mod_cache.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 2000-2005 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"

module AP_MODULE_DECLARE_DATA cache_module;
APR_OPTIONAL_FN_TYPE(ap_cache_generate_key) *cache_generate_key;

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


/* Handles for cache filters, resolved at startup to eliminate
 * a name-to-function mapping on each request
 */
static ap_filter_rec_t *cache_save_filter_handle;
static ap_filter_rec_t *cache_out_filter_handle;

/*
 * CACHE handler
 * -------------
 *
 * Can we deliver this request from the cache?
 * If yes:
 *   deliver the content by installing the CACHE_OUT filter.
 * If no:
 *   check whether we're allowed to try cache it
 *   If yes:
 *     add CACHE_SAVE filter
 *   If No:
 *     oh well.
 */

static int cache_url_handler(request_rec *r, int lookup)
{
    apr_status_t rv;
    const char *pragma, *auth;
    apr_uri_t uri;
    char *url;
    char *path;
    cache_provider_list *providers;
    cache_info *info;
    cache_request_rec *cache;
    cache_server_conf *conf;
    apr_bucket_brigade *out;

    /* Delay initialization until we know we are handling a GET */
    if (r->method_number != M_GET) {
        return DECLINED;
    }

    uri = r->parsed_uri;
    url = r->unparsed_uri;
    path = uri.path;
    info = NULL;

    conf = (cache_server_conf *) ap_get_module_config(r->server->module_config,
                                                      &cache_module);

    /*
     * Which cache module (if any) should handle this request?
     */
    if (!(providers = ap_cache_get_providers(r, conf, path))) {
        return DECLINED;
    }

    /* make space for the per request config */
    cache = (cache_request_rec *) ap_get_module_config(r->request_config,
                                                       &cache_module);
    if (!cache) {
        cache = apr_pcalloc(r->pool, sizeof(cache_request_rec));
        ap_set_module_config(r->request_config, &cache_module, cache);
    }

    /* save away the possible providers */
    cache->providers = providers;

    /*
     * Are we allowed to serve cached info at all?
     */

    /* find certain cache controlling headers */
    pragma = apr_table_get(r->headers_in, "Pragma");
    auth = apr_table_get(r->headers_in, "Authorization");

    /* first things first - does the request allow us to return
     * cached information at all? If not, just decline the request.
     *
     * Note that there is a big difference between not being allowed
     * to cache a request (no-store) and not being allowed to return
     * a cached request without revalidation (max-age=0).
     *
     * Caching is forbidden under the following circumstances:
     *
     * - RFC2616 14.9.2 Cache-Control: no-store
     * - Pragma: no-cache
     * - Any requests requiring authorization.
     */
    if (conf->ignorecachecontrol == 1 && auth == NULL) {
        ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server,
                     "incoming request is asking for a uncached version of "
                     "%s, but we know better and are ignoring it", url);
    }
    else {
        if (ap_cache_liststr(NULL, pragma, "no-cache", NULL) ||
            auth != NULL) {
            ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server,
                         "cache: no-cache or authorization forbids caching "
                         "of %s", url);
            return DECLINED;
        }
    }

    /*
     * Try to serve this request from the cache.
     *
     * If no existing cache file (DECLINED)
     *   add cache_save filter
     * If cached file (OK)
     *   clear filter stack
     *   add cache_out filter
     *   return OK
     */
    rv = cache_select_url(r, url);
    if (rv != OK) {
        if (rv == DECLINED) {
            if (!lookup) {
                /* add cache_save filter to cache this request */
                ap_add_output_filter_handle(cache_save_filter_handle, NULL, r,
                                            r->connection);
            }
        }
        else {
            /* error */
            ap_log_error(APLOG_MARK, APLOG_ERR, rv, r->server,
                         "cache: error returned while checking for cached "
                         "file by %s cache", cache->provider_name);
        }
        return DECLINED;
    }

    /* We have located a suitable cache file now. */
    info = &(cache->handle->cache_obj->info);

    if (info && info->lastmod) {
        ap_update_mtime(r, info->lastmod);
    }

    rv = ap_meets_conditions(r);
    if (rv != OK) {
        /* Return cached status. */
        return rv;
    }

    /* If we're a lookup, we can exit now instead of serving the content. */
    if (lookup) {
        return OK;
    }

    /* Serve up the content */

    /* We are in the quick handler hook, which means that no output
     * filters have been set. So lets run the insert_filter hook.
     */
    ap_run_insert_filter(r);
    ap_add_output_filter_handle(cache_out_filter_handle, NULL,
                                r, r->connection);

