- From: Jeffrey Mogul <mogul@pa.dec.com>
- Date: Fri, 14 Mar 97 16:15:39 PST
- To: http-wg@cuckoo.hpl.hp.com
Koen and I have been discussing offline whether it is possible to send Expires: Sun, 06 Nov 1994 08:49:37 GMT (or some similar ancient date) to ensure that *every* pre-HTTP/1.1 proxy cache will not, under *any* circumstances, cache the response. This is NOT a question about what HTTP/1.1 specifies, or how RFC1945 describes HTTP/1.0, or what is "right", or what is "common." This is a question about the worst case of current practice; please don't start a debate over whether current practice is good or bad. We know that HTTP/1.1 allows caches to ignore Expires under certain well-defined circumstances; we are NOT asking about that. We're also not interested in proxy cache implementations that were in use at some point in the past, if it is known for sure that they are not in use today (nor will be used in the future). Many of the proxy caches in use today are based on either the CERN httpd (written by Ari Luotonen) or the Harvest/Squid cache (written, I believe, by several people including Peter Danzig. I checked with Ari and with Peter Danzig; both say that none of their caches have ever ignored an explicit Expires. Koen mentioned this: Shel Kaphan told me about 1.5 years ago that AOL's proxy cached 1.0 responses for some minimum time no matter what. I don't know if that is still true now. Also, I think New Zealand's (academic) hierarchical proxy cache system has some kind of nontransparency for `certain sites with a low educational value'. We checked with Shel, and he replied: I'm sorry, but once I developed enough electronic counter-measures for AOL and other systems out there, I stopped paying a lot of attention to these anomolies except in cases where particular systems have given us trouble. I actually don't recall my claim about AOL, but if Koen says I said it, I must have said it. At the moment we're still not issuing Expires headers, especially to cause pages never to be cached, because of the much discussed history list interactions, so we wouldn't have been running into this lately anyway. So at this point, we're not sure. Perhaps someone with both an AOL account and the ability to generate various Expires headers can do an experiment on AOL's cache (or perhaps someone from AOL can respond?). -Jeff
Received on Friday, 14 March 1997 16:21:34 UTC