remove on_first_message authentication

in ZMQStreams. No need for weird, special first message.

- use regular cookie auth
- use url param for session id

IPython/html/base/zmqhandlers.py

@@ -1,214 +1,202 b''
 """Tornado handlers for WebSocket <-> ZMQ sockets."""
 
 # Copyright (c) IPython Development Team.
 # Distributed under the terms of the Modified BSD License.
 
 import json
 
 try:
     from urllib.parse import urlparse # Py 3
 except ImportError:
     from urlparse import urlparse # Py 2
 
 try:
     from http.cookies import SimpleCookie  # Py 3
 except ImportError:
     from Cookie import SimpleCookie  # Py 2
 import logging
 
 import tornado
 from tornado import ioloop
 from tornado import web
 from tornado import websocket
 
 from IPython.kernel.zmq.session import Session
 from IPython.utils.jsonutil import date_default
 from IPython.utils.py3compat import PY3, cast_unicode
 
 from .handlers import IPythonHandler
 
 
 class ZMQStreamHandler(websocket.WebSocketHandler):
     
     def check_origin(self, origin):
         """Check Origin == Host or Access-Control-Allow-Origin.
         
         Tornado >= 4 calls this method automatically, raising 403 if it returns False.
         We call it explicitly in `open` on Tornado < 4.
         """
         if self.allow_origin == '*':
             return True
 
         host = self.request.headers.get("Host")
 
         # If no header is provided, assume we can't verify origin
         if origin is None:
             self.log.warn("Missing Origin header, rejecting WebSocket connection.")
             return False
         if host is None:
             self.log.warn("Missing Host header, rejecting WebSocket connection.")
             return False
         
         origin = origin.lower()
         origin_host = urlparse(origin).netloc
         
         # OK if origin matches host
         if origin_host == host:
             return True
         
         # Check CORS headers
         if self.allow_origin:
             allow = self.allow_origin == origin
         elif self.allow_origin_pat:
             allow = bool(self.allow_origin_pat.match(origin))
         else:
             # No CORS headers deny the request
             allow = False
         if not allow:
             self.log.warn("Blocking Cross Origin WebSocket Attempt.  Origin: %s, Host: %s",
                 origin, host,
             )
         return allow
 
     def clear_cookie(self, *args, **kwargs):
         """meaningless for websockets"""
         pass
 
     def _reserialize_reply(self, msg_list):
         """Reserialize a reply message using JSON.
 
         This takes the msg list from the ZMQ socket, unserializes it using
         self.session and then serializes the result using JSON. This method
         should be used by self._on_zmq_reply to build messages that can
         be sent back to the browser.
         """
         idents, msg_list = self.session.feed_identities(msg_list)
         msg = self.session.unserialize(msg_list)
         try:
             msg['header'].pop('date')
         except KeyError:
             pass
         try:
             msg['parent_header'].pop('date')
         except KeyError:
             pass
         msg.pop('buffers')
         return json.dumps(msg, default=date_default)
 
     def _on_zmq_reply(self, msg_list):
         # Sometimes this gets triggered when the on_close method is scheduled in the
         # eventloop but hasn't been called.
         if self.stream.closed(): return
         try:
             msg = self._reserialize_reply(msg_list)
         except Exception:
             self.log.critical("Malformed message: %r" % msg_list, exc_info=True)
         else:
             self.write_message(msg)
 
     def allow_draft76(self):
         """Allow draft 76, until browsers such as Safari update to RFC 6455.
         
         This has been disabled by default in tornado in release 2.2.0, and
         support will be removed in later versions.
         """
         return True
 
 # ping interval for keeping websockets alive (30 seconds)
 WS_PING_INTERVAL = 30000
 
 class AuthenticatedZMQStreamHandler(ZMQStreamHandler, IPythonHandler):
     ping_callback = None
     last_ping = 0
     last_pong = 0
     
     @property
     def ping_interval(self):
         """The interval for websocket keep-alive pings.
         
         Set ws_ping_interval = 0 to disable pings.
         """
         return self.settings.get('ws_ping_interval', WS_PING_INTERVAL)
     
     @property
     def ping_timeout(self):
         """If no ping is received in this many milliseconds,
         close the websocket connection (VPNs, etc. can fail to cleanly close ws connections).
         Default is max of 3 pings or 30 seconds.
         """
         return self.settings.get('ws_ping_timeout',
             max(3 * self.ping_interval, WS_PING_INTERVAL)
         )
 
     def set_default_headers(self):
         """Undo the set_default_headers in IPythonHandler
         
         which doesn't make sense for websockets
         """
         pass
 
-    def open(self, kernel_id):
-        self.kernel_id = cast_unicode(kernel_id, 'ascii')
+    def get(self, *args, **kwargs):
         # Check to see that origin matches host directly, including ports
         # Tornado 4 already does CORS checking
         if tornado.version_info[0] < 4:
             if not self.check_origin(self.get_origin()):
                 raise web.HTTPError(403)
 
+        # authenticate the request before opening the websocket
+        if self.get_current_user() is None:
+            self.log.warn("Couldn't authenticate WebSocket connection")
+            raise web.HTTPError(403)
+        
+        if self.get_argument('session_id'):
+            self.session.session = cast_unicode(self.get_argument('session_id'))
+        else:
+            self.log.warn("No session ID specified")
+        
+        return super(AuthenticatedZMQStreamHandler, self).get(*args, **kwargs)
+    
+    def initialize(self):
         self.session = Session(config=self.config)
-        self.save_on_message = self.on_message
-        self.on_message = self.on_first_message
+    
+    def open(self, kernel_id):
+        self.kernel_id = cast_unicode(kernel_id, 'ascii')
         
