Contact emails
steven...@microsoft.com

Explainer
https://github.com/whatwg/fetch/pull/1576


Specification
https://wicg.github.io/nav-speculation/prerendering.html#interaction-with-fetch


Design docs

https://fetch.spec.whatwg.org/#ref-for-http-sec-purpose%E2%91%A0
https://wicg.github.io/nav-speculation/prefetch.html#ref-for-http-sec-purpose


Summary

Now that prefetches and prerenders are utilizing the Sec-Purpose header for 
prefetches and prerenders, we will move to remove the legacy Purpose: prefetch 
header that is still currently passed. This will be behind a feature flag/ kill 
switch to prevent compat issues. This will be scoped to speculation rules 
prefetch, speculation rules prerender, <link rel=prefetch>, and Chromium's 
non-standard <link rel=prerender>.



Blink component
Blink>Loader


TAG review
Not filed as this is a minor change of unspec'ed UA behavior for an existing 
feature. (Can start a review if recommended)


TAG review status
Not applicable


Risks




Interoperability and Compatibility

As commented at notes on Firefox and Safari, each browser uses non-standardized 
header name that is not aligned with CORS spec. This change will introduce 
better interoperability and compatibility for a long term.


Gecko: Positive (https://github.com/mozilla/standards-positions/issues/1259) 
https://bugzilla.mozilla.org/show_bug.cgi?id=1965945 They currently already 
pass the web platform tests for standardizing on using Sec-Purpose for prefetch.

WebKit: Support (https://github.com/WebKit/standards-positions/issues/114) 
Positive as part of aligning on <link rel=prefetch>

Web developers: No signals

Other signals:


WebView application risks

Does this intent deprecate or change behavior of existing APIs, such that it 
has potentially high risk for Android WebView-based applications?

None




Debuggability

None



Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, 
ChromeOS, Android, and Android WebView)?
Yes
Yes, since it affects <link rel=prefetch> which is on all platforms



Is this feature fully tested by web-platform-tests?
Yes
https://wpt.fyi/results/preload/prefetch-headers.https.html?label=experimental&label=master&aligned



Flag name on about://flags
None


Finch feature name
RemovePurposeHeaderForPrefetch


Rollout plan
Will ship enabled for all users


Requires code in //chrome?
False


Tracking bug
https://issues.chromium.org/issues/420724819


Estimated milestones


Shipping on desktop 139

Shipping on Android 139

Shipping on WebView 139




Anticipated spec changes

Open questions about a feature may be a source of future web compat or interop 
issues. Please list open issues (eg links to known github issues in the project 
for the feature specification) whose resolution may introduce web 
compat/interop risk (eg, changing to naming or structure of the API in a 
non-backward-compatible way).
None


Link to entry on the Chrome Platform Status
https://chromestatus.com/feature/5088012836536320?gate=5120193717862400


Links to previous Intent discussions
Intent to Prototype: 
https://groups.google.com/a/chromium.org/d/msgid/blink-dev/6836470b.2b0a0220.33c819.0963.GAE%40google.com



This intent message was generated by Chrome Platform Status.

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