fix(server): intercept ping requests (#13117)

Co-authored-by: 翠 / green <green@sapphi.red>

packages/vite/src/client/client.ts

@@ -321,6 +321,11 @@ async function waitForSuccessfulPing(
     try {
       await fetch(`${pingHostProtocol}://${hostAndPath}`, {
         mode: 'no-cors',
+        headers: {
+          // Custom headers won't be included in a request with no-cors so (ab)use one of the
+          // safelisted headers to identify the ping request
+          Accept: 'text/x-vite-ping',
+        },
       })
       return true
     } catch {}

packages/vite/src/node/server/index.ts

@@ -608,6 +608,16 @@ export async function _createServer(
   // open in editor support
   middlewares.use('/__open-in-editor', launchEditorMiddleware())
 
+  // ping request handler
+  // Keep the named function. The name is visible in debug logs via `DEBUG=connect:dispatcher ...`
+  middlewares.use(function viteHMRPingMiddleware(req, res, next) {
+    if (req.headers['accept'] === 'text/x-vite-ping') {
+      res.writeHead(204).end()
+    } else {
+      next()
+    }
+  })
+
   // serve static files under /public
   // this applies before the transform middleware so that these files are served
   // as-is without transforms.