         # start the pinging
         if self.ping_interval > 0:
             self.last_ping = ioloop.IOLoop.instance().time()  # Remember time of last ping
             self.last_pong = self.last_ping
             self.ping_callback = ioloop.PeriodicCallback(self.send_ping, self.ping_interval)
             self.ping_callback.start()
 
     def send_ping(self):
         """send a ping to keep the websocket alive"""
         if self.stream.closed() and self.ping_callback is not None:
             self.ping_callback.stop()
             return
         
         # check for timeout on pong.  Make sure that we really have sent a recent ping in
         # case the machine with both server and client has been suspended since the last ping.
         now = ioloop.IOLoop.instance().time()
         since_last_pong = 1e3 * (now - self.last_pong)
         since_last_ping = 1e3 * (now - self.last_ping)
         if since_last_ping < 2*self.ping_interval and since_last_pong > self.ping_timeout:
             self.log.warn("WebSocket ping timeout after %i ms.", since_last_pong)
             self.close()
             return
 
         self.ping(b'')
         self.last_ping = now
 
     def on_pong(self, data):
         self.last_pong = ioloop.IOLoop.instance().time()
-
-    def _inject_cookie_message(self, msg):
-        """Inject the first message, which is the document cookie,
-        for authentication."""
-        if not PY3 and isinstance(msg, unicode):
-            # Cookie constructor doesn't accept unicode strings
-            # under Python 2.x for some reason
-            msg = msg.encode('utf8', 'replace')
-        try:
-            identity, msg = msg.split(':', 1)
-            self.session.session = cast_unicode(identity, 'ascii')
-        except Exception:
-            logging.error("First ws message didn't have the form 'identity:[cookie]' - %r", msg)
-        
-        try:
-            self.request._cookies = SimpleCookie(msg)
-        except:
-            self.log.warn("couldn't parse cookie string: %s",msg, exc_info=True)
-
-    def on_first_message(self, msg):
-        self._inject_cookie_message(msg)
-        if self.get_current_user() is None:
-            self.log.warn("Couldn't authenticate WebSocket connection")
-            raise web.HTTPError(403)
-        self.on_message = self.save_on_message

IPython/html/services/kernels/handlers.py

@@ -1,234 +1,230 b''
 """Tornado handlers for kernels."""
 
 # Copyright (c) IPython Development Team.
 # Distributed under the terms of the Modified BSD License.
 
 import json
 import logging
 from tornado import web
 
 from IPython.utils.jsonutil import date_default
 from IPython.utils.py3compat import string_types
 from IPython.html.utils import url_path_join, url_escape
 
 from ...base.handlers import IPythonHandler, json_errors
 from ...base.zmqhandlers import AuthenticatedZMQStreamHandler
 
 from IPython.core.release import kernel_protocol_version
 
 class MainKernelHandler(IPythonHandler):
 
     @web.authenticated
     @json_errors
     def get(self):
         km = self.kernel_manager
         self.finish(json.dumps(km.list_kernels()))
 
     @web.authenticated
     @json_errors
     def post(self):
         model = self.get_json_body()
         if model is None:
             raise web.HTTPError(400, "No JSON data provided")
         try:
             name = model['name']
         except KeyError:
             raise web.HTTPError(400, "Missing field in JSON data: name")
 
         km = self.kernel_manager
         kernel_id = km.start_kernel(kernel_name=name)
         model = km.kernel_model(kernel_id)
         location = url_path_join(self.base_url, 'api', 'kernels', kernel_id)
         self.set_header('Location', url_escape(location))
         self.set_status(201)
         self.finish(json.dumps(model))
 
 
 class KernelHandler(IPythonHandler):
 
     SUPPORTED_METHODS = ('DELETE', 'GET')
 
     @web.authenticated
     @json_errors
     def get(self, kernel_id):
         km = self.kernel_manager
         km._check_kernel_id(kernel_id)
         model = km.kernel_model(kernel_id)
         self.finish(json.dumps(model))
 
     @web.authenticated
     @json_errors
     def delete(self, kernel_id):
         km = self.kernel_manager
         km.shutdown_kernel(kernel_id)
         self.set_status(204)
         self.finish()
 
 
 class KernelActionHandler(IPythonHandler):
 
     @web.authenticated
     @json_errors
     def post(self, kernel_id, action):
         km = self.kernel_manager
         if action == 'interrupt':
             km.interrupt_kernel(kernel_id)
             self.set_status(204)
         if action == 'restart':
             km.restart_kernel(kernel_id)
             model = km.kernel_model(kernel_id)
             self.set_header('Location', '{0}api/kernels/{1}'.format(self.base_url, kernel_id))
             self.write(json.dumps(model))
         self.finish()
 
 
 class ZMQChannelHandler(AuthenticatedZMQStreamHandler):
     
     def __repr__(self):
         return "%s(%s)" % (self.__class__.__name__, getattr(self, 'kernel_id', 'uninitialized'))
     
     def create_stream(self):
         km = self.kernel_manager
         meth = getattr(km, 'connect_%s' % self.channel)
         self.zmq_stream = meth(self.kernel_id, identity=self.session.bsession)
         # Create a kernel_info channel to query the kernel protocol version.
         # This channel will be closed after the kernel_info reply is received.
         self.kernel_info_channel = None
         self.kernel_info_channel = km.connect_shell(self.kernel_id)
         self.kernel_info_channel.on_recv(self._handle_kernel_info_reply)
         self._request_kernel_info()
     
     def _request_kernel_info(self):
         """send a request for kernel_info"""
         self.log.debug("requesting kernel info")
         self.session.send(self.kernel_info_channel, "kernel_info_request")
     
     def _handle_kernel_info_reply(self, msg):
         """process the kernel_info_reply
         
         enabling msg spec adaptation, if necessary
         """
         idents,msg = self.session.feed_identities(msg)
         try:
             msg = self.session.unserialize(msg)
         except:
             self.log.error("Bad kernel_info reply", exc_info=True)
             self._request_kernel_info()
             return
         else:
             if msg['msg_type'] != 'kernel_info_reply' or 'protocol_version' not in msg['content']:
                 self.log.error("Kernel info request failed, assuming current %s", msg['content'])
             else:
                 protocol_version = msg['content']['protocol_version']
                 if protocol_version != kernel_protocol_version:
                     self.session.adapt_version = int(protocol_version.split('.')[0])
                     self.log.info("adapting kernel to %s" % protocol_version)
         self.kernel_info_channel.close()
         self.kernel_info_channel = None
     
