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Re: draft-ietf-httpbis-client-hints-04; 2.2.2. The Accept-CH-Lifetime header field

From: Mark Nottingham <mnot@mnot.net>
Date: Tue, 9 May 2017 11:07:03 +1000
Cc: HTTP working group mailing list <ietf-http-wg@w3.org>
Message-Id: <349146FF-CBDE-4CF8-86AA-D13B0EA2B773@mnot.net>
To: Kari Hurtta <hurtta-ietf@elmme-mailer.org>, Ilya Grigorik <igrigorik@google.com>
Hi Kari,

> On 20 Apr 2017, at 2:41 am, Kari Hurtta <hurtta-ietf@elmme-mailer.org> wrote:
> 
> 2.2.2.  The Accept-CH-Lifetime header field
> https://tools.ietf.org/html/draft-ietf-httpbis-client-hints-04#section-2.2.2
> 
> |   Servers can ask the client to remember an origin-wide Accept-CH
> |   preference for a specified period of time to enable delivery of
> |   Client Hints on all subsequent requests to the origin, and on
> |   subresource requests initiated as a result of processing a response
> |   from the origin.
> |
> |     Accept-CH-Lifetime = #delta-seconds
> |
> |   The field-value indicates that the Accept-CH preference should be
> |   considered stale after its age is greater than the specified number
> |   of seconds.
> |
> |     Accept-CH: DPR, Viewport-Width
> |     Accept-CH-Lifetime: 86400
> 
> 
> It is not very clear why two header fields is needed to pass that information.

Accept-CH is nothing more than a list of other header field names. If you put other information in there, you have exceptional processing, which is awkward (and leads to thinks like registering the fake header field name "close" for the Connection header). 


> 2.2.1.  Advertising Support via Accept-CH header field
> https://tools.ietf.org/html/draft-ietf-httpbis-client-hints-04#section-2.2.1
> 
> |   Servers can advertise support for Client Hints using the Accept-CH
> |   header field or an equivalent HTML meta element with http-equiv
> |   attribute ([W3C.REC-html5-20141028]).
> 
> Is it assumed that "Accept-CH" is given in http-equiv
> attribute, but "Accept-CH-Lifetime" on http response ?
> 
> Or is that needed so that "Accept-CH" can be given
> on several times?
> 
> 
> What happens if there is several "Accept-CH-Lifetime"
> on response?

Ilya, any thoughts here? Clarifying these would probably be helpful.

Cheers,


--
Mark Nottingham   https://www.mnot.net/
Received on Tuesday, 9 May 2017 01:07:37 UTC

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