Adding upstream version 2.4.57.upstream/2.4.57

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2717 insertions, 0 deletions

diff --git a/modules/cache/mod_cache.c b/modules/cache/mod_cache.c
new file mode 100644
index 0000000..3b4469e
--- /dev/null
+++ b/modules/cache/mod_cache.c
@@ -0,0 +1,2717 @@
+/* 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 (overwritten 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?
+     *
+     * 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_PARTIAL_CONTENT
+        && 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 allow the caching of 206, but a cache implementation might choose
+         * to decline to cache a 206 if it doesn't know how to.
+         * We include 304 Not Modified here too as this is the origin server
+         * telling us to serve the cached copy.
+         */
+        if (exps != NULL || cc_out != NULL) {
+            /* We are also allowed to cache any response given that it has a
+             * valid Expires or Cache Control header. If we find a either of
+             * those here,  we pass request through the rest of the tests. From
+             * the RFC:
+             *
+             * A response received with any other status code (e.g. status
+             * codes 302 and 307) MUST NOT be returned in a reply to a
+             * subsequent request unless there are cache-control directives or
+             * another header(s) that explicitly allow it. For example, these
+             * include the following: an Expires header (section 14.21); a
+             * "max-age", "s-maxage",  "must-revalidate", "proxy-revalidate",
+             * "public" or "private" cache-control directive (section 14.9).
+             *
+             * FIXME: Wrong if cc_out has just an extension we don't know about 
+             */
+        }
+        else {
+            reason = apr_psprintf(p, "Response status %d", r->status);
+        }
+    }
+
+    if (reason) {
+        /* noop */
+    }
+    else if (!control.s_maxage && !control.max_age && !dconf->store_expired
+             && exps != NULL && exp == APR_DATE_BAD) {
+        /* if a broken Expires header is present, don't cache it
+         * Unless CC: s-maxage or max-age is present
+         */
+        reason = apr_pstrcat(p, "Broken expires header: ", exps, NULL);
+    }
+    else if (!control.s_maxage && !control.max_age
+            && !dconf->store_expired && exp != APR_DATE_BAD
+            && exp < r->request_time) {
+        /* if a Expires header is in the past, don't cache it 
+         * Unless CC: s-maxage or max-age is present
+         */
+        reason = "Expires header already expired; not cacheable";
+    }
+    else if (!dconf->store_expired && (control.must_revalidate
+            || control.proxy_revalidate) && (!control.s_maxage_value
+            || (!control.s_maxage && !control.max_age_value)) && lastmods
+            == NULL && etag == NULL) {
+        /* if we're already stale, but can never revalidate, don't cache it */
+        reason
+                = "s-maxage or max-age zero and no Last-Modified or Etag; not cacheable";
+    }
+    else if (!conf->ignorequerystring && query && exps == NULL
+            && !control.max_age && !control.s_maxage) {
+        /* if a query string is present but no explicit expiration time,
+         * don't cache it (RFC 2616/13.9 & 13.2.1)
+         */
+        reason = "Query string present but no explicit expiration time";
+    }
+    else if (r->status == HTTP_NOT_MODIFIED &&
+             !cache->handle && !cache->stale_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 && (exps
+            == NULL) && (dconf->no_last_mod_ignore == 0) && !control.max_age
+            && !control.s_maxage) {
+        /* 200 OK response from HTTP/1.0 and up without Last-Modified,
+         * Etag, Expires, Cache-Control:max-age, or Cache-Control:s-maxage
+         * headers.
+         */
+        /* Note: mod-include clears last_modified/expires/etags - this
+         * is why we have an optional function for a key-gen ;-)
+         */
+        reason = "No Last-Modified; Etag; Expires; Cache-Control:max-age or Cache-Control:s-maxage headers";
+    }
+    else if (!dconf->store_nostore && control.no_store) {
+        /* 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 (!dconf->store_private && control.private) {
+        /* RFC2616 14.9.1 Cache-Control: private response
+         * 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")
+            && !(control.s_maxage || control.must_revalidate
+                    || control.proxy_revalidate || control.public)) {
+        /* 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 (ap_find_token(NULL, apr_table_get(r->headers_out, "Vary"), "*")) {
+        reason = "Vary header contains '*'";
+    }
+    else if (apr_table_get(r->subprocess_env, "no-cache") != NULL) {
+        reason = "environment variable 'no-cache' is set";
+    }
+    else if (r->no_cache) {
+        /* or we've been asked not to cache it above */
+        reason = "r->no_cache present";
+    }
+    else if (cache->stale_handle
+            && APR_DATE_BAD
+                    != (date = apr_date_parse_http(
+                            apr_table_get(r->headers_out, "Date")))
+            && date < cache->stale_handle->cache_obj->info.date) {
+
+        /**
+         * 13.12 Cache Replacement:
+         *
+         * Note: a new response that has an older Date header value than
+         * existing cached responses is not cacheable.
+         */
+        reason = "updated entity is older than cached entity";
+
+        /* while this response is not cacheable, the previous response still is */
+        ap_log_rerror(APLOG_MARK, APLOG_DEBUG, 0, r, APLOGNO(02474)
+                "cache: Removing CACHE_REMOVE_URL filter.");
+        ap_remove_output_filter(cache->remove_url_filter);
+    }
+    else if (r->status == HTTP_NOT_MODIFIED && cache->stale_handle) {
+        apr_table_t *left = cache->stale_handle->resp_hdrs;
+        apr_table_t *right = r->headers_out;
+        const char *ehs = NULL;
+
+        /* and lastly, contradiction checks for revalidated responses
+         * as per RFC2616 Section 10.3.5
+         */
+        if (cache_header_cmp(r->pool, left, right, "ETag")) {
+            ehs = "ETag";
+        }
+        for (eh = MOD_CACHE_ENTITY_HEADERS; *eh; ++eh) {
+            if (cache_header_cmp(r->pool, left, right, *eh)) {
+                ehs = (ehs) ? apr_pstrcat(r->pool, ehs, ", ", *eh, NULL) : *eh;
+            }
+        }
+        if (ehs) {
+            reason = apr_pstrcat(r->pool, "contradiction: 304 Not Modified; "
+                                 "but ", ehs, " modified", NULL);
+        }
+    }
+
+    /**
+     * Enforce RFC2616 Section 10.3.5, just in case. We caught any
+     * inconsistencies above.
+     *
+     * If the conditional GET used a strong cache validator (see section
+     * 13.3.3), the response SHOULD NOT include other entity-headers.
+     * Otherwise (i.e., the conditional GET used a weak validator), the
+     * response MUST NOT include other entity-headers; this prevents
+     * inconsistencies between cached entity-bodies and updated headers.
+     */
+    if (r->status == HTTP_NOT_MODIFIED) {
+        for (eh = MOD_CACHE_ENTITY_HEADERS; *eh; ++eh) {
+            apr_table_unset(r->headers_out, *eh);
+        }
+    }
+
+    /* Hold the phone. Some servers might allow us to cache a 2xx, but
+     * then make their 304 responses non cacheable. RFC2616 says this:
+     *
+     * If a 304 response indicates an entity not currently cached, then
+     * the cache MUST disregard the response and repeat the request
+     * without the conditional.
+     *
+     * A 304 response with contradictory headers is technically a
+     * different entity, to be safe, we remove the entity from the cache.
