Fix broken request handler (#51939)

Hi!

In previous versions (13.4.2 and earlier) in the custom server I could
do the following:
```
const parsedUrl = parse(req.url, true);
const { pathname } = parsedUrl;

if (pathname === '/c') {
  await handle(req, res, parse('/b', true));
} else {
  await handle(req, res, parsedUrl);
}
```

Of course, you can replace `handle` with `app.render` in the attached
example, but in practice it is convenient to put the definition of
`parsedUrl` into middleware and substitute the necessary `parsedUrl` in
exceptional situations.

This was broken in #49805.

I'm not sure if this use of request handler is expected, but it has
always worked and people have used it (probably due to lack of
documentation about the difference between `app.render` and
`app.getRequestHandler()`). So the change looks breaking, and I don't
think it should appear in minor versions.

---------

Co-authored-by: Tim Neutkens <tim@timneutkens.nl>

packages/next/src/server/next.ts

@@ -339,23 +339,31 @@ function createServer(options: NextServerOptions): NextServer {
             case 'getRequestHandler': {
               return () => {
                 let handler: RequestHandler
-                return async (req: IncomingMessage, res: ServerResponse) => {
+                return async (
+                  req: IncomingMessage,
+                  res: ServerResponse,
+                  parsedUrl?: UrlWithParsedQuery
+                ) => {
                   if (shouldUseStandaloneMode) {
                     setupWebSocketHandler(options.httpServer, req)
-                    const parsedUrl = url.parse(
+                    const proxyParsedUrl = url.parse(
                       `http://127.0.0.1:${serverPort}${req.url}`,
                       true
                     )
                     if ((req?.socket as TLSSocket)?.encrypted) {
                       req.headers['x-forwarded-proto'] = 'https'
                     }
-                    addRequestMeta(req, '__NEXT_INIT_QUERY', parsedUrl.query)
+                    addRequestMeta(
+                      req,
+                      '__NEXT_INIT_QUERY',
+                      proxyParsedUrl.query
+                    )
 
-                    await proxyRequest(req, res, parsedUrl, undefined, req)
+                    await proxyRequest(req, res, proxyParsedUrl, undefined, req)
                     return
                   }
                   handler = handler || server.getRequestHandler()
-                  return handler(req, res)
+                  return handler(req, res, parsedUrl)
                 }
               }
             }

test/integration/custom-server/server.js

@@ -7,6 +7,7 @@ if (process.env.POLYFILL_FETCH) {
 const { readFileSync } = require('fs')
 const next = require('next')
 const { join } = require('path')
+const { parse } = require('url')
 
 const dev = process.env.NODE_ENV !== 'production'
 const dir = __dirname
@@ -68,6 +69,10 @@ app.prepare().then(() => {
       }
     }
 
+    if (/custom-url-with-request-handler/.test(req.url)) {
+      return handleNextRequests(req, res, parse('/dashboard', true))
+    }
+
     handleNextRequests(req, res)
   })
 

test/integration/custom-server/test/index.test.js

@@ -123,6 +123,18 @@ describe.skip.each([
       expect(html).toMatch(/made it to dashboard/)
     })
 
+    it('should handle custom urls with requests handler', async () => {
+      const html = await renderViaHTTP(
+        nextUrl,
+        '/custom-url-with-request-handler',
+        undefined,
+        {
+          agent,
+        }
+      )
+      expect(html).toMatch(/made it to dashboard/)
+    })
+
     it('should contain customServer in NEXT_DATA', async () => {
       const html = await renderViaHTTP(nextUrl, '/', undefined, { agent })
       const $ = cheerio.load(html)