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# Protocol Buffers - Google's data interchange format
# Copyright 2008 Google Inc.
# http://code.google.com/p/protobuf/
#
# 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
#
# http://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.
"""Defines a listener interface for observing certain
state transitions on Message objects.
Also defines a null implementation of this interface.
"""
__author__ = 'robinson@google.com (Will Robinson)'
class MessageListener(object):
"""Listens for transitions to nonempty and for invalidations of cached
byte sizes. Meant to be registered via Message._SetListener().
"""
def TransitionToNonempty(self):
"""Called the *first* time that this message becomes nonempty.
Implementations are free (but not required) to call this method multiple
times after the message has become nonempty.
"""
raise NotImplementedError
def ByteSizeDirty(self):
"""Called *every* time the cached byte size value
for this object is invalidated (transitions from being
"clean" to "dirty").
"""
raise NotImplementedError
class NullMessageListener(object):
"""No-op MessageListener implementation."""
def TransitionToNonempty(self):
pass
def ByteSizeDirty(self):
pass
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