-    
-    def initialize(self, *args, **kwargs):
+    def initialize(self):
+        super(ZMQChannelHandler, self).initialize()
         self.zmq_stream = None
     
-    def on_first_message(self, msg):
-        try:
-            super(ZMQChannelHandler, self).on_first_message(msg)
-        except web.HTTPError:
-            self.close()
-            return
+    def open(self, kernel_id):
+        super(ZMQChannelHandler, self).open(kernel_id)
         try:
             self.create_stream()
         except web.HTTPError:
             # WebSockets don't response to traditional error codes so we
             # close the connection.
             if not self.stream.closed():
                 self.stream.close()
             self.close()
         else:
             self.zmq_stream.on_recv(self._on_zmq_reply)
 
     def on_message(self, msg):
         if self.zmq_stream is None:
             return
         elif self.zmq_stream.closed():
             self.log.info("%s closed, closing websocket.", self)
             self.close()
             return
         msg = json.loads(msg)
         self.session.send(self.zmq_stream, msg)
 
     def on_close(self):
         # This method can be called twice, once by self.kernel_died and once
         # from the WebSocket close event. If the WebSocket connection is
         # closed before the ZMQ streams are setup, they could be None.
         if self.zmq_stream is not None and not self.zmq_stream.closed():
             self.zmq_stream.on_recv(None)
             # close the socket directly, don't wait for the stream
             socket = self.zmq_stream.socket
             self.zmq_stream.close()
             socket.close()
 
 
 class IOPubHandler(ZMQChannelHandler):
     channel = 'iopub'
     
     def create_stream(self):
         super(IOPubHandler, self).create_stream()
         km = self.kernel_manager
         km.add_restart_callback(self.kernel_id, self.on_kernel_restarted)
         km.add_restart_callback(self.kernel_id, self.on_restart_failed, 'dead')
     
     def on_close(self):
         km = self.kernel_manager
         if self.kernel_id in km:
             km.remove_restart_callback(
                 self.kernel_id, self.on_kernel_restarted,
             )
             km.remove_restart_callback(
                 self.kernel_id, self.on_restart_failed, 'dead',
             )
         super(IOPubHandler, self).on_close()
     
     def _send_status_message(self, status):
         msg = self.session.msg("status",
             {'execution_state': status}
         )
         self.write_message(json.dumps(msg, default=date_default))
 
     def on_kernel_restarted(self):
         logging.warn("kernel %s restarted", self.kernel_id)
         self._send_status_message('restarting')
 
     def on_restart_failed(self):
         logging.error("kernel %s restarted failed!", self.kernel_id)
         self._send_status_message('dead')
     
     def on_message(self, msg):
         """IOPub messages make no sense"""
         pass
 
 
 class ShellHandler(ZMQChannelHandler):
     channel = 'shell'
 
 
 class StdinHandler(ZMQChannelHandler):
     channel = 'stdin'
 
 
 #-----------------------------------------------------------------------------
 # URL to handler mappings
 #-----------------------------------------------------------------------------
 
 
 _kernel_id_regex = r"(?P<kernel_id>\w+-\w+-\w+-\w+-\w+)"
 _kernel_action_regex = r"(?P<action>restart|interrupt)"
 
 default_handlers = [
     (r"/api/kernels", MainKernelHandler),
     (r"/api/kernels/%s" % _kernel_id_regex, KernelHandler),
     (r"/api/kernels/%s/%s" % (_kernel_id_regex, _kernel_action_regex), KernelActionHandler),
     (r"/api/kernels/%s/iopub" % _kernel_id_regex, IOPubHandler),
     (r"/api/kernels/%s/shell" % _kernel_id_regex, ShellHandler),
     (r"/api/kernels/%s/stdin" % _kernel_id_regex, StdinHandler)
 ]

IPython/html/static/services/kernels/js/kernel.js

@@ -1,1017 +1,1014 b''
 // Copyright (c) IPython Development Team.
 // Distributed under the terms of the Modified BSD License.
 
 define([
     'base/js/namespace',
     'jquery',
     'base/js/utils',
     'services/kernels/js/comm',
     'widgets/js/init',
 ], function(IPython, $, utils, comm, widgetmanager) {
     "use strict";
 
     /**
      * A Kernel class to communicate with the Python kernel. This
      * should generally not be constructed directly, but be created
      * by.  the `Session` object. Once created, this object should be
      * used to communicate with the kernel.
      * 
      * @class Kernel
      * @param {string} kernel_service_url - the URL to access the kernel REST api
      * @param {string} ws_url - the websockets URL
      * @param {Notebook} notebook - notebook object
      * @param {string} name - the kernel type (e.g. python3)
      */
     var Kernel = function (kernel_service_url, ws_url, notebook, name) {
         this.events = notebook.events;
 
         this.id = null;
         this.name = name;
 
         this.channels = {
             'shell': null,
             'iopub': null,
             'stdin': null
         };
 
         this.kernel_service_url = kernel_service_url;
         this.kernel_url = null;
         this.ws_url = ws_url || IPython.utils.get_body_data("wsUrl");
         if (!this.ws_url) {
             // trailing 's' in https will become wss for secure web sockets
             this.ws_url = location.protocol.replace('http', 'ws') + "//" + location.host;
         }
 
         this.username = "username";
         this.session_id = utils.uuid();
         this._msg_callbacks = {};
 
         if (typeof(WebSocket) !== 'undefined') {
             this.WebSocket = WebSocket;
         } else if (typeof(MozWebSocket) !== 'undefined') {
             this.WebSocket = MozWebSocket;
         } else {
             alert('Your browser does not have WebSocket support, please try Chrome, Safari or Firefox ≥ 6. Firefox 4 and 5 are also supported by you have to enable WebSockets in about:config.');
         }
         
         this.bind_events();
         this.init_iopub_handlers();
         this.comm_manager = new comm.CommManager(this);
         this.widget_manager = new widgetmanager.WidgetManager(this.comm_manager, notebook);
         
         this.last_msg_id = null;
         this.last_msg_callbacks = {};
 
         this._autorestart_attempt = 0;
         this._reconnect_attempt = 0;
     };
 