    /* kick off the filter stack */
    out = apr_brigade_create(r->pool, r->connection->bucket_alloc);
    rv = ap_pass_brigade(r->output_filters, out);
    if (rv != APR_SUCCESS) {
        ap_log_error(APLOG_MARK, APLOG_ERR, rv, r->server,
                     "cache: error returned while trying to return %s "
                     "cached data", 
                     cache->provider_name);
        return rv;
    }

    return OK;
}

/*
 * CACHE_OUT filter
 * ----------------
 *
 * Deliver cached content (headers and body) up the stack.
 */
static int cache_out_filter(ap_filter_t *f, apr_bucket_brigade *bb)
{
    request_rec *r = f->r;
    cache_request_rec *cache;

    cache = (cache_request_rec *) ap_get_module_config(r->request_config, 
                                                       &cache_module);

    if (!cache) {
        /* user likely configured CACHE_OUT manually; they should use mod_cache
         * configuration to do that */
        ap_log_error(APLOG_MARK, APLOG_ERR, 0, r->server,
                     "CACHE_OUT enabled unexpectedly");
        ap_remove_output_filter(f);
        return ap_pass_brigade(f->next, bb);
    }

    ap_log_error(APLOG_MARK, APLOG_DEBUG, APR_SUCCESS, r->server,
                 "cache: running CACHE_OUT filter");

    /* recall_headers() was called in cache_select_url() */
    cache->provider->recall_body(cache->handle, r->pool, bb);

    /* This filter is done once it has served up its content */
    ap_remove_output_filter(f);

    ap_log_error(APLOG_MARK, APLOG_DEBUG, APR_SUCCESS, r->server,
                 "cache: serving %s", r->uri);
    return ap_pass_brigade(f->next, bb);
}


/*
 * CACHE_SAVE filter
 * ---------------
 *
 * Decide whether or not this content should be cached.
 * If we decide no it should not:
 *   remove the filter from the chain
 * If we decide yes it should:
 *   Have we already started saving the response?
 *      If we have started, pass the data to the storage manager via store_body
 *      Otherwise:
 *        Check to see if we *can* save this particular response.
 *        If we can, call cache_create_entity() and save the headers and body
 *   Finally, pass the data to the next filter (the network or whatever)
 */

static int cache_save_filter(ap_filter_t *f, apr_bucket_brigade *in)
{
    int rv;
    int date_in_errhdr = 0;
    request_rec *r = f->r;
    cache_request_rec *cache;
    cache_server_conf *conf;
    char *url = r->unparsed_uri;
    const char *cc_in, *cc_out, *cl;
    const char *exps, *lastmods, *dates, *etag;
    apr_time_t exp, date, lastmod, now;
    apr_off_t size;
    cache_info *info;
    char *reason;
    apr_pool_t *p;

    /* check first whether running this filter has any point or not */
    /* If the user has Cache-Control: no-store from RFC 2616, don't store! */
    cc_in = apr_table_get(r->headers_in, "Cache-Control");
    if (r->no_cache || ap_cache_liststr(NULL, cc_in, "no-store", NULL)) {
        ap_remove_output_filter(f);
        return ap_pass_brigade(f->next, in);
    }

    /* Setup cache_request_rec */
    cache = (cache_request_rec *) ap_get_module_config(r->request_config,
                                                       &cache_module);
    if (!cache) {
        /* user likely configured CACHE_SAVE manually; they should really use
         * mod_cache configuration to do that
         */
        cache = apr_pcalloc(r->pool, sizeof(cache_request_rec));
        ap_set_module_config(r->request_config, &cache_module, cache);
    }

    reason = NULL;
    p = r->pool;
    /*
     * Pass Data to Cache
     * ------------------
     * This section passes the brigades into the cache modules, but only
     * if the setup section (see below) is complete.
     */
    if (cache->block_response) {
        /* We've already sent down the response and EOS.  So, ignore
         * whatever comes now.
         */
        return APR_SUCCESS;
    }

    /* have we already run the cachability check and set up the
     * cached file handle? 
     */
    if (cache->in_checked) {
        /* pass the brigades into the cache, then pass them
         * up the filter stack
         */
        rv = cache->provider->store_body(cache->handle, r, in);
        if (rv != APR_SUCCESS) {
            ap_remove_output_filter(f);
        }
        return ap_pass_brigade(f->next, in);
    }

    /*
     * Setup Data in Cache
     * -------------------
     * This section opens the cache entity and sets various caching
     * parameters, and decides whether this URL should be cached at
     * all. This section is* run before the above section.
     */