mod_cache.c

/* Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.
 */

#include "mod_cache.h"

#include "cache_storage.h"
#include "cache_util.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_filter_handle;
static ap_filter_rec_t *cache_save_filter_handle;
static ap_filter_rec_t *cache_save_subreq_filter_handle;
static ap_filter_rec_t *cache_out_filter_handle;
static ap_filter_rec_t *cache_out_subreq_filter_handle;
static ap_filter_rec_t *cache_remove_url_filter_handle;
static ap_filter_rec_t *cache_invalidate_filter_handle;

/**
 * Entity headers' names
 */
static const char *MOD_CACHE_ENTITY_HEADERS[] = {
    "Allow",
    "Content-Encoding",
    "Content-Language",
    "Content-Length",
    "Content-Location",
    "Content-MD5",
    "Content-Range",
    "Content-Type",
    "Last-Modified",
    NULL
};

/*
 * 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.
 *
 * By default, the cache handler runs in the quick handler, bypassing
 * virtually all server processing and offering the cache its optimal
 * performance. In this mode, the cache bolts onto the front of the
 * server, and behaves as a discrete RFC2616 caching proxy
 * implementation.
 *
 * Under certain circumstances, an admin might want to run the cache as
 * a normal handler instead of a quick handler, allowing the cache to
 * run after the authorisation hooks, or by allowing fine control over
 * the placement of the cache in the filter chain. This option comes at
 * a performance penalty, and should only be used to achieve specific
 * caching goals where the admin understands what they are doing.
 */

static int cache_quick_handler(request_rec *r, int lookup)
{
    apr_status_t rv;
    const char *auth;
    cache_provider_list *providers;
    cache_request_rec *cache;
    apr_bucket_brigade *out;
    apr_bucket *e;
    ap_filter_t *next;
    ap_filter_rec_t *cache_out_handle;
    cache_server_conf *conf;

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

    /* only run if the quick handler is enabled */
    if (!conf->quick) {
        return DECLINED;
    }

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

    /* make space for the per request config */
    cache = apr_pcalloc(r->pool, sizeof(cache_request_rec));
    cache->size = -1;
    cache->out = apr_brigade_create(r->pool, r->connection->bucket_alloc);

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

    /*
     * Are we allowed to serve cached info at all?
     */
    if (!ap_cache_check_no_store(cache, r)) {
        return DECLINED;
    }

    /* find certain cache controlling headers */
    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.
     */
    if (auth) {
        return DECLINED;
    }

    /* Are we PUT/POST/DELETE? If so, prepare to invalidate the cached entities.
     */
    switch (r->method_number) {
    case M_PUT:
    case M_POST:
    case M_DELETE:
    {

        ap_log_rerror(APLOG_MARK, APLOG_DEBUG, APR_SUCCESS, r, APLOGNO(02461)
                "PUT/POST/DELETE: Adding CACHE_INVALIDATE filter for %s",
                r->uri);

        /* Add cache_invalidate filter to this request to force a
         * cache entry to be invalidated if the response is
         * ultimately successful (2xx).
         */
        ap_add_output_filter_handle(
                cache_invalidate_filter_handle, cache, r,
                r->connection);

        return DECLINED;
    }
    case M_GET: {
        break;
    }
    default : {

        ap_log_rerror(
                APLOG_MARK, APLOG_DEBUG, APR_SUCCESS, r, APLOGNO(02462) "cache: Method '%s' not cacheable by mod_cache, ignoring: %s", r->method, r->uri);

        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(cache, r);
    if (rv != OK) {
        if (rv == DECLINED) {
            if (!lookup) {

                /* try to obtain a cache lock at this point. if we succeed,
                 * we are the first to try and cache this url. if we fail,
                 * it means someone else is already trying to cache this
                 * url, and we should just let the request through to the
                 * backend without any attempt to cache. this stops
                 * duplicated simultaneous attempts to cache an entity.
                 */
                rv = cache_try_lock(conf, cache, r);
                if (APR_SUCCESS == rv) {

