Re: ETags vs Variants, was: Revising RFC2616 - what's happening

On Sun, 22 Oct 2006, Jamie Lokier wrote:

> Consider, for example, a server implementation that does this (this
> is reasonable):
>
>   1. Look at "Accept-Encoding" to decide if known compression methods
>      are supported as a content-encoding.
>
>   2. If compression is supported, then for some types of response,
>      look at "User-Agent" to check for certain agents that do not
>      behave correctly for some compressed content types.
>
> That server would produce the following two _correct_ responses, for
> different request headers:
>
>   a. Vary: Accept-Encoding
>
>   b. Vary: Accept-Encoding, User-Agent
>      Content-Encoding: gzip

Is it the same server with the same configuration on the same URI ? 
because if it's the case, then only b) is right. The server has the 
knowledge of the variability axis and should populate the Vary: header 
accordingly and not on a case-by-case basis.
My reading of the spec is that Vary should carry the list of all headers 
used to send compute the variant, so f(x,y), and not send f(5, y) = g(y).
Cheers,

-- 
Yves Lafon - W3C
"Baroula que barouleras, au tiéu toujou t'entourneras."