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From Sander Striker <stri...@apache.org>
Subject Re: mod_cache
Date Mon, 07 Mar 2005 01:03:34 GMT
> Sander Striker wrote:
>> Justin Erenkrantz wrote:
>>> Sander Striker wrote:

>>> AIUI, we can cache "302 Found" (HTTP_MOVED_TEMPORARILY) when it has an
>>> Expires or Cache-Control indicating that the request can be cached.
>>
>>
>> Fair enough.  Feel free to add it, if you like.
> 
> 
> Well, I'm first going to check if we are doing the right thing with
> cached 301s (I saw some wonkiness earlier, but need to reverify).  If
> that is all good, I'll add 302 support.

I'm fairly sure this doesn't work too well yet.  See below.
 
> [...]
> 
>>>         /* Were we initially a conditional request? */
>>>         if (ap_cache_request_is_conditional(cache->stale_headers)) {
>>>             /* FIXME: We must ensure that the request meets 
>>> conditions. */
>>>
>>>             /* Set the status to be a 304. */
>>>             r->status = HTTP_NOT_MODIFIED;
>>>
>>> Is this as simple as clearing r->headers_in, overwriting with
>>> cache->stale_headers,
>>> and the calling ap_meets_conditions()?
>>
>> Yes, I *believe* so.  But, we should double-check that 
>> ap_meets_condition would do the 'right' thing.  I'm not 100% sure here.
> 
> I'm fairly sure it would.  Considering we have the final response headers,
> and the original request headers, this is just like a normal request.
> So ap_meets_condition should do the trick just fine when it comes to
> figuring out what to send back to the client.  I'll test, and if it works,
> I'll commit it.

It works (gave the correct results on cached, cached revalidating, not cached)
so I committed it (r156330).

However, I do think you are right that ap_meets_conditions() doesn't do the
right thing.  But that is in general, not just in this case.  It doesn't
seem to take responses other than 2xx into account.  In those cases it shouldn't
return a 304, yet it does.  We'll have to visit all the places where
ap_meets_conditions() is called to make sure r->status is set, and check
r->status in ap_meets_conditions() to fix this.

Luckily for us, there is more work left even in mod_cache.  Right now,
whenever we hit a Cache-Control: no-cache in the request, the cache declines
to handle the request, while it could be handling it (be it with a required
validation request to the backend).  That would be a lot more efficient.
And within bounds of the spec.

Furthermore, Cache-Control: max-age=0 or even max-age=X seems to be completely
ignored.  A response is given back with an Age header with a larger value then
what max-age was set to in the request.


Sander

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