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Re: lists in header fields, was: How to reset ALTSVC

"Roy T. Fielding" <fielding@gbiv.com> Tue, 08 September 2015 11:03 UTC

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From: "Roy T. Fielding" <fielding@gbiv.com>
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Date: Tue, 08 Sep 2015 11:59:23 +0100
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To: Julian Reschke <julian.reschke@gmx.de>
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Subject: Re: lists in header fields, was: How to reset ALTSVC
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On Sep 8, 2015, at 11:04 AM, Julian Reschke <julian.reschke@gmx.de> wrote:
> 
> On 2015-08-27 07:07, Julian Reschke wrote:
>> ...
>>> Also, since "clear" clears entries including the ones in the same
>>> header, why could there be multiple alt-values?  Would instead of
>>> 
>>> Alt-Svc       = 1#alt-value
>>> alt-value     = clear / ( alternative *( OWS ";" OWS parameter ) )
>>> 
>>> the following:
>>> 
>>> Alt-Svc       = clear / 1#alt-value
>>> alt-value     = alternative *( OWS ";" OWS parameter )
>>> 
>>> not make more sense?
>>> ...
>> 
>> It would, but we are constrained by the HTTP header field semantics. A
>> header field value is either list-shaped or it is not. We can't choose
>> based on the field contents.
>> ...
> 
> But then, RFC 7231 has (in <http://greenbytes.de/tech/webdav/rfc7231.html#header.vary>):
> 
>>  Vary = "*" / 1#field-name
> 
> I'm not totally happy with this, but it's a precedent and maybe I'm just too pedantic :-)

Just a tad.

> Are people ok with changing the definition as proposed by Bence Béky, or should I open a ticket for rfc7231bis?

I think it should be clear that HTTP allows zero, singular, and infinity
as effectively separate potential value syntax for the same field name.
I don't see any problem with that (assuming the zero and singular syntax don't
contain a comma and the singular syntax is readily distinguished from 1#1value).

IOW, it's a feature.

....Roy

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