Re: Using server-driven negotiation

I have a question. Is the server required to supply a Vary header when it
did not actually vary the current response?
In the example below, in the absence of a header line Accept-Geo-Position in
the request, the server may be returning a generic response. In this case, I
would assume that the server will not set the Vary header. I am unable to
find any reference to this in 2616. Hence the question.

Regards,
Subbu

On Dec 6, 2007 7:07 AM, Henrik Nordstrom <henrik@henriknordstrom.net> wrote:

> On tis, 2007-12-04 at 13:34 -0800, Andrew Daviel wrote:
> '
> > As I read the RFC, a server should send a Vary header to indicate that
> > the response should only be cached if the listed header values match.
> > When I look at the Apache server, I see that it sends "Vary: lang"
> > even for requests without "Accept: lang", so maybe it's also an
> > indication that different languages are available if the client were to
> > ask.
>
> Yes. Vary lists the header the server looked for when determining the
> response. Not only the headers the server found..
>
> > What I was wondering is, would it be acceptable for a server to
> > send "Vary: geo-position" to an initial request, which would then
> > generate a user dialogue if the server was not previously known.
>
> Yes, if the response varies based on the position.
>
> > The client would then send "Geo-Postion: lat;long" (or not)
> > in the next and subsequent requests, and cached responses could be
> > re-used on match.
>
> Yes, that's fine.
>
> > Or, should we use a different extension header for the server to
> indicate
> > its willingness to accept position data and hence trigger a dialogue,
> > such as "Accept-Geo-Position: true"
>
> The two doesn't exclude each other.
>
> With "Vary: Geo-Position" the server says "I am interested in your
> position as the response varies depending on where you are.
>
> With a new "I want Geo-Position" header without using Vary the server
> says "I want to know your position for tracking reasons, but it doesn't
> affect the response I send to you".
>
> Accept-Geo-Position is probably not a name for the header unless you
> want to define a syntax for specifying what kinds of geo-position the
> server accepts.. should be someting not starting with Accept- I think.
>
> I suggest you start with Vary, and then look into additional in-band or
> out-of-band negotiation of the feature if found needed.
>
> Note: There was a releated proposal some timeago how to negotiate
> extensions, with the aim of controlling transmission of user personal
> information / profile.
>
> Regards
> Henrik
>