backport WebSocket.send_error from tornado 4.1

raising an exception in a websocket results in
"Method not supported" on tornado 4.0

IPython/html/base/zmqhandlers.py

@@ -1,263 +1,276 b''
 # coding: utf-8
 """Tornado handlers for WebSocket <-> ZMQ sockets."""
 
 # Copyright (c) IPython Development Team.
 # Distributed under the terms of the Modified BSD License.
 
 import os
 import json
 import struct
 import warnings
 
 try:
     from urllib.parse import urlparse # Py 3
 except ImportError:
     from urlparse import urlparse # Py 2
 
 import tornado
 from tornado import gen, ioloop, web
 from tornado.websocket import WebSocketHandler
 
 from IPython.kernel.zmq.session import Session
 from IPython.utils.jsonutil import date_default, extract_dates
 from IPython.utils.py3compat import cast_unicode
 
 from .handlers import IPythonHandler
 
 def serialize_binary_message(msg):
     """serialize a message as a binary blob
 
     Header:
 
     4 bytes: number of msg parts (nbufs) as 32b int
     4 * nbufs bytes: offset for each buffer as integer as 32b int
 
     Offsets are from the start of the buffer, including the header.
 
     Returns
     -------
 
     The message serialized to bytes.
 
     """
     # don't modify msg or buffer list in-place
     msg = msg.copy()
     buffers = list(msg.pop('buffers'))
     bmsg = json.dumps(msg, default=date_default).encode('utf8')
     buffers.insert(0, bmsg)
     nbufs = len(buffers)
     offsets = [4 * (nbufs + 1)]
     for buf in buffers[:-1]:
         offsets.append(offsets[-1] + len(buf))
     offsets_buf = struct.pack('!' + 'I' * (nbufs + 1), nbufs, *offsets)
     buffers.insert(0, offsets_buf)
     return b''.join(buffers)
 
 
 def deserialize_binary_message(bmsg):
     """deserialize a message from a binary blog
 
     Header:
 
     4 bytes: number of msg parts (nbufs) as 32b int
     4 * nbufs bytes: offset for each buffer as integer as 32b int
 
     Offsets are from the start of the buffer, including the header.
 
     Returns
     -------
 
     message dictionary
     """
     nbufs = struct.unpack('!i', bmsg[:4])[0]
     offsets = list(struct.unpack('!' + 'I' * nbufs, bmsg[4:4*(nbufs+1)]))
     offsets.append(None)
     bufs = []
     for start, stop in zip(offsets[:-1], offsets[1:]):
         bufs.append(bmsg[start:stop])
     msg = json.loads(bufs[0].decode('utf8'))
     msg['header'] = extract_dates(msg['header'])
     msg['parent_header'] = extract_dates(msg['parent_header'])
     msg['buffers'] = bufs[1:]
     return msg
 
 # ping interval for keeping websockets alive (30 seconds)
 WS_PING_INTERVAL = 30000
 
 if os.environ.get('IPYTHON_ALLOW_DRAFT_WEBSOCKETS_FOR_PHANTOMJS', False):
     warnings.warn("""Allowing draft76 websocket connections!
     This should only be done for testing with phantomjs!""")
     from IPython.html import allow76
     WebSocketHandler = allow76.AllowDraftWebSocketHandler
     # draft 76 doesn't support ping
     WS_PING_INTERVAL = 0
 
 class ZMQStreamHandler(WebSocketHandler):
     
+    if tornado.version_info < (4,1):
+        """Backport send_error from tornado 4.1 to 4.0"""
+        def send_error(self, *args, **kwargs):
+            if self.stream is None:
+                super(WebSocketHandler, self).send_error(*args, **kwargs)
+            else:
+                # If we get an uncaught exception during the handshake,
+                # we have no choice but to abruptly close the connection.
+                # TODO: for uncaught exceptions after the handshake,
+                # we can close the connection more gracefully.
+                self.stream.close()
+
+
     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, channel=None):
         """Reserialize a reply message using JSON.
 
         This takes the msg list from the ZMQ socket, deserializes 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.deserialize(msg_list)
         if channel:
             msg['channel'] = channel
         if msg['buffers']:
             buf = serialize_binary_message(msg)
             return buf
         else:
             smsg = json.dumps(msg, default=date_default)
             return cast_unicode(smsg)
 
     def _on_zmq_reply(self, stream, msg_list):
         # Sometimes this gets triggered when the on_close method is scheduled in the
         # eventloop but hasn't been called.
         if stream.closed(): return
         channel = getattr(stream, 'channel', None)
         try:
             msg = self._reserialize_reply(msg_list, channel=channel)
         except Exception:
             self.log.critical("Malformed message: %r" % msg_list, exc_info=True)
         else:
             self.write_message(msg, binary=isinstance(msg, bytes))
 
 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 pre_get(self):
         """Run before finishing the GET request
         
         Extend this method to add logic that should fire before
         the websocket finishes completing.
         """
         # 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', False):
             self.session.session = cast_unicode(self.get_argument('session_id'))
         else:
             self.log.warn("No session ID specified")
     
     @gen.coroutine
     def get(self, *args, **kwargs):
         # pre_get can be a coroutine in subclasses
         # assign and yield in two step to avoid tornado 3 issues
         res = self.pre_get()
         yield gen.maybe_future(res)
         super(AuthenticatedZMQStreamHandler, self).get(*args, **kwargs)
     
     def initialize(self):
         self.log.debug("Initializing websocket connection %s", self.request.path)
         self.session = Session(config=self.config)
     
     def open(self, *args, **kwargs):
         self.log.debug("Opening websocket %s", self.request.path)
         
         # start the pinging
         if self.ping_interval > 0:
             loop = ioloop.IOLoop.current()
             self.last_ping = loop.time()  # Remember time of last ping
             self.last_pong = self.last_ping
             self.ping_callback = ioloop.PeriodicCallback(
                 self.send_ping, self.ping_interval, io_loop=loop,
             )
             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.current().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.current().time()