Upgrade websocket proxies without initial http request

lib/Server.js

@@ -127,6 +127,9 @@ function Server(compiler, options) {
 		contentBase = process.cwd();
 	}
 
+	// Keep track of websocket proxies for external websocket upgrade.
+	const websocketProxies = [];
+
 	const features = {
 		compress() {
 			if(options.compress) {
@@ -205,6 +208,9 @@ function Server(compiler, options) {
 					}
 
 					proxyMiddleware = getProxyMiddleware(proxyConfig);
+					if(proxyConfig.ws) {
+						websocketProxies.push(proxyMiddleware);
+					}
 
 					app.use((req, res, next) => {
 						if(typeof proxyConfigOrCallback === "function") {
@@ -361,6 +367,12 @@ function Server(compiler, options) {
 	} else {
 		this.listeningApp = http.createServer(app);
 	}
+
+	// Proxy websockets without the initial http request
+	// https://github.com/chimurai/http-proxy-middleware#external-websocket-upgrade
+	websocketProxies.forEach(function(wsProxy) {
+		this.listeningApp.on("upgrade", wsProxy.upgrade);
+	});
 }
 
 Server.prototype.use = function() {