     /**
      * @function _get_msg
      */
     Kernel.prototype._get_msg = function (msg_type, content, metadata) {
         var msg = {
             header : {
                 msg_id : utils.uuid(),
                 username : this.username,
                 session : this.session_id,
                 msg_type : msg_type,
                 version : "5.0"
             },
             metadata : metadata || {},
             content : content,
             parent_header : {}
         };
         return msg;
     };
 
     /**
      * @function bind_events
      */
     Kernel.prototype.bind_events = function () {
         var that = this;
         this.events.on('send_input_reply.Kernel', function(evt, data) { 
             that.send_input_reply(data);
         });
 
         var record_status = function (evt, info) {
             console.log('Kernel: ' + evt.type + ' (' + info.kernel.id + ')');
         };
 
         this.events.on('kernel_created.Kernel', record_status);
         this.events.on('kernel_reconnecting.Kernel', record_status);
         this.events.on('kernel_connected.Kernel', record_status);
         this.events.on('kernel_starting.Kernel', record_status);
         this.events.on('kernel_restarting.Kernel', record_status);
         this.events.on('kernel_autorestarting.Kernel', record_status);
         this.events.on('kernel_interrupting.Kernel', record_status);
         this.events.on('kernel_disconnected.Kernel', record_status);
         // these are commented out because they are triggered a lot, but can
         // be uncommented for debugging purposes
         //this.events.on('kernel_idle.Kernel', record_status);
         //this.events.on('kernel_busy.Kernel', record_status);
         this.events.on('kernel_ready.Kernel', record_status);
         this.events.on('kernel_killed.Kernel', record_status);
         this.events.on('kernel_dead.Kernel', record_status);
 
         this.events.on('kernel_ready.Kernel', function () {
             that._autorestart_attempt = 0;
         });
         this.events.on('kernel_connected.Kernel', function () {
             that._reconnect_attempt = 0;
         });
     };
 
     /**
      * Initialize the iopub handlers.
      *
      * @function init_iopub_handlers
      */
     Kernel.prototype.init_iopub_handlers = function () {
         var output_msg_types = ['stream', 'display_data', 'execute_result', 'error'];
         this._iopub_handlers = {};
         this.register_iopub_handler('status', $.proxy(this._handle_status_message, this));
         this.register_iopub_handler('clear_output', $.proxy(this._handle_clear_output, this));
         
         for (var i=0; i < output_msg_types.length; i++) {
             this.register_iopub_handler(output_msg_types[i], $.proxy(this._handle_output_message, this));
         }
     };
 
     /**
      * GET /api/kernels
      *
      * Get the list of running kernels.
      *
      * @function list
      * @param {function} [success] - function executed on ajax success
      * @param {function} [error] - functon executed on ajax error
      */
     Kernel.prototype.list = function (success, error) {
         $.ajax(this.kernel_service_url, {
             processData: false,
             cache: false,
             type: "GET",
             dataType: "json",
             success: success,
             error: this._on_error(error)
         });
     };
 
     /**
      * POST /api/kernels
      *
      * Start a new kernel.
      *
      * In general this shouldn't be used -- the kernel should be
      * started through the session API. If you use this function and
      * are also using the session API then your session and kernel
      * WILL be out of sync!
      *
      * @function start
      * @param {params} [Object] - parameters to include in the query string
      * @param {function} [success] - function executed on ajax success
      * @param {function} [error] - functon executed on ajax error
      */
     Kernel.prototype.start = function (params, success, error) {
         var url = this.kernel_service_url;
         var qs = $.param(params || {}); // query string for sage math stuff
         if (qs !== "") {
             url = url + "?" + qs;
         }
 
         var that = this;
         var on_success = function (data, status, xhr) {
             that.events.trigger('kernel_created.Kernel', {kernel: that});
             that._kernel_created(data);
             if (success) {
                 success(data, status, xhr);
             }
         };
 
         $.ajax(url, {
             processData: false,
             cache: false,
             type: "POST",
             data: JSON.stringify({name: this.name}),
             dataType: "json",
             success: this._on_success(on_success),
             error: this._on_error(error)
         });
 
         return url;
     };
 
     /**
      * GET /api/kernels/[:kernel_id]
      *
      * Get information about the kernel.
      *
      * @function get_info
      * @param {function} [success] - function executed on ajax success
      * @param {function} [error] - functon executed on ajax error
      */
     Kernel.prototype.get_info = function (success, error) {
         $.ajax(this.kernel_url, {
             processData: false,
             cache: false,
             type: "GET",
             dataType: "json",
             success: this._on_success(success),
             error: this._on_error(error)
         });
     };
 
     /**
      * DELETE /api/kernels/[:kernel_id]
      *
      * Shutdown the kernel.
      *
      * If you are also using sessions, then this function shoul NOT be
      * used. Instead, use Session.delete. Otherwise, the session and
      * kernel WILL be out of sync.
      *
      * @function kill
      * @param {function} [success] - function executed on ajax success
      * @param {function} [error] - functon executed on ajax error
      */
     Kernel.prototype.kill = function (success, error) {
         this.events.trigger('kernel_killed.Kernel', {kernel: this});
         this._kernel_dead();
         $.ajax(this.kernel_url, {
             processData: false,
             cache: false,
             type: "DELETE",
             dataType: "json",
             success: this._on_success(success),
             error: this._on_error(error)
         });
     };
 