+     */
+    if (reason && r->status == HTTP_NOT_MODIFIED && cache->stale_handle) {
+
+        ap_log_rerror(APLOG_MARK, APLOG_INFO, 0, r, APLOGNO(02473) 
+                "cache: %s responded with an uncacheable 304, " 
+                "retrying the request %s. Reason: %s", 
+                cache->key, r->unparsed_uri, reason);
+
+        /* we've got a cache conditional miss! tell anyone who cares */
+        cache_run_cache_status(cache->handle, r, r->headers_out, AP_CACHE_MISS,
+                apr_psprintf(r->pool,
+                        "conditional cache miss: 304 was uncacheable, entity removed: %s",
+                        reason));
+
+        /* remove the cached entity immediately, we might cache it again */
+        ap_remove_output_filter(cache->remove_url_filter);
+        cache_remove_url(cache, r);
+
+        /* let someone else attempt to cache */
+        cache_remove_lock(conf, cache, r, NULL);
+
+        /* remove this filter from the chain */
+        ap_remove_output_filter(f);
+
+        /* retry without the conditionals */
+        apr_table_unset(r->headers_in, "If-Match");
+        apr_table_unset(r->headers_in, "If-Modified-Since");
+        apr_table_unset(r->headers_in, "If-None-Match");
+        apr_table_unset(r->headers_in, "If-Range");
+        apr_table_unset(r->headers_in, "If-Unmodified-Since");
+
+        /* Currently HTTP_NOT_MODIFIED, and after the redirect, handlers won't think to set status to HTTP_OK */
+        r->status = HTTP_OK; 
+        ap_internal_redirect(r->unparsed_uri, r);
+
+        return APR_SUCCESS;
+    }
+
+    /* Set the content length if known.
+     */
+    cl = apr_table_get(r->err_headers_out, "Content-Length");
+    if (cl == NULL) {
+        cl = apr_table_get(r->headers_out, "Content-Length");
+    }
+    if (cl && !ap_parse_strict_length(&size, cl)) {
+        reason = "invalid content length";
+    }
+
+    if (reason) {
+        ap_log_rerror(APLOG_MARK, APLOG_DEBUG, 0, r, APLOGNO(00768)
+                "cache: %s not cached for request %s. Reason: %s",
+                cache->key, r->unparsed_uri, reason);
+
+        /* we've got a cache miss! tell anyone who cares */
+        cache_run_cache_status(cache->handle, r, r->headers_out, AP_CACHE_MISS,
+                reason);
+
+        /* remove this filter from the chain */
+        ap_remove_output_filter(f);
+
+        /* remove the lock file unconditionally */
+        cache_remove_lock(conf, cache, r, NULL);
+
+        /* ship the data up the stack */
+        return ap_pass_brigade(f->next, in);
+    }
+
+    /* Make it so that we don't execute this path again. */
+    cache->in_checked = 1;
+
+    if (!cl) {
+        /* if we don't get the content-length, see if we have all the
+         * buckets and use their length to calculate the size
+         */
+        int all_buckets_here=0;
+        size=0;
+        for (e = APR_BRIGADE_FIRST(in);
+             e != APR_BRIGADE_SENTINEL(in);
+             e = APR_BUCKET_NEXT(e))
+        {
+            if (APR_BUCKET_IS_EOS(e)) {
+                all_buckets_here=1;
+                break;
+            }
+            if (APR_BUCKET_IS_FLUSH(e)) {
+                continue;
+            }
+            if (e->length == (apr_size_t)-1) {
+                break;
+            }
+            size += e->length;
+        }
+        if (!all_buckets_here) {
+            size = -1;
+        }
+    }
+
+    /* remember content length to check response size against later */
+    cache->size = size;
+
+    /* It's safe to cache the response.
+     *
+     * There are two possibilities 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->stale_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).
+     */
+
+    /* Did we have a stale cache entry that really is stale?
+     */
+    if (cache->stale_handle) {
+        if (r->status == HTTP_NOT_MODIFIED) {
+            /* Oh, hey.  It isn't that stale!  Yay! */
+            cache->handle = cache->stale_handle;
+            info = &cache->handle->cache_obj->info;
+            rv = OK;
+        }
+        else {
+            /* Oh, well.  Toss it. */
+            cache->provider->remove_entity(cache->stale_handle);
+            /* Treat the request as if it wasn't conditional. */
+            cache->stale_handle = NULL;
+            /*
+             * Restore the original request headers as they may be needed
+             * by further output filters like the byterange filter to make
+             * the correct decisions.
+             */
+            r->headers_in = cache->stale_headers;
+        }
+    }
+
+    /* no cache handle, create a new entity */
+    if (!cache->handle) {
+        rv = cache_create_entity(cache, r, size, in);
+        info = apr_pcalloc(r->pool, sizeof(cache_info));
+        /* We only set info->status upon the initial creation. */
+        info->status = r->status;
+    }
+
+    if (rv != OK) {
+        /* we've got a cache miss! tell anyone who cares */
+        cache_run_cache_status(cache->handle, r, r->headers_out, AP_CACHE_MISS,
+                "cache miss: cache unwilling to store response");
+
+        /* Caching layer declined the opportunity to cache the response */
+        ap_remove_output_filter(f);
+        cache_remove_lock(conf, cache, r, NULL);
+        return ap_pass_brigade(f->next, in);
+    }
+
+    ap_log_rerror(APLOG_MARK, APLOG_DEBUG, 0, r, APLOGNO(00769)
+            "cache: Caching url %s for request %s",
+            cache->key, r->unparsed_uri);
+
+    /* We are actually caching this response. So it does not
+     * make sense to remove this entity any more.
+     */
+    ap_log_rerror(APLOG_MARK, APLOG_DEBUG, 0, r, APLOGNO(00770)
+            "cache: Removing CACHE_REMOVE_URL filter.");
+    ap_remove_output_filter(cache->remove_url_filter);
+
+    /*
+     * 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.
+     */
+
+    /* store away the previously parsed cache control headers */
+    memcpy(&info->control, &control, sizeof(cache_control_t));
+
+    /* Read the date. Generate one if one is not supplied */
+    dates = apr_table_get(r->err_headers_out, "Date");
+    if (dates == NULL) {
+        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 */
+        /* no date header (or bad header)! */
+        info->date = now;
+    }
+    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 */
+    if (lastmod != APR_DATE_BAD && lastmod > date) {
+        /* if it's in the future, then replace by date */
+        lastmod = date;
+        ap_log_rerror(APLOG_MARK, APLOG_DEBUG, 0,
+                r, APLOGNO(00771) "cache: Last modified is in the future, "
+                "replacing with now");
+    }
+
+
+    /* CC has priority over Expires.  */
+    if (control.s_maxage || control.max_age) {
+        apr_int64_t x;
+
+        x = control.s_maxage ? control.s_maxage_value : control.max_age_value;
+        x = x * MSEC_ONE_SEC;
+
+        if (x < dconf->minex) {
+            x = dconf->minex;
+        }
+        if (x > dconf->maxex) {
+            x = dconf->maxex;
+        }
+        exp = date + x;
+    }
+
+    /* if no expiry date then
+     *   if Cache-Control: s-maxage
+     *      expiry date = date + smaxage
+     *   if Cache-Control: max-age
+     *      expiry date = date + max-age
+     *   else if lastmod
+     *      expiry date = date + min((date - lastmod) * factor, maxexpire)
+     *   else
+     *      expire date = date + defaultexpire
+     */
+
+    if (exp == APR_DATE_BAD) {
+        if ((lastmod != APR_DATE_BAD) && (lastmod < date)) {
+            /* 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...
