[feat] Allow to set the protocols for the websocket transport (#546)

Some WebSocket implementations require the protocols parameter or will
fail connection.

README.md

@@ -225,9 +225,12 @@ Exposed as `eio` in the browser standalone build.
         - `threshold` (`Number`): data is compressed only if the byte size is above this value. This option is ignored on the browser. (`1024`)
       - `extraHeaders` (`Object`): Headers that will be passed for each request to the server (via xhr-polling and via websockets). These values then can be used during handshake or for special proxies. Can only be used in Node.js client environment.
       - `onlyBinaryUpgrades` (`Boolean`): whether transport upgrades should be restricted to transports supporting binary data (`false`)
-      - `requestTimeout` (`Number`): Timeout for xhr-polling requests in milliseconds (`0`)
       - `forceNode` (`Boolean`): Uses NodeJS implementation for websockets - even if there is a native Browser-Websocket available, which is preferred by default over the NodeJS implementation. (This is useful when using hybrid platforms like nw.js or electron) (`false`, NodeJS only)
       - `localAddress` (`String`): the local IP address to connect to
+    - **Polling-only options**
+      - `requestTimeout` (`Number`): Timeout for xhr-polling requests in milliseconds (`0`)
+    - **Websocket-only options**
+      - `protocols` (`Array`): a list of subprotocols (see [MDN reference](https://developer.mozilla.org/en-US/docs/Web/API/WebSockets_API/Writing_WebSocket_servers#Subprotocols))
 - `send`
     - Sends a message to the server
     - **Parameters**

lib/socket.js

@@ -196,7 +196,8 @@ Socket.prototype.createTransport = function (name) {
     extraHeaders: options.extraHeaders || this.extraHeaders,
     forceNode: options.forceNode || this.forceNode,
     localAddress: options.localAddress || this.localAddress,
-    requestTimeout: options.requestTimeout || this.requestTimeout
+    requestTimeout: options.requestTimeout || this.requestTimeout,
+    protocols: options.protocols || void (0)
   });
 
   return transport;

lib/transports/websocket.js

@@ -47,6 +47,7 @@ function WS (opts) {
   }
   this.perMessageDeflate = opts.perMessageDeflate;
   this.usingBrowserWebSocket = BrowserWebSocket && !opts.forceNode;
+  this.protocols = opts.protocols;
   if (!this.usingBrowserWebSocket) {
     WebSocket = NodeWebSocket;
   }
@@ -86,7 +87,7 @@ WS.prototype.doOpen = function () {
   }
 
   var uri = this.uri();
-  var protocols = void (0);
+  var protocols = this.protocols;
   var opts = {
     agent: this.agent,
     perMessageDeflate: this.perMessageDeflate
@@ -108,7 +109,7 @@ WS.prototype.doOpen = function () {
   }
 
   try {
-    this.ws = this.usingBrowserWebSocket ? new WebSocket(uri) : new WebSocket(uri, protocols, opts);
+    this.ws = this.usingBrowserWebSocket ? (protocols ? new WebSocket(uri, protocols) : new WebSocket(uri)) : new WebSocket(uri, protocols, opts);
   } catch (err) {
     return this.emit('error', err);
   }