1# Protocol Buffers - Google's data interchange format
2# Copyright 2008 Google Inc.  All rights reserved.
3# http://code.google.com/p/protobuf/
4#
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29# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
30
31# TODO(robinson): We should just make these methods all "pure-virtual" and move
32# all implementation out, into reflection.py for now.
33
34
35"""Contains an abstract base class for protocol messages."""
36
37__author__ = 'robinson@google.com (Will Robinson)'
38
39
40class Error(Exception): pass
41class DecodeError(Error): pass
42class EncodeError(Error): pass
43
44
45class Message(object):
46
47  """Abstract base class for protocol messages.
48
49  Protocol message classes are almost always generated by the protocol
50  compiler.  These generated types subclass Message and implement the methods
51  shown below.
52
53  TODO(robinson): Link to an HTML document here.
54
55  TODO(robinson): Document that instances of this class will also
56  have an Extensions attribute with __getitem__ and __setitem__.
57  Again, not sure how to best convey this.
58
59  TODO(robinson): Document that the class must also have a static
60    RegisterExtension(extension_field) method.
61    Not sure how to best express at this point.
62  """
63
64  # TODO(robinson): Document these fields and methods.
65
66  __slots__ = []
67
68  DESCRIPTOR = None
69
70  def __deepcopy__(self, memo=None):
71    clone = type(self)()
72    clone.MergeFrom(self)
73    return clone
74
75  def __eq__(self, other_msg):
76    """Recursively compares two messages by value and structure."""
77    raise NotImplementedError
78
79  def __ne__(self, other_msg):
80    # Can't just say self != other_msg, since that would infinitely recurse. :)
81    return not self == other_msg
82
83  def __hash__(self):
84    raise TypeError('unhashable object')
85
86  def __str__(self):
87    """Outputs a human-readable representation of the message."""
88    raise NotImplementedError
89
90  def __unicode__(self):
91    """Outputs a human-readable representation of the message."""
92    raise NotImplementedError
93
94  def MergeFrom(self, other_msg):
95    """Merges the contents of the specified message into current message.
96
97    This method merges the contents of the specified message into the current
98    message. Singular fields that are set in the specified message overwrite
99    the corresponding fields in the current message. Repeated fields are
100    appended. Singular sub-messages and groups are recursively merged.
101
102    Args:
103      other_msg: Message to merge into the current message.
104    """
105    raise NotImplementedError
106
107  def CopyFrom(self, other_msg):
108    """Copies the content of the specified message into the current message.
109
110    The method clears the current message and then merges the specified
111    message using MergeFrom.
112
113    Args:
114      other_msg: Message to copy into the current one.
115    """
116    if self is other_msg:
117      return
118    self.Clear()
119    self.MergeFrom(other_msg)
120
121  def Clear(self):
122    """Clears all data that was set in the message."""
123    raise NotImplementedError
124
125  def SetInParent(self):
126    """Mark this as present in the parent.
127
128    This normally happens automatically when you assign a field of a
129    sub-message, but sometimes you want to make the sub-message
130    present while keeping it empty.  If you find yourself using this,
131    you may want to reconsider your design."""
132    raise NotImplementedError
133
134  def IsInitialized(self):
135    """Checks if the message is initialized.
136
137    Returns:
138      The method returns True if the message is initialized (i.e. all of its
139      required fields are set).
140    """
141    raise NotImplementedError
142
143  # TODO(robinson): MergeFromString() should probably return None and be
144  # implemented in terms of a helper that returns the # of bytes read.  Our
145  # deserialization routines would use the helper when recursively
146  # deserializing, but the end user would almost always just want the no-return
147  # MergeFromString().
148
149  def MergeFromString(self, serialized):
150    """Merges serialized protocol buffer data into this message.
151
152    When we find a field in |serialized| that is already present
153    in this message:
154      - If it's a "repeated" field, we append to the end of our list.
155      - Else, if it's a scalar, we overwrite our field.
156      - Else, (it's a nonrepeated composite), we recursively merge
157        into the existing composite.
