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Update early hints document

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Now it's enabled by default. Remove text related to activation.

Bug: N/A
Change-Id: I65d1abb13f7e635bb287991cb7f2a925737c288e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4258666
Commit-Queue: Kenichi Ishibashi <bashi@chromium.org>
Reviewed-by: Adam Rice <ricea@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1106042}
This commit is contained in:
Kenichi Ishibashi
2023-02-16 03:09:45 +00:00
committed by Chromium LUCI CQ
parent 4f801d0b3b
commit 392a760d97
1 changed files with 6 additions and 49 deletions

55
docs/early-hints.md

@ -1,19 +1,14 @@
# 103 Early Hints
Contact: early-hints-experiment@chromium.org
Contact: net-dev@chromium.org
As of version 95, Chrome experimentally supports
As of version 103, Chrome supports
[Early Hints](https://datatracker.ietf.org/doc/html/rfc8297).
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
web developers who want to try the feature. This document describes the status
of the current implementation and how to enable Early Hints support.
## What’s supported
Chrome supports [preload](https://w3c.github.io/preload/) and
@ -39,48 +34,7 @@ Chrome doesn’t handle
[prefetch](https://w3c.github.io/resource-hints/#dfn-prefetch) in Early Hints
yet. We consider supporting them in the future.
## Activation
Early Hints can be enabled by a command line flag, or via
[Origin Trial](https://developer.chrome.com/blog/origin-trials/).
### Using command line flag
Passing the `--enable-features=EarlyHintsPreloadForNavigation` command line flag
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
recognize your pages opted in Early Hints.
```
HTTP/1.1 103 Early Hints
Origin-Trial: **your token**
Link: </style.css>; rel="preload"; as="style"
Link: <https://cdn.test>; rel="preconnect"
HTTP/1.1 200 OK
Origin-Trial: **your token**
Link: </style.css>; rel="preload"; as="style"
Link: <https://cdn.test>; rel="preconnect"
Content-Type: text/html; charset=utf-8
<!DOCTYPE html>
...
```
`<meta http-equiv="origin-trial" content="**your token**">` also works for the
final response but doesn’t work for Early Hints since Early Hints cannot convey
a response body.
### Checking Early Hints preload is working
## Checking Early Hints preload is working
If a resource is preloaded by Early Hints, the corresponding
[PerformanceResourceTiming](https://w3c.github.io/resource-timing/#sec-performanceresourcetiming)
@ -90,6 +44,9 @@ performance.getEntriesByName('https://a.test/style.css')[0].initiatorType
// => 'early-hints'
```
Caveat: `initiatorType` may not always set to "early-hints" due to an
implementation limitation. We would like to fix the issue in the future.
## Resources
* [Fastly's test page](https://early-hints.fastlylabs.com/)