                    /*
                     * Add cache_save filter to cache this request. Choose
                     * the correct filter by checking if we are a subrequest
                     * or not.
                     */
                    if (r->main) {
                        ap_log_rerror(APLOG_MARK, APLOG_DEBUG, APR_SUCCESS,
                                r, APLOGNO(00749) "Adding CACHE_SAVE_SUBREQ filter for %s",
                                r->uri);
                        cache->save_filter = ap_add_output_filter_handle(
                                cache_save_subreq_filter_handle, cache, r,
                                r->connection);
                    }
                    else {
                        ap_log_rerror(APLOG_MARK, APLOG_DEBUG, APR_SUCCESS,
                                r, APLOGNO(00750) "Adding CACHE_SAVE filter for %s",
                                r->uri);
                        cache->save_filter = ap_add_output_filter_handle(
                                cache_save_filter_handle, cache, r,
                                r->connection);
                    }

                    apr_pool_userdata_setn(cache, CACHE_CTX_KEY, NULL, r->pool);

                    ap_log_rerror(APLOG_MARK, APLOG_DEBUG, APR_SUCCESS, r, APLOGNO(00751)
                            "Adding CACHE_REMOVE_URL filter for %s",
                            r->uri);

                    /* Add cache_remove_url filter to this request to remove a
                     * stale cache entry if needed. Also put the current cache
                     * request rec in the filter context, as the request that
                     * is available later during running the filter may be
                     * different due to an internal redirect.
                     */
                    cache->remove_url_filter = ap_add_output_filter_handle(
                            cache_remove_url_filter_handle, cache, r,
                            r->connection);

                }
                else {
                    ap_log_rerror(APLOG_MARK, APLOG_DEBUG, rv,
                            r, APLOGNO(00752) "Cache locked for url, not caching "
                            "response: %s", r->uri);
                    /* cache_select() may have added conditional headers */
                    if (cache->stale_headers) {
                        r->headers_in = cache->stale_headers;
                    }

                }
            }
            else {
                if (cache->stale_headers) {
                    ap_log_rerror(APLOG_MARK, APLOG_DEBUG, APR_SUCCESS,
                            r, APLOGNO(00753) "Restoring request headers for %s",
                            r->uri);

                    r->headers_in = cache->stale_headers;
                }
            }
        }
        else {
            /* error */
            return rv;
        }
        return DECLINED;
    }

    /* we've got a cache hit! tell everyone who cares */
    cache_run_cache_status(cache->handle, r, r->headers_out, AP_CACHE_HIT,
            "cache hit");

    /* if we are a lookup, we are exiting soon one way or another; Restore
     * the headers. */
    if (lookup) {
        if (cache->stale_headers) {
            ap_log_rerror(APLOG_MARK, APLOG_DEBUG, APR_SUCCESS, r, APLOGNO(00754)
                    "Restoring request headers.");
            r->headers_in = cache->stale_headers;
        }
    }

    rv = ap_meets_conditions(r);
    if (rv != OK) {
        /* If we are a lookup, we have to return DECLINED as we have no
         * way of knowing if we will be able to serve the content.
         */
        if (lookup) {
            return DECLINED;
        }

        /* 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);

    /*
     * Add cache_out filter to serve this request. Choose
     * the correct filter by checking if we are a subrequest
     * or not.
     */
    if (r->main) {
        cache_out_handle = cache_out_subreq_filter_handle;
    }
    else {
        cache_out_handle = cache_out_filter_handle;
    }
    ap_add_output_filter_handle(cache_out_handle, cache, r, r->connection);

    /*
     * Remove all filters that are before the cache_out filter. This ensures
     * that we kick off the filter stack with our cache_out filter being the
     * first in the chain. This make sense because we want to restore things
     * in the same manner as we saved them.
     * There may be filters before our cache_out filter, because
     *
     * 1. We call ap_set_content_type during cache_select. This causes
     *    Content-Type specific filters to be added.
     * 2. We call the insert_filter hook. This causes filters e.g. like
     *    the ones set with SetOutputFilter to be added.
     */
    next = r->output_filters;
    while (next && (next->frec != cache_out_handle)) {
        ap_remove_output_filter(next);
        next = next->next;
    }

