Re: Vary VS URI with an eye towards caching

>  varying = field-name | "external-factor"

I was thinking just "Vary:" with an empty value would indicate that it
varied but not on any header.  A special tag would work too, but obviously
it would have to be a tag that could never be a header.

>200.3) No URI, a Vary, no Location:
>
>    - opaque negotiation
>    - response body varies on things in the Vary header,
>    - but no `send-no-body-for' possible

'Send-no-body-for' might still be possible if we adopt a content-id opaque
validator scheme in addition to the Location scheme.

So basically I'm advocating a 2^4 combination.  Just great...

>200.8) A URI, a Vary, a Location:
>    - partly opaque, partly transparent negotiation:
>    - URI header varies on the things in the Vary header
>    - Location and response body are a variant given by preemptive
>      negotiation using the variants in the URI header
>    - `send-no-body-for' possible
>300.7) A URI, a Vary, no Location:
>    - do transparent reactive negotiation using the URI header
>    - URI header varies on the things in the Vary header
>300.8) A URI, a Vary, a Location:
>    - as 300.7.
>    - If not capable of reactive negotiation, use the URI in the Location
>      header.

I'm a little fuzzy on the behavior in these cases (especailly the 300s), so
let's make sure if we allow this, what it mean gets explained in great
detail.  It's not clear to me that a proxy can do anything with 200.8 except
call the server, unless it takes on the responsibility of saving previous
request headers to compare on the Vary: header.  I suppose that's a proxy
implementation choice, but I'd like it to be explicit.

We might also need to explore in more detail whether or not Vary:
Authentication needs to be sent, and if it actually indicates anything in
terms of behavior.  [Personally, I think I'd like to see "Vary:
Authentication" safely ignore-able, and WWW-Authenticate'd responses not
proxy-cached unless there was a Cache-Control: public directive (for
needlessly Authenticaiton:'ed imagaes and the like).]
-----
Dan DuBois, Software Animal             http://www.spyglass.com/~ddubois/
		I absolutely do not speak for Spyglass.

Received on Friday, 12 January 1996 16:29:52 UTC