Re: Client Hint Reliability

David Benjamin <davidben@chromium.org> Thu, 27 August 2020 19:02 UTC

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From: David Benjamin <davidben@chromium.org>
Date: Thu, 27 Aug 2020 14:59:34 -0400
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Subject: Re: Client Hint Reliability
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As a quick update, I've just uploaded draft-01 of the document. I've
matched draft-ietf-httpbis-client-hints in using "user agent" instead of
"client", and we've realized that the HTTP/2 frame didn't quite work right
with HTTP caching (by the time you've made a network connection, you've
already evaluated Vary and potentially conditionalized the request), so
it's now been reworked as a funny restart which I think mirrors Critical-CH
fairly nicely.

https://tools.ietf.org/html/draft-davidben-http-client-hint-reliability-01
https://www.ietf.org/rfcdiff?url2=draft-davidben-http-client-hint-reliability-01

David

On Mon, Jul 20, 2020 at 1:35 PM David Benjamin <davidben@chromium.org>
wrote:

> Hi all,
>
> One of the bits of developer feedback we’ve gotten on Client Hints is the
> first view problem, or more generally the reliability problem:
> https://github.com/WICG/client-hints-infrastructure/issues/16
>
> An HTTP request can only take into account previous HTTP responses’
> Accept-CH headers, which means the first resource request to a site, either
> overall or after a config change, may be missing Client Hints. Fixing this
> requires detecting the reason for the missing header, which is tricky for
> the server (maybe the client just never sends it), and costs a round-trip.
> This makes Client Hints unattractive for top-level resources, or use cases
> where the header meaningfully changes the page.
>
> We’ve been looking at a pair of mechanisms to address this. The first is
> an HTTP response header for the server to trigger a client retry if needed.
> The second builds on Victor Vasiliev’s ALPS drafts to get the information
> to the client before its first request in most cases, avoiding the
> performance hit.
>
> I’ve written up an initial draft describing the two:
> https://tools.ietf.org/html/draft-davidben-http-client-hint-reliability-00
>
> There’s also an overview in W3C-style explainer
> <https://w3ctag.github.io/explainers> form in the Client Hints
> infrastructure WICG repo:
>
> https://github.com/WICG/client-hints-infrastructure/blob/master/reliability.md
>
> I would be interested in hearing the WG’s thoughts on this.
>
> David
>