froofle/protobuf/internal/message_listener.py

# Protocol Buffers - Google's data interchange format
# Copyright 2008 Google Inc.  All rights reserved.
# http://code.google.com/p/protobuf/
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are
# met:
#
#     * Redistributions of source code must retain the above copyright
# notice, this list of conditions and the following disclaimer.
#     * Redistributions in binary form must reproduce the above
# copyright notice, this list of conditions and the following disclaimer
# in the documentation and/or other materials provided with the
# distribution.
#     * Neither the name of Google Inc. nor the names of its
# contributors may be used to endorse or promote products derived from
# this software without specific prior written permission.
#
# 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.

"""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