[css-values][all] Define all URL usages in terms of Fetch

[tabatkins]

The platform has settled on using the Fetch model to define fetching. CSS currently hand-waves a bunch of this, and as a result there are some browser-compat issues with corner cases, like what referrer to use in various situations.

WebAppSec defines some of this behavior for us (and here), which we should move into a CSS spec.

(This is mostly a tracking bug to remind me to do this, and track links to useful resources. If anyone else clueful would like to help, feel free.)

[noamr]

I don't believe this is going to be difficult to accomplish.
Where should a common algorithm for fetching style resources sit? [css-values]?

[tabatkins]

My own experience so far suggests that it definitely is difficult to accomplish. ^_^ But I'd absolutely welcome help in defining this, if you have better insight into the problem.

Currently our attempts at fetching things are spread between CSSOM (for top-level stylesheet; currently broken and not invoking the Fetch algos correctly) and Cascade (for @import; currently being written by me in an attempt to use the Fetch algos correctly but definitely currently broken too).

I suspect that url() usage in properties should generally be quite easy; there's a lot less observable behavior we have to worry about, but there's still some piping of document state thru stylesheets that probably needs to be done in CSSOM. Values & Units is indeed the appropriate place to define the general handling of url() tho; PRs absolutely welcome.

[noamr]

My own experience so far suggests that it definitely is difficult to accomplish. ^_^ But I'd absolutely welcome help in defining this, if you have better insight into the problem.

Fair enough :) this was a motivated offer of help rather than an attempt to belittle the challenge

Currently our attempts at fetching things are spread between CSSOM (for top-level stylesheet; currently broken and not invoking the Fetch algos correctly) and Cascade (for @import; currently being written by me in an attempt to use the Fetch algos correctly but definitely currently broken too).

I suspect that url() usage in properties should generally be quite easy; there's a lot less observable behavior we have to worry about, but there's still some piping of document state thru stylesheets that probably needs to be done in CSSOM. Values & Units is indeed the appropriate place to define the general handling of url() tho; PRs absolutely welcome.

They’re coming, be warned. 😉
Will probably have a multi-spec PR with some open issues in the next couple of days

[noamr]

@tabatkins I believe this can be closed.