Re: p6: Returning the freshest response

Mark Nottingham <mnot@mnot.net> Mon, 22 April 2013 04:11 UTC

Return-Path: <ietf-http-wg-request@listhub.w3.org>
X-Original-To: ietfarch-httpbisa-archive-bis2Juki@ietfa.amsl.com
Delivered-To: ietfarch-httpbisa-archive-bis2Juki@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id B6D3021F8928 for <ietfarch-httpbisa-archive-bis2Juki@ietfa.amsl.com>; Sun, 21 Apr 2013 21:11:49 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -10.469
X-Spam-Level:
X-Spam-Status: No, score=-10.469 tagged_above=-999 required=5 tests=[AWL=0.130, BAYES_00=-2.599, RCVD_IN_DNSWL_HI=-8]
Received: from mail.ietf.org ([12.22.58.30]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 7oLWWgpxGE6O for <ietfarch-httpbisa-archive-bis2Juki@ietfa.amsl.com>; Sun, 21 Apr 2013 21:11:48 -0700 (PDT)
Received: from frink.w3.org (frink.w3.org [128.30.52.56]) by ietfa.amsl.com (Postfix) with ESMTP id DA9C721F86C0 for <httpbisa-archive-bis2Juki@lists.ietf.org>; Sun, 21 Apr 2013 21:11:48 -0700 (PDT)
Received: from lists by frink.w3.org with local (Exim 4.72) (envelope-from <ietf-http-wg-request@listhub.w3.org>) id 1UU7yf-0001fT-Bf for ietf-http-wg-dist@listhub.w3.org; Mon, 22 Apr 2013 04:03:41 +0000
Resent-Date: Mon, 22 Apr 2013 04:03:41 +0000
Resent-Message-Id: <E1UU7yf-0001fT-Bf@frink.w3.org>
Received: from lisa.w3.org ([128.30.52.41]) by frink.w3.org with esmtp (Exim 4.72) (envelope-from <mnot@mnot.net>) id 1UU7yb-0001ek-Jy for ietf-http-wg@listhub.w3.org; Mon, 22 Apr 2013 04:03:37 +0000
Received: from mxout-08.mxes.net ([216.86.168.183]) by lisa.w3.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.72) (envelope-from <mnot@mnot.net>) id 1UU7ya-0001g2-QD for ietf-http-wg@w3.org; Mon, 22 Apr 2013 04:03:37 +0000
Received: from [192.168.1.80] (unknown [118.209.190.66]) (using TLSv1 with cipher AES128-SHA (128/128 bits)) (No client certificate requested) by smtp.mxes.net (Postfix) with ESMTPSA id 3075850A87 for <ietf-http-wg@w3.org>; Mon, 22 Apr 2013 00:03:14 -0400 (EDT)
Content-Type: text/plain; charset=us-ascii
Mime-Version: 1.0 (Mac OS X Mail 6.3 \(1503\))
From: Mark Nottingham <mnot@mnot.net>
In-Reply-To: <E56A5FA7-555D-4283-95A1-FD0030D4616A@mnot.net>
Date: Mon, 22 Apr 2013 14:03:12 +1000
Content-Transfer-Encoding: quoted-printable
Message-Id: <98485D93-5957-4508-B817-90FE7B5BBDA4@mnot.net>
References: <E56A5FA7-555D-4283-95A1-FD0030D4616A@mnot.net>
To: "ietf-http-wg@w3.org Group" <ietf-http-wg@w3.org>
X-Mailer: Apple Mail (2.1503)
Received-SPF: pass client-ip=216.86.168.183; envelope-from=mnot@mnot.net; helo=mxout-08.mxes.net
X-W3C-Hub-Spam-Status: No, score=-4.3
X-W3C-Hub-Spam-Report: AWL=-2.392, BAYES_00=-1.9, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001
X-W3C-Scan-Sig: lisa.w3.org 1UU7ya-0001g2-QD c3e46bc14a13af11ce7f49f7a20905a5
X-Original-To: ietf-http-wg@w3.org
Subject: Re: p6: Returning the freshest response
Archived-At: <http://www.w3.org/mid/98485D93-5957-4508-B817-90FE7B5BBDA4@mnot.net>
Resent-From: ietf-http-wg@w3.org
X-Mailing-List: <ietf-http-wg@w3.org> archive/latest/17456
X-Loop: ietf-http-wg@w3.org
Resent-Sender: ietf-http-wg-request@w3.org
Precedence: list
List-Id: <ietf-http-wg.w3.org>
List-Help: <http://www.w3.org/Mail/>
List-Post: <mailto:ietf-http-wg@w3.org>
List-Unsubscribe: <mailto:ietf-http-wg-request@w3.org?subject=unsubscribe>

Now:
  http://trac.tools.ietf.org/wg/httpbis/trac/ticket/453


On 29/03/2013, at 2:10 PM, Mark Nottingham <mnot@mnot.net> wrote:

> p6 currently says;
> 
>> When more than one suitable response is stored, a cache must use the most recent response (as determined by the Date header field).
> 
> https://svn.tools.ietf.org/svn/wg/httpbis/draft-ietf-httpbis/latest/p6-cache.html#constructing.responses.from.caches
> 
> ... which was sourced pretty directly from 2616:
> 
>> A correct cache MUST respond to a request with the most up-to-date response held by the cache that is appropriate to the request
> 
> Interpreted strictly*, this means that if a cache has two fresh representations:
> 
>  Content-Type: image/jpeg
>  Date: Thu, 14 Feb 2013 03:08:09 GMT
> 
>  Content-Type: image/png
>  Date: Thu, 14 Feb 2013 03:08:08 GMT
> 
> and it gets a request with:
> 
>  Accept: image/jpeg;q=0.1, image/png;q=1.0
> 
> then it'll return the JPEG because it's fresher, even though the client clearly prefers the PNG.
> 
> However that's not the whole story. To get to those multiple responses, the cache goes through the process of winnowing down the potentially matching stored responses, using the process described in <https://svn.tools.ietf.org/svn/wg/httpbis/draft-ietf-httpbis/latest/p6-cache.html#caching.negotiated.responses>.
> 
> That section says:
> 
>> If multiple selected responses are available, the most recent response (as determined by the Date header field) is used; see Section 4.
> 
> which I put into p6 based upon the above.
> 
> So, I'm wondering if we should change that to something like:
> 
> """
> If multiple selected responses are available, the cache will need to choose one to use. If a selecting header has a known mechanism for doing so (e.g., qvalues on Accept and similar request headers), it MAY be used to select one; otherwise, the most recent response (as determined by the Date header field) is used, as per Section 4.
> """
> 
> Thoughts?
> 
> 
> * "appropriately" doesn't give us enough leeway here on its own; see the context.
> 
> --
> Mark Nottingham   http://www.mnot.net/
> 
> 
> 
> 

--
Mark Nottingham   http://www.mnot.net/