modules/experimental/mod_cache.c

	mod_cache.c revision 98545bfcdf6b9ad9f293cdc0743bb831d785a2f7
/* ====================================================================
 * The Apache Software License, Version 1.1
 *
 * Copyright (c) 2000-2002 The Apache Software Foundation.  All rights
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Apache" and "Apache Software Foundation" must
 *    not be used to endorse or promote products derived from this
 *    software without prior written permission. For written
 *    permission, please contact apache@apache.org.
 *
 * 5. Products derived from this software may not be called "Apache",
 *    nor may "Apache" appear in their name, without prior written
 *    permission of the Apache Software Foundation.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 *
 * Portions of this software are based upon public domain software
 * originally written at the National Center for Supercomputing Applications,
 * University of Illinois, Urbana-Champaign.
 */

#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_in_filter_handle;
static ap_filter_rec_t *cache_out_filter_handle;
static ap_filter_rec_t *cache_conditional_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_IN filter
 *   If No:
 *     oh well.
 */

static int cache_url_handler(request_rec *r, int lookup)
{
    apr_status_t rv;
    const char *cc_in, *pragma, *auth;
    apr_uri_t uri = r->parsed_uri;
    char *url = r->unparsed_uri;
    apr_size_t urllen;
    char *path = uri.path;
    const char *types;
    cache_info *info = NULL;
    cache_request_rec *cache;
    cache_server_conf *conf;

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

    /* we don't handle anything but GET */
    if (r->method_number != M_GET) {
        return DECLINED;
    }

    /*
     * Which cache module (if any) should handle this request?
     */
    if (!(types = ap_cache_get_cachetype(r, conf, path))) {
        return DECLINED;
    }
    ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server,
                 "cache: URL %s is being handled by %s", path, types);

    urllen = strlen(url);
    if (urllen > MAX_URL_LENGTH) {
        ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server,
                     "cache: URL exceeds length threshold: %s", url);
        return DECLINED;
    }
    /* DECLINE urls ending in / ??? EGP: why? */
    if (url[urllen-1] == '/') {
        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 type */
    cache->types = types;

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

    /* find certain cache controlling headers */
    cc_in = apr_table_get(r->headers_in, "Cache-Control");
    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, cc_in, "no-store", NULL) ||
            ap_cache_liststr(NULL, pragma, "no-cache", NULL) || (auth != NULL)) {
            /* delete the previously cached file */
            cache_remove_url(r, cache->types, url);

            ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server,
                         "cache: no-store forbids caching of %s", url);
            return DECLINED;
        }
    }

    /*
     * Try to serve this request from the cache.
     *
     * If no existing cache file
     *   add cache_in filter
     * If stale cache file
     *   If conditional request
     *     add cache_in filter
     *   If non-conditional request
     *     fudge response into a conditional
     *     add cache_conditional filter
     * If fresh cache file
     *   clear filter stack
     *   add cache_out filter
     */

    rv = cache_select_url(r, cache->types, url);
    if (DECLINED == rv) {
        if (!lookup) {
            /* no existing cache file */
            ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server,
                         "cache: no cache - add cache_in filter and DECLINE");
            /* add cache_in filter to cache this request */
            ap_add_output_filter_handle(cache_in_filter_handle, NULL, r,
                                        r->connection);
        }
        return DECLINED;
    }
    else if (OK == rv) {
        /* RFC2616 13.2 - Check cache object expiration */
        cache->fresh = ap_cache_check_freshness(cache, r);
        if (cache->fresh) {
            /* fresh data available */
            apr_bucket_brigade *out;
            conn_rec *c = r->connection;

            if (lookup) {
                return OK;
            }
            rv = ap_meets_conditions(r);
            if (rv != OK) {
                ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server,
                             "cache: fresh cache - returning status %d", rv);
                return rv;
            }

            /*
             * Not a conditionl request. Serve up the content
             */
            ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server,
                         "cache: fresh cache - add cache_out filter and "
                         "handle request");

