cache_util.c

Apache HTTP Server 是一个功能强大的灵活的与HTTP/1.1相兼容的web服务器.这里给出的是Apache HTTP服务器的源码。

/* Copyright 2001-2005 The Apache Software Foundation or its licensors, as
 * applicable.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#define CORE_PRIVATE

#include "mod_cache.h"

#include <ap_provider.h>

/* -------------------------------------------------------------- */

/* return true if the request is conditional */
CACHE_DECLARE(int) ap_cache_request_is_conditional(apr_table_t *table)
{
    if (apr_table_get(table, "If-Match") ||
        apr_table_get(table, "If-None-Match") ||
        apr_table_get(table, "If-Modified-Since") ||
        apr_table_get(table, "If-Unmodified-Since")) {
        return 1;
    }
    return 0;
}

CACHE_DECLARE(cache_provider_list *)ap_cache_get_providers(request_rec *r,
                                                  cache_server_conf *conf, 
                                                  const char *url)
{
    cache_provider_list *providers = NULL;
    int i;

    /* we can't cache if there's no URL */
    /* Is this case even possible?? */
    if (!url) return NULL;

    /* loop through all the cacheenable entries */
    for (i = 0; i < conf->cacheenable->nelts; i++) {
        struct cache_enable *ent = 
                                (struct cache_enable *)conf->cacheenable->elts;
        if ((ent[i].url) && !strncasecmp(url, ent[i].url, ent[i].urllen)) {
            /* Fetch from global config and add to the list. */
            cache_provider *provider;
            provider = ap_lookup_provider(CACHE_PROVIDER_GROUP, ent[i].type,
                                          "0");
            if (!provider) {
                /* Log an error! */
            }
            else {
                cache_provider_list *newp;
                newp = apr_pcalloc(r->pool, sizeof(cache_provider_list));
                newp->provider_name = ent[i].type;
                newp->provider = provider;

                if (!providers) {
                    providers = newp;
                }
                else {
                    cache_provider_list *last = providers;

                    while (last->next) {
                        last = last->next;
                    }
                    last->next = newp;
                }
            }
        }
    }

    /* then loop through all the cachedisable entries
     * Looking for urls that contain the full cachedisable url and possibly
     * more.
     * This means we are disabling cachedisable url and below...
     */
    for (i = 0; i < conf->cachedisable->nelts; i++) {
        struct cache_disable *ent = 
                               (struct cache_disable *)conf->cachedisable->elts;
        if ((ent[i].url) && !strncasecmp(url, ent[i].url, ent[i].urllen)) {
            /* Stop searching now. */
            return NULL;
        }
    }

    return providers;
}


/* do a HTTP/1.1 age calculation */
CACHE_DECLARE(apr_int64_t) ap_cache_current_age(cache_info *info,
                                                const apr_time_t age_value,
                                                apr_time_t now)
{
    apr_time_t apparent_age, corrected_received_age, response_delay,
               corrected_initial_age, resident_time, current_age,
               age_value_usec;

    age_value_usec = apr_time_from_sec(age_value);

    /* Perform an HTTP/1.1 age calculation. (RFC2616 13.2.3) */

    apparent_age = MAX(0, info->response_time - info->date);
    corrected_received_age = MAX(apparent_age, age_value_usec);
    response_delay = info->response_time - info->request_time;
    corrected_initial_age = corrected_received_age + response_delay;
    resident_time = now - info->response_time;
    current_age = corrected_initial_age + resident_time;

    return apr_time_sec(current_age);
}

CACHE_DECLARE(int) ap_cache_check_freshness(cache_handle_t *h,
                                            request_rec *r)
{
    apr_int64_t age, maxage_req, maxage_cresp, maxage, smaxage, maxstale;
    apr_int64_t minfresh;
    int age_in_errhdr = 0;
    const char *cc_cresp, *cc_ceresp, *cc_req;
    const char *agestr = NULL;
    const char *expstr = NULL;
    char *val;
    apr_time_t age_c = 0;
    cache_info *info = &(h->cache_obj->info);

