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Request that the WG reconsider section 3.4: Content Negotiation

From: Henry S. Thompson <ht@inf.ed.ac.uk>
Date: Mon, 04 Nov 2013 16:53:30 +0000
To: ietf-http-wg@w3.org
Cc: apps-discuss@ietf.org, www-tag@w3.org
Message-ID: <f5biow8glbp.fsf@troutbeck.inf.ed.ac.uk>
It's my impression that content negotiation hasn't turned out to play
the kind of significant role in Web Architecture in general, or in
HTTP use in particular, that was expected for it.

I think the section on conneg in p2-semantics [1] is so out-of-step
with actually deployment, usage and expectations that to publish it as
it stands would be a serious mistake.

In particular, the discussion of the relative disadvantages of the
newly (re-)named 'proactive' and 'reactive' variants are not only
out-of-date, but also this discussion appears to at least this reader
to amount to a recommendation for 'reactive' negotiation.  Yet as far
as I can tell no user agents _or_ servers actually support this
approach today, as it's described here.

I was sufficiently concerned about this question to undertake a
moderately extensive empirical investigation [2].  To summarise
perhaps too briefly, I found _no_ evidence of the use of reactive
conneg in over 75 million HTTP request/response exchanges.

I think 3.4 can and should be substantially simplified, with all the
evaluative/speculative prose removed, focussing simply on the
semantics of the Accept... headers and the 300 and 406 status codes,
perhaps also making clear that 'proactive' conneg is the only form of
conneg with any signficant degree of server-side support.

[2] discusses all this at more length -- I hope it will be helpful.  I
am of course aware that personal experience, backed up by one small
study, may well be misleading, but I did look moderately hard to find
any other relevant experimental results without success.  It is less
likely, but not impossible, that what I report in [2] about what is
implemented in IIS, Apache and the major web browsers is also
mistaken.  On either count, I would welcome concrete evidence of where
I've misunderstood or misrepresented the actual situation.


[1] http://tools.ietf.org/html/draft-ietf-httpbis-p2-semantics-24#section-3.4
[2] http://www.ltg.ed.ac.uk/~ht/reactive_conneg.html
       Henry S. Thompson, School of Informatics, University of Edinburgh
      10 Crichton Street, Edinburgh EH8 9AB, SCOTLAND -- (44) 131 650-4440
                Fax: (44) 131 650-4587, e-mail: ht@inf.ed.ac.uk
                       URL: http://www.ltg.ed.ac.uk/~ht/
 [mail from me _always_ has a .sig like this -- mail without it is forged spam]
Received on Monday, 4 November 2013 16:54:13 UTC

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