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Update early-hints.md

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To match the current implementation.

Bug: N/A
Change-Id: Ia25268ee7a45340e684a5f96d342b70a1ceafdad
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3592000
Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Commit-Queue: Kenichi Ishibashi <bashi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#994011}
This commit is contained in:
Kenichi Ishibashi
2022-04-20 02:28:54 +00:00
committed by Chromium LUCI CQ
parent 7fe33e343d
commit 6d43eb85ad
1 changed files with 16 additions and 8 deletions

24
docs/early-hints.md

@ -4,9 +4,10 @@ Contact: early-hints-experiment@chromium.org
As of version 95, Chrome experimentally supports
[Early Hints](https://datatracker.ietf.org/doc/html/rfc8297).
Early Hints enable browsers to start preload before the main response is served.
In addition, this can be used with other
[Resource Hints](https://w3c.github.io/resource-hints/) APIs like preconnect.
Early Hints enable browsers to preload subresources or preconnect to servers
before the main response is served. See the
[explainer](https://github.com/bashi/early-hints-explainer/blob/main/explainer.md)
how it works.
Currently Chrome is running A/B testing in the field to evaluate the performance
impact of Early Hints. Chrome also provides some ways to opt-in Early Hints for
@ -17,19 +18,22 @@ of the current implementation and how to enable Early Hints support.
Chrome supports [preload](https://w3c.github.io/preload/) and
[preconnect](https://w3c.github.io/resource-hints/#dfn-preconnect) in
Early Hints for top-level frame navigation. See the
[explainer](https://github.com/bashi/early-hints-explainer/blob/main/explainer.md)
how it works.
Early Hints for top-level frame navigation.
## What’s not supported
To reduce security and privacy implications, Chrome ignores Early hints sent in
the following situations.
To reduce security and privacy implications, the HTML and Fetch living standards
have some restrictions on when Early Hints can be handled. Chrome ignores Early
Hints sent in the following situations to comply these specifications.
* Early Hints sent on subresource requests
* Early Hints sent on iframe navigation
* Early Hints sent on HTTP/1.1 or earlier
Chrome ignores the second and following Early Hints responses. Chrome only
handles the first Early Hints response so that Chrome doesn't apply inconsistent
security policies (e.g. Content-Security-Policy).
Chrome doesn’t handle
[dns-prefetch](https://w3c.github.io/resource-hints/#dfn-dns-prefetch) and
[prefetch](https://w3c.github.io/resource-hints/#dfn-prefetch) in Early Hints
@ -47,6 +51,10 @@ to Chrome enables Early Hints support.
### Using Origin Trial
**Note**: As of version 98 the origin trial has expired. The Chrome networking
team is preparing to ship the feature and the origin trial may be available
again in the near future until it's fully shipped.
You can opt any page on your origin into Early Hints by
[requesting a token for your origin](https://developer.chrome.com/origintrials/#/view_trial/2856408063659737089).
Include the token in both Early Hints and the final response so that Chrome can