commit 2fd4b6efce9465948fadc2fcf5b110d4bd4f4035
author Domenic Denicola <domenic@chromium.org> Mon Dec 02 09:00:14 2024
committer Chromium LUCI CQ <chromium-scoped@luci-project-accounts.iam.gserviceaccount.com> Mon Dec 02 09:00:14 2024
tree 826cc1c2d94a68018ea641eb26c816664d1f99cc
parent bc417ea6835b1dec4f36721a9e3908a40964cb70

Ship PrefetchFollowsNormalCacheSemantics

This removes the "5-minute rule" for prefetches, where they ignore
normal HTTP cache semantics for 5 minutes and instead stay cached in the
HTTP cache. This applies to <link rel=prefetch>, NoStatePrefetch (i.e.
<link rel=prerender>), and speculation rules prefetch.

Note that for speculation rules prefetch, because there is the separate
in-memory speculation rules prefetch cache, 2xx responses without
caching headers will still be stored in that in-memory cache. They just
won't be HTTP cached, in a way that was counter to the website's
expressed preferences.

Shipping this was approved back in May 2023, with an accompanying Finch
study to check for regressions [1]. However, we forgot to actually
change the default.

This is of new urgency now because of the impact on speculation rules
prefetch, which is is causing web developer pain. A web platform test is
included for the specific painful scenario, which fails before this
change and passes afterward.

Most of this CL consists of test updates: many of our tests relied on
not needing caching headers to make <link rel=prefetch> or
<link rel=prerender> work, and so do things like assume there will never
be a second request to those URLs. The general fix is to apply caching
headers to the resources in question, as that represents the intended
real-world usage of <link rel=prefetch>. (And, to a lesser extent, the
nonstandard and hopefully-one-day-removed <link rel=prerender>.)

Notably, the WPT prefetch-document.html was failing in all browsers
before this, including in Firefox which has a highly spec-conformant
implementation. It should now be passing.

PrerendererImplBrowserTestPrefetchAhead.PrefetchSuccessPrefetchMatchResolverTimeoutPrerenderFailure
was disabled, since it appears to never have been working as expected,
with the HTTP caching hiding the real problem. Issue 372851198 tracks
fixing that test.

Tests specifically for the 5-minute rule were deleted.

[1]: https://groups.google.com/a/chromium.org/g/blink-dev/c/Zdo71C0k9C0

Bug: 40232065, 381099745, 356624471, 372851198
Change-Id: I7d42c43efd89486587d8b7fc8ddd4412b31ef0bf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6056830
Reviewed-by: Rakina Zata Amni <rakina@chromium.org>
Commit-Queue: Domenic Denicola <domenic@chromium.org>
Reviewed-by: Adam Rice <ricea@chromium.org>
Reviewed-by: Hiroki Nakagawa <nhiroki@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1390213}