Added more docstrings to IPython.zmq.session.

I have gone through and clarified the different usages of the
phrase "message" in the docstrings. I have also changed some
instances of "msg" to "msg_list" in the *code* to reflect the
difference.

IPython/zmq/session.py

@@ -1,628 +1,679 b''
 #!/usr/bin/env python
 """Session object for building, serializing, sending, and receiving messages in
 IPython. The Session object supports serialization, HMAC signatures, and
 metadata on messages.
 
 Also defined here are utilities for working with Sessions:
 * A SessionFactory to be used as a base class for configurables that work with
 Sessions.
 * A Message object for convenience that allows attribute-access to the msg dict.
 
 Authors:
 
 * Min RK
 * Brian Granger
 * Fernando Perez
 """
 #-----------------------------------------------------------------------------
 #  Copyright (C) 2010-2011  The IPython Development Team
 #
 #  Distributed under the terms of the BSD License.  The full license is in
 #  the file COPYING, distributed as part of this software.
 #-----------------------------------------------------------------------------
 
 #-----------------------------------------------------------------------------
 # Imports
 #-----------------------------------------------------------------------------
 
 import hmac
 import logging
 import os
 import pprint
 import uuid
 from datetime import datetime
 
 try:
     import cPickle
     pickle = cPickle
 except:
     cPickle = None
     import pickle
 
 import zmq
 from zmq.utils import jsonapi
 from zmq.eventloop.ioloop import IOLoop
 from zmq.eventloop.zmqstream import ZMQStream
 
 from IPython.config.configurable import Configurable, LoggingConfigurable
 from IPython.utils.importstring import import_item
 from IPython.utils.jsonutil import extract_dates, squash_dates, date_default
 from IPython.utils.traitlets import (CBytes, Unicode, Bool, Any, Instance, Set,
                                         DottedObjectName)
 
 #-----------------------------------------------------------------------------
 # utility functions
 #-----------------------------------------------------------------------------
 
 def squash_unicode(obj):
     """coerce unicode back to bytestrings."""
     if isinstance(obj,dict):
         for key in obj.keys():
             obj[key] = squash_unicode(obj[key])
             if isinstance(key, unicode):
                 obj[squash_unicode(key)] = obj.pop(key)
     elif isinstance(obj, list):
         for i,v in enumerate(obj):
             obj[i] = squash_unicode(v)
     elif isinstance(obj, unicode):
         obj = obj.encode('utf8')
     return obj
 
 #-----------------------------------------------------------------------------
 # globals and defaults
 #-----------------------------------------------------------------------------
 key = 'on_unknown' if jsonapi.jsonmod.__name__ == 'jsonlib' else 'default'
 json_packer = lambda obj: jsonapi.dumps(obj, **{key:date_default})
 json_unpacker = lambda s: extract_dates(jsonapi.loads(s))
 
 pickle_packer = lambda o: pickle.dumps(o,-1)
 pickle_unpacker = pickle.loads
 
 default_packer = json_packer
 default_unpacker = json_unpacker
 
 
 DELIM=b"<IDS|MSG>"
 
 #-----------------------------------------------------------------------------
 # Classes
 #-----------------------------------------------------------------------------
 
 class SessionFactory(LoggingConfigurable):
     """The Base class for configurables that have a Session, Context, logger,
     and IOLoop.
     """
     
     logname = Unicode('')
     def _logname_changed(self, name, old, new):
         self.log = logging.getLogger(new)
     
     # not configurable:
     context = Instance('zmq.Context')
     def _context_default(self):
         return zmq.Context.instance()
     
     session = Instance('IPython.zmq.session.Session')
     
     loop = Instance('zmq.eventloop.ioloop.IOLoop', allow_none=False)
     def _loop_default(self):
         return IOLoop.instance()
     
     def __init__(self, **kwargs):
         super(SessionFactory, self).__init__(**kwargs)
         
         if self.session is None:
             # construct the session
             self.session = Session(**kwargs)
     
 
 class Message(object):
     """A simple message object that maps dict keys to attributes.
 
