Re: Pragma: header and preventing caching in general

Reinier Post (
Wed, 8 Jun 1994 11:49:52 +0200 (MET DST)

You (Rainer Klute) write:
>>The second question: several occasions have arisen in which it would be useful
>>for the remote server (not the client) to explicitly indicate that
>>the document sent must not be cached. (For example, the case of WIRED,
>>where fragments of copyrighted material are cached, but copyright is not
>>on the individual fragments.) Can I suggest that the Pragma: no-cache header
>>is added to the valid HTTP response headers?
>Of course you can suggest that, but there is already the Expires: header which
>gives the server complete control over when a document should be regarded
>out-dated. If only information providers would support that header!

Agreed, but there would be a subtle difference. If a document is expired,
the cache knows it's going to serve an outdated copy, and is free to do so.
If a document is marked 'not to be cached', the cache is not allowed to
cache it at all. (For example, because of copyright violation.)
Of course 'Expires: 0' could be assigned to have that meaning, which would
eliminate the need for an extra header.

I'll retry this question on www-proxy.

Reinier Post
a.k.a. <A HREF="">me</A>