            /* 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, c->bucket_alloc);
            if (APR_SUCCESS
                != (rv = ap_pass_brigade(r->output_filters, out))) {
                ap_log_error(APLOG_MARK, APLOG_ERR, rv, r->server,
                             "cache: error returned while trying to return %s "
                             "cached data",
                             cache->type);
                return rv;
            }
            return OK;
        }
        else {
	    r->err_headers_out = apr_table_make(r->pool, 3);
            /* stale data available */
            if (lookup) {
                return DECLINED;
            }

            ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server,
                         "cache: stale cache - test conditional");
            /* if conditional request */
            if (ap_cache_request_is_conditional(r)) {
                ap_log_error(APLOG_MARK, APLOG_DEBUG, 0,
                             r->server,
                             "cache: conditional - add cache_in filter and "
                             "DECLINE");
                /* Why not add CACHE_CONDITIONAL? */
                ap_add_output_filter_handle(cache_in_filter_handle, NULL,
                                            r, r->connection);

                return DECLINED;
            }
            /* else if non-conditional request */
            else {
                /* fudge response into a conditional */
                if (info && info->etag) {
                    ap_log_error(APLOG_MARK, APLOG_DEBUG, 0,
                                 r->server,
                                 "cache: nonconditional - fudge conditional "
                                 "by etag");
                    /* if we have a cached etag */
                    apr_table_set(r->headers_in, "If-None-Match", info->etag);
                }
                else if (info && info->lastmods) {
                    ap_log_error(APLOG_MARK, APLOG_DEBUG, 0,
                                 r->server,
                                 "cache: nonconditional - fudge conditional "
                                 "by lastmod");
                    /* if we have a cached IMS */
                    apr_table_set(r->headers_in,
                                  "If-Modified-Since",
                                  info->lastmods);
                }
                else {
                    /* something else - pretend there was no cache */
                    ap_log_error(APLOG_MARK, APLOG_DEBUG, 0,
                                 r->server,
                                 "cache: nonconditional - no cached "
                                 "etag/lastmods - add cache_in and DECLINE");

                    ap_add_output_filter_handle(cache_in_filter_handle, NULL,
                                                r, r->connection);

                    return DECLINED;
                }
                /* add cache_conditional filter */
                ap_log_error(APLOG_MARK, APLOG_DEBUG, 0,
                             r->server,
                             "cache: nonconditional - add cache_conditional "
                             "and DECLINE");
                ap_add_output_filter_handle(cache_conditional_filter_handle,
                                            NULL,
                                            r,
                                            r->connection);

                return DECLINED;
            }
        }
    }
    else {
        /* error */
        ap_log_error(APLOG_MARK, APLOG_ERR, rv,
                     r->server,
                     "cache: error returned while checking for cached file by "
                     "%s cache",
                     cache->type);
        return DECLINED;
    }
}

/*
 * 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");

    /* cache_read_entity_headers() was called in cache_select_url() */
    cache_read_entity_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_CONDITIONAL filter
 * ------------------------
 *
 * Decide whether or not cached content should be delivered
 * based on our fudged conditional request.
 * If response HTTP_NOT_MODIFIED
 *   replace ourselves with cache_out filter
 * Otherwise
 *   replace ourselves with cache_in filter
 */

static int cache_conditional_filter(ap_filter_t *f, apr_bucket_brigade *in)
{
    ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, f->r->server,
                 "cache: running CACHE_CONDITIONAL filter");

    if (f->r->status == HTTP_NOT_MODIFIED) {
        /* replace ourselves with CACHE_OUT filter */
        ap_add_output_filter_handle(cache_out_filter_handle, NULL,
                                    f->r, f->r->connection);
    }
    else {
        /* replace ourselves with CACHE_IN filter */
        ap_add_output_filter_handle(cache_in_filter_handle, NULL,
                                    f->r, f->r->connection);
    }
    ap_remove_output_filter(f);