+             */
+            apr_time_t x = (apr_time_t) ((date - lastmod) * dconf->factor);
+
+            if (x < dconf->minex) {
+                x = dconf->minex;
+            }
+            if (x > dconf->maxex) {
+                x = dconf->maxex;
+            }
+            exp = date + x;
+        }
+        else {
+            exp = date + dconf->defex;
+        }
+    }
+    info->expire = exp;
+
+    /* We found a stale entry which wasn't really stale. */
+    if (cache->stale_handle) {
+
+        /* RFC 2616 10.3.5 states that entity headers are not supposed
+         * to be in the 304 response.  Therefore, we need to combine the
+         * response headers with the cached headers *before* we update
+         * the cached headers.
+         *
+         * However, before doing that, we need to first merge in
+         * err_headers_out (note that store_headers() below already selects
+         * the cacheable only headers using ap_cache_cacheable_headers_out(),
+         * here we want to keep the original headers in r->headers_out and
+         * forward all of them to the client, including non-cacheable ones).
+         */
+        r->headers_out = cache_merge_headers_out(r);
+        apr_table_clear(r->err_headers_out);
+
+        /* Merge in our cached headers.  However, keep any updated values. */
+        /* take output, overlay on top of cached */
+        cache_accept_headers(cache->handle, r, r->headers_out,
+                cache->handle->resp_hdrs, 1);
+    }
+
+    /* Write away header information to cache. It is possible that we are
+     * trying to update headers for an entity which has already been cached.
+     *
+     * This may fail, due to an unwritable cache area. E.g. filesystem full,
+     * permissions problems or a read-only (re)mount. This must be handled
+     * later.
+     */
+    rv = cache->provider->store_headers(cache->handle, r, info);
+
+    /* Did we just update the cached headers on a revalidated response?
+     *
+     * If so, we can now decide what to serve to the client.  This is done in
+     * the same way as with a regular response, but conditions are now checked
+     * against the cached or merged response headers.
+     */
+    if (cache->stale_handle) {
+        apr_bucket_brigade *bb;
+        apr_bucket *bkt;
+        int status;
+
+        /* Load in the saved status and clear the status line. */
+        r->status = info->status;
+        r->status_line = NULL;
+
+        /* We're just saving response headers, so we are done. Commit
+         * the response at this point, unless there was a previous error.
+         */
+        if (rv == APR_SUCCESS) {
+            rv = cache->provider->commit_entity(cache->handle, r);
+        }
+
+        bb = apr_brigade_create(r->pool, r->connection->bucket_alloc);
+
+        /* Restore the original request headers and see if we need to
+         * return anything else than the cached response (ie. the original
+         * request was conditional).
+         */
+        r->headers_in = cache->stale_headers;
+        status = ap_meets_conditions(r);
+        if (status != OK) {
+            r->status = status;
+
+            /* Strip the entity headers merged from the cached headers before
+             * updating the entry (see cache_accept_headers() above).
+             */
+            for (eh = MOD_CACHE_ENTITY_HEADERS; *eh; ++eh) {
+                apr_table_unset(r->headers_out, *eh);
+            }
+
+            bkt = apr_bucket_flush_create(bb->bucket_alloc);
+            APR_BRIGADE_INSERT_TAIL(bb, bkt);
+        }
+        else {
+            cache->provider->recall_body(cache->handle, r->pool, bb);
+
+            bkt = apr_bucket_eos_create(bb->bucket_alloc);
+            APR_BRIGADE_INSERT_TAIL(bb, bkt);
+        }
+
+        cache->block_response = 1;
+
+        /* Before returning we need to handle the possible case of an
+         * unwritable cache. Rather than leaving the entity in the cache
+         * and having it constantly re-validated, now that we have recalled
+         * the body it is safe to try and remove the url from the cache.
+         */
+        if (rv != APR_SUCCESS) {
+            ap_log_rerror(APLOG_MARK, APLOG_DEBUG, rv, r, APLOGNO(00772)
+                    "cache: updating headers with store_headers failed. "
+                    "Removing cached url.");
+
+            rv = cache->provider->remove_url(cache->stale_handle, r);
+            if (rv != OK) {
+                /* Probably a mod_cache_disk cache area has been (re)mounted
+                 * read-only, or that there is a permissions problem.
+                 */
+                ap_log_rerror(APLOG_MARK, APLOG_DEBUG, rv, r, APLOGNO(00773)
+                        "cache: attempt to remove url from cache unsuccessful.");
+            }
+
+            /* we've got a cache conditional hit! tell anyone who cares */
+            cache_run_cache_status(cache->handle, r, r->headers_out,
+                    AP_CACHE_REVALIDATE,
+                    "conditional cache hit: entity refresh failed");
+
+        }
+        else {
+
+            /* we've got a cache conditional hit! tell anyone who cares */
+            cache_run_cache_status(cache->handle, r, r->headers_out,
+                    AP_CACHE_REVALIDATE,
+                    "conditional cache hit: entity refreshed");
+
+        }
+
+        /* let someone else attempt to cache */
+        cache_remove_lock(conf, cache, r, NULL);
+
+        ap_log_rerror(APLOG_MARK, APLOG_DEBUG, APR_SUCCESS, r, APLOGNO(02971)
+                    "cache: serving %s (revalidated)", r->uri);
+
+        return ap_pass_brigade(f->next, bb);
+    }
+
+    if (rv != APR_SUCCESS) {
+        ap_log_rerror(APLOG_MARK, APLOG_DEBUG, rv, r, APLOGNO(00774)
+                "cache: store_headers failed");
+
+        /* we've got a cache miss! tell anyone who cares */
+        cache_run_cache_status(cache->handle, r, r->headers_out, AP_CACHE_MISS,
+                "cache miss: store_headers failed");
+
+        ap_remove_output_filter(f);
+        cache_remove_lock(conf, cache, r, NULL);
+        return ap_pass_brigade(f->next, in);
+    }
+
+    /* we've got a cache miss! tell anyone who cares */
+    cache_run_cache_status(cache->handle, r, r->headers_out, AP_CACHE_MISS,
+            "cache miss: attempting entity save");
+
+    return cache_save_store(f, in, conf, cache);
+}
+
+/*
+ * CACHE_REMOVE_URL filter
+ * -----------------------
+ *
+ * This filter gets added in the quick handler every time the CACHE_SAVE filter
+ * gets inserted. Its purpose is to remove a confirmed stale cache entry from
+ * the cache.
+ *
+ * CACHE_REMOVE_URL has to be a protocol filter to ensure that is run even if
+ * the response is a canned error message, which removes the content filters
+ * and thus the CACHE_SAVE filter from the chain.
+ *
+ * CACHE_REMOVE_URL expects cache request rec within its context because the
+ * request this filter runs on can be different from the one whose cache entry
+ * should be removed, due to internal redirects.
+ *
+ * Note that CACHE_SAVE_URL (as a content-set filter, hence run before the
+ * protocol filters) will remove this filter if it decides to cache the file.
+ * Therefore, if this filter is left in, it must mean we need to toss any
+ * existing files.
