- From: Roy T. Fielding <fielding@avron.ICS.UCI.EDU>
- Date: Sun, 18 Feb 1996 00:33:08 -0800
- To: Shel Kaphan <sjk@amazon.com>
- Cc: hardie@nasa.gov, http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com
> Roy T. Fielding writes:
>> > On a related note, does cache-control: max-age 0 also force
>> > a reload (by asking for a copy of the resource that is no older than
>> > 0 seconds old?).
>>
>> No, it forces a "refresh" (i.e., a conditional GET on the next inbound
>> server w/max-age=0, which results in a conditional GET on the origin).
>> It is possible that the refresh will result in a reload, but only if
>> the server decides that the resource has changed.
>
> How is a request containing
> cache-control: max-age=0
> but NOT
> if-modified-since: <last modified date of resource>
>
> conditional? Without if-modified-since, the origin server would
> always have to return a full response, wouldn't it?
Yes, but I said the request *would* include an IMS by saying "conditional GET"
(the reason for not saying IMS is because there are now other proposed ways
to make a request conditional).
What "cache-control: max-age=0" does is force the cache to do a refresh,
and the refresh action is a conditional GET on the next inbound server.
By including max-age in the request (in addition to IMS), the
conditional GET can only be answered by a cache with age <= max-age
or by the origin server. Thus, max-age=0 will effectively propagate
a condional GET all the way to the origin.
...Roy T. Fielding
Department of Information & Computer Science (fielding@ics.uci.edu)
University of California, Irvine, CA 92717-3425 fax:+1(714)824-4056
http://www.ics.uci.edu/~fielding/
Received on Sunday, 18 February 1996 00:37:24 UTC