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


/*
 * CACHE_IN filter
 * ---------------
 *
 * Decide whether or not this content should be cached.
 * If we decide no it should:
 *   remove the filter from the chain
 * If we decide yes it should:
 *   pass the data to the storage manager
 *   pass the data to the next filter (the network)
 *
 */

static int cache_in_filter(ap_filter_t *f, apr_bucket_brigade *in)
{
    int rv;
    request_rec *r = f->r;
    cache_request_rec *cache;
    cache_server_conf *conf;
    char *url = r->unparsed_uri;
    const char *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(r->no_cache) {
        ap_remove_output_filter(f);
        return ap_pass_brigade(f->next, in);
    }

    ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server,
                 "cache: running CACHE_IN filter");

    /* Setup cache_request_rec */
    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);
    }

    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.
     */

    /* 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_write_entity_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.
     */
    info = apr_pcalloc(r->pool, sizeof(cache_info));

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

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

    conf = (cache_server_conf *) ap_get_module_config(r->server->module_config, &cache_module);
    /* read the etag and cache-control from the entity */
    etag = apr_table_get(r->headers_out, "Etag");
    cc_out = apr_table_get(r->headers_out, "Cache-Control");

    /*
     * what responses should we not cache?
     *
     * At this point we decide based on the response headers whether it
     * is appropriate _NOT_ to cache the data from the server. There are
     * a whole lot of conditions that prevent us from caching this data.
     * They are tested here one by one to be clear and unambiguous.
     */
    if (r->status != HTTP_OK && r->status != HTTP_NON_AUTHORITATIVE
        && r->status != HTTP_MULTIPLE_CHOICES
        && r->status != HTTP_MOVED_PERMANENTLY
        && r->status != HTTP_NOT_MODIFIED) {
        /* RFC2616 13.4 we are allowed to cache 200, 203, 206, 300, 301 or 410
         * We don't cache 206, because we don't (yet) cache partial responses.
         * We include 304 Not Modified here too as this is the origin server
         * telling us to serve the cached copy.
         */
        reason = apr_psprintf(p, "Response status %d", r->status);
    }
    else if (exps != NULL && exp == APR_DATE_BAD) {
        /* if a broken Expires header is present, don't cache it */
        reason = apr_pstrcat(p, "Broken expires header: ", exps, NULL);
    }
    else if (r->args && exps == NULL) {
        /* if query string present but no expiration time, don't cache it
         * (RFC 2616/13.9)
         */
        reason = "Query string present but no expires header";
    }
    else if (r->status == HTTP_NOT_MODIFIED && (NULL == cache->handle)) {
        /* if the server said 304 Not Modified but we have no cache
         * file - pass this untouched to the user agent, it's not for us.
         */
        reason = "HTTP Status 304 Not Modified";
    }
    else if (r->status == HTTP_OK && lastmods == NULL && etag == NULL
             && (conf->no_last_mod_ignore ==0)) {
        /* 200 OK response from HTTP/1.0 and up without a Last-Modified
         * header/Etag
         */
        /* XXX mod-include clears last_modified/expires/etags - this
         * is why we have an optional function for a key-gen ;-)
         */
        reason = "No Last-Modified or Etag header";
    }
    else if (r->header_only) {
        /* HEAD requests */
        reason = "HTTP HEAD request";
    }
    else if (ap_cache_liststr(NULL, cc_out, "no-store", NULL)) {
        /* RFC2616 14.9.2 Cache-Control: no-store response
         * indicating do not cache, or stop now if you are
         * trying to cache it */
        reason = "Cache-Control: no-store present";
    }
    else if (ap_cache_liststr(NULL, cc_out, "private", NULL)) {
        /* RFC2616 14.9.1 Cache-Control: private
         * this object is marked for this user's eyes only. Behave
         * as a tunnel.
         */
        reason = "Cache-Control: private present";
    }
    else if (apr_table_get(r->headers_in, "Authorization") != NULL
             && !(ap_cache_liststr(NULL, cc_out, "s-maxage", NULL)
                  || ap_cache_liststr(NULL, cc_out, "must-revalidate", NULL)
                  || ap_cache_liststr(NULL, cc_out, "public", NULL))) {
        /* RFC2616 14.8 Authorisation:
         * if authorisation is included in the request, we don't cache,
         * but we can cache if the following exceptions are true:
         * 1) If Cache-Control: s-maxage is included
         * 2) If Cache-Control: must-revalidate is included
         * 3) If Cache-Control: public is included
         */
        reason = "Authorization required";
    }
    else if (r->no_cache) {
        /* or we've been asked not to cache it above */
        reason = "no_cache present";
    }

    if (reason) {
        ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server,
                     "cache: %s not cached. Reason: %s", url, reason);
        /* remove this object from the cache
         * BillS Asks.. Why do we need to make this call to remove_url?
         * leave it in for now..
         */
        cache_remove_url(r, cache->types, url);

