fix: never proxy hot-reload websocket requests

Both create-react-app and vue-cli-service have introduced workarounds for this, but it seems to me that this is always desirable behaviour for webpack-dev-server.

vuejs/vue-cli@72ba750
react/create-react-app#7444

Author: ajhyndman

lib/Server.js

@@ -1850,13 +1850,31 @@ class Server {
       /** @type {RequestHandler[]} */
       (this.webSocketProxies);
 
+    const hmrPath =
+      this.options.webSocketServer &&
+      /** @type {WebSocketServerConfiguration} */
+      (this.options.webSocketServer).options &&
+      /** @type {NonNullable<WebSocketServerConfiguration["options"]>} */
+      (
+        /** @type {WebSocketServerConfiguration} */
+        (this.options.webSocketServer).options
+      ).path;
+
     for (const webSocketProxy of webSocketProxies) {
-      /** @type {S} */
-      (this.server).on(
-        "upgrade",
+      const proxyUpgrade =
         /** @type {RequestHandler & { upgrade: NonNullable<RequestHandler["upgrade"]> }} */
-        (webSocketProxy).upgrade,
-      );
+        (webSocketProxy).upgrade;
+
+      /** @type {S} */
+      (this.server).on("upgrade", (req, socket, head) => {
+        if (hmrPath && req.url) {
+          const { pathname } = new URL(req.url, "http://0.0.0.0");
+          if (pathname === hmrPath) {
+            return;
+          }
+        }
+        proxyUpgrade(req, socket, head);
+      });
     }
   }