fix(fetch): remove content-length header on redirect

[KhafraDev]

Fixes #2021

[annevk]

If you don't forbid content-length, how do you deal with conflicts when someone passes content-length and a string that's quite a bit longer or shorter? The layering here is quite a bit different from how Fetch does it.

[ronag]

Remind me again why we can't just check for this in Headers.append like the spec does?

[KhafraDev]

how do you deal with conflicts when someone passes content-length and a string that's quite a bit longer or shorter?

An error is thrown when a content-length header mismatches

Remind me again why we can't just check for this in Headers.append like the spec does?

There's a few reasons I could think of:

1. If we filter out every header that the spec does, we bring back issues with cookie headers (linked in the issue).
2. If choose to only filter some headers, it will create subtle bugs for people, who can no longer use the spec or another environment (Deno, cfw, bun) as reference. This will probably cause issues w/ wintercg in the future? Basically node would be doing its own thing, while browsers follow the spec and other server environments have the same behavior as one another.
3. It'll break setting some headers with node's setHeaders.

const server = http.createServer((req, res) => {
  const headers = new Headers({ 'content-length': '5' })
  res.setHeaders(headers)
  res.write('hello')
  res.end()
}).listen(0)

[ronag]

I don't think any (?) of those are valid. Since this logic would only occur if the header guard is set to "request" which is only the case internally inside of fetch?

[KhafraDev]

1 & 2 are still relevant? Filtering headers caused issues in the past so we removed it

[ronag]

1 partly, and yea I guess 2 is still relevant.

[ronag]

I'm not sure... as soon as we go away from the spec, things get complicated.

[KhafraDev]

We've been away from the spec for a while now in regards to Headers, it hasn't caused too many issues. It's definitely more complicated 😄.

Relevant tweet: https://twitter.com/matteocollina/status/1537466032490700802

[KhafraDev]

It's an unfortunate situation since neither option is good. Filtering headers causes issues and not filtering them also causes issues. But I also think the spec, regarding headers, is too restrictive for the backend.

edit: an example of this is that origin, host, and referer headers are forbidden header names in the spec, but have no alternative in undici. How do we pick which headers get filtered and which don't?

[KhafraDev]

not sure if it's needed but if we need to discuss filtering headers a new issue might be a better place

[geryogam]

Thank you for the PR @KhafraDev!