alert client on failed and lost web socket connections

A long message is given if the connection fails within 1s.  Otherwise, it is a short 'connection closed unexpectedly'.

This also means that clients are notified on server termination.

IPython/frontend/html/notebook/static/js/kernel.js

@@ -1,165 +1,199 b''
 //----------------------------------------------------------------------------
 //  Copyright (C) 2008-2011  The IPython Development Team
 //
 //  Distributed under the terms of the BSD License.  The full license is in
 //  the file COPYING, distributed as part of this software.
 //----------------------------------------------------------------------------
 
 //============================================================================
 // Kernel
 //============================================================================
 
 var IPython = (function (IPython) {
 
     var utils = IPython.utils;
 
     var Kernel = function () {
         this.kernel_id = null;
         this.shell_channel = null;
         this.iopub_channel = null;
         this.base_url = $('body').data('baseKernelUrl') + "kernels";
         this.running = false;
         this.username = "username";
         this.session_id = utils.uuid();
         
         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.');
+            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.');
         };
     };
 
 
     Kernel.prototype.get_msg = function (msg_type, content) {
         var msg = {
             header : {
                 msg_id : utils.uuid(),
                 username : this.username,
                 session : this.session_id,
                 msg_type : msg_type
             },
             content : content,
             parent_header : {}
         };
         return msg;
     }
 
     Kernel.prototype.start = function (notebook_id, callback) {
         var that = this;
         if (!this.running) {
             var qs = $.param({notebook:notebook_id});
             var url = this.base_url + '?' + qs
             $.post(url,
                 function (kernel_id) {
                     that._handle_start_kernel(kernel_id, callback);
                 }, 
                 'json'
             );
         };
     };
 
 
     Kernel.prototype.restart = function (callback) {
         IPython.kernel_status_widget.status_restarting();
         var url = this.kernel_url + "/restart";
         var that = this;
         if (this.running) {
             this.stop_channels();
             $.post(url,
                 function (kernel_id) {
                     that._handle_start_kernel(kernel_id, callback);
                 },
                 'json'
             );
         };
     };
 
 
     Kernel.prototype._handle_start_kernel = function (json, callback) {
         this.running = true;
         this.kernel_id = json.kernel_id;
         this.ws_url = json.ws_url;
         this.kernel_url = this.base_url + "/" + this.kernel_id;
         this.start_channels();
         callback();
         IPython.kernel_status_widget.status_idle();
     };
 
 
     Kernel.prototype.start_channels = function () {
+        var that = this;
         this.stop_channels();
         var ws_url = this.ws_url + this.kernel_url;
         console.log("Starting WS:", ws_url);
         this.shell_channel = new this.WebSocket(ws_url + "/shell");
         this.iopub_channel = new this.WebSocket(ws_url + "/iopub");
         send_cookie = function(){
             this.send(document.cookie);
         }
+        var already_called_onclose = false; // only alert once
+        ws_closed_early = function(evt){
+            if (already_called_onclose){
+                return;
+            }
+            already_called_onclose = true;
+            if ( ! evt.wasClean ){
+                alert("Websocket connection to " + ws_url + " could not be established." +
+                " You will not be able to run code." +
+                " Your browser may not be compatible with the websocket version in the server," +
+                " or if the url does not look right, there could be an error in the" +
+                " server's configuration.");
+            }
+        }
+        ws_closed_late = function(evt){
+            if (already_called_onclose){
+                return;
+            }
+            already_called_onclose = true;
+            if ( ! evt.wasClean ){
+                alert("Websocket connection has closed unexpectedly." +
+                " The kernel will no longer be responsive.");
+            }
+        }
         this.shell_channel.onopen = send_cookie;
+        this.shell_channel.onclose = ws_closed_early;
         this.iopub_channel.onopen = send_cookie;
+        this.iopub_channel.onclose = ws_closed_early;
+        // switch from early-close to late-close message after 1s
+        setTimeout(function(){
+            that.shell_channel.onclose = ws_closed_late;
+            that.iopub_channel.onclose = ws_closed_late;
+        }, 1000);
     };
 
 
     Kernel.prototype.stop_channels = function () {
         if (this.shell_channel !== null) {
+            this.shell_channel.onclose = function (evt) {null};
             this.shell_channel.close();
             this.shell_channel = null;
         };
         if (this.iopub_channel !== null) {
+            this.iopub_channel.onclose = function (evt) {null};
             this.iopub_channel.close();
             this.iopub_channel = null;
         };
     };
 
     Kernel.prototype.execute = function (code) {
         var content = {
             code : code,
             silent : false,
             user_variables : [],
             user_expressions : {},
             allow_stdin : false,
         };
         var msg = this.get_msg("execute_request", content);
         this.shell_channel.send(JSON.stringify(msg));
         return msg.header.msg_id;
     }
 
 
     Kernel.prototype.complete = function (line, cursor_pos) {
         var content = {
             text : '',
             line : line,
             cursor_pos : cursor_pos
         };
         var msg = this.get_msg("complete_request", content);
         this.shell_channel.send(JSON.stringify(msg));
         return msg.header.msg_id;
     }
 
 
     Kernel.prototype.interrupt = function () {
         if (this.running) {
             $.post(this.kernel_url + "/interrupt");
         };
     };
 
 
     Kernel.prototype.kill = function () {
         if (this.running) {
             this.running = false;
             var settings = {
                 cache : false,
                 type : "DELETE",
             };
             $.ajax(this.kernel_url, settings);
         };
     };
 
     IPython.Kernel = Kernel;
 
     return IPython;
 
 }(IPython));