Re: Cache servers and Date: header

Roy T. Fielding (fielding@avron.ICS.UCI.EDU)
Sat, 17 Sep 1994 09:20:10 +0200

John Franks writes:

> Do caching servers add there own headers before passing along the document?

Not in general -- there is no standard for doing so. Adding received headers
has been discussed on www-proxy.

> I hope so. As with mail it should be possible from the header to learn
> through whose hands a document has passed on the way to the client. Also
> each caching server should add a Date-cached: header similar to the mail
> Received: header.
> If this is done there really isn't much reason for having a Date:
> header from the original server (the Last-Modified-Date: is analogous
> to the Date: in mail). On the other hand it isn't very expensive
> either.

There are several reasons, which I outlined in a prior message. Perhaps
most important, however, is that the whole reason we are passing all these
inefficient text headers around is so that the message is a valid
rfc822/MIME message and can thus be passed on to various mail and news
gateways without changing the format. The Date: header is a REQUIRED
header for rfc822.

Yes, clients and caching proxies and cache managers and gateways can all
be hacked to parse all the headers and, if no Date is present, tack on one
of their own. But why should they? The server is at fault for sending
an invalid message -- it should be fixed.

.....Roy Fielding ICS Grad Student, University of California, Irvine USA