Squid internals

Flow of a typical request
Once the redirectors have finished maiming the URL clientRedirectDone() is called
clientRedirectDone() handles substituting any new URL and request type, and then checks whether we don't cache this object through clientCheckNoCache()

clientCheckNoCache() checks the no_cache ACL

clientCheckNoCacheDone() is then called which simply marks the request as cacheable or not depending upon the result of the ACL

clientCheckNoCacheDone() then calls clientProcessRequest() to start processing the request