Next 13 fetch in server component stuck forever if response is larger than ~15kb

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: Ubuntu 20.04.0 LTS Wed Oct 26 2022 14:44:18 GMT+0200 (Central European Summer Time)
Binaries:
  Node: 16.14.2
  npm: 7.17.0
  Yarn: 1.22.19
  pnpm: 7.13.6
Relevant packages:
  next: 13.0.0
  eslint-config-next: N/A
  react: 18.2.0
  react-dom: 18.2.0

What browser are you using? (if relevant)

No response

How are you deploying your application? (if relevant)

No response

Describe the Bug

When fetching data as described in the docs, the fetch function gets stuck and never resolves, if the payload reaches a certain size.

I created a minimal stackblitz and a mock api to reproduce the problem. If I fetch 75 posts from the mock api it will never resolve, if I only fetch 50 it works fine. Since I was able to reproduce this problem with multiple mock apis and even when using something like supabase to fetch some data I think it might be a size issue? Here the difference is 14kb vs 20kb for the two requests.

EDIT: I tried to nail the problem down further. fetch does indeed resolve but .json() does not. Does this have to do with the highWaterMark buffer size limit on nodejs streams?

Expected Behavior

Fetch should not get stuck forever.

Link to reproduction

https://stackblitz.com/edit/nextjs-vv7ryj?file=app/page.tsx

To Reproduce

• Open the stackblitz
• Comment out line 3 and comment in in line 4 in pages.tsx to fetch 75 instead of 50 posts
• See that fetch never resolves

[t3dotgg]

This hurts me deeply

[balazsorban44]

Thanks for reporting, I did some digging, and the issue seems to be node-fetch-specific.

Currently, on the server, Next.js uses node-fetch to polyfill fetch when Node.js <18 is used. Above Node.js 18, or when the experimental: {enableUndici: true} option in next.config.js is present, we will use undici instead, which does not have this problem.

So current workarounds are:

1. Use Node.js 18 or above, if possible
2. Add the following to next.config.js:

module.exports = {
  experimental: {
    enableUndici: true
  }
}