Non-GET http2 requests without a body hang indefninitely

[ktaekwon000]

Bug Description

When using fetch to make non-GET/HEAD http2 requests, the function call hangs indefinitely. Passing in an empty string in place of the body fixes this issue.

Reproducible By

The following js script triggers the issue on undici v6.2.1

'use strict'

const { fetch, Client } = require('undici')

async function main () {
    const client = new Client("https://google.com", { allowH2: true });
    const res = await fetch("https://google.com", {
        dispatcher: client,
        baseURL: 'https://google.com',
        url: 'https://google.com/',
        method: "POST",
    })

    const data = await res.text()
    console.log('response received', res.status)
    console.log('headers', res.headers)
    console.log('data', data)
}
main()

Expected Behavior

The function call should send the request with an empty body.

Environment

macOS 14.0, node v20.8.1, undici v6.2.1

Additional context

I believe the issue is closely related to #2258 , but while this PR had only fixed GET/HEAD requests, this actually affects all kinds of requests.

[metcoder95]

Hey! Thanks for the report

I believe this should be scope to validate wether or not there's a body at all being sent.

Would you like to submit a PR?

[ronag]

I believe this should be scope to validate wether or not there's a body at all being sent.

I'm confused. It should be possible to send a fetch without body? Also this sounds like we are missing something in the spec language? @KhafraDev

[KhafraDev]

this isn't an issue with fetch afaict

[timursevimli]

While I was trying to investigate this problem, I discovered a completely different problem.

When we pass body the following object appears:

{
   finalBody: {
     stream: ReadableStream { locked: false, state: 'readable', supportsBYOB: true },
     source: 'helloWorld',
     length: 10
   }
}

(For this output I used output a variable called finalBody in undici/lib/fetch/request.js:505)

Well, if we pass an object to body, then we get the following output:

{
   finalBody: {
     stream: ReadableStream { locked: false, state: 'readable', supportsBYOB: true },
     source: '[object Object]',
     length: 15
   }
}

In this case, regardless of the size of our object, length will always be 15 and source will be incorrect.

[ktaekwon000]

@timursevimli I believe the problem you're facing is not a bug, and not related to the problem I've posted in the OP. Try passing in your object as data not body, or stringifiying the JSON yourself and setting the respective content-type if using body.

[Piyush-Kumar-Ghosh]

Proposed Solutions:

1. Enhancing undici Library:

   • File to Modify: lib/fetch.js
   • Approach: I suggest a tweak in the undici library where we can specifically check for an empty body. This adjustment would involve handling the content-length header appropriately.

2. Adjusting Fetch Options:

   • Resolution Approach: To address the issue, consider adjusting the fetch options. Explicitly include an empty body in the request.

   // Example Code Snippet
   const res = await fetch("https://google.com", {
       dispatcher: client,
       baseURL: 'https://google.com',
       url: 'https://google.com/',
       method: "POST",
       // Include an empty body
       body: ''
   });

   This modification ensures that the function call sends the request with an empty body, effectively resolving the hanging behavior.

[mcollina]

Given this works with HTTP/1.1, it's not a bug in fetch() but in our HTTP/2 implementation.

[ktaekwon000]

I can verify that the script in the OP runs without issues on v6.4.0 of undici. Thanks everyone for the comments and @timursevimli for the PR!