Merge pull request #3510 from cwillisf/scratch-link-ws

support Scratch Link on ws://127.0.0.1:20111

src/util/scratch-link-websocket.js

@@ -23,26 +23,75 @@ class ScratchLinkWebSocket {
     }
 
     open () {
+        if (!(this._onOpen && this._onClose && this._onError && this._handleMessage)) {
+            throw new Error('Must set open, close, message and error handlers before calling open on the socket');
+        }
+
+        let pathname;
         switch (this._type) {
         case 'BLE':
-            this._ws = new WebSocket('wss://device-manager.scratch.mit.edu:20110/scratch/ble');
+            pathname = 'scratch/ble';
             break;
         case 'BT':
-            this._ws = new WebSocket('wss://device-manager.scratch.mit.edu:20110/scratch/bt');
+            pathname = 'scratch/bt';
             break;
         default:
             throw new Error(`Unknown ScratchLink socket Type: ${this._type}`);
         }
 
-        if (this._onOpen && this._onClose && this._onError && this._handleMessage) {
+        // Try ws:// (the new way) and wss:// (the old way) simultaneously. If either connects, close the other. If we
+        // were to try one and fall back to the other on failure, that could mean a delay of 30 seconds or more for
+        // those who need the fallback.
+        // If both connections fail we should report only one error.
+
+        const setSocket = (socketToUse, socketToClose) => {
+            socketToClose.onopen = socketToClose.onerror = null;
+            socketToClose.close();
+
+            this._ws = socketToUse;
             this._ws.onopen = this._onOpen;
             this._ws.onclose = this._onClose;
             this._ws.onerror = this._onError;
-        } else {
+            this._ws.onmessage = this._onMessage.bind(this);
-            throw new Error('Must set open, close, message and error handlers before calling open on the socket');
+        };
-        }
 
-        this._ws.onmessage = this._onMessage.bind(this);
+        const ws = new WebSocket(`ws://127.0.0.1:20111/${pathname}`);
+        const wss = new WebSocket(`wss://device-manager.scratch.mit.edu:20110/${pathname}`);
+
+        const connectTimeout = setTimeout(() => {
+            // neither socket succeeded before the timeout
+            setSocket(ws, wss);
+            this._ws.onerror(new Event('timeout'));
+        }, 15 * 1000);
+        ws.onopen = openEvent => {
+            clearTimeout(connectTimeout);
+            setSocket(ws, wss);
+            this._ws.onopen(openEvent);
+        };
+        wss.onopen = openEvent => {
+            clearTimeout(connectTimeout);
+            setSocket(wss, ws);
+            this._ws.onopen(openEvent);
+        };
+
+        let wsError;
+        let wssError;
+        const errorHandler = () => {
+            // if only one has received an error, we haven't overall failed yet
+            if (wsError && wssError) {
+                clearTimeout(connectTimeout);
+                setSocket(ws, wss);
+                this._ws.onerror(wsError);
+            }
+        };
+        ws.onerror = errorEvent => {
+            wsError = errorEvent;
+            errorHandler();
+        };
+        wss.onerror = errorEvent => {
+            wssError = errorEvent;
+            errorHandler();
+        };
     }
 
     close () {