     /**
      * POST /api/kernels/[:kernel_id]/interrupt
      *
      * Interrupt the kernel.
      *
      * @function interrupt
      * @param {function} [success] - function executed on ajax success
      * @param {function} [error] - functon executed on ajax error
      */
     Kernel.prototype.interrupt = function (success, error) {
         this.events.trigger('kernel_interrupting.Kernel', {kernel: this});
 
         var that = this;
         var on_success = function (data, status, xhr) {
             // get kernel info so we know what state the kernel is in
             that.kernel_info();
             if (success) {
                 success(data, status, xhr);
             }
         };
 
         var url = utils.url_join_encode(this.kernel_url, 'interrupt');
         $.ajax(url, {
             processData: false,
             cache: false,
             type: "POST",
             dataType: "json",
             success: this._on_success(on_success),
             error: this._on_error(error)
         });
     };
 
     /**
      * POST /api/kernels/[:kernel_id]/restart
      *
      * Restart the kernel.
      *
      * @function interrupt
      * @param {function} [success] - function executed on ajax success
      * @param {function} [error] - functon executed on ajax error
      */
     Kernel.prototype.restart = function (success, error) {
         this.events.trigger('kernel_restarting.Kernel', {kernel: this});
         this.stop_channels();
 
         var that = this;
         var on_success = function (data, status, xhr) {
             that.events.trigger('kernel_created.Kernel', {kernel: that});
             that._kernel_created(data);
             if (success) {
                 success(data, status, xhr);
             }
         };
 
         var on_error = function (xhr, status, err) {
             that.events.trigger('kernel_dead.Kernel', {kernel: that});
             that._kernel_dead();
             if (error) {
                 error(xhr, status, err);
             }
         };
 
         var url = utils.url_join_encode(this.kernel_url, 'restart');
         $.ajax(url, {
             processData: false,
             cache: false,
             type: "POST",
             dataType: "json",
             success: this._on_success(on_success),
             error: this._on_error(on_error)
         });
     };
 
     /**
      * Reconnect to a disconnected kernel. This is not actually a
      * standard HTTP request, but useful function nonetheless for
      * reconnecting to the kernel if the connection is somehow lost.
      *
      * @function reconnect
      */
     Kernel.prototype.reconnect = function () {
         this.events.trigger('kernel_reconnecting.Kernel', {kernel: this});
         setTimeout($.proxy(this.start_channels, this), 3000);
     };
 
     /**
      * Handle a successful AJAX request by updating the kernel id and
      * name from the response, and then optionally calling a provided
      * callback.
      *
      * @function _on_success
      * @param {function} success - callback
      */
     Kernel.prototype._on_success = function (success) {
         var that = this;
         return function (data, status, xhr) {
             if (data) {
                 that.id = data.id;
                 that.name = data.name;
             }
             that.kernel_url = utils.url_join_encode(that.kernel_service_url, that.id);
             if (success) {
                 success(data, status, xhr);
             }
         };
     };
 
     /**
      * Handle a failed AJAX request by logging the error message, and
      * then optionally calling a provided callback.
      *
      * @function _on_error
      * @param {function} error - callback
      */
     Kernel.prototype._on_error = function (error) {
         return function (xhr, status, err) {
             utils.log_ajax_error(xhr, status, err);
             if (error) {
                 error(xhr, status, err);
             }
         };
     };
 
     /**
      * Perform necessary tasks once the kernel has been started,
      * including actually connecting to the kernel.
      *
      * @function _kernel_created
      * @param {Object} data - information about the kernel including id
      */
     Kernel.prototype._kernel_created = function (data) {
         this.id = data.id;
         this.kernel_url = utils.url_join_encode(this.kernel_service_url, this.id);
         this.start_channels();
     };
 
     /**
      * Perform necessary tasks once the connection to the kernel has
      * been established. This includes requesting information about
      * the kernel.
      *
      * @function _kernel_connected
      */
     Kernel.prototype._kernel_connected = function () {
         this.events.trigger('kernel_connected.Kernel', {kernel: this});
         this.events.trigger('kernel_starting.Kernel', {kernel: this});
         // get kernel info so we know what state the kernel is in
         var that = this;
         this.kernel_info(function () {
             that.events.trigger('kernel_ready.Kernel', {kernel: that});
         });
     };
 
     /**
      * Perform necessary tasks after the kernel has died. This closing
      * communication channels to the kernel if they are still somehow
      * open.
      *
      * @function _kernel_dead
      */
     Kernel.prototype._kernel_dead = function () {
         this.stop_channels();
     };
 
     /**
      * Start the `shell`and `iopub` channels.
      * Will stop and restart them if they already exist.
      *
      * @function start_channels
      */
     Kernel.prototype.start_channels = function () {
         var that = this;
         this.stop_channels();
         var ws_host_url = this.ws_url + this.kernel_url;
 
         console.log("Starting WebSockets:", ws_host_url);
 
