Intent to Extend Experiment: No-Vary-Search support in navigation prefetch cache
Liviu Tinta
Contact emails
dom...@chromium.org, jbr...@chromium.org, liviu...@chromium.org
Original I2E
https://groups.google.com/a/chromium.org/g/blink-dev/c/6gsc52WQgrU/m/qcTayjt6DAAJ
No-Vary-Search Spec
https://wicg.github.io/nav-speculation/no-vary-search.html
No-Vary-Search hint explainer
https://github.com/WICG/nav-speculation/blob/main/triggers.md#no-vary-search-hint
Origin Trial
https://developer.chrome.com/origintrials/#/view_trial/4146689356901384193
Summary
We propose extending the "No-Vary-Search support in navigation prefetch cache" origin trial. We decided to extend the experiment based on positive feedback from the developer experimenting with the header. Discussions with the developer resulted in additional functionality for this experiment in the form of No-Vary-Search hint (see ChromeStatus entry: https://chromestatus.com/feature/4887338302308352).
We are planning to extend the experiment for 3 more milestones M116 to M118 inclusive.
Blink component
Motivation
The developer we are working with would like to experiment with No-Vary-Search hint in the context of No-Vary-Search header to evaluate the added impact of the new functionality.
TAG review
https://github.com/w3ctag/design-reviews/issues/797
TAG review status
Complete at this time. TAG didn't see any major issue and encouraged us to continue experimenting.
Risks
Interoperability and Compatibility
Gecko: No signal. Request for Standards Position: https://github.com/mozilla/standards-positions/issues/717.
WebKit: No signal. Informal positive signals from individual engineers at TPAC 2022. Request for Standards Position: https://github.com/WebKit/standards-positions/issues/106.
Web developers: Positive. Google Search is interested in experimenting with the header, specifically for the customizing server behavior use case.
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?
No. This is a new opt-in feature.
Debuggability
The website owner can debug the feature in DevTools by making sure that, when navigating to a prefetched page by using a URL that matches under No-Vary-Search conditions, the navigation happens from the prefetch cache by looking at the Size column in the Network tab. In case of success, when hovering over the Size column in the Network tab of Dev Tools, they should see: "Served from prefetch cache, resource size: yyyB"
We are also working on a preloading panel (https://crbug.com/1410709) which shows all ongoing preloads, including both the targeted URL and the cached URL, if they differ due to No-Vary-Search.
Is this feature fully tested by web-platform-tests?
Yes. WPTs landed under the external/wpt/speculation-rules/prefetch/no-vary-search folder.
Tracking bug
Link to entry on the Chrome Platform Status
https://chromestatus.com/feature/5071247189213184
https://chromestatus.com/feature/4887338302308352
Yoav Weiss
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