+ */
+static apr_status_t cache_remove_url_filter(ap_filter_t *f,
+                                            apr_bucket_brigade *in)
+{
+    request_rec *r = f->r;
+    cache_request_rec *cache;
+
+    /* Setup cache_request_rec */
+    cache = (cache_request_rec *) f->ctx;
+
+    if (!cache) {
+        /* user likely configured CACHE_REMOVE_URL manually; they should really
+         * use mod_cache configuration to do that. So:
+         * 1. Remove ourselves
+         * 2. Do nothing and bail out
+         */
+        ap_log_rerror(APLOG_MARK, APLOG_DEBUG, 0, r, APLOGNO(00775)
+                "cache: CACHE_REMOVE_URL enabled unexpectedly");
+        ap_remove_output_filter(f);
+        return ap_pass_brigade(f->next, in);
+    }
+
+    /* Now remove this cache entry from the cache */
+    cache_remove_url(cache, r);
+
+    /* remove ourselves */
+    ap_remove_output_filter(f);
+    return ap_pass_brigade(f->next, in);
+}
+
+/*
+ * CACHE_INVALIDATE filter
+ * -----------------------
+ *
+ * This filter gets added in the quick handler should a PUT, POST or DELETE
+ * method be detected. If the response is successful, we must invalidate any
+ * cached entity as per RFC2616 section 13.10.
+ *
+ * CACHE_INVALIDATE has to be a protocol filter to ensure that is run even if
+ * the response is a canned error message, which removes the content filters
+ * from the chain.
+ *
+ * CACHE_INVALIDATE expects cache request rec within its context because the
+ * request this filter runs on can be different from the one whose cache entry
+ * should be removed, due to internal redirects.
+ */
+static apr_status_t cache_invalidate_filter(ap_filter_t *f,
+                                            apr_bucket_brigade *in)
+{
+    request_rec *r = f->r;
+    cache_request_rec *cache;
+
+    /* Setup cache_request_rec */
+    cache = (cache_request_rec *) f->ctx;
+
+    if (!cache) {
+        /* user likely configured CACHE_INVALIDATE manually; they should really
+         * use mod_cache configuration to do that. So:
+         * 1. Remove ourselves
+         * 2. Do nothing and bail out
+         */
+        ap_log_rerror(APLOG_MARK, APLOG_DEBUG, 0, r, APLOGNO(02465)
+                "cache: CACHE_INVALIDATE enabled unexpectedly: %s", r->uri);
+    }
+    else {
+
+        if (r->status > 299) {
+
+            ap_log_rerror(APLOG_MARK, APLOG_DEBUG, 0, r, APLOGNO(02466)
+                    "cache: response status to '%s' method is %d (>299), not invalidating cached entity: %s", r->method, r->status, r->uri);
+
+        }
+        else {
+
+            ap_log_rerror(APLOG_MARK, APLOG_DEBUG, APR_SUCCESS, r, APLOGNO(02467)
+                    "cache: Invalidating all cached entities in response to '%s' request for %s",
+                    r->method, r->uri);
+
+            cache_invalidate(cache, r);
+
+            /* we've got a cache invalidate! tell everyone who cares */
+            cache_run_cache_status(cache->handle, r, r->headers_out,
+                    AP_CACHE_INVALIDATE, apr_psprintf(r->pool,
+                            "cache invalidated by %s", r->method));
+
+        }
+
+    }
+
+    /* remove ourselves */
+    ap_remove_output_filter(f);
+    return ap_pass_brigade(f->next, in);
+}
+
+/*
+ * CACHE filter
+ * ------------
+ *
+ * This filter can be optionally inserted into the filter chain by the admin as
+ * a marker representing the precise location within the filter chain where
+ * caching is to be performed.
+ *
+ * When the filter chain is set up in the non-quick version of the URL handler,
+ * the CACHE filter is replaced by the CACHE_OUT or CACHE_SAVE filter,
+ * effectively inserting the caching filters at the point indicated by the
+ * admin. The CACHE filter is then removed.
+ *
+ * This allows caching to be performed before the content is passed to the
+ * INCLUDES filter, or to a filter that might perform transformations unique
+ * to the specific request and that would otherwise be non-cacheable.
+ */
+static apr_status_t cache_filter(ap_filter_t *f, apr_bucket_brigade *in)
+{
+
+    cache_server_conf
+            *conf =
+                    (cache_server_conf *) ap_get_module_config(f->r->server->module_config,
+                            &cache_module);
+
+    /* was the quick handler enabled */
+    if (conf->quick) {
+        ap_log_rerror(APLOG_MARK, APLOG_WARNING, 0, f->r, APLOGNO(00776)
+                "cache: CACHE filter was added in quick handler mode and "
+                "will be ignored: %s", f->r->unparsed_uri);
+    }
+    /* otherwise we may have been bypassed, nothing to see here */
+    else {
+        ap_log_rerror(APLOG_MARK, APLOG_DEBUG, 0, f->r, APLOGNO(00777)
+                "cache: CACHE filter was added twice, or was added where "
+                "the cache has been bypassed and will be ignored: %s",
+                f->r->unparsed_uri);
+    }
+
+    /* we are just a marker, so let's just remove ourselves */
+    ap_remove_output_filter(f);
+    return ap_pass_brigade(f->next, in);
+}
+
+/**
+ * If configured, add the status of the caching attempt to the subprocess
+ * environment, and if configured, to headers in the response.
+ *
+ * The status is saved below the broad category of the status (hit, miss,
+ * revalidate), as well as a single cache-status key. This can be used for
+ * conditional logging.
+ *
+ * The status is optionally saved to an X-Cache header, and the detail of
+ * why a particular cache entry was cached (or not cached) is optionally
+ * saved to an X-Cache-Detail header. This extra detail is useful for
+ * service developers who may need to know whether their Cache-Control headers
+ * are working correctly.
+ */
+static int cache_status(cache_handle_t *h, request_rec *r,
+        apr_table_t *headers, ap_cache_status_e status, const char *reason)
+{
+    cache_server_conf
+            *conf =
+                    (cache_server_conf *) ap_get_module_config(r->server->module_config,
+                            &cache_module);
+
+    cache_dir_conf *dconf = ap_get_module_config(r->per_dir_config, &cache_module);
+    int x_cache = 0, x_cache_detail = 0;
+
+    switch (status) {
+    case AP_CACHE_HIT: {
+        apr_table_setn(r->subprocess_env, AP_CACHE_HIT_ENV, reason);
+        break;
+    }
+    case AP_CACHE_REVALIDATE: {
+        apr_table_setn(r->subprocess_env, AP_CACHE_REVALIDATE_ENV, reason);
+        break;
+    }
+    case AP_CACHE_MISS: {
+        apr_table_setn(r->subprocess_env, AP_CACHE_MISS_ENV, reason);
+        break;
+    }
+    case AP_CACHE_INVALIDATE: {
+        apr_table_setn(r->subprocess_env, AP_CACHE_INVALIDATE_ENV, reason);
+        break;
+    }
+    }
+
+    apr_table_setn(r->subprocess_env, AP_CACHE_STATUS_ENV, reason);
+
+    if (dconf && dconf->x_cache_set) {
+        x_cache = dconf->x_cache;
+    }
+    else {
+        x_cache = conf->x_cache;
+    }
+    if (x_cache) {
+        apr_table_setn(headers, "X-Cache", apr_psprintf(r->pool, "%s from %s",
+                status == AP_CACHE_HIT ? "HIT"
+                        : status == AP_CACHE_REVALIDATE ? "REVALIDATE" : status
+                                == AP_CACHE_INVALIDATE ? "INVALIDATE" : "MISS",
+                r->server->server_hostname));
+    }
+
+    if (dconf && dconf->x_cache_detail_set) {
+        x_cache_detail = dconf->x_cache_detail;
+    }
+    else {
+        x_cache_detail = conf->x_cache_detail;
+    }
+    if (x_cache_detail) {
+        apr_table_setn(headers, "X-Cache-Detail", apr_psprintf(r->pool,
+                "\"%s\" from %s", reason, r->server->server_hostname));
+    }
+
+    return OK;
+}
+
+/**
+ * If an error has occurred, but we have a stale cached entry, restore the
+ * filter stack from the save filter onwards. The canned error message will
+ * be discarded in the process, and replaced with the cached response.