        /* remove this filter from the chain */
        ap_remove_output_filter(f);

        /* ship the data up the stack */
        return ap_pass_brigade(f->next, in);
    }
    cache->in_checked = 1;

    /* Set the content length if known.
     */
    cl = apr_table_get(r->headers_out, "Content-Length");
    if (cl) {
        size = apr_atoi64(cl);
    }
    else {
        /* if we don't get the content-length, see if we have all the
         * buckets and use their length to calculate the size
         */
        apr_bucket *e;
        int all_buckets_here=0;
        int unresolved_length = 0;
        size=0;
        APR_BRIGADE_FOREACH(e, in) {
            if (APR_BUCKET_IS_EOS(e)) {
                all_buckets_here=1;
                break;
            }
            if (APR_BUCKET_IS_FLUSH(e)) {
                unresolved_length = 1;
                continue;
            }
            if (e->length == (apr_size_t)-1) {
                break;
            }
            size += e->length;
        }
        if (!all_buckets_here) {
            size = -1;
        }
    }

    /* It's safe to cache the response.
     *
     * There are two possiblities at this point:
     * - cache->handle == NULL. In this case there is no previously
     * cached entity anywhere on the system. We must create a brand
     * new entity and store the response in it.
     * - cache->handle != NULL. In this case there is a stale
     * entity in the system which needs to be replaced by new
     * content (unless the result was 304 Not Modified, which means
     * the cached entity is actually fresh, and we should update
     * the headers).
     */
    /* no cache handle, create a new entity */
    if (!cache->handle) {
        rv = cache_create_entity(r, cache->types, url, size);
    }
    /* pre-existing cache handle and 304, make entity fresh */
    else if (r->status == HTTP_NOT_MODIFIED) {
        /* update headers */

        /* remove this filter ??? */

        /* XXX is this right?  we must set rv to something other than OK
         * in this path
         */
        rv = HTTP_NOT_MODIFIED;
    }
    /* pre-existing cache handle and new entity, replace entity
     * with this one
     */
    else {
        cache_remove_entity(r, cache->types, cache->handle);
        rv = cache_create_entity(r, cache->types, url, size);
    }

    if (rv != OK) {
        /* Caching layer declined the opportunity to cache the response */
        ap_remove_output_filter(f);
        return ap_pass_brigade(f->next, in);
    }

    ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server,
                 "cache: Caching url: %s", url);

    /*
     * We now want to update the cache file header information with
     * the new date, last modified, expire and content length and write
     * it away to our cache file. First, we determine these values from
     * the response, using heuristics if appropriate.
     *
     * In addition, we make HTTP/1.1 age calculations and write them away
     * too.
     */

    /* Read the date. Generate one if one is not supplied */
    dates = apr_table_get(r->headers_out, "Date");
    if (dates != NULL) {
        info->date = apr_date_parse_http(dates);
    }
    else {
        info->date = APR_DATE_BAD;
    }

    now = apr_time_now();
    if (info->date == APR_DATE_BAD) {  /* No, or bad date */
        char *dates;
        /* no date header! */
        /* add one; N.B. use the time _now_ rather than when we were checking
         * the cache
         */
        date = now;
        dates = apr_pcalloc(r->pool, MAX_STRING_LEN);
        apr_rfc822_date(dates, now);
        apr_table_set(r->headers_out, "Date", dates);
        ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server,
                     "cache: Added date header");
        info->date = date;
    }
    else {
        date = info->date;
    }

    /* set response_time for HTTP/1.1 age calculations */
    info->response_time = now;

