Critical CH: Client Hints Reliability mechanism

[amtunlimited]

Request for Mozilla Position on an Emerging Web Specification

• Specification Title: This is part of the Client Hint Reliability proposal
• Specification or proposal URL(s):
  • Draft spec: https://datatracker.ietf.org/doc/draft-davidben-http-client-hint-reliability/ (see section 3)
  • Explainer: https://github.com/WICG/client-hints-infrastructure/blob/master/reliability.md#critical-ch

Other information

The Client Hint Reliability proposal is a set of features aimed at making Client Hints more reliably available and mitigating mis-matches between a site's preferences and the preferences stored in the browser. The idea behind the Critical-CH response header is to signal to browsers that there are hints the server would rather pay a round trip for than not have not the first request. The basic algorithm is as follows:

If, after receiving a request with Critical-CH and Accept-CH headers, there is a hint indicated in the Critical-CH header that the browser did not send but would not block sending, the browser should store the new CH preferences, drop the request, and start a new one with the new headers included.

[annevk]

(See also #79 and #202 about Client Hints, both non-harmful.)