+ */
+static void cache_insert_error_filter(request_rec *r)
+{
+    void *dummy;
+    cache_dir_conf *dconf;
+
+    /* ignore everything except for 5xx errors */
+    if (r->status < HTTP_INTERNAL_SERVER_ERROR) {
+        return;
+    }
+
+    dconf = ap_get_module_config(r->per_dir_config, &cache_module);
+
+    if (!dconf->stale_on_error) {
+        return;
+    }
+
+    /* 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 the error was generated by our server via
+     * ap_die().
+     */
+    apr_pool_userdata_get(&dummy, CACHE_CTX_KEY, r->pool);
+    if (dummy) {
+        cache_request_rec *cache = (cache_request_rec *) dummy;
+
+        ap_remove_output_filter(cache->remove_url_filter);
+
+        if (cache->stale_handle && cache->save_filter
+                && !cache->stale_handle->cache_obj->info.control.must_revalidate
+                && !cache->stale_handle->cache_obj->info.control.proxy_revalidate
+                && !cache->stale_handle->cache_obj->info.control.s_maxage) {
+            const char *warn_head;
+            cache_server_conf
+                    *conf =
+                            (cache_server_conf *) ap_get_module_config(r->server->module_config,
+                                    &cache_module);
+
+            /* morph the current save filter into the out filter, and serve from
+             * cache.
+             */
+            cache->handle = cache->stale_handle;
+            if (r->main) {
+                cache->save_filter->frec = cache_out_subreq_filter_handle;
+            }
+            else {
+                cache->save_filter->frec = cache_out_filter_handle;
+            }
+
+            r->output_filters = cache->save_filter;
+
+            r->err_headers_out = cache->stale_handle->resp_hdrs;
+
+            /* 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->err_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, r, NULL);
+
+        }
+    }
+
+    return;
+}
+
+/* -------------------------------------------------------------- */
+/* Setup configurable data */
+
+static void *create_dir_config(apr_pool_t *p, char *dummy)
+{
+    cache_dir_conf *dconf = apr_pcalloc(p, sizeof(cache_dir_conf));
+
+    dconf->no_last_mod_ignore = 0;
+    dconf->store_expired = 0;
+    dconf->store_private = 0;
+    dconf->store_nostore = 0;
+
+    /* maximum time to cache a document */
+    dconf->maxex = DEFAULT_CACHE_MAXEXPIRE;
+    dconf->minex = DEFAULT_CACHE_MINEXPIRE;
+    /* default time to cache a document */
+    dconf->defex = DEFAULT_CACHE_EXPIRE;
+
+    /* factor used to estimate Expires date from LastModified date */
+    dconf->factor = DEFAULT_CACHE_LMFACTOR;
+
+    dconf->x_cache = DEFAULT_X_CACHE;
+    dconf->x_cache_detail = DEFAULT_X_CACHE_DETAIL;
+
+    dconf->stale_on_error = DEFAULT_CACHE_STALE_ON_ERROR;
+
+    /* array of providers for this URL space */
+    dconf->cacheenable = apr_array_make(p, 10, sizeof(struct cache_enable));
+
+    return dconf;
+}
+
+static void *merge_dir_config(apr_pool_t *p, void *basev, void *addv) {
+    cache_dir_conf *new = (cache_dir_conf *) apr_pcalloc(p, sizeof(cache_dir_conf));
+    cache_dir_conf *add = (cache_dir_conf *) addv;
+    cache_dir_conf *base = (cache_dir_conf *) basev;
+
+    new->no_last_mod_ignore = (add->no_last_mod_ignore_set == 0) ? base->no_last_mod_ignore : add->no_last_mod_ignore;
+    new->no_last_mod_ignore_set = add->no_last_mod_ignore_set || base->no_last_mod_ignore_set;
+
+    new->store_expired = (add->store_expired_set == 0) ? base->store_expired : add->store_expired;
+    new->store_expired_set = add->store_expired_set || base->store_expired_set;
+    new->store_private = (add->store_private_set == 0) ? base->store_private : add->store_private;
+    new->store_private_set = add->store_private_set || base->store_private_set;
+    new->store_nostore = (add->store_nostore_set == 0) ? base->store_nostore : add->store_nostore;
+    new->store_nostore_set = add->store_nostore_set || base->store_nostore_set;
+
+    /* maximum time to cache a document */
+    new->maxex = (add->maxex_set == 0) ? base->maxex : add->maxex;
+    new->maxex_set = add->maxex_set || base->maxex_set;
+    new->minex = (add->minex_set == 0) ? base->minex : add->minex;
+    new->minex_set = add->minex_set || base->minex_set;
+
+    /* default time to cache a document */
+    new->defex = (add->defex_set == 0) ? base->defex : add->defex;
+    new->defex_set = add->defex_set || base->defex_set;
+
+    /* factor used to estimate Expires date from LastModified date */
+    new->factor = (add->factor_set == 0) ? base->factor : add->factor;
+    new->factor_set = add->factor_set || base->factor_set;
+
+    new->x_cache = (add->x_cache_set == 0) ? base->x_cache : add->x_cache;
+    new->x_cache_set = add->x_cache_set || base->x_cache_set;
+    new->x_cache_detail = (add->x_cache_detail_set == 0) ? base->x_cache_detail
+            : add->x_cache_detail;
+    new->x_cache_detail_set = add->x_cache_detail_set
+            || base->x_cache_detail_set;
+
+    new->stale_on_error = (add->stale_on_error_set == 0) ? base->stale_on_error
+            : add->stale_on_error;
+    new->stale_on_error_set = add->stale_on_error_set
+            || base->stale_on_error_set;
+
+    new->cacheenable = add->enable_set ? apr_array_append(p, base->cacheenable,
+            add->cacheenable) : base->cacheenable;
+    new->enable_set = add->enable_set || base->enable_set;
+    new->disable = (add->disable_set == 0) ? base->disable : add->disable;
+    new->disable_set = add->disable_set || base->disable_set;
+
+    return new;
+}
+
+static void * create_cache_config(apr_pool_t *p, server_rec *s)
+{
+    const char *tmppath = NULL;
+    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));
+    ps->ignorecachecontrol = 0;
+    ps->ignorecachecontrol_set = 0;
+    /* array of headers that should not be stored in cache */
+    ps->ignore_headers = apr_array_make(p, 10, sizeof(char *));
+    ps->ignore_headers_set = CACHE_IGNORE_HEADERS_UNSET;
+    /* flag indicating that query-string should be ignored when caching */
+    ps->ignorequerystring = 0;
+    ps->ignorequerystring_set = 0;
+    /* by default, run in the quick handler */
+    ps->quick = 1;
+    ps->quick_set = 0;
+    /* array of identifiers that should not be used for key calculation */
+    ps->ignore_session_id = apr_array_make(p, 10, sizeof(char *));
+    ps->ignore_session_id_set = CACHE_IGNORE_SESSION_ID_UNSET;
+    ps->lock = 0; /* thundering herd lock defaults to off */
+    ps->lock_set = 0;
+    apr_temp_dir_get(&tmppath, p);
+    if (tmppath) {
+        ps->lockpath = apr_pstrcat(p, tmppath, DEFAULT_CACHE_LOCKPATH, NULL);
+    }
+    ps->lockmaxage = apr_time_from_sec(DEFAULT_CACHE_MAXAGE);
+    ps->x_cache = DEFAULT_X_CACHE;
+    ps->x_cache_detail = DEFAULT_X_CACHE_DETAIL;
+    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);
+
+    ps->ignorecachecontrol  =
