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Re: Multiple header fields with the same field name - unwritten assumption about quoted commas in values?

From: Mark Nottingham <mnot@mnot.net>
Date: Sun, 20 Jan 2013 13:51:20 +1100
Cc: Zhong Yu <zhong.j.yu@gmail.com>, "Roy T. Fielding" <fielding@gbiv.com>, Nico Williams <nico@cryptonector.com>, Karl Dubost <karld@opera.com>, Julian Reschke <julian.reschke@gmx.de>, Piotr Dobrogost <p@ietf.dobrogost.net>, ietf-http-wg@w3.org
Message-Id: <F509ACE8-C27C-4869-91CC-1296E476DF48@mnot.net>
To: Willy Tarreau <w@1wt.eu>

On 17/01/2013, at 6:41 AM, Willy Tarreau <w@1wt.eu> wrote:

> Hi,
> On Wed, Jan 16, 2013 at 12:32:22PM -0600, Zhong Yu wrote:
>> If different applications interpret duplicate headers differently, we
>> have a serious problem
>>    Location: http://abc.com
>>    Location: http://xyz.com
>> Some chooses the 1st one, some chooses the 2nd one, and some may see
>> the merged `http://abc.com,http://xyz.com` (a valid URI)
> Obviously and the issue is the same with many headers. I was just explaining
> that this is an example of a *non-compliant* input which is then turned into
> a different non-compliant output by a middlebox. The problem clearly is with
> the input and not with the operation performed by the middlebox. So we could
> recommend middlebox authors against merging the headers because it's hard to
> do it right, but we have no reason to add a SHOULD NOT which would turn some
> existing implementations to non-compliant for no reason.

I think the middlebox aspect of this is a red herring. What's happening above is that a non-conformant message is being turned into, potentially, conformant input (if there's no space around the comma) -- regardless of where it takes place. I.e., that combination into a single value could just as easily be done in the UA, before the Location is followed.

It seems to me that that's worth at least a note in Security Considerations. I do agree that a requirement -- especially targeted at a particular kind of recipient, rather than *all* recipients -- is probably too much. This is more on the scale of implementation advice. YMMV.

Mark Nottingham   http://www.mnot.net/
Received on Sunday, 20 January 2013 02:51:50 UTC

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