1855388 - `<link rel="preload" as="audio" ...>` and other potential destinations aren't preloaded

Status: NEW

(Core :: Networking, defect, P2)

Description

[Mirko Brodesser (:mbrodesser-Igalia)]

STR: open https://jsfiddle.net/toy5k3p6/

Expected: in devtool's "Network" tab, a request to "test.wav." should be shown.
Actual: no such request is shown.

As a sanity check, preloading a script ("x.js") is shown in the "Network" tab.

Comment 1

[Mirko Brodesser (:mbrodesser-Igalia)]

as="audioworklet" also sends no request.

Comment 2

[Mirko Brodesser (:mbrodesser-Igalia)]

as="document" also not.

Comment 3

[Mirko Brodesser (:mbrodesser-Igalia)]

as="embed" also not.

Comment 4

[Tom Schuster]

I would suggest you look at the source code, which would make it obvious what is actually supported: https://searchfox.org/mozilla-central/rev/fd2325f5b2a5be8f8f2acf9307285f2b7de06582/uriloader/preload/PreloadService.cpp#135-212

Comment 5

[Mirko Brodesser (:mbrodesser-Igalia)]

(In reply to Tom Schuster (MoCo) from comment #4)

I would suggest you look at the source code, which would make it obvious what is actually supported: https://searchfox.org/mozilla-central/rev/fd2325f5b2a5be8f8f2acf9307285f2b7de06582/uriloader/preload/PreloadService.cpp#135-212

Thanks, that's helpful.

Comment 6

[Mirko Brodesser (:mbrodesser-Igalia)]

Be aware that MDN claims Firefox offers full support: https://developer.mozilla.org/en-US/docs/Web/HTML/Attributes/rel/preload#browser_compatibility.

Comment 7

[Mirko Brodesser (:mbrodesser-Igalia)]

Filed https://github.com/mdn/browser-compat-data/issues/20824 to update MDN.

Comment 8

[Mirko Brodesser (:mbrodesser-Igalia)]

Btw, non-potential destinations (e.g. "audioX") lead to a warning in the developer console:

"Preload of https://fiddle.jshell.net/_display/test.wav was ignored due to unknown “as” or “type” values, or non-matching “media” attribute."

No warning for "audio".

Comment 9

[Mirko Brodesser (:mbrodesser-Igalia)]

It would be helpful to warn in that case too.

Comment 10

[Mirko Brodesser (:mbrodesser-Igalia)]

(In reply to Tom Schuster (MoCo) from comment #4)

I would suggest you look at the source code, which would make it obvious what is actually supported: https://searchfox.org/mozilla-central/rev/fd2325f5b2a5be8f8f2acf9307285f2b7de06582/uriloader/preload/PreloadService.cpp#135-212

Btw., part of the confusion stems from https://searchfox.org/mozilla-central/rev/431bcb0e88e49b92c6913c0916c7ad15e8a4875c/dom/webidl/Request.webidl#71-76.

Comment 11

[Frédéric Wang (:fredw)]

https://wpt.live/fetch/api/request/destination/fetch-destination.https.html has some tests involving <link as=>

The parsing only seems to support a subset of allowed as values:

https://searchfox.org/mozilla-central/rev/b3f40fd7c4671537ed29a232e76c962977650045/netwerk/base/nsNetUtil.cpp#3883