+        (overrides->ignorecachecontrol_set == 0)
+        ? base->ignorecachecontrol
+        : overrides->ignorecachecontrol;
+    ps->ignore_headers =
+        (overrides->ignore_headers_set == CACHE_IGNORE_HEADERS_UNSET)
+        ? base->ignore_headers
+        : overrides->ignore_headers;
+    ps->ignorequerystring =
+        (overrides->ignorequerystring_set == 0)
+        ? base->ignorequerystring
+        : overrides->ignorequerystring;
+    ps->ignore_session_id =
+        (overrides->ignore_session_id_set == CACHE_IGNORE_SESSION_ID_UNSET)
+        ? base->ignore_session_id
+        : overrides->ignore_session_id;
+    ps->lock =
+        (overrides->lock_set == 0)
+        ? base->lock
+        : overrides->lock;
+    ps->lockpath =
+        (overrides->lockpath_set == 0)
+        ? base->lockpath
+        : overrides->lockpath;
+    ps->lockmaxage =
+        (overrides->lockmaxage_set == 0)
+        ? base->lockmaxage
+        : overrides->lockmaxage;
+    ps->quick =
+        (overrides->quick_set == 0)
+        ? base->quick
+        : overrides->quick;
+    ps->x_cache =
+        (overrides->x_cache_set == 0)
+        ? base->x_cache
+        : overrides->x_cache;
+    ps->x_cache_detail =
+        (overrides->x_cache_detail_set == 0)
+        ? base->x_cache_detail
+        : overrides->x_cache_detail;
+    ps->base_uri =
+        (overrides->base_uri_set == 0)
+        ? base->base_uri
+        : overrides->base_uri;
+    return ps;
+}
+
+static const char *set_cache_quick_handler(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->quick = flag;
+    conf->quick_set = 1;
+    return NULL;
+
+}
+
+static const char *set_cache_ignore_no_last_mod(cmd_parms *parms, void *dummy,
+                                                int flag)
+{
+    cache_dir_conf *dconf = (cache_dir_conf *)dummy;
+
+    dconf->no_last_mod_ignore = flag;
+    dconf->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 *set_cache_store_expired(cmd_parms *parms, void *dummy,
+                                           int flag)
+{
+    cache_dir_conf *dconf = (cache_dir_conf *)dummy;
+
+    dconf->store_expired = flag;
+    dconf->store_expired_set = 1;
+    return NULL;
+}
+
+static const char *set_cache_store_private(cmd_parms *parms, void *dummy,
+                                           int flag)
+{
+    cache_dir_conf *dconf = (cache_dir_conf *)dummy;
+
+    dconf->store_private = flag;
+    dconf->store_private_set = 1;
+    return NULL;
+}
+
+static const char *set_cache_store_nostore(cmd_parms *parms, void *dummy,
+                                           int flag)
+{
+    cache_dir_conf *dconf = (cache_dir_conf *)dummy;
+
+    dconf->store_nostore = flag;
+    dconf->store_nostore_set = 1;
+    return NULL;
+}
+
+static const char *add_ignore_header(cmd_parms *parms, void *dummy,
+                                     const char *header)
+{
+    cache_server_conf *conf;
+    char **new;
+
+    conf =
+        (cache_server_conf *)ap_get_module_config(parms->server->module_config,
+                                                  &cache_module);
+    if (!strcasecmp(header, "None")) {
+        /* if header None is listed clear array */
+        conf->ignore_headers->nelts = 0;
+    }
+    else {
+        if ((conf->ignore_headers_set == CACHE_IGNORE_HEADERS_UNSET) ||
+            (conf->ignore_headers->nelts)) {
+            /* Only add header if no "None" has been found in header list
+             * so far.
+             * (When 'None' is passed, IGNORE_HEADERS_SET && nelts == 0.)
+             */
+            new = (char **)apr_array_push(conf->ignore_headers);
+            (*new) = (char *)header;
+        }
+    }
+    conf->ignore_headers_set = CACHE_IGNORE_HEADERS_SET;
+    return NULL;
+}
+
+static const char *add_ignore_session_id(cmd_parms *parms, void *dummy,
+                                         const char *identifier)
+{
+    cache_server_conf *conf;
+    char **new;
+
+    conf =
+        (cache_server_conf *)ap_get_module_config(parms->server->module_config,
+                                                  &cache_module);
+    if (!strcasecmp(identifier, "None")) {
+        /* if identifier None is listed clear array */
+        conf->ignore_session_id->nelts = 0;
+    }
+    else {
+        if ((conf->ignore_session_id_set == CACHE_IGNORE_SESSION_ID_UNSET) ||
+            (conf->ignore_session_id->nelts)) {
+            /*
+             * Only add identifier if no "None" has been found in identifier
+             * list so far.
+             */
+            new = (char **)apr_array_push(conf->ignore_session_id);
+            (*new) = (char *)identifier;
+        }
+    }
+    conf->ignore_session_id_set = CACHE_IGNORE_SESSION_ID_SET;
+    return NULL;
+}
+
+static const char *add_cache_enable(cmd_parms *parms, void *dummy,
+                                    const char *type,
+                                    const char *url)
+{
+    cache_dir_conf *dconf = (cache_dir_conf *)dummy;
+    cache_server_conf *conf;
+    struct cache_enable *new;
+
+    const char *err = ap_check_cmd_context(parms,
+                                           NOT_IN_DIRECTORY|NOT_IN_LIMIT|NOT_IN_FILES);
+    if (err != NULL) {
+        return err;
+    }
+
+    if (*type == '/') {
+        return apr_psprintf(parms->pool,
+          "provider (%s) starts with a '/'.  Are url and provider switched?",
+          type);
+    }
+
+    if (!url) {
+        url = parms->path;
+    }
+    if (!url) {
+        return apr_psprintf(parms->pool,
+          "CacheEnable provider (%s) is missing an URL.", type);
+    }
+    if (parms->path && strncmp(parms->path, url, strlen(parms->path))) {
+        return "When in a Location, CacheEnable must specify a path or an URL below "
+        "that location.";
+    }
+
+    conf =
+        (cache_server_conf *)ap_get_module_config(parms->server->module_config,
+                                                  &cache_module);
+
+    if (parms->path) {
+        new = apr_array_push(dconf->cacheenable);
+        dconf->enable_set = 1;
+    }
+    else {
+        new = apr_array_push(conf->cacheenable);
+    }
+
+    new->type = type;
+    if (apr_uri_parse(parms->pool, url, &(new->url))) {
+        return NULL;
+    }
+    if (new->url.path) {
+        new->pathlen = strlen(new->url.path);
+    } else {
+        new->pathlen = 1;
+        new->url.path = "/";
+    }
+    return NULL;
+}
+
+static const char *add_cache_disable(cmd_parms *parms, void *dummy,
+                                     const char *url)
+{
+    cache_dir_conf *dconf = (cache_dir_conf *)dummy;
+    cache_server_conf *conf;
+    struct cache_disable *new;
+
+    const char *err = ap_check_cmd_context(parms,
+                                           NOT_IN_DIRECTORY|NOT_IN_LIMIT|NOT_IN_FILES);
+    if (err != NULL) {
+        return err;
+    }
+
+    conf =