     A Message can be created from a dict and a dict from a Message instance
     simply by calling dict(msg_obj)."""
     
     def __init__(self, msg_dict):
         dct = self.__dict__
         for k, v in dict(msg_dict).iteritems():
             if isinstance(v, dict):
                 v = Message(v)
             dct[k] = v
 
     # Having this iterator lets dict(msg_obj) work out of the box.
     def __iter__(self):
         return iter(self.__dict__.iteritems())
     
     def __repr__(self):
         return repr(self.__dict__)
 
     def __str__(self):
         return pprint.pformat(self.__dict__)
 
     def __contains__(self, k):
         return k in self.__dict__
 
     def __getitem__(self, k):
         return self.__dict__[k]
 
 
 def msg_header(msg_id, msg_type, username, session):
     date = datetime.now()
     return locals()
 
 def extract_header(msg_or_header):
     """Given a message or header, return the header."""
     if not msg_or_header:
         return {}
     try:
         # See if msg_or_header is the entire message.
         h = msg_or_header['header']
     except KeyError:
         try:
             # See if msg_or_header is just the header
             h = msg_or_header['msg_id']
         except KeyError:
             raise
         else:
             h = msg_or_header
     if not isinstance(h, dict):
         h = dict(h)
     return h
 
 class Session(Configurable):
     """Object for handling serialization and sending of messages.
     
     The Session object handles building messages and sending them
     with ZMQ sockets or ZMQStream objects.  Objects can communicate with each
     other over the network via Session objects, and only need to work with the
     dict-based IPython message spec. The Session will handle 
     serialization/deserialization, security, and metadata.
     
     Sessions support configurable serialiization via packer/unpacker traits,
     and signing with HMAC digests via the key/keyfile traits.
     
     Parameters
     ----------
     
     debug : bool
         whether to trigger extra debugging statements
     packer/unpacker : str : 'json', 'pickle' or import_string
         importstrings for methods to serialize message parts.  If just
         'json' or 'pickle', predefined JSON and pickle packers will be used.
         Otherwise, the entire importstring must be used.
         
         The functions must accept at least valid JSON input, and output *bytes*.
         
         For example, to use msgpack:
         packer = 'msgpack.packb', unpacker='msgpack.unpackb'
     pack/unpack : callables
         You can also set the pack/unpack callables for serialization directly.
     session : bytes
         the ID of this Session object.  The default is to generate a new UUID.
     username : unicode
         username added to message headers.  The default is to ask the OS.
     key : bytes
         The key used to initialize an HMAC signature.  If unset, messages
         will not be signed or checked.
     keyfile : filepath
         The file containing a key.  If this is set, `key` will be initialized
         to the contents of the file.
     
     """
     
     debug=Bool(False, config=True, help="""Debug output in the Session""")
     
     packer = DottedObjectName('json',config=True,
             help="""The name of the packer for serializing messages.
             Should be one of 'json', 'pickle', or an import name
             for a custom callable serializer.""")
     def _packer_changed(self, name, old, new):
         if new.lower() == 'json':
             self.pack = json_packer
             self.unpack = json_unpacker
         elif new.lower() == 'pickle':
             self.pack = pickle_packer
             self.unpack = pickle_unpacker
         else:
             self.pack = import_item(str(new))
 
     unpacker = DottedObjectName('json', config=True,
         help="""The name of the unpacker for unserializing messages.
         Only used with custom functions for `packer`.""")
     def _unpacker_changed(self, name, old, new):
         if new.lower() == 'json':
             self.pack = json_packer
             self.unpack = json_unpacker
         elif new.lower() == 'pickle':
             self.pack = pickle_packer
             self.unpack = pickle_unpacker
         else:
             self.unpack = import_item(str(new))
         
     session = CBytes(b'', config=True,
         help="""The UUID identifying this session.""")
     def _session_default(self):
         return bytes(uuid.uuid4())
     
     username = Unicode(os.environ.get('USER','username'), config=True,
         help="""Username for the Session. Default is your system username.""")
     
     # message signature related traits:
     key = CBytes(b'', config=True,
         help="""execution key, for extra authentication.""")
     def _key_changed(self, name, old, new):
         if new:
             self.auth = hmac.HMAC(new)
         else:
             self.auth = None
     auth = Instance(hmac.HMAC)
     digest_history = Set()
     
     keyfile = Unicode('', config=True,
         help="""path to file containing execution key.""")
     def _keyfile_changed(self, name, old, new):
         with open(new, 'rb') as f:
             self.key = f.read().strip()
 
     pack = Any(default_packer) # the actual packer function
     def _pack_changed(self, name, old, new):
         if not callable(new):
             raise TypeError("packer must be callable, not %s"%type(new))
     
     unpack = Any(default_unpacker) # the actual packer function
     def _unpack_changed(self, name, old, new):
         # unpacker is not checked - it is assumed to be 
         if not callable(new):
             raise TypeError("unpacker must be callable, not %s"%type(new))
 
     def __init__(self, **kwargs):
         """create a Session object
         
         Parameters
         ----------
 
         debug : bool
             whether to trigger extra debugging statements
         packer/unpacker : str : 'json', 'pickle' or import_string
             importstrings for methods to serialize message parts.  If just
             'json' or 'pickle', predefined JSON and pickle packers will be used.
             Otherwise, the entire importstring must be used.
 