    /* kick off the filter stack */
    out = apr_brigade_create(r->pool, r->connection->bucket_alloc);
    e = apr_bucket_eos_create(out->bucket_alloc);
    APR_BRIGADE_INSERT_TAIL(out, e);

    return ap_pass_brigade_fchk(r, out,
                                "cache_quick_handler(%s): ap_pass_brigade returned",
                                cache->provider_name);
}

/**
 * If the two filter handles are present within the filter chain, replace
 * the last instance of the first filter with the last instance of the
 * second filter, and return true. If the second filter is not present at
 * all, the first filter is removed, and false is returned. If neither
 * filter is present, false is returned and this function does nothing.
 * If a stop filter is specified, processing will stop once this filter is
 * reached.
 */
static int cache_replace_filter(ap_filter_t *next, ap_filter_rec_t *from,
        ap_filter_rec_t *to, ap_filter_rec_t *stop) {
    ap_filter_t *ffrom = NULL, *fto = NULL;
    while (next && next->frec != stop) {
        if (next->frec == from) {
            ffrom = next;
        }
        if (next->frec == to) {
            fto = next;
        }
        next = next->next;
    }
    if (ffrom && fto) {
        ffrom->frec = fto->frec;
        ffrom->ctx = fto->ctx;
        ap_remove_output_filter(fto);
        return 1;
    }
    if (ffrom) {
        ap_remove_output_filter(ffrom);
    }
    return 0;
}

/**
 * Find the given filter, and return it if found, or NULL otherwise.
 */
static ap_filter_t *cache_get_filter(ap_filter_t *next, ap_filter_rec_t *rec) {
    while (next) {
        if (next->frec == rec && next->ctx) {
            break;
        }
        next = next->next;
    }
    return next;
}

/**
 * The cache handler is functionally similar to the cache_quick_hander,
 * however a number of steps that are required by the quick handler are
 * not required here, as the normal httpd processing has already handled
 * these steps.
 */
static int cache_handler(request_rec *r)
{
    apr_status_t rv;
    cache_provider_list *providers;
    cache_request_rec *cache;
    apr_bucket_brigade *out;
    apr_bucket *e;
    ap_filter_t *next;
    ap_filter_rec_t *cache_out_handle;
    ap_filter_rec_t *cache_save_handle;
    cache_server_conf *conf;

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

    /* only run if the quick handler is disabled */
    if (conf->quick) {
        return DECLINED;
    }

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

    /* make space for the per request config */
    cache = apr_pcalloc(r->pool, sizeof(cache_request_rec));
    cache->size = -1;
    cache->out = apr_brigade_create(r->pool, r->connection->bucket_alloc);

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

    /*
     * Are we allowed to serve cached info at all?
     */
    if (!ap_cache_check_no_store(cache, r)) {
        return DECLINED;
    }

    /* Are we PUT/POST/DELETE? If so, prepare to invalidate the cached entities.
     */
    switch (r->method_number) {
    case M_PUT:
    case M_POST:
    case M_DELETE:
    {

        ap_log_rerror(APLOG_MARK, APLOG_DEBUG, APR_SUCCESS, r, APLOGNO(02463)
                "PUT/POST/DELETE: Adding CACHE_INVALIDATE filter for %s",
                r->uri);

        /* Add cache_invalidate filter to this request to force a
         * cache entry to be invalidated if the response is
         * ultimately successful (2xx).
         */
        ap_add_output_filter_handle(
                cache_invalidate_filter_handle, cache, r,
                r->connection);

        return DECLINED;
    }
    case M_GET: {
        break;
    }
    default : {

        ap_log_rerror(
                APLOG_MARK, APLOG_DEBUG, APR_SUCCESS, r, APLOGNO(02464) "cache: Method '%s' not cacheable by mod_cache, ignoring: %s", r->method, r->uri);

        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(cache, r);
    if (rv != OK) {
        if (rv == DECLINED) {

            /* try to obtain a cache lock at this point. if we succeed,
             * we are the first to try and cache this url. if we fail,
             * it means someone else is already trying to cache this
             * url, and we should just let the request through to the
             * backend without any attempt to cache. this stops
             * duplicated simultaneous attempts to cache an entity.
             */
            rv = cache_try_lock(conf, cache, r);
            if (APR_SUCCESS == rv) {