+        (cache_server_conf *)ap_get_module_config(parms->server->module_config,
+                                                  &cache_module);
+
+    if (parms->path) {
+        if (!strcasecmp(url, "on")) {
+            dconf->disable = 1;
+            dconf->disable_set = 1;
+            return NULL;
+        }
+        else {
+            return "CacheDisable must be followed by the word 'on' when in a Location.";
+        }
+    }
+
+    if (!url || (url[0] != '/' && !ap_strchr_c(url, ':'))) {
+        return "CacheDisable must specify a path or an URL.";
+    }
+
+    new = apr_array_push(conf->cachedisable);
+    if (apr_uri_parse(parms->pool, url, &(new->url))) {
+        return NULL;
+    }
+    if (new->url.path) {
+        new->pathlen = strlen(new->url.path);
+    } else {
+        new->pathlen = 1;
+        new->url.path = "/";
+    }
+    return NULL;
+}
+
+static const char *set_cache_maxex(cmd_parms *parms, void *dummy,
+                                   const char *arg)
+{
+    cache_dir_conf *dconf = (cache_dir_conf *)dummy;
+
+    dconf->maxex = (apr_time_t) (atol(arg) * MSEC_ONE_SEC);
+    dconf->maxex_set = 1;
+    return NULL;
+}
+
+static const char *set_cache_minex(cmd_parms *parms, void *dummy,
+                                   const char *arg)
+{
+    cache_dir_conf *dconf = (cache_dir_conf *)dummy;
+
+    dconf->minex = (apr_time_t) (atol(arg) * MSEC_ONE_SEC);
+    dconf->minex_set = 1;
+    return NULL;
+}
+
+static const char *set_cache_defex(cmd_parms *parms, void *dummy,
+                                   const char *arg)
+{
+    cache_dir_conf *dconf = (cache_dir_conf *)dummy;
+
+    dconf->defex = (apr_time_t) (atol(arg) * MSEC_ONE_SEC);
+    dconf->defex_set = 1;
+    return NULL;
+}
+
+static const char *set_cache_factor(cmd_parms *parms, void *dummy,
+                                    const char *arg)
+{
+    cache_dir_conf *dconf = (cache_dir_conf *)dummy;
+    double val;
+
+    if (sscanf(arg, "%lg", &val) != 1) {
+        return "CacheLastModifiedFactor value must be a float";
+    }
+    dconf->factor = val;
+    dconf->factor_set = 1;
+    return NULL;
+}
+
+static const char *set_cache_ignore_querystring(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->ignorequerystring = flag;
+    conf->ignorequerystring_set = 1;
+    return NULL;
+}
+
+static const char *set_cache_lock(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->lock = flag;
+    conf->lock_set = 1;
+    return NULL;
+}
+
+static const char *set_cache_lock_path(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->lockpath = ap_server_root_relative(parms->pool, arg);
+    if (!conf->lockpath) {
+        return apr_pstrcat(parms->pool, "Invalid CacheLockPath path ",
+                           arg, NULL);
+    }
+    conf->lockpath_set = 1;
+    return NULL;
+}
+
+static const char *set_cache_lock_maxage(cmd_parms *parms, void *dummy,
+                                    const char *arg)
+{
+    cache_server_conf *conf;
+    apr_int64_t seconds;
+
+    conf =
+        (cache_server_conf *)ap_get_module_config(parms->server->module_config,
+                                                  &cache_module);
+    seconds = apr_atoi64(arg);
+    if (seconds <= 0) {
+        return "CacheLockMaxAge value must be a non-zero positive integer";
+    }
+    conf->lockmaxage = apr_time_from_sec(seconds);
+    conf->lockmaxage_set = 1;
+    return NULL;
+}
+
+static const char *set_cache_x_cache(cmd_parms *parms, void *dummy, int flag)
+{
+
+    if (parms->path) {
+        cache_dir_conf *dconf = (cache_dir_conf *)dummy;
+
+        dconf->x_cache = flag;
+        dconf->x_cache_set = 1;
+
+    }
+    else {
+        cache_server_conf *conf =
+            (cache_server_conf *)ap_get_module_config(parms->server->module_config,
+                                                      &cache_module);
+
+        conf->x_cache = flag;
+        conf->x_cache_set = 1;
+
+    }
+
+    return NULL;
+}
+
+static const char *set_cache_x_cache_detail(cmd_parms *parms, void *dummy, int flag)
+{
+
+    if (parms->path) {
+        cache_dir_conf *dconf = (cache_dir_conf *)dummy;
+
+        dconf->x_cache_detail = flag;
+        dconf->x_cache_detail_set = 1;
+
+    }
+    else {
+        cache_server_conf *conf =
+            (cache_server_conf *)ap_get_module_config(parms->server->module_config,
+                                                      &cache_module);
+
+        conf->x_cache_detail = flag;
+        conf->x_cache_detail_set = 1;
+
+    }
+
+    return NULL;
+}
+
+static const char *set_cache_key_base_url(cmd_parms *parms, void *dummy,
+        const char *arg)
+{
+    cache_server_conf *conf;
+    apr_status_t rv;
+
+    conf =
+        (cache_server_conf *)ap_get_module_config(parms->server->module_config,
+                                                  &cache_module);
+    conf->base_uri = apr_pcalloc(parms->pool, sizeof(apr_uri_t));
+    rv = apr_uri_parse(parms->pool, arg, conf->base_uri);
+    if (rv != APR_SUCCESS) {
+        return apr_psprintf(parms->pool, "Could not parse '%s' as an URL.", arg);
+    }
+    else if (!conf->base_uri->scheme && !conf->base_uri->hostname &&
+            !conf->base_uri->port_str) {
+        return apr_psprintf(parms->pool, "URL '%s' must contain at least one of a scheme, a hostname or a port.", arg);
+    }
+    conf->base_uri_set = 1;
+    return NULL;
+}
+
+static const char *set_cache_stale_on_error(cmd_parms *parms, void *dummy,
+        int flag)
+{
+    cache_dir_conf *dconf = (cache_dir_conf *)dummy;
+
+    dconf->stale_on_error = flag;
+    dconf->stale_on_error_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
+     * implementations (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_TAKE12("CacheEnable", add_cache_enable, NULL, RSRC_CONF|ACCESS_CONF,
+                   "A cache type and partial URL prefix below which "
+                   "caching is enabled"),
+    AP_INIT_TAKE1("CacheDisable", add_cache_disable, NULL, RSRC_CONF|ACCESS_CONF,
+                  "A partial URL prefix below which caching is disabled"),
+    AP_INIT_TAKE1("CacheMaxExpire", set_cache_maxex, NULL, RSRC_CONF|ACCESS_CONF,
+                  "The maximum time in seconds to cache a document"),
+    AP_INIT_TAKE1("CacheMinExpire", set_cache_minex, NULL, RSRC_CONF|ACCESS_CONF,
+                  "The minimum time in seconds to cache a document"),
+    AP_INIT_TAKE1("CacheDefaultExpire", set_cache_defex, NULL, RSRC_CONF|ACCESS_CONF,
+                  "The default time in seconds to cache a document"),
+    AP_INIT_FLAG("CacheQuickHandler", set_cache_quick_handler, NULL,
+                 RSRC_CONF,
+                 "Run the cache in the quick handler, default on"),
+    AP_INIT_FLAG("CacheIgnoreNoLastMod", set_cache_ignore_no_last_mod, NULL,
+                 RSRC_CONF|ACCESS_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_FLAG("CacheStoreExpired", set_cache_store_expired,