158
159    TODO(robinson): Document handling of unknown fields.
160
161    Args:
162      serialized: Any object that allows us to call buffer(serialized)
163        to access a string of bytes using the buffer interface.
164
165    TODO(robinson): When we switch to a helper, this will return None.
166
167    Returns:
168      The number of bytes read from |serialized|.
169      For non-group messages, this will always be len(serialized),
170      but for messages which are actually groups, this will
171      generally be less than len(serialized), since we must
172      stop when we reach an END_GROUP tag.  Note that if
173      we *do* stop because of an END_GROUP tag, the number
174      of bytes returned does not include the bytes
175      for the END_GROUP tag information.
176    """
177    raise NotImplementedError
178
179  def ParseFromString(self, serialized):
180    """Like MergeFromString(), except we clear the object first."""
181    self.Clear()
182    self.MergeFromString(serialized)
183
184  def SerializeToString(self):
185    """Serializes the protocol message to a binary string.
186
187    Returns:
188      A binary string representation of the message if all of the required
189      fields in the message are set (i.e. the message is initialized).
190
191    Raises:
192      message.EncodeError if the message isn't initialized.
193    """
194    raise NotImplementedError
195
196  def SerializePartialToString(self):
197    """Serializes the protocol message to a binary string.
198
199    This method is similar to SerializeToString but doesn't check if the
200    message is initialized.
201
202    Returns:
203      A string representation of the partial message.
204    """
205    raise NotImplementedError
206
207  # TODO(robinson): Decide whether we like these better
208  # than auto-generated has_foo() and clear_foo() methods
209  # on the instances themselves.  This way is less consistent
210  # with C++, but it makes reflection-type access easier and
211  # reduces the number of magically autogenerated things.
212  #
213  # TODO(robinson): Be sure to document (and test) exactly
214  # which field names are accepted here.  Are we case-sensitive?
215  # What do we do with fields that share names with Python keywords
216  # like 'lambda' and 'yield'?
217  #
218  # nnorwitz says:
219  # """
220  # Typically (in python), an underscore is appended to names that are
221  # keywords. So they would become lambda_ or yield_.
222  # """
223  def ListFields(self):
224    """Returns a list of (FieldDescriptor, value) tuples for all
225    fields in the message which are not empty.  A singular field is non-empty
226    if HasField() would return true, and a repeated field is non-empty if
227    it contains at least one element.  The fields are ordered by field
228    number"""
229    raise NotImplementedError
230
231  def HasField(self, field_name):
232    """Checks if a certain field is set for the message. Note if the
233    field_name is not defined in the message descriptor, ValueError will be
234    raised."""
235    raise NotImplementedError
236
237  def ClearField(self, field_name):
238    raise NotImplementedError
239
240  def HasExtension(self, extension_handle):
241    raise NotImplementedError
242
243  def ClearExtension(self, extension_handle):
244    raise NotImplementedError
245
246  def ByteSize(self):
247    """Returns the serialized size of this message.
248    Recursively calls ByteSize() on all contained messages.
249    """
250    raise NotImplementedError
251
252  def _SetListener(self, message_listener):
253    """Internal method used by the protocol message implementation.
254    Clients should not call this directly.
255
256    Sets a listener that this message will call on certain state transitions.
257
258    The purpose of this method is to register back-edges from children to
259    parents at runtime, for the purpose of setting "has" bits and
260    byte-size-dirty bits in the parent and ancestor objects whenever a child or
261    descendant object is modified.
262
263    If the client wants to disconnect this Message from the object tree, she
264    explicitly sets callback to None.
265
266    If message_listener is None, unregisters any existing listener.  Otherwise,
267    message_listener must implement the MessageListener interface in
268    internal/message_listener.py, and we discard any listener registered
269    via a previous _SetListener() call.
270    """
271    raise NotImplementedError
272
273  def __getstate__(self):
274    """Support the pickle protocol."""
275    return dict(serialized=self.SerializePartialToString())
276
277  def __setstate__(self, state):
278    """Support the pickle protocol."""
279    self.__init__()
280    self.ParseFromString(state['serialized'])
281