feat(standalone): allow configuring KEEP_ALIVE_TIMEOUT via env var (#46052)

Resolves #39689, partially resolves #28642 (see notes below)
Inspired by #44627

In #28642 it was also asked to expose `server.headersTimeout`, but it is
probably not needed for most use cases and not implemented even in `next
start`. It was needed to change this option before
nodejs/node#27363.
There also exists a rare bug that is described here
nodejs/node#32329 (comment). To fix
this exposing `server.headersTimeout` might be required both in
`server.js` and in `next start`.

Co-authored-by: JJ Kasper <[email protected]>

Author: AdamKatzDev

packages/next/src/build/utils.ts

@@ -1935,7 +1935,15 @@ const server = http.createServer(async (req, res) => {
 })
 const currentPort = parseInt(process.env.PORT, 10) || 3000
 const hostname = process.env.HOSTNAME || 'localhost'
+const keepAliveTimeout = parseInt(process.env.KEEP_ALIVE_TIMEOUT, 10);
 
+if (
+  !Number.isNaN(keepAliveTimeout) &&
+    Number.isFinite(keepAliveTimeout) &&
+    keepAliveTimeout >= 0
+) {
+  server.keepAliveTimeout = keepAliveTimeout
+}
 server.listen(currentPort, (err) => {
   if (err) {
     console.error("Failed to start server", err)