                /*
                 * Add cache_save filter to cache this request. Choose
                 * the correct filter by checking if we are a subrequest
                 * or not.
                 */
                if (r->main) {
                    ap_log_rerror(APLOG_MARK, APLOG_DEBUG, APR_SUCCESS,
                            r, APLOGNO(00756) "Adding CACHE_SAVE_SUBREQ filter for %s",
                            r->uri);
                    cache_save_handle = cache_save_subreq_filter_handle;
                }
                else {
                    ap_log_rerror(APLOG_MARK, APLOG_DEBUG, APR_SUCCESS,
                            r, APLOGNO(00757) "Adding CACHE_SAVE filter for %s",
                            r->uri);
                    cache_save_handle = cache_save_filter_handle;
                }
                ap_add_output_filter_handle(cache_save_handle, cache, r,
                        r->connection);

                /*
                 * Did the user indicate the precise location of the
                 * CACHE_SAVE filter by inserting the CACHE filter as a
                 * marker?
                 *
                 * If so, we get cunning and replace CACHE with the
                 * CACHE_SAVE filter. This has the effect of inserting
                 * the CACHE_SAVE filter at the precise location where
                 * the admin wants to cache the content. All filters that
                 * lie before and after the original location of the CACHE
                 * filter will remain in place.
                 */
                if (cache_replace_filter(r->output_filters,
                        cache_filter_handle, cache_save_handle,
                        ap_get_input_filter_handle("SUBREQ_CORE"))) {
                    ap_log_rerror(APLOG_MARK, APLOG_DEBUG, APR_SUCCESS,
                            r, APLOGNO(00758) "Replacing CACHE with CACHE_SAVE "
                            "filter for %s", r->uri);
                }

                /* save away the save filter stack */
                cache->save_filter = cache_get_filter(r->output_filters,
                        cache_save_filter_handle);

                apr_pool_userdata_setn(cache, CACHE_CTX_KEY, NULL, r->pool);

                ap_log_rerror(APLOG_MARK, APLOG_DEBUG, APR_SUCCESS, r, APLOGNO(00759)
                        "Adding CACHE_REMOVE_URL filter for %s",
                        r->uri);

                /* Add cache_remove_url filter to this request to remove a
                 * stale cache entry if needed. Also put the current cache
                 * request rec in the filter context, as the request that
                 * is available later during running the filter may be
                 * different due to an internal redirect.
                 */
                cache->remove_url_filter
                        = ap_add_output_filter_handle(
                                cache_remove_url_filter_handle, cache, r,
                                r->connection);

            }
            else {
                ap_log_rerror(APLOG_MARK, APLOG_DEBUG, rv,
                        r, APLOGNO(00760) "Cache locked for url, not caching "
                        "response: %s", r->uri);
            }
        }
        else {
            /* error */
            return rv;
        }
        return DECLINED;
    }

    /* we've got a cache hit! tell everyone who cares */
    cache_run_cache_status(cache->handle, r, r->headers_out, AP_CACHE_HIT,
            "cache hit");

    rv = ap_meets_conditions(r);
    if (rv != OK) {
        return rv;
    }

    /* Serve up the content */

    /*
     * Add cache_out filter to serve this request. Choose
     * the correct filter by checking if we are a subrequest
     * or not.
     */
    if (r->main) {
        cache_out_handle = cache_out_subreq_filter_handle;
    }
    else {
        cache_out_handle = cache_out_filter_handle;
    }
    ap_add_output_filter_handle(cache_out_handle, cache, r, r->connection);

    /*
     * Did the user indicate the precise location of the CACHE_OUT filter by
     * inserting the CACHE filter as a marker?
     *
     * If so, we get cunning and replace CACHE with the CACHE_OUT filters.
     * This has the effect of inserting the CACHE_OUT filter at the precise
     * location where the admin wants to cache the content. All filters that
     * lie *after* the original location of the CACHE filter will remain in
     * place.
     */
    if (cache_replace_filter(r->output_filters, cache_filter_handle,
            cache_out_handle, ap_get_input_filter_handle("SUBREQ_CORE"))) {
        ap_log_rerror(APLOG_MARK, APLOG_DEBUG, APR_SUCCESS,
                r, APLOGNO(00761) "Replacing CACHE with CACHE_OUT filter for %s",
                r->uri);
    }

