Fix reconnection loop when devserver is offline (#56698)

Ensures the webpack-hmr socket is not reconnected infinitely while (and
very quickly) when the dev server is offline. I've implemented a gradual
backoff, after 5 tries at 1 second it'll try 20 times at 5 seconds.
After those 25 retries it reloads the page as something must be wrong
(i.e. the server is offline).

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Author: timneutkens

packages/next/src/client/dev/error-overlay/websocket.ts

@@ -26,11 +26,14 @@ export function sendMessage(data: string) {
   return source.send(data)
 }
 
+let reconnections = 0
+
 export function connectHMR(options: { path: string; assetPrefix: string }) {
   function init() {
     if (source) source.close()
 
     function handleOnline() {
+      reconnections = 0
       window.console.log('[HMR] connected')
     }
 
@@ -42,11 +45,21 @@ export function connectHMR(options: { path: string; assetPrefix: string }) {
       }
     }
 
+    let timer: ReturnType<typeof setTimeout>
     function handleDisconnect() {
       source.onerror = null
       source.onclose = null
       source.close()
-      init()
+      reconnections++
+      // After 25 reconnects we'll want to reload the page as it indicates the dev server is no longer running.
+      if (reconnections > 25) {
+        window.location.reload()
+        return
+      }
+
+      clearTimeout(timer)
+      // Try again after 5 seconds
+      timer = setTimeout(init, reconnections > 5 ? 5000 : 1000)
     }
 
     const { hostname, port } = location