# 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.
# TODO(robinson): We should just make these methods all "pure-virtual" and move
# all implementation out, into reflection.py for now.
"""Contains an abstract base class for protocol messages."""
__author__ = 'robinson@google.com (Will Robinson)'
from google.protobuf import text_format
class Error(Exception): pass
class DecodeError(Error): pass
class EncodeError(Error): pass
class Message(object):
"""Abstract base class for protocol messages.
Protocol message classes are almost always generated by the protocol
compiler. These generated types subclass Message and implement the methods
shown below.
TODO(robinson): Link to an HTML document here.
TODO(robinson): Document that instances of this class will also
have an Extensions attribute with __getitem__ and __setitem__.
Again, not sure how to best convey this.
TODO(robinson): Document that the class must also have a static
RegisterExtension(extension_field) method.
Not sure how to best express at this point.
"""
# TODO(robinson): Document these fields and methods.
__slots__ = []
DESCRIPTOR = None
def __eq__(self, other_msg):
raise NotImplementedError
def __ne__(self, other_msg):
# Can't just say self != other_msg, since that would infinitely recurse. :)
return not self == other_msg
def __str__(self):
return text_format.MessageToString(self)
def MergeFrom(self, other_msg):
raise NotImplementedError
def CopyFrom(self, other_msg):
raise NotImplementedError
def Clear(self):
raise NotImplementedError
def IsInitialized(self):
raise NotImplementedError
# TODO(robinson): MergeFromString() should probably return None and be
# implemented in terms of a helper that returns the # of bytes read. Our
# deserialization routines would use the helper when recursively
# deserializing, but the end user would almost always just want the no-return
# MergeFromString().
def MergeFromString(self, serialized):
"""Merges serialized protocol buffer data into this message.
When we find a field in |serialized| that is already present
in this message:
- If it's a "repeated" field, we append to the end of our list.
- Else, if it's a scalar, we overwrite our field.
- Else, (it's a nonrepeated composite), we recursively merge
into the existing composite.
TODO(robinson): Document handling of unknown fields.
Args:
serialized: Any object that allows us to call buffer(serialized)
to access a string of bytes using the buffer interface.
TODO(robinson): When we switch to a helper, this will return None.
Returns:
The number of bytes read from |serialized|.
For non-group messages, this will always be len(serialized),
but for messages which are actually groups, this will
generally be less than len(serialized), since we must
stop when we reach an END_GROUP tag. Note that if
we *do* stop because of an END_GROUP tag, the number
of bytes returned does not include the bytes
for the END_GROUP tag information.
"""
raise NotImplementedError
def ParseFromString(self, serialized):
"""Like MergeFromString(), except we clear the object first."""
self.Clear()
self.MergeFromString(serialized)
def SerializeToString(self):
raise NotImplementedError
# TODO(robinson): Decide whether we like these better
# than auto-generated has_foo() and clear_foo() methods
# on the instances themselves. This way is less consistent
# with C++, but it makes reflection-type access easier and
# reduces the number of magically autogenerated things.
#
# TODO(robinson): Be sure to document (and test) exactly
# which field names are accepted here. Are we case-sensitive?
# What do we do with fields that share names with Python keywords
# like 'lambda' and 'yield'?
#
# nnorwitz says:
# """
# Typically (in python), an underscore is appended to names that are
# keywords. So they would become lambda_ or yield_.
# """
def ListFields(self, field_name):
"""Returns a list of (FieldDescriptor, value) tuples for all
fields in the message which are not empty. A singular field is non-empty
if HasField() would return true, and a repeated field is non-empty if
it contains at least one element. The fields are ordered by field
number"""
raise NotImplementedError
def HasField(self, field_name):
raise NotImplementedError
def ClearField(self, field_name):
raise NotImplementedError
def HasExtension(self, extension_handle):
raise NotImplementedError
def ClearExtension(self, extension_handle):
raise NotImplementedError
def ByteSize(self):
"""Returns the serialized size of this message.
Recursively calls ByteSize() on all contained messages.
"""
raise NotImplementedError
def _SetListener(self, message_listener):
"""Internal method used by the protocol message implementation.
Clients should not call this directly.
Sets a listener that this message will call on certain state transitions.
The purpose of this method is to register back-edges from children to
parents at runtime, for the purpose of setting "has" bits and
byte-size-dirty bits in the parent and ancestor objects whenever a child or
descendant object is modified.
If the client wants to disconnect this Message from the object tree, she
explicitly sets callback to None.
If message_listener is None, unregisters any existing listener. Otherwise,
message_listener must implement the MessageListener interface in
internal/message_listener.py, and we discard any listener registered
via a previous _SetListener() call.
"""
raise NotImplementedError