    /* get the request time */
    info->request_time = r->request_time;

    /* check last-modified date */
    /* XXX FIXME we're referencing date on a path where we didn't set it */
    if (lastmod != APR_DATE_BAD && lastmod > date) {
        /* if it's in the future, then replace by date */
        lastmod = date;
        lastmods = dates;
        ap_log_error(APLOG_MARK, APLOG_DEBUG, 0,
                     r->server,
                     "cache: Last modified is in the future, "
                     "replacing with now");
    }
    info->lastmod = lastmod;

    /* if no expiry date then
     *   if lastmod
     *      expiry date = now + min((date - lastmod) * factor, maxexpire)
     *   else
     *      expire date = now + defaultexpire
     */
    if (exp == APR_DATE_BAD) {
        /* if lastmod == date then you get 0*conf->factor which results in
         *   an expiration time of now. This causes some problems with
         *   freshness calculations, so we choose the else path...
         */
        if ((lastmod != APR_DATE_BAD) && (lastmod < date)) {
            apr_time_t x = (apr_time_t) ((date - lastmod) * conf->factor);
            if (x > conf->maxex) {
                x = conf->maxex;
            }
            exp = now + x;
        }
        else {
            exp = now + conf->defex;
        }
    }
    info->expire = exp;

    info->content_type = apr_pstrdup(r->pool, r->content_type);
    info->filename = apr_pstrdup(r->pool, r->filename );

    /*
     * Write away header information to cache.
     */
    rv = cache_write_entity_headers(cache->handle, r, info);
    if (rv == APR_SUCCESS) {
        rv = cache_write_entity_body(cache->handle, r, in);
    }
    if (rv != APR_SUCCESS) {
        ap_remove_output_filter(f);
    }

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

/* -------------------------------------------------------------- */
/* Setup configurable data */

static void * create_cache_config(apr_pool_t *p, server_rec *s)
{
    cache_server_conf *ps = apr_pcalloc(p, sizeof(cache_server_conf));

    /* array of URL prefixes for which caching is enabled */
    ps->cacheenable = apr_array_make(p, 10, sizeof(struct cache_enable));
    /* array of URL prefixes for which caching is disabled */
    ps->cachedisable = apr_array_make(p, 10, sizeof(struct cache_disable));
    /* maximum time to cache a document */
    ps->maxex = DEFAULT_CACHE_MAXEXPIRE;
    ps->maxex_set = 0;
    /* default time to cache a document */
    ps->defex = DEFAULT_CACHE_EXPIRE;
    ps->defex_set = 0;
    /* factor used to estimate Expires date from LastModified date */
    ps->factor = DEFAULT_CACHE_LMFACTOR;
    ps->factor_set = 0;
    /* default percentage to force cache completion */
    ps->complete = DEFAULT_CACHE_COMPLETION;
    ps->complete_set = 0;
    ps->no_last_mod_ignore_set = 0;
    ps->no_last_mod_ignore = 0;
    ps->ignorecachecontrol = 0;
    ps->ignorecachecontrol_set = 0 ;
    return ps;
}

static void * merge_cache_config(apr_pool_t *p, void *basev, void *overridesv)
{
    cache_server_conf *ps = apr_pcalloc(p, sizeof(cache_server_conf));
    cache_server_conf *base = (cache_server_conf *) basev;
    cache_server_conf *overrides = (cache_server_conf *) overridesv;

    /* array of URL prefixes for which caching is disabled */
    ps->cachedisable = apr_array_append(p,
                                        base->cachedisable,
                                        overrides->cachedisable);
    /* array of URL prefixes for which caching is enabled */
    ps->cacheenable = apr_array_append(p,
                                       base->cacheenable,
                                       overrides->cacheenable);
    /* maximum time to cache a document */
    ps->maxex = (overrides->maxex_set == 0) ? base->maxex : overrides->maxex;
    /* default time to cache a document */
    ps->defex = (overrides->defex_set == 0) ? base->defex : overrides->defex;
    /* factor used to estimate Expires date from LastModified date */
    ps->factor =
        (overrides->factor_set == 0) ? base->factor : overrides->factor;
    /* default percentage to force cache completion */
    ps->complete =
        (overrides->complete_set == 0) ? base->complete : overrides->complete;