             The functions must accept at least valid JSON input, and output
             *bytes*.
 
             For example, to use msgpack:
             packer = 'msgpack.packb', unpacker='msgpack.unpackb'
         pack/unpack : callables
             You can also set the pack/unpack callables for serialization
             directly.
         session : bytes
             the ID of this Session object.  The default is to generate a new 
             UUID.
         username : unicode
             username added to message headers.  The default is to ask the OS.
         key : bytes
             The key used to initialize an HMAC signature.  If unset, messages
             will not be signed or checked.
         keyfile : filepath
             The file containing a key.  If this is set, `key` will be 
             initialized to the contents of the file.
         """
         super(Session, self).__init__(**kwargs)
         self._check_packers()
         self.none = self.pack({})
 
     @property
     def msg_id(self):
         """always return new uuid"""
         return str(uuid.uuid4())
 
     def _check_packers(self):
         """check packers for binary data and datetime support."""
         pack = self.pack
         unpack = self.unpack
         
         # check simple serialization
         msg = dict(a=[1,'hi'])
         try:
             packed = pack(msg)
         except Exception:
             raise ValueError("packer could not serialize a simple message")
         
         # ensure packed message is bytes
         if not isinstance(packed, bytes):
             raise ValueError("message packed to %r, but bytes are required"%type(packed))
         
         # check that unpack is pack's inverse
         try:
             unpacked = unpack(packed)
         except Exception:
             raise ValueError("unpacker could not handle the packer's output")
         
         # check datetime support
         msg = dict(t=datetime.now())
         try:
             unpacked = unpack(pack(msg))
         except Exception:
             self.pack = lambda o: pack(squash_dates(o))
             self.unpack = lambda s: extract_dates(unpack(s))
     
     def msg_header(self, msg_type):
         return msg_header(self.msg_id, msg_type, self.username, self.session)
 
     def msg(self, msg_type, content=None, parent=None, subheader=None):
+        """Return the nested message dict.
+
+        This format is different from what is sent over the wire. The
+        self.serialize method converts this nested message dict to the wire
+        format, which uses a message list.
+        """
         msg = {}
         msg['header'] = self.msg_header(msg_type)
         msg['msg_id'] = msg['header']['msg_id']
         msg['parent_header'] = {} if parent is None else extract_header(parent)
         msg['msg_type'] = msg_type
         msg['content'] = {} if content is None else content
         sub = {} if subheader is None else subheader
         msg['header'].update(sub)
         return msg
 
-    def sign(self, msg):
-        """Sign a message with HMAC digest. If no auth, return b''."""
+    def sign(self, msg_list):
+        """Sign a message with HMAC digest. If no auth, return b''.
+
+        Parameters
+        ----------
+        msg_list : list
+            The [p_header,p_parent,p_content] part of the message list. 
+        """
         if self.auth is None:
             return b''
         h = self.auth.copy()
-        for m in msg:
+        for m in msg_list:
             h.update(m)
         return h.hexdigest()
     
     def serialize(self, msg, ident=None):
         """Serialize the message components to bytes.
-        
+
+        Parameters
+        ----------
+        msg : dict or Message
+            The nexted message dict as returned by the self.msg method.
+
         Returns
         -------
-        
-        list of bytes objects
-        
+        msg_list : list
+            The list of bytes objects to be sent with the format:
+            [ident1,ident2,...,DELIM,HMAC,p_header,p_parent,p_content,
+             buffer1,buffer2,...]. In this list, the p_* entities are
+            the packed or serialized versions, so if JSON is used, these
+            are uft8 encoded JSON strings.
         """
         content = msg.get('content', {})
         if content is None:
             content = self.none
         elif isinstance(content, dict):
             content = self.pack(content)
         elif isinstance(content, bytes):
             # content is already packed, as in a relayed message
             pass
         elif isinstance(content, unicode):
             # should be bytes, but JSON often spits out unicode
             content = content.encode('utf8')
         else:
             raise TypeError("Content incorrect type: %s"%type(content))
         
         real_message = [self.pack(msg['header']), 
                         self.pack(msg['parent_header']), 
                         content
         ]
         
         to_send = []
 
         if isinstance(ident, list):
             # accept list of idents
             to_send.extend(ident)
         elif ident is not None:
             to_send.append(ident)
         to_send.append(DELIM)
         
         signature = self.sign(real_message)
         to_send.append(signature)
         
         to_send.extend(real_message)
 
         return to_send
         
     def send(self, stream, msg_or_type, content=None, parent=None, ident=None, 
                                     buffers=None, subheader=None, track=False):
         """Build and send a message via stream or socket.
-        
+
+        The message format used by this function internally is as follows:
+
+        [ident1,ident2,...,DELIM,HMAC,p_header,p_parent,p_content,
+         buffer1,buffer2,...] 
+
+        The self.serialize method converts the nested message dict into this
+        format.
+
         Parameters
         ----------
         
         stream : zmq.Socket or ZMQStream
             the socket-like object used to send the data
         msg_or_type : str or Message/dict
             Normally, msg_or_type will be a msg_type unless a message is being 
             sent more than once.
         
