Re: Preemptive and reactive content negotiation
Brian Behlendorf (brian@organic.com)
Wed, 6 Sep 1995 14:55:17 -0700 (PDT)
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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