-        this.channels.shell = new this.WebSocket(
-            this.ws_url + utils.url_join_encode(this.kernel_url, "shell")
-        );
-        this.channels.stdin = new this.WebSocket(
-            this.ws_url + utils.url_join_encode(this.kernel_url, "stdin")
-        );
-        this.channels.iopub = new this.WebSocket(
-            this.ws_url + utils.url_join_encode(this.kernel_url, "iopub")
-        );
+        var channel_url = function(channel) {
+            return [
+                that.ws_url,
+                utils.url_join_encode(that.kernel_url, channel),
+                "?session_id=" + that.session_id
+            ].join('');
+        };
+        this.channels.shell = new this.WebSocket(channel_url("shell"));
+        this.channels.stdin = new this.WebSocket(channel_url("stdin"));
+        this.channels.iopub = new this.WebSocket(channel_url("iopub"));
         
         var already_called_onclose = false; // only alert once
         var ws_closed_early = function(evt){
             if (already_called_onclose){
                 return;
             }
             already_called_onclose = true;
             if ( ! evt.wasClean ){
                 // If the websocket was closed early, that could mean
                 // that the kernel is actually dead. Try getting
                 // information about the kernel from the API call --
                 // if that fails, then assume the kernel is dead,
                 // otherwise just follow the typical websocket closed
                 // protocol.
                 that.get_info(function () {
                     that._ws_closed(ws_host_url, false);
                 }, function () {
                     that.events.trigger('kernel_dead.Kernel', {kernel: that});
                     that._kernel_dead();
                 });
             }
         };
         var ws_closed_late = function(evt){
             if (already_called_onclose){
                 return;
             }
             already_called_onclose = true;
             if ( ! evt.wasClean ){
                 that._ws_closed(ws_host_url, false);
             }
         };
         var ws_error = function(evt){
             if (already_called_onclose){
                 return;
             }
             already_called_onclose = true;
             that._ws_closed(ws_host_url, true);
         };
 
         for (var c in this.channels) {
             this.channels[c].onopen = $.proxy(this._ws_opened, this);
             this.channels[c].onclose = ws_closed_early;
             this.channels[c].onerror = ws_error;
         }
         // switch from early-close to late-close message after 1s
         setTimeout(function() {
             for (var c in that.channels) {
                 if (that.channels[c] !== null) {
                     that.channels[c].onclose = ws_closed_late;
                 }
             }
         }, 1000);
         this.channels.shell.onmessage = $.proxy(this._handle_shell_reply, this);
         this.channels.iopub.onmessage = $.proxy(this._handle_iopub_message, this);
         this.channels.stdin.onmessage = $.proxy(this._handle_input_request, this);
     };
 
     /**
-     * Handle a websocket entering the open state sends session and
-     * cookie authentication info as first message.
+     * Handle a websocket entering the open state,
+     * signaling that the kernel is connected when all channels are open.
      *
      * @function _ws_opened
      */
     Kernel.prototype._ws_opened = function (evt) {
-        // send the session id so the Session object Python-side
-        // has the same identity
-        evt.target.send(this.session_id + ':' + document.cookie);
-
         if (this.is_connected()) {
             // all events ready, trigger started event.
             this._kernel_connected();
         }
     };
 
     /**
      * Handle a websocket entering the closed state. This closes the
      * other communication channels if they are open. If the websocket
      * was not closed due to an error, try to reconnect to the kernel.
      *
      * @function _ws_closed
      * @param {string} ws_url - the websocket url
      * @param {bool} error - whether the connection was closed due to an error
      */
     Kernel.prototype._ws_closed = function(ws_url, error) {
         this.stop_channels();
 
         this.events.trigger('kernel_disconnected.Kernel', {kernel: this});
         if (error) {
             console.log('WebSocket connection failed: ', ws_url);
             this._reconnect_attempt = this._reconnect_attempt + 1;
             this.events.trigger('kernel_connection_failed.Kernel', {kernel: this, ws_url: ws_url, attempt: this._reconnect_attempt});
         }
         this.reconnect();
     };
 
     /**
      * Close the websocket channels. After successful close, the value
      * in `this.channels[channel_name]` will be null.
      *
      * @function stop_channels
      */
     Kernel.prototype.stop_channels = function () {
         var that = this;
         var close = function (c) {
             return function () {
                 if (that.channels[c] && that.channels[c].readyState === WebSocket.CLOSED) {
                     that.channels[c] = null;
                 }
             };
         };
         for (var c in this.channels) {
             if ( this.channels[c] !== null ) {
                 if (this.channels[c].readyState === WebSocket.OPEN) {
                     this.channels[c].onclose = close(c);
                     this.channels[c].close();
                 } else {
                     close(c)();
                 }
             }
         }
     };
 
     /**
      * Check whether there is a connection to the kernel. This
      * function only returns true if all channel objects have been
      * created and have a state of WebSocket.OPEN.
      *
      * @function is_connected
      * @returns {bool} - whether there is a connection
      */
     Kernel.prototype.is_connected = function () {
         for (var c in this.channels) {
             // if any channel is not ready, then we're not connected
             if (this.channels[c] === null) {
                 return false;
             }
             if (this.channels[c].readyState !== WebSocket.OPEN) {
                 return false;
             }
         }
         return true;
     };
 
     /**
      * Check whether the connection to the kernel has been completely
      * severed. This function only returns true if all channel objects
      * are null.
      *
      * @function is_fully_disconnected
      * @returns {bool} - whether the kernel is fully disconnected
      */
     Kernel.prototype.is_fully_disconnected = function () {
         for (var c in this.channels) {
             if (this.channels[c] === null) {
                 return true;
             }
         }
         return false;
     };
     
     /**
      * Send a message on the Kernel's shell channel
      *
      * @function send_shell_message
      */
     Kernel.prototype.send_shell_message = function (msg_type, content, callbacks, metadata) {
         if (!this.is_connected()) {
             throw new Error("kernel is not connected");
         }
         var msg = this._get_msg(msg_type, content, metadata);
         this.channels.shell.send(JSON.stringify(msg));
         this.set_callbacks_for_msg(msg.header.msg_id, callbacks);
         return msg.header.msg_id;
     };
 
     /**
      * Get kernel info
      *
      * @function kernel_info
      * @param callback {function}
      *
      * When calling this method, pass a callback function that expects one argument.
      * The callback will be passed the complete `kernel_info_reply` message documented
      * [here](http://ipython.org/ipython-doc/dev/development/messaging.html#kernel-info)
      */
     Kernel.prototype.kernel_info = function (callback) {
         var callbacks;
         if (callback) {
             callbacks = { shell : { reply : callback } };
         }
         return this.send_shell_message("kernel_info_request", {}, callbacks);
     };
 