    /*
     * Remove all filters that are before the cache_out filter. This ensures
     * that we kick off the filter stack with our cache_out filter being the
     * first in the chain. This make sense because we want to restore things
     * in the same manner as we saved them.
     * There may be filters before our cache_out filter, because
     *
     * 1. We call ap_set_content_type during cache_select. This causes
     *    Content-Type specific filters to be added.
     * 2. We call the insert_filter hook. This causes filters e.g. like
     *    the ones set with SetOutputFilter to be added.
     */
    next = r->output_filters;
    while (next && (next->frec != cache_out_handle)) {
        ap_remove_output_filter(next);
        next = next->next;
    }

    /* kick off the filter stack */
    out = apr_brigade_create(r->pool, r->connection->bucket_alloc);
    e = apr_bucket_eos_create(out->bucket_alloc);
    APR_BRIGADE_INSERT_TAIL(out, e);
    return ap_pass_brigade_fchk(r, out, "cache(%s): ap_pass_brigade returned",
                                cache->provider_name);
}

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

    if (!cache) {
        /* user likely configured CACHE_OUT manually; they should use mod_cache
         * configuration to do that */
        ap_log_rerror(APLOG_MARK, APLOG_ERR, 0, r, APLOGNO(00762)
                "CACHE/CACHE_OUT filter enabled while caching is disabled, ignoring");
        ap_remove_output_filter(f);
        return ap_pass_brigade(f->next, in);
    }

    ap_log_rerror(APLOG_MARK, APLOG_DEBUG, APR_SUCCESS, r, APLOGNO(00763)
            "cache: running CACHE_OUT filter");

    /* clean out any previous response up to EOS, if any */
    while (!APR_BRIGADE_EMPTY(in)) {
        apr_bucket *e = APR_BRIGADE_FIRST(in);
        if (APR_BUCKET_IS_EOS(e)) {
            apr_bucket_brigade *bb = apr_brigade_create(r->pool,
                    r->connection->bucket_alloc);

            /* restore content type of cached response if available */
            /* Needed especially when stale content gets served. */
            const char *ct = apr_table_get(cache->handle->resp_hdrs, "Content-Type");
            if (ct) {
                ap_set_content_type(r, ct);
            }

            /* restore status of cached response */
            r->status = cache->handle->cache_obj->info.status;

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

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

            ap_log_rerror(APLOG_MARK, APLOG_DEBUG, APR_SUCCESS, r, APLOGNO(00764)
                    "cache: serving %s", r->uri);
            return ap_pass_brigade(f->next, in);

        }
        apr_bucket_delete(e);
    }

    return APR_SUCCESS;
}

/*
 * Having jumped through all the hoops and decided to cache the
 * response, call store_body() for each brigade, handling the
 * case where the provider can't swallow the full brigade. In this
 * case, we write the brigade we were passed out downstream, and
 * loop around to try and cache some more until the in brigade is
 * completely empty. As soon as the out brigade contains eos, call
 * commit_entity() to finalise the cached element.
 */
static int cache_save_store(ap_filter_t *f, apr_bucket_brigade *in,
        cache_server_conf *conf, cache_request_rec *cache)
{
    int rv = APR_SUCCESS;
    apr_bucket *e;

    /* pass the brigade in into the cache provider, which is then
     * expected to move cached buckets to the out brigade, for us
     * to pass up the filter stack. repeat until in is empty, or
     * we fail.
     */
    while (APR_SUCCESS == rv && !APR_BRIGADE_EMPTY(in)) {

        rv = cache->provider->store_body(cache->handle, f->r, in, cache->out);
        if (rv != APR_SUCCESS) {
            ap_log_rerror(APLOG_MARK, APLOG_DEBUG, rv, f->r, APLOGNO(00765)
                    "cache: Cache provider's store_body failed for URI %s", f->r->uri);
            ap_remove_output_filter(f);

            /* give someone else the chance to cache the file */
            cache_remove_lock(conf, cache, f->r, NULL);

            /* give up trying to cache, just step out the way */
            APR_BRIGADE_PREPEND(in, cache->out);
            return ap_pass_brigade(f->next, in);

