mod_cache: caching status

[Graham Leggett <mi...@sharp.fm>]

Hi all,

One of the things that mod_cache doesn't do very well is tell the  
world what it is doing. This can vary from "did this request score a  
miss/hit/revalidate?" to "how efficient is this url space overall  
generally". This problem is highlighted in https://issues.apache.org/bugzilla/show_bug.cgi?id=48241 
.

I have implemented a cache_status hook that is called once mod_cache  
has made up it's mind as to whether the entity is a HIT, a MISS or a  
REVALIDATE, along with the detailed reason for the cache's decision.  
Other modules can hook themselves in to do more detailed cache  
statistics gathering should they choose to do so.

A default simple cache_status hook is provided that optionally logs  
the cache status to the X-Cache header. For the benefit of developers  
of restful services, the cache also optionally places the detailed  
cache reason into an X-Cache-Detail header, which can be used during  
development of restful applications to validate whether cache  
behaviour is correct.

Regards,
Graham
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