Re: Can you cache the unknown? (was Re: Session-ID proposal)

Roy Fielding (
Wed, 23 Aug 1995 18:48:28 -0400

>Is a caching proxy permitted to cache HTTP headers that it doesn't

Yes. In fact, it must.

>Do existing caching proxies cache such headers?


>I'm concerned that there may be a serious problem with use of Dave Kristol's
>State-Info headers prior to general support by caching proxies of his
>requirement that: "...cache... must not cache the State-Info header..." The
>problem I see with this is one that must have already been exprienced with
>Cookies if caching proxies cache headers they don't understand.

Yes. That is why we can't deploy protocol additions properly without
also changing the protocol version. Both State-Info and Cookies are
protocol additions and will not work reliably until they are defined
as part of a new version of the protocol.

Applications receiving these headers must look at the protocol version,
determine whether or not that feature was implemented for that version,
and chose whether or not to believe the header based on that comparison.

>On a slightly different tack... It seems like this whole business of caching
>is getting a bit complicated... It also seems that much of the data needed
>to responsibly cache things is not covered in the HTTP specs themselves.

It will be in the HTTP/1.1 specification.

....Roy T. Fielding Department of ICS, University of California, Irvine USA
Visiting Scholar, MIT/LCS + World-Wide Web Consortium
( (