         content : dict or None
             the content of the message (ignored if msg_or_type is a message)
         parent : Message or dict or None
             the parent or parent header describing the parent of this message
         ident : bytes or list of bytes
             the zmq.IDENTITY routing path
         subheader : dict or None
             extra header keys for this message's header
         buffers : list or None
             the already-serialized buffers to be appended to the message
         track : bool
             whether to track.  Only for use with Sockets, 
             because ZMQStream objects cannot track messages.
         
         Returns
         -------
         msg : message dict
             the constructed message
         (msg,tracker) : (message dict, MessageTracker)
             if track=True, then a 2-tuple will be returned, 
             the first element being the constructed
             message, and the second being the MessageTracker
             
         """
 
         if not isinstance(stream, (zmq.Socket, ZMQStream)):
             raise TypeError("stream must be Socket or ZMQStream, not %r"%type(stream))
         elif track and isinstance(stream, ZMQStream):
             raise TypeError("ZMQStream cannot track messages")
         
         if isinstance(msg_or_type, (Message, dict)):
             # we got a Message, not a msg_type
             # don't build a new Message
             msg = msg_or_type
         else:
             msg = self.msg(msg_or_type, content, parent, subheader)
         
         buffers = [] if buffers is None else buffers
         to_send = self.serialize(msg, ident)
         flag = 0
         if buffers:
             flag = zmq.SNDMORE
             _track = False
         else:
             _track=track
         if track:
             tracker = stream.send_multipart(to_send, flag, copy=False, track=_track)
         else:
             tracker = stream.send_multipart(to_send, flag, copy=False)
         for b in buffers[:-1]:
             stream.send(b, flag, copy=False)
         if buffers:
             if track:
                 tracker = stream.send(buffers[-1], copy=False, track=track)
             else:
                 tracker = stream.send(buffers[-1], copy=False)
-                
+
         # omsg = Message(msg)
         if self.debug:
             pprint.pprint(msg)
             pprint.pprint(to_send)
             pprint.pprint(buffers)
         
         msg['tracker'] = tracker
         
         return msg
     
-    def send_raw(self, stream, msg, flags=0, copy=True, ident=None):
+    def send_raw(self, stream, msg_list, flags=0, copy=True, ident=None):
         """Send a raw message via ident path.
-        
+
+        This method is used to send a already serialized message.
+
         Parameters
         ----------
-        msg : list of sendable buffers"""
+        stream : ZMQStream or Socket
+            The ZMQ stream or socket to use for sending the message.
+        msg_list : list
+            The serialized list of messages to send. This only includes the
+            [p_header,p_parent,p_content,buffer1,buffer2,...] portion of
+            the message.
+        ident : ident or list
+            A single ident or a list of idents to use in sending.
+        """
         to_send = []
         if isinstance(ident, bytes):
             ident = [ident]
         if ident is not None:
             to_send.extend(ident)
             
         to_send.append(DELIM)
-        to_send.append(self.sign(msg))
-        to_send.extend(msg)
-        stream.send_multipart(msg, flags, copy=copy)
+        to_send.append(self.sign(msg_list))
+        to_send.extend(msg_list)
+        stream.send_multipart(msg_list, flags, copy=copy)
     
     def recv(self, socket, mode=zmq.NOBLOCK, content=True, copy=True):
-        """receives and unpacks a message
-        returns [idents], msg"""
+        """Receive and unpack a message.
+
+        Parameters
+        ----------
+        socket : ZMQStream or Socket
+            The socket or stream to use in receiving.
+
+        Returns
+        -------
+        [idents], msg
+            [idents] is a list of idents and msg is a nested message dict of
+            same format as self.msg returns.
+        """
         if isinstance(socket, ZMQStream):
             socket = socket.socket
         try:
-            msg = socket.recv_multipart(mode)
+            msg_list = socket.recv_multipart(mode)
         except zmq.ZMQError as e:
             if e.errno == zmq.EAGAIN:
                 # We can convert EAGAIN to None as we know in this case
                 # recv_multipart won't return None.
                 return None,None
             else:
                 raise
         # split multipart message into identity list and message dict
         # invalid large messages can cause very expensive string comparisons
-        idents, msg = self.feed_identities(msg, copy)
+        idents, msg_list = self.feed_identities(msg_list, copy)
         try:
-            return idents, self.unpack_message(msg, content=content, copy=copy)
+            return idents, self.unpack_message(msg_list, content=content, copy=copy)
         except Exception as e:
-            print (idents, msg)
+            print (idents, msg_list)
             # TODO: handle it
             raise e
     
