split serialize step of Session.send into separate method

This allows other objects to call it, and build serialized messages without sending.

IPython/parallel/streamsession.py

@@ -176,6 +176,34 b' class StreamSession(object):'
         header = extract_header(msg_or_header)
         return header.get('key', None) == self.key
             
+
+    def serialize(self, msg, ident=None):
+        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
+        else:
+            raise TypeError("Content incorrect type: %s"%type(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)
+        if self.key is not None:
+            to_send.append(self.key)
+        to_send.append(self.pack(msg['header']))
+        to_send.append(self.pack(msg['parent_header']))
+        to_send.append(content)
+
+        return to_send
         
     def send(self, stream, msg_or_type, content=None, buffers=None, parent=None, subheader=None, ident=None, track=False):
         """Build and send a message via stream or socket.
@@ -221,33 +249,11 b' class StreamSession(object):'
             # we got a Message, not a msg_type
             # don't build a new Message
             msg = msg_or_type
-            content = msg['content']
         else:
             msg = self.msg(msg_or_type, content, parent, subheader)
         
         buffers = [] if buffers is None else buffers
-        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)
-        if self.key is not None:
-            to_send.append(self.key)
-        to_send.append(self.pack(msg['header']))
-        to_send.append(self.pack(msg['parent_header']))
-        
-        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
-        else:
-            raise TypeError("Content incorrect type: %s"%type(content))
-        to_send.append(content)
+        to_send = self.serialize(msg, ident)
         flag = 0
         if buffers:
             flag = zmq.SNDMORE