     /**
      * Get info on an object
      *
      * When calling this method, pass a callback function that expects one argument.
      * The callback will be passed the complete `inspect_reply` message documented
      * [here](http://ipython.org/ipython-doc/dev/development/messaging.html#object-information)
      *
      * @function inspect
      * @param code {string}
      * @param cursor_pos {integer}
      * @param callback {function}
      */
     Kernel.prototype.inspect = function (code, cursor_pos, callback) {
         var callbacks;
         if (callback) {
             callbacks = { shell : { reply : callback } };
         }
         
         var content = {
             code : code,
             cursor_pos : cursor_pos,
             detail_level : 0
         };
         return this.send_shell_message("inspect_request", content, callbacks);
     };
 
     /**
      * Execute given code into kernel, and pass result to callback.
      *
      * @async
      * @function execute
      * @param {string} code
      * @param [callbacks] {Object} With the following keys (all optional)
      *      @param callbacks.shell.reply {function}
      *      @param callbacks.shell.payload.[payload_name] {function}
      *      @param callbacks.iopub.output {function}
      *      @param callbacks.iopub.clear_output {function}
      *      @param callbacks.input {function}
      * @param {object} [options]
      *      @param [options.silent=false] {Boolean}
      *      @param [options.user_expressions=empty_dict] {Dict}
      *      @param [options.allow_stdin=false] {Boolean} true|false
      *
      * @example
      *
      * The options object should contain the options for the execute
      * call. Its default values are:
      *
      *      options = {
      *        silent : true,
      *        user_expressions : {},
      *        allow_stdin : false
      *      }
      *
      * When calling this method pass a callbacks structure of the
      * form:
      *
      *      callbacks = {
      *       shell : {
      *         reply : execute_reply_callback,
      *         payload : {
      *           set_next_input : set_next_input_callback,
      *         }
      *       },
      *       iopub : {
      *         output : output_callback,
      *         clear_output : clear_output_callback,
      *       },
      *       input : raw_input_callback
      *      }
      *
      * Each callback will be passed the entire message as a single
      * arugment.  Payload handlers will be passed the corresponding
      * payload and the execute_reply message.
      */
     Kernel.prototype.execute = function (code, callbacks, options) {
         var content = {
             code : code,
             silent : true,
             store_history : false,
             user_expressions : {},
             allow_stdin : false
         };
         callbacks = callbacks || {};
         if (callbacks.input !== undefined) {
             content.allow_stdin = true;
         }
         $.extend(true, content, options);
         this.events.trigger('execution_request.Kernel', {kernel: this, content: content});
         return this.send_shell_message("execute_request", content, callbacks);
     };
 
     /**
      * When calling this method, pass a function to be called with the
      * `complete_reply` message as its only argument when it arrives.
      *
      * `complete_reply` is documented
      * [here](http://ipython.org/ipython-doc/dev/development/messaging.html#complete)
      *
      * @function complete
      * @param code {string}
      * @param cursor_pos {integer}
      * @param callback {function}
      */
     Kernel.prototype.complete = function (code, cursor_pos, callback) {
         var callbacks;
         if (callback) {
             callbacks = { shell : { reply : callback } };
         }
         var content = {
             code : code,
             cursor_pos : cursor_pos
         };
         return this.send_shell_message("complete_request", content, callbacks);
     };
 
     /**
      * @function send_input_reply
      */
     Kernel.prototype.send_input_reply = function (input) {
         if (!this.is_connected()) {
             throw new Error("kernel is not connected");
         }
         var content = {
             value : input
         };
         this.events.trigger('input_reply.Kernel', {kernel: this, content: content});
         var msg = this._get_msg("input_reply", content);
         this.channels.stdin.send(JSON.stringify(msg));
         return msg.header.msg_id;
     };
 
     /**
      * @function register_iopub_handler
      */
     Kernel.prototype.register_iopub_handler = function (msg_type, callback) {
         this._iopub_handlers[msg_type] = callback;
     };
 
     /**
      * Get the iopub handler for a specific message type.
      *
      * @function get_iopub_handler
      */
     Kernel.prototype.get_iopub_handler = function (msg_type) {
         return this._iopub_handlers[msg_type];
     };
 
     /**
      * Get callbacks for a specific message.
      *
      * @function get_callbacks_for_msg
      */
     Kernel.prototype.get_callbacks_for_msg = function (msg_id) {
         if (msg_id == this.last_msg_id) {
             return this.last_msg_callbacks;
         } else {
             return this._msg_callbacks[msg_id];
         }
     };
 
     /**
      * Clear callbacks for a specific message.
      *
      * @function clear_callbacks_for_msg
      */
     Kernel.prototype.clear_callbacks_for_msg = function (msg_id) {
         if (this._msg_callbacks[msg_id] !== undefined ) {
             delete this._msg_callbacks[msg_id];
         }
     };
     
     /**
      * @function _finish_shell
      */
     Kernel.prototype._finish_shell = function (msg_id) {
         var callbacks = this._msg_callbacks[msg_id];
         if (callbacks !== undefined) {
             callbacks.shell_done = true;
             if (callbacks.iopub_done) {
                 this.clear_callbacks_for_msg(msg_id);
             }
         }
     };
 
     /**
      * @function _finish_iopub
      */
     Kernel.prototype._finish_iopub = function (msg_id) {
         var callbacks = this._msg_callbacks[msg_id];
         if (callbacks !== undefined) {
             callbacks.iopub_done = true;
             if (callbacks.shell_done) {
                 this.clear_callbacks_for_msg(msg_id);
             }
         }
     };
     
