Re: p2: Content-Length in HEAD responses

Mark Nottingham <mnot@mnot.net> Sat, 20 April 2013 09:12 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 ADC4B21F9195 for <ietfarch-httpbisa-archive-bis2Juki@ietfa.amsl.com>; Sat, 20 Apr 2013 02:12:42 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -10.423
X-Spam-Level:
X-Spam-Status: No, score=-10.423 tagged_above=-999 required=5 tests=[AWL=0.176, 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 BTum44On9p-y for <ietfarch-httpbisa-archive-bis2Juki@ietfa.amsl.com>; Sat, 20 Apr 2013 02:12:42 -0700 (PDT)
Received: from frink.w3.org (frink.w3.org [128.30.52.56]) by ietfa.amsl.com (Postfix) with ESMTP id F1A9121F914C for <httpbisa-archive-bis2Juki@lists.ietf.org>; Sat, 20 Apr 2013 02:12:41 -0700 (PDT)
Received: from lists by frink.w3.org with local (Exim 4.72) (envelope-from <ietf-http-wg-request@listhub.w3.org>) id 1UTTqM-0007zL-MP for ietf-http-wg-dist@listhub.w3.org; Sat, 20 Apr 2013 09:12:26 +0000
Resent-Date: Sat, 20 Apr 2013 09:12:26 +0000
Resent-Message-Id: <E1UTTqM-0007zL-MP@frink.w3.org>
Received: from maggie.w3.org ([128.30.52.39]) by frink.w3.org with esmtp (Exim 4.72) (envelope-from <mnot@mnot.net>) id 1UTTqJ-0007yg-Hg for ietf-http-wg@listhub.w3.org; Sat, 20 Apr 2013 09:12:23 +0000
Received: from mxout-08.mxes.net ([216.86.168.183]) by maggie.w3.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.72) (envelope-from <mnot@mnot.net>) id 1UTTqI-00056O-RB for ietf-http-wg@w3.org; Sat, 20 Apr 2013 09:12:23 +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 0271C509B5; Sat, 20 Apr 2013 05:12:00 -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: <20130420090647.GQ26517@1wt.eu>
Date: Sat, 20 Apr 2013 19:11:57 +1000
Cc: "ietf-http-wg@w3.org Group" <ietf-http-wg@w3.org>
Content-Transfer-Encoding: quoted-printable
Message-Id: <4C6961E9-2EFC-418F-81BF-C7F0E31A1056@mnot.net>
References: <6EAF151D-EBE7-456D-B5D1-A35933CCDCF8@mnot.net> <20130420090647.GQ26517@1wt.eu>
To: Willy Tarreau <w@1wt.eu>
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=-3.3
X-W3C-Hub-Spam-Report: AWL=-3.273, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001
X-W3C-Scan-Sig: maggie.w3.org 1UTTqI-00056O-RB 826f7869c47fb9116a844bee91faa56e
X-Original-To: ietf-http-wg@w3.org
Subject: Re: p2: Content-Length in HEAD responses
Archived-At: <http://www.w3.org/mid/4C6961E9-2EFC-418F-81BF-C7F0E31A1056@mnot.net>
Resent-From: ietf-http-wg@w3.org
X-Mailing-List: <ietf-http-wg@w3.org> archive/latest/17417
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>

On 20/04/2013, at 7:06 PM, Willy Tarreau <w@1wt.eu> wrote:

> On Sat, Apr 20, 2013 at 06:41:01PM +1000, Mark Nottingham wrote:
>> p2 4.3.2 says:
>> 
>>    Aside from the payload header fields (Section 3.3), the server SHOULD
>>    send the same header fields in response to a HEAD request as it would
>>    have sent if the request had been a GET.
>> 
>> The payload header fields include Content-Length, which in my testing is
>> pretty common in HEAD responses. Was this an oversight, or intentional?
> 
> In my opinion it was intentional, as it's the only way for a client
> to know the payload size in advance without retrieving the file.

I was asking if it was intentional that, as currently specified, we say that C-L should be *omitted* from HEAD responses.

> Also I remember about at least one cache which used to truncate cached
> contents when a server returned "content-length: 0" in response to a
> HEAD request. So most likely, especially due to caches, we don't want
> the server to return a different content-length on HEAD as much as
> possible.

Yes, I see that quite a bit.

>> (We already have an exception for HEAD responses in p1's message body length
>> algorithm, section 3.3.3).
> 
> Exactly, so the SHOULD above should not cause any issue.


At best it's a sloppy SHOULD, but I think it's actively misleading, at the moment... it's saying you SHOULD send the headers back, EXCEPT for a set which includes C-L.

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