Shared compression dictionaries

[tunetheweb]

Summary

Shared Compression Dictionary is a new standard to allow much smaller resource sizes by reusing either previous resources as dictionaries, or having a separate disctionary.

It is available using Brotli or the newer ZStd compression standards and has been available in Chrome since 130

This PR adds the changes to HTTP headers to BCD.

Test results and supporting details

https://chromestatus.com/feature/5124977788977152

Related issues

Equivalent Doc PR: mdn/content#38722

[tunetheweb]

@pmeenan could you review this too?

[pmeenan]

LGTM. The links will probably need to be updated once the RFC publishes (already approved, just waiting for the gears to turn).

[tunetheweb]

Linting issue should be fixed once w3c/browser-specs#1737 is merged and released

[tunetheweb]

Oh if there's a proper RFC then we should wait for that. Unless it's going to be a while? Do you know the RFC number yet?

[pmeenan]

Don't have a number yet but it may take a while because it is waiting for the shared brotli draft to get a RFC number first (also approved for publication). I'll see if I can nudge it but it's probably a few months out if history is any indicator

[tunetheweb]

The current version spec has been included in [email protected]. Waiting for it to be updated here, and then CI should (hopefully) pass, and then will mark this PR as ready for review.

[tunetheweb]

Woo hoo checks pass now so think this is ready for review.

@wbamberg I dunno if you wanna review this along with your kind offer to review mdn/content#38722? And if we should hold off merging these until they are both ready? What's the usual way here as sure this is a fairly common thing to do BCD and related content for the same feature.