Fetching an url that redirects with a (stream) body

[feugy]

Hello Undici community!

I'd like to understand the behavior in a very specific corner case. Maybe it's intended.

I have this endpoint which returns a 302 redirection to another route, with a stream body containing a0a1a2a3a4a5.

When fetched with curl the body is displayed.

curl command & results

curl -i https://responseheader-logging-feugy-damien-s-test-team.vercel.app/api/redirect
HTTP/2 302
cache-control: public, max-age=0, must-revalidate
date: Fri, 26 Aug 2022 14:48:02 GMT
location: /api/route
server: Vercel
strict-transport-security: max-age=63072000; includeSubDomains; preload
x-robots-tag: noindex
x-vercel-cache: MISS
x-vercel-id: cdg1::6thck-1661525281810-22290825160c

a0a1a2a3a4a5%

When fetched with Undici, the request is aborted and fails if one attempts to consume the body (reproduction), as opposed to node-fetch.

The spec (step #8)) provides guidance about redirection with body over http2, but also states that the client should return the response.

What's your take?
Thanks a million.

Here's the endpoint code, for the curious

// running on vercel, edge function
export default function handle(request) {
  const location = new URL('/api/route', request.url)
  const stream = new ReadableStream({
    start(controller) {
      let count = 0
      const l = setInterval(() => {
        controller.enqueue('a' + count++)
        if (count > 5) {
          controller.close()
          clearInterval(l)
        }
      }, 100)
    },
  })
  return new Response(stream, { status: 302, headers: { location } })
}

export const config = { runtime: 'experimental-edge' }

[mcollina]

cc @KhafraDev could you take a look?

[KhafraDev]

Yes, this appears to be a mistake in undici (step 8.1, as mentioned).

The connection is destroyed here:

undici/lib/fetch/index.js

Line 1051 in 6a87bfb

fetchParams.controller.connection.destroy()

Which then aborts the request here:

undici/lib/fetch/index.js

Line 1553 in 6a87bfb

this.abort?.(err ?? new DOMException('The operation was aborted.', 'AbortError'))

which you can then follow the stack trace, but is relatively unimportant.

---

The connection should not be destroyed because undici doesn't support http/2.

You could submit a PR to remove this line with a reproducible example or I can (a little busy atm).

[KhafraDev]

I understand what you're saying now, makes sense.

[feugy]

Thanks for jumping on the question folks.
Trying @ronag's suggestion on this particular case works.
What other cases is it breacking @KhafraDev?

I just wrapped the original fetchParams.controller.connection.destroy() into an if

  if (redirectStatus.includes(actualResponse.status)) {
    // 1. If actualResponse’s status is not 303, request’s body is not null,
    // and the connection uses HTTP/2, then user agents may, and are even
    // encouraged to, transmit an RST_STREAM frame.
    // See, https://github.com/whatwg/fetch/issues/1288
    if (request.redirect !== 'manual') {
      fetchParams.controller.connection.destroy()
    } 

[KhafraDev]

It works, I was writing a test which was inherently wrong which caused the issue 😄.

[feugy]

Oh, great!
Do you have something ready, or should I open a PR?

[KhafraDev]

I don't have much, feel free to open a pr

[feugy]

Here's the PR: #1627