core: fix socket.io endpoint path

Socket.io will try to connect to `domain.com/socket.io` to establish
communication by default. This is problematic when the frontend is
served on an HTTP path that isn't `/`.

Update the path supplied to Socket.io to take the current location into
account.

packages/core/src/browser/messaging/ws-connection-provider.ts

@@ -15,7 +15,7 @@
 // *****************************************************************************
 
 import { injectable, interfaces, decorate, unmanaged } from 'inversify';
-import { JsonRpcProxyFactory, JsonRpcProxy, Emitter, Event } from '../../common';
+import { JsonRpcProxyFactory, JsonRpcProxy, Emitter, Event, Path } from '../../common';
 import { WebSocketChannel } from '../../common/messaging/web-socket-channel';
 import { Endpoint } from '../endpoint';
 import { AbstractConnectionProvider } from '../../common/messaging/abstract-connection-provider';
@@ -91,11 +91,10 @@ export class WebSocketConnectionProvider extends AbstractConnectionProvider<WebS
     }
 
     /**
-     * Creates a websocket URL to the current location
+     * @param path The handler to reach in the backend.
      */
     protected createWebSocketUrl(path: string): string {
-        const endpoint = new Endpoint({ path });
-        return endpoint.getWebSocketUrl().toString();
+        return path;
     }
 
     protected createHttpWebSocketUrl(path: string): string {
@@ -108,6 +107,7 @@ export class WebSocketConnectionProvider extends AbstractConnectionProvider<WebS
      */
     protected createWebSocket(url: string): Socket {
         return io(url, {
+            path: this.createSocketIoPath(url),
             reconnection: true,
             reconnectionDelay: 1000,
             reconnectionDelayMax: 10000,
@@ -120,6 +120,10 @@ export class WebSocketConnectionProvider extends AbstractConnectionProvider<WebS
         });
     }
 
+    protected createSocketIoPath(url: string): string | undefined {
+        return new Path(location.pathname).join('socket.io').toString();
+    }
+
     protected fireSocketDidOpen(): void {
         this.onSocketDidOpenEmitter.fire(undefined);
     }