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Re: Preemptive and reactive content negotiation

From: Brian Behlendorf <brian@organic.com>
Date: Wed, 6 Sep 1995 14:55:17 -0700 (PDT)
To: Koen Holtman <koen@win.tue.nl>
Cc: Roy Fielding <fielding@beach.w3.org>, http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com, Koen Holtman <koen@win.tue.nl>
Message-Id: <Pine.SGI.3.91.950906145013.14691J-100000@fully.organic.com>
On Wed, 6 Sep 1995, Koen Holtman wrote:
> Roy Fielding:
> >There are two ways to do content negotiation: preemptive or reactive.
> >I think preemptive content negotiation is doomed to failure in the
> >long term, which is why I added the 300 response code.  When the
> >day comes that preemptive content negotiation (Accept* headers) are
> >more costly than reactive (an extra round-trip carrying a URC),
> >then browsers and server can switch without changing the protocol.
> 
> I think preemptive content negotiation on *all* types a browser
> supports is too costly already.

Correct - but you don't need to do it for all, just the ones you would 
prefer to see.  If a browser *can* do HTML 3.0, it says "I can do HTML 
3.0", the server might come back and say "sorry (406), I only have HTML 
2.0 and a PDF version of this file", so the browser goes "okay, I'll take 
the HTML 2.0".  The browser should decide where that tradeoff point is 
for itself - the tradeoff between being conservative in what types you 
declare you can accept, and the overhead of getting a 406.

Not everything has to go in the Accept header, just what you'd really 
like to see.

	Brian

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Received on Wednesday, 6 September 1995 15:00:56 EDT

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