    ps->no_last_mod_ignore =
        (overrides->no_last_mod_ignore_set == 0)
        ? base->no_last_mod_ignore
        : overrides->no_last_mod_ignore;
    ps->ignorecachecontrol  =
        (overrides->ignorecachecontrol_set == 0)
        ? base->ignorecachecontrol
        : overrides->ignorecachecontrol;
    return ps;
}
static const char *set_cache_ignore_no_last_mod(cmd_parms *parms, void *dummy,
                                                int flag)
{
    cache_server_conf *conf;

    conf =
        (cache_server_conf *)ap_get_module_config(parms->server->module_config,
                                                  &cache_module);
    conf->no_last_mod_ignore = flag;
    conf->no_last_mod_ignore_set = 1;
    return NULL;

}

static const char *set_cache_ignore_cachecontrol(cmd_parms *parms,
                                                 void *dummy, int flag)
{
    cache_server_conf *conf;

    conf =
        (cache_server_conf *)ap_get_module_config(parms->server->module_config,
                                                  &cache_module);
    conf->ignorecachecontrol = flag;
    conf->ignorecachecontrol_set = 1;
    return NULL;
}

static const char *add_cache_enable(cmd_parms *parms, void *dummy,
                                    const char *type,
                                    const char *url)
{
    cache_server_conf *conf;
    struct cache_enable *new;

    conf =
        (cache_server_conf *)ap_get_module_config(parms->server->module_config,
                                                  &cache_module);
    new = apr_array_push(conf->cacheenable);
    new->type = type;
    new->url = url;
    return NULL;
}

static const char *add_cache_disable(cmd_parms *parms, void *dummy,
                                     const char *url)
{
    cache_server_conf *conf;
    struct cache_enable *new;

    conf =
        (cache_server_conf *)ap_get_module_config(parms->server->module_config,
                                                  &cache_module);
    new = apr_array_push(conf->cachedisable);
    new->url = url;
    return NULL;
}

static const char *set_cache_maxex(cmd_parms *parms, void *dummy,
                                   const char *arg)
{
    cache_server_conf *conf;

    conf =
        (cache_server_conf *)ap_get_module_config(parms->server->module_config,
                                                  &cache_module);
    conf->maxex = (apr_time_t) (atol(arg) * MSEC_ONE_SEC);
    conf->maxex_set = 1;
    return NULL;
}

static const char *set_cache_defex(cmd_parms *parms, void *dummy,
                                   const char *arg)
{
    cache_server_conf *conf;

    conf =
        (cache_server_conf *)ap_get_module_config(parms->server->module_config,
                                                  &cache_module);
    conf->defex = (apr_time_t) (atol(arg) * MSEC_ONE_SEC);
    conf->defex_set = 1;
    return NULL;
}

static const char *set_cache_factor(cmd_parms *parms, void *dummy,
                                    const char *arg)
{
    cache_server_conf *conf;
    double val;

    conf =
        (cache_server_conf *)ap_get_module_config(parms->server->module_config,
                                                  &cache_module);
    if (sscanf(arg, "%lg", &val) != 1) {
        return "CacheLastModifiedFactor value must be a float";
    }
    conf->factor = val;
    conf->factor_set = 1;
    return NULL;
}

static const char *set_cache_complete(cmd_parms *parms, void *dummy,
                                      const char *arg)
{
    cache_server_conf *conf;
    int val;

    conf =
        (cache_server_conf *)ap_get_module_config(parms->server->module_config,
                                                  &cache_module);
    if (sscanf(arg, "%u", &val) != 1) {
        return "CacheForceCompletion value must be a percentage";
    }
    conf->complete = val;
    conf->complete_set = 1;
    return NULL;
}

