HTTP does not allow content for 204 anymore

[JannisBush]

MDN URL

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/204

What specific section or headline is this issue about?

Compatibility notes

What information was incorrect, unhelpful, or incomplete?

The HTTP protocol allows browsers to handle such responses differently (there is an ongoing discussion regarding the specification text in the HTTPWG http-core GitHub repository).

What did you expect to see?

The issue was closed with the most recent HTTP specifications that now do not allow any content (except CRLF?) for 204 anymore, if I understood the spec correctly.

Do you have any supporting links, references, or citations?

httpwg/http-core#26

Do you have anything more you want to share?

No response

MDN metadata

Page report details

• Folder: en-us/web/http/status/204
• MDN URL: https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/204
• GitHub URL: https://github.com/mdn/content/blob/main/files/en-us/web/http/status/204/index.md
• Last commit: 3f68a96
• Document last modified: 2024-08-06T08:25:07.000Z

[bsmth]

Thanks for raising this one. You are right in saying that there should be no content. The specs have been more and more consistent / explicit, as far as I see, in saying 204 (No Content) doesn't have a message body( and doesn't have a Content-Length: 0, either).

• https://datatracker.ietf.org/doc/html/rfc7230#section-3.3.3
• https://datatracker.ietf.org/doc/html/rfc9110#section-15.3.5-5

From RFC9110:

A 204 response is terminated by the end of the header section; it cannot contain content or trailers.

The note at the end of the MDN page is covering unspecified behavior, essentially: what browsers have done when they receive malformed responses. Sending garbage data as a message body in 204 responses may have happened in buggy server software versions in the past, possibly due to compression configuration. I'm not sure if that info really belongs on the article itself, though, as this might not be useful for readers.

[bsmth]

See also some context how this landed on these pages: https://bugzilla.mozilla.org/show_bug.cgi?id=1356614

[hamishwillee]

@bsmth Might be worth you assigning yourself the issue, given your other work in the area?

[bsmth]

I already started to draft some changes earlier in the week, so what I think we need is:

• content PR: fix(http): Clarify content length in 204 responses #37928
• BCD: TODO