Function cache_select

modules/cache/cache_storage.c:214–426

* select a specific URL entity in the cache * * It is possible to store more than one entity per URL. Content * negotiation is used to select an entity. Once an entity is * selected, details of it are stored in the per request * config to save time when serving the request later. * * This function returns OK if successful, DECLINED if no * cached entity fits the bill. */

 * cached entity fits the bill.
 */
int cache_select(cache_request_rec *cache, request_rec *r)
{
    cache_provider_list *list;
    apr_status_t rv;
    cache_handle_t *h;

    if (!cache) {
        /* This should never happen */
        ap_log_rerror(APLOG_MARK, APLOG_ERR, APR_EGENERAL, r, APLOGNO(00693)
                "cache: No cache request information available for key"
                " generation");
        return DECLINED;
    }

    /* if no-cache, we can't serve from the cache, but we may store to the
     * cache.
     */
    if (!ap_cache_check_no_cache(cache, r)) {
        return DECLINED;
    }

    if (!cache->key) {
        rv = cache_generate_key(r, r->pool, &cache->key);
        if (rv != APR_SUCCESS) {
            return DECLINED;
        }
    }

    /* go through the cache types till we get a match */
    h = apr_palloc(r->pool, sizeof(cache_handle_t));

    list = cache->providers;

    while (list) {
        switch ((rv = list->provider->open_entity(h, r, cache->key))) {
        case OK: {
            char *vary = NULL;
            int mismatch = 0;
            char *last = NULL;

            if (list->provider->recall_headers(h, r) != APR_SUCCESS) {
                /* try again with next cache type */
                list = list->next;
                continue;
            }

            /*
             * Check Content-Negotiation - Vary
             *
             * At this point we need to make sure that the object we found in
             * the cache is the same object that would be delivered to the
             * client, when the effects of content negotiation are taken into
             * effect.
             *
             * In plain english, we want to make sure that a language-negotiated
             * document in one language is not given to a client asking for a
             * language negotiated document in a different language by mistake.
             *