     /**
      * Set callbacks for a particular message.
      * Callbacks should be a struct of the following form:
      * shell : {
      * 
      * }
      *
      * @function set_callbacks_for_msg
      */
     Kernel.prototype.set_callbacks_for_msg = function (msg_id, callbacks) {
         this.last_msg_id = msg_id;
         if (callbacks) {
             // shallow-copy mapping, because we will modify it at the top level
             var cbcopy = this._msg_callbacks[msg_id] = this.last_msg_callbacks = {};
             cbcopy.shell = callbacks.shell;
             cbcopy.iopub = callbacks.iopub;
             cbcopy.input = callbacks.input;
             cbcopy.shell_done = (!callbacks.shell);
             cbcopy.iopub_done = (!callbacks.iopub);
         } else {
             this.last_msg_callbacks = {};
         }
     };
 
     /**
      * @function _handle_shell_reply
      */
     Kernel.prototype._handle_shell_reply = function (e) {
         var reply = $.parseJSON(e.data);
         this.events.trigger('shell_reply.Kernel', {kernel: this, reply: reply});
         var content = reply.content;
         var metadata = reply.metadata;
         var parent_id = reply.parent_header.msg_id;
         var callbacks = this.get_callbacks_for_msg(parent_id);
         if (!callbacks || !callbacks.shell) {
             return;
         }
         var shell_callbacks = callbacks.shell;
         
         // signal that shell callbacks are done
         this._finish_shell(parent_id);
         
         if (shell_callbacks.reply !== undefined) {
             shell_callbacks.reply(reply);
         }
         if (content.payload && shell_callbacks.payload) {
             this._handle_payloads(content.payload, shell_callbacks.payload, reply);
         }
     };
 
     /**
      * @function _handle_payloads
      */
     Kernel.prototype._handle_payloads = function (payloads, payload_callbacks, msg) {
         var l = payloads.length;
         // Payloads are handled by triggering events because we don't want the Kernel
         // to depend on the Notebook or Pager classes.
         for (var i=0; i<l; i++) {
             var payload = payloads[i];
             var callback = payload_callbacks[payload.source];
             if (callback) {
                 callback(payload, msg);
             }
         }
     };
 
     /**
      * @function _handle_status_message
      */
     Kernel.prototype._handle_status_message = function (msg) {
         var execution_state = msg.content.execution_state;
         var parent_id = msg.parent_header.msg_id;
         
         // dispatch status msg callbacks, if any
         var callbacks = this.get_callbacks_for_msg(parent_id);
         if (callbacks && callbacks.iopub && callbacks.iopub.status) {
             try {
                 callbacks.iopub.status(msg);
             } catch (e) {
                 console.log("Exception in status msg handler", e, e.stack);
             }
         }
         
         if (execution_state === 'busy') {
             this.events.trigger('kernel_busy.Kernel', {kernel: this});
 
         } else if (execution_state === 'idle') {
             // signal that iopub callbacks are (probably) done
             // async output may still arrive,
             // but only for the most recent request
             this._finish_iopub(parent_id);
             
             // trigger status_idle event
             this.events.trigger('kernel_idle.Kernel', {kernel: this});
 
         } else if (execution_state === 'starting') {
             this.events.trigger('kernel_starting.Kernel', {kernel: this});
             var that = this;
             this.kernel_info(function () {
                 that.events.trigger('kernel_ready.Kernel', {kernel: that});
             });
 
         } else if (execution_state === 'restarting') {
             // autorestarting is distinct from restarting,
             // in that it means the kernel died and the server is restarting it.
             // kernel_restarting sets the notification widget,
             // autorestart shows the more prominent dialog.
             this._autorestart_attempt = this._autorestart_attempt + 1;
             this.events.trigger('kernel_restarting.Kernel', {kernel: this});
             this.events.trigger('kernel_autorestarting.Kernel', {kernel: this, attempt: this._autorestart_attempt});
 
         } else if (execution_state === 'dead') {
             this.events.trigger('kernel_dead.Kernel', {kernel: this});
             this._kernel_dead();
         }
     };
     
     /**
      * Handle clear_output message
      *
      * @function _handle_clear_output
      */
     Kernel.prototype._handle_clear_output = function (msg) {
         var callbacks = this.get_callbacks_for_msg(msg.parent_header.msg_id);
         if (!callbacks || !callbacks.iopub) {
             return;
         }
         var callback = callbacks.iopub.clear_output;
         if (callback) {
             callback(msg);
         }
     };
 
     /**
      * handle an output message (execute_result, display_data, etc.)
      *
      * @function _handle_output_message
      */
     Kernel.prototype._handle_output_message = function (msg) {
         var callbacks = this.get_callbacks_for_msg(msg.parent_header.msg_id);
         if (!callbacks || !callbacks.iopub) {
             return;
         }
         var callback = callbacks.iopub.output;
         if (callback) {
             callback(msg);
         }
     };
 
     /**
      * Dispatch IOPub messages to respective handlers. Each message
      * type should have a handler.
      *
      * @function _handle_iopub_message
      */
     Kernel.prototype._handle_iopub_message = function (e) {
         var msg = $.parseJSON(e.data);
 
         var handler = this.get_iopub_handler(msg.header.msg_type);
         if (handler !== undefined) {
             handler(msg);
         }
     };
 
     /**
      * @function _handle_input_request
      */
     Kernel.prototype._handle_input_request = function (e) {
         var request = $.parseJSON(e.data);
         var header = request.header;
         var content = request.content;
         var metadata = request.metadata;
         var msg_type = header.msg_type;
         if (msg_type !== 'input_request') {
             console.log("Invalid input request!", request);
             return;
         }
         var callbacks = this.get_callbacks_for_msg(request.parent_header.msg_id);
         if (callbacks) {
             if (callbacks.input) {
                 callbacks.input(request);
             }
         }
     };
 
     // Backwards compatability.
     IPython.Kernel = Kernel;
 
     return {'Kernel': Kernel};
 });