Re: Comments on draft-ietf-http-negotiation-00.txt

Roy T. Fielding:
>
  [Koen Holtman:]
>>So I think a server being aware of an internal configuration error qualifies
>>for sending a 5xx.
>
>Except that
>
>   1) There is no internal configuration error.  There is no reason
>      why a server must be prevented from having multiple levels of
>      negotiation, 

You _can_ have multiple levels of negotiation under TCN, that is why the
variant-vary header is there.  What you cannot have is a second level of
_transparent_ negotiation.

The reason why is simple: presenting a multiple-leveled list of variants to
the user would be a nightmare for user interface authors.  Especially
because the user agent would need to query all variant resources before you
even _know_ that there are multiple levels, and you can't query them because
of efficiency reasons.  Thus, multiple levels would kind of take the
transparency out of transparent content negotiation.

As a result, the draft treats multiple-level variant lists as a
configuration error, and does its best to report them.

> aside from the fact it isn't in your conception of TCN.

As opposed to your conception of TCN?  If you have a simple solution to the
above presentation problem, by all means post the edits.  If they make sense
to me I will gladly incorporate them.

>   2) The server has neither erred nor become incapable of servicing
>      the request, since all it needs to do is supply the client with
>      whatever message it got from the upstream server.

506 always signals an error in the _origin_ server, even if it is not the
origin server that detects the error.  I see that the draft says `server',
not `origin server'.  This is indeed a mistake, and I will correct it.

>I am saying that the 506 code has no useful purpose, and shouldn't exist.

I argue that it should exist.  Detecting configuration errors is a good
thing.

>....Roy

Koen.