    /*
     * We now want to check if our cached data is still fresh. This depends
     * on a few things, in this order:
     *
     * - RFC2616 14.9.4 End to end reload, Cache-Control: no-cache. no-cache in
     * either the request or the cached response means that we must
     * revalidate the request unconditionally, overriding any expiration
     * mechanism. It's equivalent to max-age=0,must-revalidate.
     * 
     * - RFC2616 14.32 Pragma: no-cache This is treated the same as
     * Cache-Control: no-cache.
     * 
     * - RFC2616 14.9.3 Cache-Control: max-stale, must-revalidate,
     * proxy-revalidate if the max-stale request header exists, modify the
     * stale calculations below so that an object can be at most <max-stale>
     * seconds stale before we request a revalidation, _UNLESS_ a
     * must-revalidate or proxy-revalidate cached response header exists to
     * stop us doing this.
     * 
     * - RFC2616 14.9.3 Cache-Control: s-maxage the origin server specifies the
     * maximum age an object can be before it is considered stale. This
     * directive has the effect of proxy|must revalidate, which in turn means
     * simple ignore any max-stale setting.
     * 
     * - RFC2616 14.9.4 Cache-Control: max-age this header can appear in both
     * requests and responses. If both are specified, the smaller of the two
     * takes priority.
     * 
     * - RFC2616 14.21 Expires: if this request header exists in the cached
     * entity, and it's value is in the past, it has expired.
     * 
     */
    cc_cresp = apr_table_get(h->resp_hdrs, "Cache-Control");
    cc_ceresp = apr_table_get(h->resp_err_hdrs, "Cache-Control");
    cc_req = apr_table_get(h->req_hdrs, "Cache-Control");

    if ((agestr = apr_table_get(h->resp_hdrs, "Age"))) {
        age_c = apr_atoi64(agestr);
    }
    else if ((agestr = apr_table_get(h->resp_err_hdrs, "Age"))) {
        age_c = apr_atoi64(agestr);
        age_in_errhdr = 1;
    }

    if (!(expstr = apr_table_get(h->resp_err_hdrs, "Expires"))) {
        expstr = apr_table_get(h->resp_hdrs, "Expires");
    }

    /* calculate age of object */
    age = ap_cache_current_age(info, age_c, r->request_time);

    /* extract s-maxage */
    if (cc_cresp && ap_cache_liststr(r->pool, cc_cresp, "s-maxage", &val)) {
        smaxage = apr_atoi64(val);
    }
    else if (cc_ceresp && ap_cache_liststr(r->pool, cc_ceresp, "s-maxage", &val)) {
        smaxage = apr_atoi64(val);
    }
    else {
        smaxage = -1;
    }

    /* extract max-age from request */
    if (cc_req && ap_cache_liststr(r->pool, cc_req, "max-age", &val)) {
        maxage_req = apr_atoi64(val);
    }
    else {
        maxage_req = -1;
    }

    /* extract max-age from response */
    if (cc_cresp && ap_cache_liststr(r->pool, cc_cresp, "max-age", &val)) {
        maxage_cresp = apr_atoi64(val);
    }
    else if (cc_ceresp && ap_cache_liststr(r->pool, cc_ceresp, "max-age", &val)) {
        maxage_cresp = apr_atoi64(val);
    }
    else
    {
        maxage_cresp = -1;
    }

    /*
     * if both maxage request and response, the smaller one takes priority
     */
    if (-1 == maxage_req) {
        maxage = maxage_cresp;
    }
    else if (-1 == maxage_cresp) {
        maxage = maxage_req;
    }
    else {
        maxage = MIN(maxage_req, maxage_cresp);
    }

    /* extract max-stale */
    if (cc_req && ap_cache_liststr(r->pool, cc_req, "max-stale", &val)) {
        maxstale = apr_atoi64(val);
    }
    else {
        maxstale = 0;
    }

    /* extract min-fresh */
    if (cc_req && ap_cache_liststr(r->pool, cc_req, "min-fresh", &val)) {
        minfresh = apr_atoi64(val);
    }
    else {
        minfresh = 0;
    }

    /* override maxstale if must-revalidate or proxy-revalidate */
    if (maxstale && ((cc_cresp &&
                      ap_cache_liststr(NULL, cc_cresp,
                                       "must-revalidate", NULL)) ||
                     (cc_cresp &&
                      ap_cache_liststr(NULL, cc_cresp,
                                       "proxy-revalidate", NULL)) ||
                     (cc_ceresp &&
                      ap_cache_liststr(NULL, cc_ceresp,
                                       "must-revalidate", NULL)) ||
                     (cc_ceresp &&
                      ap_cache_liststr(NULL, cc_ceresp,
                                       "proxy-revalidate", NULL)))) {
        maxstale = 0;
    }

    /* handle expiration */
    if (((smaxage != -1) && (age < (smaxage - minfresh))) ||
        ((maxage != -1) && (age < (maxage + maxstale - minfresh))) ||
        ((smaxage == -1) && (maxage == -1) &&
         (info->expire != APR_DATE_BAD) &&
         (age < (apr_time_sec(info->expire - info->date) + maxstale - minfresh)))) {
        const char *warn_head;
        apr_table_t *head_ptr;