methods described in the Message class. We
also create properties to allow getting/setting all fields in the protocol
message. Finally, we create slots to prevent users from accidentally
"setting" nonexistent fields in the protocol message, which then wouldn't get
serialized / deserialized properly.
The protocol compiler currently uses this metaclass to create protocol
message classes at runtime. Clients can also manually create their own
classes at runtime, as in this example:
mydescriptor = Descriptor(.....)
class MyProtoClass(Message):
__metaclass__ = GeneratedProtocolMessageType
DESCRIPTOR = mydescriptor
myproto_instance = MyProtoClass()
myproto.foo_field = 23
...
"""
# Must be consistent with the protocol-compiler code in
# proto2/compiler/internal/generator.*.
_DESCRIPTOR_KEY = 'DESCRIPTOR'
def __new__(cls, name, bases, dictionary):
"""Custom allocation for runtime-generated class types.
We override __new__ because this is apparently the only place
where we can meaningfully set __slots__ on the class we're creating(?).
(The interplay between metaclasses and slots is not very well-documented).
Args:
name: Name of the class (ignored, but required by the
metaclass protocol).
bases: Base classes of the class we're constructing.
(Should be message.Message). We ignore this field, but
it's required by the metaclass protocol
dictionary: The class dictionary of the class we're
constructing. dictionary[_DESCRIPTOR_KEY] must contain
a Descriptor object describing this protocol message
type.
Returns:
Newly-allocated class.
"""
descriptor = dictionary[GeneratedProtocolMessageType._DESCRIPTOR_KEY]
_NewMessage(descriptor, dictionary)
superclass = super(GeneratedProtocolMessageType, cls)
new_class = superclass.__new__(cls, name, bases, dictionary)
setattr(descriptor, '_concrete_class', new_class)
return new_class
def __init__(cls, name, bases, dictionary):
"""Here we perform the majority of our work on the class.
We add enum getters, an __init__ method, implementations
of all Message methods, and properties for all fields
in the protocol type.
Args:
name: Name of the class (ignored, but required by the
metaclass protocol).
bases: Base classes of the class we're constructing.
(Should be message.Message). We ignore this field, but
it's required by the metaclass protocol
dictionary: The class dictionary of the class we're
constructing. dictionary[_DESCRIPTOR_KEY] must contain
a Descriptor object describing this protocol message
type.
"""
descriptor = dictionary[GeneratedProtocolMessageType._DESCRIPTOR_KEY]
_InitMessage(descriptor, cls)
superclass = super(GeneratedProtocolMessageType, cls)
superclass.__init__(name, bases, dictionary)
