No-Vary-Search: Deprecate and remove old syntax

Category: Network / Connectivity
Type: Feature removal
Status: Proposed (Chrome Proposed)
Intent stage: None

Breaking change: No
Enterprise impact: None
Spec maturity: Unknown status
Web Platform Tests: Yes

WPT details: https://wpt.fyi/results/fetch/http-cache/no-vary-search.tentative.any.html https://wpt.fyi/results/speculation-rules/prefetch/no-vary-search

Summary

Deprecates and removes support for the boolean params syntax in the No-Vary-Search HTTP response header, conforming to the updated IETF draft specification. The except member is now used independently instead of in combination with params.

Motivation

The IETF draft specification for the No-Vary-Search HTTP response header has changed. The params member can no longer take a boolean value, and except is now used on its own rather than in combination with params. Chrome will migrate to the new syntax in stages to ensure compatibility.

Standards & signals

Specification: https://httpwg.org/http-extensions/draft-ietf-httpbis-no-vary-search.html
Firefox: No signal
Safari: No signal
Web developers: No signals

Ecosystem

Web Platform Tests: https://wpt.fyi/results/?q=fetch%2Fhttp-cache%2Fno-vary-search
Chrome Platform Showcase: https://chrome-platform-showcase.paulkinlan-ea.deno.net/features
GenDN reference: https://gendn.paulkinlan-ea.deno.net/features
chrome.dev demos search: https://www.google.com/search?q=site%3Achrome.dev+No-Vary-Search%3A%20Deprecate%20and%20remove%20old%20syntax
MDN Web Docs: https://developer.mozilla.org/en-US/search?q=No-Vary-Search%3A%20Deprecate%20and%20remove%20old%20syntax
Baseline status: https://webstatus.dev/?q=No-Vary-Search%3A%20Deprecate%20and%20remove%20old%20syntax

Explainers: https://docs.google.com/document/d/11n4VQ2lI2SOTEIDvnGozgDEEPjGzV6A8h__1wDyCByU/edit

View on chromestatus.com