TypeError: handler is not a function before server is fully online

[masterkain]

Verify canary release

• I verified that the issue exists in the latest Next.js canary release

Provide environment information

Operating System:
      Platform: linux
      Arch: x64
      Version: #1 SMP Tue Sep 13 07:51:46 UTC 2022
    Binaries:
      Node: 20.1.0
      npm: 9.6.4
      Yarn: 1.22.19
      pnpm: N/A
    Relevant packages:
      next: 13.4.1
      eslint-config-next: 13.4.1
      react: 18.2.0
      react-dom: 18.2.0

Which area(s) of Next.js are affected? (leave empty if unsure)

To Reproduce

I'm building the app for docker in standalone mode, so I start the server with node server.js.
I'm also deploying in kubernetes, and this is happening. at the moment it's unclear if it's happening because traffic is hitting the pod before the server is fully ready or there's something else.

/** @type {import('next').NextConfig} */
const nextConfig = {
  reactStrictMode: true,
  output: 'standalone'
};

module.exports = nextConfig;

Describe the Bug

│ TypeError: handler is not a function                                                                                                                                               │
│     at Server.<anonymous> (/app/server.js:29:11)                                                                                                                                   │
│     at Server.emit (node:events:511:28)                                                                                                                                            │
│     at parserOnIncoming (node:_http_server:1109:12)                                                                                                                                │
│     at HTTPParser.parserOnHeadersComplete (node:_http_common:119:17)                                                                                                               │
│ TypeError: handler is not a function                                                                                                                                               │
│     at Server.<anonymous> (/app/server.js:29:11)                                                                                                                                   │
│     at Server.emit (node:events:511:28)                                                                                                                                            │
│     at parserOnIncoming (node:_http_server:1109:12)                                                                                                                                │
│     at HTTPParser.parserOnHeadersComplete (node:_http_common:119:17)                                                                                                               │
│ TypeError: handler is not a function                                                                                                                                               │
│     at Server.<anonymous> (/app/server.js:29:11)                                                                                                                                   │
│     at Server.emit (node:events:511:28)                                                                                                                                            │
│     at parserOnIncoming (node:_http_server:1109:12)                                                                                                                                │
│     at HTTPParser.parserOnHeadersComplete (node:_http_common:119:17)                                                                                                               │
│ Listening on port 3000 url: http://airbroke-web-f88f4dbc7-dvxqb:3000     

Expected Behavior

I'm debugging an issue with prisma connections and stumbled upon this, so I took a look at the compiled server.js

maybe to ensure the server is fully initialized before it starts accepting incoming traffic, we can move the handler initialization to be before the createServer call, like this?

(async () => {
  handler = await createServerHandler({
    port: currentPort,
    hostname,
    dir,
    conf: nextConfig,
  })

  const server = http.createServer(async (req, res) => {
    try {
      await handler(req, res)
    } catch (err) {
      console.error(err);
      res.statusCode = 500
      res.end('Internal Server Error')
    }
  })

  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)
      process.exit(1)
    }

    console.log(
      'Listening on port',
      currentPort,
      'url: http://' + hostname + ':' + currentPort
    )
  })
})()

Which browser are you using? (if relevant)

No response

How are you deploying your application? (if relevant)

No response

[ferdingler]

The issue appears to have been introduced here: 83b774e where the creation of the Next Server now returns a promise that takes a while to resolve

[masterkain]

that's interesting, that also might be source of my prisma issues

[ferdingler]

Here is a server.js that works if it helps you:

const http = require("http");
const path = require("path");
const {
  createServerHandler,
} = require("next/dist/server/lib/render-server-standalone");

const dir = path.join(__dirname);

process.env.NODE_ENV = "production";
process.chdir(__dirname);

// Make sure commands gracefully respect termination signals (e.g. from Docker)
// Allow the graceful termination to be manually configurable
if (!process.env.NEXT_MANUAL_SIG_HANDLE) {
  process.on("SIGTERM", () => process.exit(0));
  process.on("SIGINT", () => process.exit(0));
}

const currentPort = parseInt(process.env.PORT, 10) || 3000;
const hostname = process.env.HOSTNAME || "localhost";
const keepAliveTimeout = parseInt(process.env.KEEP_ALIVE_TIMEOUT, 10);

// const nextConfig = {}; // ommitted for brevity

process.env.__NEXT_PRIVATE_STANDALONE_CONFIG = JSON.stringify(nextConfig);

createServerHandler({
  port: currentPort,
  hostname,
  dir,
  conf: nextConfig,
}).then((nextHandler) => {
  console.log("Creating http server");
  const server = http.createServer(async (req, res) => {
    try {
      console.log("Handling request");
      await nextHandler(req, res);
    } catch (err) {
      console.error("Failed to call handler", err);
      res.statusCode = 500;
      res.end("Internal Server Error");
    }
  });

  if (
    !Number.isNaN(keepAliveTimeout) &&
    Number.isFinite(keepAliveTimeout) &&
    keepAliveTimeout >= 0
  ) {
    console.log("Setting keep alive timeout", keepAliveTimeout);
    server.keepAliveTimeout = keepAliveTimeout;
  }

  server.listen(currentPort, async (err) => {
    if (err) {
      console.error("Failed to start server", err);
      process.exit(1);
    }

    console.log(
      "Listening on port",
      currentPort,
      "url: http://" + hostname + ":" + currentPort
    );
  });
}).catch(err => {
  console.error("Failed to create next server handler", err);
  process.exit(1);
});

You can copy it manually to the standalone directory to override the one Next.js generates after running a build:

cp server.js .next/standalone/server.js

[petertflem]

I might have seen the same issue. We're on 13.4. What I saw was a blank page, with only the word "Internal server error" written. After a few moments, the error went away. Has happened twice now. Checked the logs right after the last time, and I have this error with a timestamp that looked reasonable:

TypeError: handler is not a function

We are using output: 'standalone' also, the site running in a docker container. Tried to reproduce it locally with just building it and running with node .next/standalone/server.js, but it didn't work. Maybe it would have to be in a docker container, or some other processes to slow things down.

So I am not a 100% sure it is the same issue, but seems plausible.

EDIT: Managed to trigger it by changing revisions in GCP. Here is a screenshot of what I see:

[julieca-magloft]

I might have seen the same issue. We're on 13.4. What I saw was a blank page, with only the word "Internal server error" written. After a few moments, the error went away. Has happened twice now. Checked the logs right after the last time, and I have this error with a timestamp that looked reasonable:

TypeError: handler is not a function

We are using output: 'standalone' also, the site running in a docker container. Tried to reproduce it locally with just building it and running with node .next/standalone/server.js, but it didn't work. Maybe it would have to be in a docker container, or some other processes to slow things down.

So I am not a 100% sure it is the same issue, but seems plausible.

EDIT: Managed to trigger it by changing revisions in GCP. Here is a screenshot of what I see:

I experience the same as you, do you already have any clue?

[github-actions]

This closed issue has been automatically locked because it had no new activity for a month. If you are running into a similar issue, please create a new issue with the steps to reproduce. Thank you.