Set kernel_id before checking websocket

If websocket attempt fails and cross origin attempt is detected, a HTTPError(404) error is raised. However, in the process of closing connections because of this 404 error, an unhandled Attribute exception (kernel_id not an attribute) is raised. Setting the kernel_id first avoids this.

IPython/html/base/zmqhandlers.py

@@ -1,134 +1,134 b''
 """Tornado handlers for WebSocket <-> ZMQ sockets."""
 
 # Copyright (c) IPython Development Team.
 # Distributed under the terms of the Modified BSD License.
 
 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
 from tornado import web
 from tornado import websocket
 
 from zmq.utils import jsonapi
 
 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 same_origin(self):
         """Check to see that origin and host match in the headers."""
 
         # The difference between version 8 and 13 is that in 8 the
         # client sends a "Sec-Websocket-Origin" header and in 13 it's
         # simply "Origin".
         if self.request.headers.get("Sec-WebSocket-Version") in ("7", "8"):
             origin_header = self.request.headers.get("Sec-Websocket-Origin")
         else:
             origin_header = self.request.headers.get("Origin")
 
         host = self.request.headers.get("Host")
 
         # If no header is provided, assume we can't verify origin
         if(origin_header is None or host is None):
             return False
 
         parsed_origin = urlparse(origin_header)
         origin = parsed_origin.netloc
 
         # Check to see that origin matches host directly, including ports
         return origin == host
 
     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 jsonapi.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
 
 
 class AuthenticatedZMQStreamHandler(ZMQStreamHandler, IPythonHandler):
 
     def open(self, kernel_id):
+        self.kernel_id = cast_unicode(kernel_id, 'ascii')
         # Check to see that origin matches host directly, including ports
         if not self.same_origin():
             self.log.warn("Cross Origin WebSocket Attempt.")
             raise web.HTTPError(404)
 
-        self.kernel_id = cast_unicode(kernel_id, 'ascii')
         self.session = Session(config=self.config)
         self.save_on_message = self.on_message
         self.on_message = self.on_first_message
 
     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