        }

        /* does the out brigade contain eos? if so, we're done, commit! */
        for (e = APR_BRIGADE_FIRST(cache->out);
             e != APR_BRIGADE_SENTINEL(cache->out);
             e = APR_BUCKET_NEXT(e))
        {
            if (APR_BUCKET_IS_EOS(e)) {
                rv = cache->provider->commit_entity(cache->handle, f->r);
                break;
            }
        }

        /* conditionally remove the lock as soon as we see the eos bucket */
        cache_remove_lock(conf, cache, f->r, cache->out);

        if (APR_BRIGADE_EMPTY(cache->out)) {
            if (APR_BRIGADE_EMPTY(in)) {
                /* cache provider wants more data before passing the brigade
                 * upstream, oblige the provider by leaving to fetch more.
                 */
                break;
            }
            else {
                /* oops, no data out, but not all data read in either, be
                 * safe and stand down to prevent a spin.
                 */
                ap_log_rerror(APLOG_MARK, APLOG_WARNING, rv, f->r, APLOGNO(00766)
                        "cache: Cache provider's store_body returned an "
                        "empty brigade, but didn't consume all of the "
                        "input brigade, standing down to prevent a spin");
                ap_remove_output_filter(f);

                /* give someone else the chance to cache the file */
                cache_remove_lock(conf, cache, f->r, NULL);

                return ap_pass_brigade(f->next, in);
            }
        }

        rv = ap_pass_brigade(f->next, cache->out);
    }

    return rv;
}

/**
 * Sanity check for 304 Not Modified responses, as per RFC2616 Section 10.3.5.
 */
static int cache_header_cmp(apr_pool_t *pool, apr_table_t *left,
        apr_table_t *right, const char *key)
{
    const char *h1, *h2;

    if ((h1 = cache_table_getm(pool, left, key))
            && (h2 = cache_table_getm(pool, right, key)) && (strcmp(h1, h2))) {
        return 1;
    }
    return 0;
}

/*
 * 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)
 *
 * After the various failure cases, the cache lock is proactively removed, so
 * that another request is given the opportunity to attempt to cache without
 * waiting for a potentially slow client to acknowledge the failure.
 */

static apr_status_t cache_save_filter(ap_filter_t *f, apr_bucket_brigade *in)
{
    int rv = !OK;
    request_rec *r = f->r;
    cache_request_rec *cache = (cache_request_rec *)f->ctx;
    cache_server_conf *conf;
    cache_dir_conf *dconf;
    cache_control_t control;
    const char *cc_out, *cl, *pragma;
    const char *exps, *lastmods, *dates, *etag;
    apr_time_t exp, date, lastmod, now;
    apr_off_t size = -1;
    cache_info *info = NULL;
    const char *reason, **eh;
    apr_pool_t *p;
    apr_bucket *e;
    apr_table_t *headers;
    const char *query;

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

    /* Setup cache_request_rec */
    if (!cache) {
        /* user likely configured CACHE_SAVE manually; they should really use
         * mod_cache configuration to do that
         */
        ap_log_rerror(APLOG_MARK, APLOG_ERR, 0, r, APLOGNO(00767)
                "CACHE/CACHE_SAVE filter enabled while caching is disabled, ignoring");
        ap_remove_output_filter(f);
        return ap_pass_brigade(f->next, in);
    }

    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 cacheability check and set up the
     * cached file handle?
     */
    if (cache->in_checked) {
        return cache_save_store(f, in, conf, cache);
    }

    /*
     * 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.
     */

    dconf = ap_get_module_config(r->per_dir_config, &cache_module);

    /* RFC2616 13.8 Errors or Incomplete Response Cache Behavior:
     * If a cache receives a 5xx response while attempting to revalidate an
     * entry, it MAY either forward this response to the requesting client,
     * or act as if the server failed to respond. In the latter case, it MAY
     * return a previously received response unless the cached entry
     * includes the "must-revalidate" cache-control directive (see section
     * 14.9).
     *
     * This covers the case where an error was generated behind us, for example
     * by a backend server via mod_proxy.
     */
    if (dconf->stale_on_error && r->status >= HTTP_INTERNAL_SERVER_ERROR) {

        ap_remove_output_filter(cache->remove_url_filter);

        if (cache->stale_handle
                && !cache->stale_handle->cache_obj->info.control.must_revalidate
                && !cache->stale_handle->cache_obj->info.control.proxy_revalidate) {
            const char *warn_head;

