Date is properly removed from JSON reply before WebSocket forward.

* Both the header and parent_header have a date field that cannot
  be json serialized. This field is just removed for now, but
  in the future, we will covert the date to a ISO8601 field.
* Better error handling around this code has also been added
  to prevent the server from crashing due to malformed messages.

IPython/frontend/html/notebook/handlers.py

@@ -101,10 +101,25 b' class ZMQStreamHandler(websocket.WebSocketHandler):'
         """
         idents, msg_list = self.session.feed_identities(msg_list)
         msg = self.session.unserialize(msg_list)
-        msg['header'].pop('date')
+        try:
+            msg['header'].pop('date')
+        except KeyError:
+            pass
+        try:
+            msg['parent_header'].pop('date')
+        except KeyError:
+            pass
         msg.pop('buffers')
         return jsonapi.dumps(msg)
 
+    def _on_zmq_reply(self, msg_list):
+        try:
+            msg = self._reserialize_reply(msg_list)
+        except:
+            self.application.kernel_manager.log.critical("Malformed message: %r" % msg_list)
+        else:
+            self.write_message(msg)
+
 
 class IOPubHandler(ZMQStreamHandler):
 
@@ -122,10 +137,6 b' class IOPubHandler(ZMQStreamHandler):'
         self.iopub_stream.on_recv(self._on_zmq_reply)
         self.start_hb(self.kernel_died)
 
-    def _on_zmq_reply(self, msg_list):
-        msg = self._reserialize_reply(msg_list)
-        self.write_message(msg)
-
     def on_close(self):
         self.stop_hb()
         self.iopub_stream.close()
@@ -186,10 +197,6 b' class ShellHandler(ZMQStreamHandler):'
         self.shell_stream = self.application.kernel_manager.create_shell_stream(kernel_id)
         self.shell_stream.on_recv(self._on_zmq_reply)
 
-    def _on_zmq_reply(self, msg_list):
-        msg = self._reserialize_reply(msg_list)
-        self.write_message(msg)
-
     def on_message(self, msg):
         if len(msg) < self.max_msg_size:
             msg = jsonapi.loads(msg)