-    def feed_identities(self, msg, copy=True):
-        """feed until DELIM is reached, then return the prefix as idents and
-        remainder as msg. This is easily broken by setting an IDENT to DELIM,
+    def feed_identities(self, msg_list, copy=True):
+        """Split the identities from the rest of the message.
+
+        Feed until DELIM is reached, then return the prefix as idents and
+        remainder as msg_list. This is easily broken by setting an IDENT to DELIM,
         but that would be silly.
         
         Parameters
         ----------
-        msg : a list of Message or bytes objects
-            the message to be split
+        msg_list : a list of Message or bytes objects
+            The message to be split.
         copy : bool
             flag determining whether the arguments are bytes or Messages
         
         Returns
         -------
-        (idents,msg) : two lists
+        (idents,msg_list) : two lists
             idents will always be a list of bytes - the indentity prefix
-            msg will be a list of bytes or Messages, unchanged from input
-            msg should be unpackable via self.unpack_message at this point.
+            msg_list will be a list of bytes or Messages, unchanged from input
+            msg_list should be unpackable via self.unpack_message at this point.
         """
         if copy:
-            idx = msg.index(DELIM)
-            return msg[:idx], msg[idx+1:]
+            idx = msg_list.index(DELIM)
+            return msg_list[:idx], msg_list[idx+1:]
         else:
             failed = True
-            for idx,m in enumerate(msg):
+            for idx,m in enumerate(msg_list):
                 if m.bytes == DELIM:
                     failed = False
                     break
             if failed:
-                raise ValueError("DELIM not in msg")
-            idents, msg = msg[:idx], msg[idx+1:]
-            return [m.bytes for m in idents], msg
+                raise ValueError("DELIM not in msg_list")
+            idents, msg_list = msg_list[:idx], msg_list[idx+1:]
+            return [m.bytes for m in idents], msg_list
     
-    def unpack_message(self, msg, content=True, copy=True):
+    def unpack_message(self, msg_list, content=True, copy=True):
         """Return a message object from the format
         sent by self.send.
         
         Parameters:
         -----------
         
         content : bool (True)
             whether to unpack the content dict (True), 
             or leave it serialized (False)
         
         copy : bool (True)
             whether to return the bytes (True), 
             or the non-copying Message object in each place (False)
         
         """
         minlen = 4
         message = {}
         if not copy:
             for i in range(minlen):
-                msg[i] = msg[i].bytes
+                msg_list[i] = msg_list[i].bytes
         if self.auth is not None:
-            signature = msg[0]
+            signature = msg_list[0]
             if signature in self.digest_history:
                 raise ValueError("Duplicate Signature: %r"%signature)
             self.digest_history.add(signature)
-            check = self.sign(msg[1:4])
+            check = self.sign(msg_list[1:4])
             if not signature == check:
                 raise ValueError("Invalid Signature: %r"%signature)
-        if not len(msg) >= minlen:
+        if not len(msg_list) >= minlen:
             raise TypeError("malformed message, must have at least %i elements"%minlen)
-        message['header'] = self.unpack(msg[1])
+        message['header'] = self.unpack(msg_list[1])
         message['msg_type'] = message['header']['msg_type']
-        message['parent_header'] = self.unpack(msg[2])
+        message['parent_header'] = self.unpack(msg_list[2])
         if content:
-            message['content'] = self.unpack(msg[3])
+            message['content'] = self.unpack(msg_list[3])
         else:
-            message['content'] = msg[3]
+            message['content'] = msg_list[3]
         
-        message['buffers'] = msg[4:]
+        message['buffers'] = msg_list[4:]
         return message
 
 def test_msg2obj():
     am = dict(x=1)
     ao = Message(am)
     assert ao.x == am['x']
 
     am['y'] = dict(z=1)
     ao = Message(am)
     assert ao.y.z == am['y']['z']
     
     k1, k2 = 'y', 'z'
     assert ao[k1][k2] == am[k1][k2]
     
     am2 = dict(ao)
     assert am['x'] == am2['x']
     assert am['y']['z'] == am2['y']['z']