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fix: add pickling support to proto messages (#280)
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FBO of frameworks such as Apache Beam, which use them for sharing
state between trusted hosts.

Closes #260.
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tseaver authored Dec 9, 2021
1 parent 437fb9f commit 2b7be35
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7 changes: 5 additions & 2 deletions docs/messages.rst
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Expand Up @@ -246,8 +246,11 @@ already allows construction from mapping types.
.. note::

Protobuf messages **CANNOT** be safely pickled or unpickled. This has serious consequences for programs that use multiprocessing or write messages to files.
The preferred mechanism for serializing proto messages is :meth:`~.Message.serialize`.
Although Python's pickling protocol has known issues when used with
untrusted collaborators, some frameworks do use it for communication
between trusted hosts. To support such frameworks, protobuf messages
**can** be pickled and unpickled, although the preferred mechanism for
serializing proto messages is :meth:`~.Message.serialize`.

Multiprocessing example:

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9 changes: 9 additions & 0 deletions proto/message.py
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Expand Up @@ -642,6 +642,15 @@ def __setattr__(self, key, value):
if pb_value is not None:
self._pb.MergeFrom(self._meta.pb(**{key: pb_value}))

def __getstate__(self):
"""Serialize for pickling."""
return self._pb.SerializeToString()

def __setstate__(self, value):
"""Deserialization for pickling."""
new_pb = self._meta.pb().FromString(value)
super().__setattr__("_pb", new_pb)


class _MessageInfo:
"""Metadata about a message.
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51 changes: 51 additions & 0 deletions tests/test_message_pickling.py
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@@ -0,0 +1,51 @@
# Copyright 2018 Google LLC
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

import itertools
import pickle

import pytest

import proto


class Squid(proto.Message):
# Test primitives, enums, and repeated fields.
class Chromatophore(proto.Message):
class Color(proto.Enum):
UNKNOWN = 0
RED = 1
BROWN = 2
WHITE = 3
BLUE = 4

color = proto.Field(Color, number=1)

mass_kg = proto.Field(proto.INT32, number=1)
chromatophores = proto.RepeatedField(Chromatophore, number=2)


def test_pickling():

s = Squid(mass_kg=20)
colors = ["RED", "BROWN", "WHITE", "BLUE"]
s.chromatophores = [
{"color": c} for c in itertools.islice(itertools.cycle(colors), 10)
]

pickled = pickle.dumps(s)

unpickled = pickle.loads(pickled)

assert unpickled == s

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