Automatically use different port to start dev server for non-explicit…

… port (#30736)

* Automatically using different port to start dev server for non-explicit port

* return correct port

* more reasonable changes

* fix isExplicitPort

* 1. rename isExplicitPort to allowRetry 2.restrict the number of retries

Co-authored-by: Steven <steven@ceriously.com>

packages/next/cli/next-dev.ts

@@ -73,7 +73,7 @@ const nextDev: cliCommand = (argv) => {
       )
     }
   }
-
+  const allowRetry = !args['--port']
   let port: number =
     args['--port'] || (process.env.PORT && parseInt(process.env.PORT)) || 3000
 
@@ -88,7 +88,11 @@ const nextDev: cliCommand = (argv) => {
   // some set-ups that rely on listening on other interfaces
   const host = args['--hostname']
 
-  startServer({ dir, dev: true, isNextDevCommand: true }, port, host)
+  startServer(
+    { dir, dev: true, isNextDevCommand: true, allowRetry },
+    port,
+    host
+  )
     .then(async ({ app, actualPort }) => {
       const appUrl = `http://${
         !host || host === '0.0.0.0' ? 'localhost' : host

packages/next/server/lib/start-server.ts

@@ -1,5 +1,6 @@
 import http from 'http'
 import next from '../next'
+import { warn } from '../../build/output/log'
 
 export default async function start(
   serverOptions: any,
@@ -18,8 +19,23 @@ export default async function start(
   requestHandler = app.getRequestHandler()
 
   await new Promise<void>((resolve, reject) => {
-    // This code catches EADDRINUSE error if the port is already in use
-    srv.on('error', reject)
+    let retryCount = 0
+    srv.on('error', (err: NodeJS.ErrnoException) => {
+      // This code catches EADDRINUSE error if the port is already in use
+      if (
+        err.code === 'EADDRINUSE' &&
+        serverOptions.allowRetry &&
+        port &&
+        retryCount < 10
+      ) {
+        warn(`Port ${port} is in use, trying ${port + 1} instead.`)
+        port += 1
+        retryCount += 1
+        srv.listen(port, hostname)
+      } else {
+        reject(err)
+      }
+    })
     srv.on('listening', () => resolve())
     srv.listen(port, hostname)
   })