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Re: Request that the WG reconsider section 3.4: Content Negotiation

From: Henry S. Thompson <ht@inf.ed.ac.uk>
Date: Tue, 05 Nov 2013 12:10:11 +0000
To: Bjoern Hoehrmann <derhoermi@gmx.net>
Cc: ietf-http-wg@w3.org, www-tag@w3.org
Message-ID: <f5b7gcnf3rw.fsf@troutbeck.inf.ed.ac.uk>
Bjoern Hoehrmann writes:

> * Henry S. Thompson wrote:
>>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out-of-date, but also this discussion appears to at least this reader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.
>
> It does not seem far off, it just so happens that for sub-resources a
> substantial part of the process often happens on a level above HTTP.

Then it doesn't belong in the HTTP spec., surely!

> As noted in the draft, it can be costly to contact the server first,
> and then contact it again to request some alternative representation,
> compared to encoding "we serve WOFF and SVG fonts, take your pick" in
> HTML or CSS code. It might be good to note that shift in the document,
> but I do not agree that keeping the text as is would be a "serious
> mistake".

When it's not supported as part of HTTP, anything which suggests that
it is is surely just that, seriously misleading.

>>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.
>
> So with `<a href='example.txt' rel='alternate'>Download plain text
> version of this document</a>`, if the user downloads the plain text
> version, would that be evidence?

Not as far as inclusion in HTTPbis, no.

> If not, is the problem that the user agent did not generate a
> redundant selection menu,

In response to what?  A 300 response?  Yes, that's the point.  No user
agent I'm aware of does _anything_ with a 300 response (except insofar
as they treat it as a 200).

> or perhaps because people do not include the `rel='alternate'`
> attribute

What does rel='alternate' have to do with conneg, or HTTP?  Its
semantics are defined, as you say above, at an entirely different
level.

Although intended as a rejoinder, your response in fact reads to me as
an endorsement.

ht
-- 
       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 Tuesday, 5 November 2013 12:10:39 UTC

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