1983387 - Fetch requests with the `range` header don't set `Accept-Encoding: identity`

Status: RESOLVED FIXED

(Core :: DOM: Networking, defect, P3)

Description

[valadaptive]

Attachment: fetchbug.html

User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:141.0) Gecko/20100101 Firefox/141.0

Steps to reproduce:

Make an HTTP request that uses the range header (see the attached file for a demo).

Actual results:

In servers that gzip the response, Firefox will not behave properly because it does not set Accept-Encoding: identity. In the attached demo, compare the results in Chrome and Firefox (you'll need to use the network tab in the inspector since Content-Encoding on the response side is not CORS-safelisted, or at least I think that's why it's not showing up).

In Chrome, the demo functions properly--the request headers contain Accept-Encoding: identity and the response headers omit Content-Encoding. In Firefox, the demo is broken--no results are shown, the request headers contain Accept-Encoding: gzip, deflate, br, zstd, identity, and the response headers contain content-encoding: gzip.

Expected results:

Fetch requests with the range header set should also set accept-encoding: identity, per https://github.com/whatwg/fetch/pull/751. This was apparently implemented in https://bugzilla.mozilla.org/show_bug.cgi?id=1782835, but seems to have regressed?

I'm running Firefox 141.0 as packaged for Fedora 42. Not sure if this is platform-specific.

Comment 1

[BugBot [:suhaib / :marco/ :calixte]]

The Bugbug bot thinks this bug should belong to the 'Core::DOM: Networking' component, and is moving the bug to that component. Please correct in case you think the bot is wrong.

Comment 2

[valadaptive]

Attachment: Bug 1983387 - Don't merge Accept-Encoding: identity. r?#necko-reviewers

The merge flag in HttpBaseChannel::SetRequestHeader corresponds to the
"combine a header" behavior in the fetch spec, in which we add a value
to a comma-separated list of values in the header. The fetch spec does
not tell us to combine (Accept-Encoding, identity), it tells us to
append it. We got away with this before because of a sneaky WPT change
that I'm fixing upstream
(https://github.com/web-platform-tests/wpt/pull/54373).

Comment 4

[Valentin Gosu [:valentin]]

We should land this. I think the WPT need updating.

Comment 5

[Valentin Gosu [:valentin]]

Attachment: Bug 1983387 - Update WPT expectations r=#necko

Comment 6

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/a653050dec04
https://hg.mozilla.org/integration/autoland/rev/9e3407d0a287
Don't merge Accept-Encoding: identity. r=necko-reviewers,jesup
https://github.com/mozilla-firefox/firefox/commit/d16c83fddd2d
https://hg.mozilla.org/integration/autoland/rev/a936cc213f6d
Update WPT expectations r=necko-reviewers,kershaw

Comment 7

[amarc]

https://hg.mozilla.org/mozilla-central/rev/9e3407d0a287
https://hg.mozilla.org/mozilla-central/rev/a936cc213f6d