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From Ruediger Pluem <>
Subject Re: HTTP Protocol: How frequently should browser repeat requests after 304 responses?
Date Wed, 17 Sep 2008 21:34:51 GMT

On 09/17/2008 10:00 PM, Dan Poirier wrote:
> I've looked at mod_expires doc and RFC 2616, but can't really
> tell what the right behavior is supposed to be in this case.
> Using mod_expire to set the expiration time to something like
> "access plus 1 hour", we see a browser request a file, get back
> a 200 with the expiration, and not request it again for an hour,
> as expected.  The next time, it uses an if-modified-since and
> gets back a 304, also good.  But from then on, it keeps coming
> back to the server every time and getting back 304's.
> The 304 responses won't have any cache control information, of
> course, per RFC 2616 10.3.5.

I don't read from RFC 2616 10.3.5 that there shouldn't be any cache control
related headers contained in the response. On the contrary: If the values
for Expires or Cache-Control changed these values MUST be included.
So I guess we have a bug in mod_expires here. I guess this is caused by
the position of the MOD_EXPIRES filter in the filter chain. It is
AP_FTYPE_CONTENT_SET-2 as it needs to run before the cache save filter.
I guess (haven't checked so far) that we do not run through these filters
if a handler simply returns a 304.



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