static int cache_post_config(apr_pool_t *p, apr_pool_t *plog,
                             apr_pool_t *ptemp, server_rec *s)
{
    /* This is the means by which unusual (non-unix) os's may find alternate
     * means to run a given command (e.g. shebang/registry parsing on Win32)
     */
    cache_generate_key = APR_RETRIEVE_OPTIONAL_FN(ap_cache_generate_key);
    if (!cache_generate_key) {
        cache_generate_key = cache_generate_key_default;
    }
    return OK;
}

static const command_rec cache_cmds[] =
{
    /* XXX
     * Consider a new config directive that enables loading specific cache
     * implememtations (like mod_cache_mem, mod_cache_file, etc.).
     * Rather than using a LoadModule directive, admin would use something
     * like CacheModule  mem_cache_module | file_cache_module, etc,
     * which would cause the approprpriate cache module to be loaded.
     * This is more intuitive that requiring a LoadModule directive.
     */

    AP_INIT_TAKE2("CacheEnable", add_cache_enable, NULL, RSRC_CONF,
                  "A cache type and partial URL prefix below which "
                  "caching is enabled"),
    AP_INIT_TAKE1("CacheDisable", add_cache_disable, NULL, RSRC_CONF,
                  "A partial URL prefix below which caching is disabled"),
    AP_INIT_TAKE1("CacheMaxExpire", set_cache_maxex, NULL, RSRC_CONF,
                  "The maximum time in seconds to cache a document"),
     AP_INIT_TAKE1("CacheDefaultExpire", set_cache_defex, NULL, RSRC_CONF,
                   "The default time in seconds to cache a document"),
     AP_INIT_FLAG("CacheIgnoreNoLastMod", set_cache_ignore_no_last_mod, NULL,
                  RSRC_CONF,
                  "Ignore Responses where there is no Last Modified Header"),
     AP_INIT_FLAG("CacheIgnoreCacheControl", set_cache_ignore_cachecontrol,
                  NULL,
                  RSRC_CONF,
                  "Ignore requests from the client for uncached content"),
    AP_INIT_TAKE1("CacheLastModifiedFactor", set_cache_factor, NULL, RSRC_CONF,
                  "The factor used to estimate Expires date from "
                  "LastModified date"),
    AP_INIT_TAKE1("CacheForceCompletion", set_cache_complete, NULL, RSRC_CONF,
                  "Percentage of download to arrive for the cache to force "
                  "complete transfer"),
    {NULL}
};

static void register_hooks(apr_pool_t *p)
{
    /* cache initializer */
    /* cache handler */
    ap_hook_quick_handler(cache_url_handler, NULL, NULL, APR_HOOK_FIRST);
    /* cache filters
     * XXX The cache filters need to run right after the handlers and before
     * any other filters. Consider creating AP_FTYPE_CACHE for this purpose.
     * Make them AP_FTYPE_CONTENT for now.
     * XXX ianhH:they should run AFTER all the other content filters.
     */
    cache_in_filter_handle =
        ap_register_output_filter("CACHE_IN",
                                  cache_in_filter,
                                  NULL,
                                  AP_FTYPE_CONTENT_SET-1);
    /* CACHE_OUT must go into the filter chain before SUBREQ_CORE to
     * handle subrequsts. Decrementing filter type by 1 ensures this
     * happens.
     */
    cache_out_filter_handle =
        ap_register_output_filter("CACHE_OUT",
                                  cache_out_filter,
                                  NULL,
                                  AP_FTYPE_CONTENT_SET-1);
    cache_conditional_filter_handle =
        ap_register_output_filter("CACHE_CONDITIONAL",
                                  cache_conditional_filter,
                                  NULL,
                                  AP_FTYPE_CONTENT_SET);
    ap_hook_post_config(cache_post_config, NULL, NULL, APR_HOOK_REALLY_FIRST);
}

module AP_MODULE_DECLARE_DATA cache_module =
{
    STANDARD20_MODULE_STUFF,
    NULL,                   /* create per-directory config structure */
    NULL,                   /* merge per-directory config structures */
    create_cache_config,    /* create per-server config structure */
    merge_cache_config,     /* merge per-server config structures */
    cache_cmds,             /* command apr_table_t */
    register_hooks
};