1# Protocol Buffers - Google's data interchange format
2# Copyright 2008 Google Inc.  All rights reserved.
3# https://developers.google.com/protocol-buffers/
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    """Parse serialized protocol buffer data into this message.
181
182    Like MergeFromString(), except we clear the object first and
183    do not return the value that MergeFromString returns.
184    """
185    self.Clear()
186    self.MergeFromString(serialized)
187
188  def SerializeToString(self):
189    """Serializes the protocol message to a binary string.
190
191    Returns:
192      A binary string representation of the message if all of the required
193      fields in the message are set (i.e. the message is initialized).
194
195    Raises:
196      message.EncodeError if the message isn't initialized.
197    """
198    raise NotImplementedError
199
200  def SerializePartialToString(self):
201    """Serializes the protocol message to a binary string.
202
203    This method is similar to SerializeToString but doesn't check if the
204    message is initialized.
205
206    Returns:
207      A string representation of the partial message.
208    """
209    raise NotImplementedError
210
211  # TODO(robinson): Decide whether we like these better
212  # than auto-generated has_foo() and clear_foo() methods
213  # on the instances themselves.  This way is less consistent
214  # with C++, but it makes reflection-type access easier and
215  # reduces the number of magically autogenerated things.
216  #
217  # TODO(robinson): Be sure to document (and test) exactly
218  # which field names are accepted here.  Are we case-sensitive?
219  # What do we do with fields that share names with Python keywords
220  # like 'lambda' and 'yield'?
221  #
222  # nnorwitz says:
223  # """
224  # Typically (in python), an underscore is appended to names that are
225  # keywords. So they would become lambda_ or yield_.
226  # """
227  def ListFields(self):
228    """Returns a list of (FieldDescriptor, value) tuples for all
229    fields in the message which are not empty.  A singular field is non-empty
230    if HasField() would return true, and a repeated field is non-empty if
231    it contains at least one element.  The fields are ordered by field
232    number"""
233    raise NotImplementedError
234
235  def HasField(self, field_name):
236    """Checks if a certain field is set for the message. Note if the
237    field_name is not defined in the message descriptor, ValueError will be
238    raised."""
239    raise NotImplementedError
240
241  def ClearField(self, field_name):
242    raise NotImplementedError
243
244  def HasExtension(self, extension_handle):
245    raise NotImplementedError
246
247  def ClearExtension(self, extension_handle):
248    raise NotImplementedError
249
250  def ByteSize(self):
251    """Returns the serialized size of this message.
252    Recursively calls ByteSize() on all contained messages.
253    """
254    raise NotImplementedError
255
256  def _SetListener(self, message_listener):
257    """Internal method used by the protocol message implementation.
258    Clients should not call this directly.
259
260    Sets a listener that this message will call on certain state transitions.
261
262    The purpose of this method is to register back-edges from children to
263    parents at runtime, for the purpose of setting "has" bits and
264    byte-size-dirty bits in the parent and ancestor objects whenever a child or
265    descendant object is modified.
266
267    If the client wants to disconnect this Message from the object tree, she
268    explicitly sets callback to None.
269
270    If message_listener is None, unregisters any existing listener.  Otherwise,
271    message_listener must implement the MessageListener interface in
272    internal/message_listener.py, and we discard any listener registered
273    via a previous _SetListener() call.
274    """
275    raise NotImplementedError
276
277  def __getstate__(self):
278    """Support the pickle protocol."""
279    return dict(serialized=self.SerializePartialToString())
280
281  def __setstate__(self, state):
282    """Support the pickle protocol."""
283    self.__init__()
284    self.ParseFromString(state['serialized'])
285