            /* morph the current save filter into the out filter, and serve from
             * cache.
             */
            cache->handle = cache->stale_handle;
            if (r->main) {
                f->frec = cache_out_subreq_filter_handle;
            }
            else {
                f->frec = cache_out_filter_handle;
            }

            r->headers_out = cache->stale_handle->resp_hdrs;

            ap_set_content_type(r, apr_table_get(
                    cache->stale_handle->resp_hdrs, "Content-Type"));

            /* add a revalidation warning */
            warn_head = apr_table_get(r->err_headers_out, "Warning");
            if ((warn_head == NULL) || ((warn_head != NULL)
                    && (ap_strstr_c(warn_head, "111") == NULL))) {
                apr_table_mergen(r->err_headers_out, "Warning",
                        "111 Revalidation failed");
            }

            cache_run_cache_status(cache->handle, r, r->headers_out, AP_CACHE_HIT,
                    apr_psprintf(r->pool,
                            "cache hit: %d status; stale content returned",
                            r->status));

            /* give someone else the chance to cache the file */
            cache_remove_lock(conf, cache, f->r, NULL);

            /* pass brigade to our morphed out filter */
            return ap_pass_brigade(f, in);
        }
    }

    query = cache_use_early_url(r) ? r->parsed_uri.query : r->args;

    /* read expiry date; if a bad date, then leave it so the client can
     * read it
     */
    exps = apr_table_get(r->err_headers_out, "Expires");
    if (exps == NULL) {
        exps = apr_table_get(r->headers_out, "Expires");
    }
    if (exps != NULL) {
        exp = apr_date_parse_http(exps);
    }
    else {
        exp = APR_DATE_BAD;
    }

    /* read the last-modified date; if the date is bad, then delete it */
    lastmods = apr_table_get(r->err_headers_out, "Last-Modified");
    if (lastmods == NULL) {
        lastmods = apr_table_get(r->headers_out, "Last-Modified");
    }
    if (lastmods != NULL) {
        lastmod = apr_date_parse_http(lastmods);
        if (lastmod == APR_DATE_BAD) {
            lastmods = NULL;
        }
    }
    else {
        lastmod = APR_DATE_BAD;
    }

    /* read the etag and cache-control from the entity */
    etag = apr_table_get(r->err_headers_out, "Etag");
    if (etag == NULL) {
        etag = apr_table_get(r->headers_out, "Etag");
    }
    cc_out = cache_table_getm(r->pool, r->err_headers_out, "Cache-Control");
    pragma = cache_table_getm(r->pool, r->err_headers_out, "Pragma");
    headers = r->err_headers_out;
    if (!cc_out && !pragma) {
        cc_out = cache_table_getm(r->pool, r->headers_out, "Cache-Control");
        pragma = cache_table_getm(r->pool, r->headers_out, "Pragma");
        headers = r->headers_out;
    }

    /* Have we received a 304 response without any headers at all? Fall back to
     * the original headers in the original cached request.
     */
    if (r->status == HTTP_NOT_MODIFIED && cache->stale_handle) {
        if (!cc_out && !pragma) {
            cc_out = cache_table_getm(r->pool, cache->stale_handle->resp_hdrs,
                    "Cache-Control");
            pragma = cache_table_getm(r->pool, cache->stale_handle->resp_hdrs,
                    "Pragma");
        }

        /* 304 does not contain Content-Type and mod_mime regenerates the
         * Content-Type based on the r->filename. This would lead to original
         * Content-Type to be lost (overwriten by whatever mod_mime generates).
         * We preserves the original Content-Type here. */
        ap_set_content_type(r, apr_table_get(
                cache->stale_handle->resp_hdrs, "Content-Type"));
    }

    /* Parse the cache control header */
    memset(&control, 0, sizeof(cache_control_t));
    ap_cache_control(r, &control, cc_out, pragma, headers);

    /*
     * what responses should we not cache?