Morning list;
While playing around with mod_cache & Drupal (Pressflow actually) I
think I may have found a problem in mod_cache's implementation of the
http/1.1 cache expiration mechanism.
According to the spec (rfc 2616, 14.9.3), cache-control max-age
overrules expires:
"If a response includes both an Expires header and a max-age
directive, the max-age directive overrides the Expires header, even if
the Expires header is more restrictive. This rule allows an origin
server to provide, for a given response, a longer expiration time to
an HTTP/1.1 (or later) cache than to an HTTP/1.0 cache. This might be
useful if certain HTTP/1.0 caches improperly calculate ages or
expiration times, perhaps due to desynchronized clocks."
Indeed, this part of the spec is used by Pressflow to tell http/1.0
caches not to cache (with an expires in the past) because those don't
understand vary:cookie, while cache-control's max-age specifies a
value > 0, which should allow http/1.1 caches to store the object.
Now while testing Pressflow with mod_cache (with Apache's loglevel set
to debug), I got "not cached. Reason: Expires header already expired,
not cacheable" entries in my logfile, although there was a valid
cache-control:max-age present. Judging by the mod_cache.c sourcecode
(warning: i'm not a C-developer by any account) it indeed seems
Expires in the past are enough to not cache an object, disregarding a
potential cache-control's max-age;
---
else if (exp != APR_DATE_BAD && exp < r->request_time)
{
/* if a Expires header is in the past, don't cache it */
reason = "Expires header already expired, not cacheable";
}
---
(cfr. http://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x/modules/cache/mod_cache.c
line 503)
So shouldn't the condition be expanded with checks on
cache-control:max-age to comply with the spec? Or am I missing
something here?
Kind regards,
frank
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