close websocket connections on ping/pong timeout

we recently added ws pings for keep alive,
and we can now use the longs to close dead connections.

This can apparently happen when connections are not closed cleanly,
e.g. on VPNs.

Setting ws_ping_timeout = 0 disables the ping mechanism altogether.

IPython/html/base/zmqhandlers.py

@@ -109,6 +109,25 b' WS_PING_INTERVAL = 30000'
 
 class AuthenticatedZMQStreamHandler(ZMQStreamHandler, IPythonHandler):
     ping_callback = None
+    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
@@ -129,16 +148,30 b' class AuthenticatedZMQStreamHandler(ZMQStreamHandler, IPythonHandler):'
         self.session = Session(config=self.config)
         self.save_on_message = self.on_message
         self.on_message = self.on_first_message
-        self.ping_callback = ioloop.PeriodicCallback(self.send_ping, WS_PING_INTERVAL)
-        self.ping_callback.start()
+        
+        # start the pinging
+        if self.ping_interval > 0:
+            self.last_pong = ioloop.IOLoop.instance().time()
+            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
+        since_last_pong = 1e3 * (ioloop.IOLoop.instance().time() - self.last_pong)
+        if since_last_pong > self.ping_timeout:
+            self.log.warn("WebSocket ping timeout after %i ms.", since_last_pong)
+            self.close()
+            return
 
         self.ping(b'')
+    
+    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,