fix(http): Clarify content length in 204 responses

[bsmth]

Description

The example has a Content-Length: 0 in a 204, which is not allowed:

https://datatracker.ietf.org/doc/html/rfc9110#section-8.6-8

A server MUST NOT send a Content-Length header field in any response with a status code of 1xx (Informational) or 204 (No Content).

Also removing compat info which is maybe not useful for readers. There's an interesting history behind this:

servers may erroneously include data after the headers

and browsers deviate in how lenient they are with this erroneous behavior.
The details were added to prose in https://bugzilla.mozilla.org/show_bug.cgi?id=1356614

I think we can put this in BCD, but open to reviewer feedback.

depends on:

• TODO capture browser behavior in BCD

Related issues and pull requests

Fixes #36146

[github-actions]

Preview URLs

• /en-US/docs/Web/HTTP/Status/204
• /en-US/docs/Web/HTTP/Status/205

Flaws (1)

Note! 1 document with no flaws that don't need to be listed. 🎉

URL: /en-US/docs/Web/HTTP/Status/205
Title: 205 Reset Content
Flaw count: 1

• unknown:
  • No generic content config found

(comment last updated: 2025-02-18 11:53:07)

[hamishwillee]

If the spec now explicitly states that there can be no content or trailers after the headers, and that Content-Length may not be specified, this should be mentioned in the description.

Removing the compatibility notes to BCD makes sense, but only once that corresponding BCD item has merged. Can you create it?

[bsmth]

Removing the compatibility notes to BCD makes sense, but only once that corresponding BCD item has merged. Can you create it?

Sounds good to me, I've added it as a subtask / checklist item