+                 NULL, RSRC_CONF|ACCESS_CONF,
+                 "Ignore expiration dates when populating cache, resulting in "
+                 "an If-Modified-Since request to the backend on retrieval"),
+    AP_INIT_FLAG("CacheStorePrivate", set_cache_store_private,
+                 NULL, RSRC_CONF|ACCESS_CONF,
+                 "Ignore 'Cache-Control: private' and store private content"),
+    AP_INIT_FLAG("CacheStoreNoStore", set_cache_store_nostore,
+                 NULL, RSRC_CONF|ACCESS_CONF,
+                 "Ignore 'Cache-Control: no-store' and store sensitive content"),
+    AP_INIT_ITERATE("CacheIgnoreHeaders", add_ignore_header, NULL, RSRC_CONF,
+                    "A space separated list of headers that should not be "
+                    "stored by the cache"),
+    AP_INIT_FLAG("CacheIgnoreQueryString", set_cache_ignore_querystring,
+                 NULL, RSRC_CONF,
+                 "Ignore query-string when caching"),
+    AP_INIT_ITERATE("CacheIgnoreURLSessionIdentifiers", add_ignore_session_id,
+                    NULL, RSRC_CONF, "A space separated list of session "
+                    "identifiers that should be ignored for creating the key "
+                    "of the cached entity."),
+    AP_INIT_TAKE1("CacheLastModifiedFactor", set_cache_factor, NULL, RSRC_CONF|ACCESS_CONF,
+                  "The factor used to estimate Expires date from "
+                  "LastModified date"),
+    AP_INIT_FLAG("CacheLock", set_cache_lock,
+                 NULL, RSRC_CONF,
+                 "Enable or disable the thundering herd lock."),
+    AP_INIT_TAKE1("CacheLockPath", set_cache_lock_path, NULL, RSRC_CONF,
+                  "The thundering herd lock path. Defaults to the '"
+                  DEFAULT_CACHE_LOCKPATH "' directory in the system "
+                  "temp directory."),
+    AP_INIT_TAKE1("CacheLockMaxAge", set_cache_lock_maxage, NULL, RSRC_CONF,
+                  "Maximum age of any thundering herd lock."),
+    AP_INIT_FLAG("CacheHeader", set_cache_x_cache, NULL, RSRC_CONF | ACCESS_CONF,
+                 "Add a X-Cache header to responses. Default is off."),
+    AP_INIT_FLAG("CacheDetailHeader", set_cache_x_cache_detail, NULL,
+                 RSRC_CONF | ACCESS_CONF,
+                 "Add a X-Cache-Detail header to responses. Default is off."),
+    AP_INIT_TAKE1("CacheKeyBaseURL", set_cache_key_base_url, NULL, RSRC_CONF,
+                  "Override the base URL of reverse proxied cache keys."),
+    AP_INIT_FLAG("CacheStaleOnError", set_cache_stale_on_error,
+                 NULL, RSRC_CONF|ACCESS_CONF,
+                 "Serve stale content on 5xx errors if present. Defaults to on."),
+    {NULL}
+};
+
+static void register_hooks(apr_pool_t *p)
+{
+    /* cache initializer */
+    /* cache quick handler */
+    ap_hook_quick_handler(cache_quick_handler, NULL, NULL, APR_HOOK_FIRST);
+    /* cache handler */
+    ap_hook_handler(cache_handler, NULL, NULL, APR_HOOK_REALLY_FIRST);
+    /* cache status */
+    cache_hook_cache_status(cache_status, NULL, NULL, APR_HOOK_MIDDLE);
+    /* cache error handler */
+    ap_hook_insert_error_filter(cache_insert_error_filter, NULL, NULL, APR_HOOK_MIDDLE);
+    /* 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.
+     *
+     * Depending on the type of request (subrequest / main request) they
+     * need to be run before AP_FTYPE_CONTENT_SET / after AP_FTYPE_CONTENT_SET
+     * filters. Thus create two filter handles for each type:
+     * cache_save_filter_handle / cache_out_filter_handle to be used by
+     * main requests and
+     * cache_save_subreq_filter_handle / cache_out_subreq_filter_handle
+     * to be run by subrequest
+     */
+    /*
+     * CACHE is placed into the filter chain at an admin specified location,
+     * and when the cache_handler is run, the CACHE filter is swapped with
+     * the CACHE_OUT filter, or CACHE_SAVE filter as appropriate. This has
+     * the effect of offering optional fine control of where the cache is
+     * inserted into the filter chain.
+     */
+    cache_filter_handle =
+        ap_register_output_filter("CACHE",
+                                  cache_filter,
+                                  NULL,
+                                  AP_FTYPE_RESOURCE);
+    /*
+     * CACHE_SAVE must go into the filter chain after a possible DEFLATE
+     * filter to ensure that the compressed content is stored.
+     * Incrementing filter type by 1 ensures this happens.
+     */
+    cache_save_filter_handle =
+        ap_register_output_filter("CACHE_SAVE",
+                                  cache_save_filter,
+                                  NULL,
+                                  AP_FTYPE_CONTENT_SET+1);
+    /*
+     * CACHE_SAVE_SUBREQ must go into the filter chain before SUBREQ_CORE to
+     * handle subrequsts. Decrementing filter type by 1 ensures this
+     * happens.
+     */
+    cache_save_subreq_filter_handle =
+        ap_register_output_filter("CACHE_SAVE_SUBREQ",
+                                  cache_save_filter,
+                                  NULL,
+                                  AP_FTYPE_CONTENT_SET-1);
+    /*
+     * CACHE_OUT must go into the filter chain after a possible DEFLATE
+     * filter to ensure that already compressed cache objects do not
+     * get compressed again. Incrementing 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_OUT_SUBREQ must go into the filter chain before SUBREQ_CORE to
+     * handle subrequsts. Decrementing filter type by 1 ensures this
+     * happens.
+     */
+    cache_out_subreq_filter_handle =
+        ap_register_output_filter("CACHE_OUT_SUBREQ",
+                                  cache_out_filter,
+                                  NULL,
+                                  AP_FTYPE_CONTENT_SET-1);
+    /* CACHE_REMOVE_URL has to be a protocol filter to ensure that is
+     * run even if the response is a canned error message, which
+     * removes the content filters.
+     */
+    cache_remove_url_filter_handle =
+        ap_register_output_filter("CACHE_REMOVE_URL",
+                                  cache_remove_url_filter,
+                                  NULL,
+                                  AP_FTYPE_PROTOCOL);
+    cache_invalidate_filter_handle =
+        ap_register_output_filter("CACHE_INVALIDATE",
+                                  cache_invalidate_filter,
+                                  NULL,
+                                  AP_FTYPE_PROTOCOL);
+    ap_hook_post_config(cache_post_config, NULL, NULL, APR_HOOK_REALLY_FIRST);
+}
+
+AP_DECLARE_MODULE(cache) =
+{
+    STANDARD20_MODULE_STUFF,
+    create_dir_config,      /* create per-directory config structure */
+    merge_dir_config,       /* 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
+};
+
+APR_HOOK_STRUCT(
+    APR_HOOK_LINK(cache_status)
+)
+
+APR_IMPLEMENT_EXTERNAL_HOOK_RUN_ALL(cache, CACHE, int, cache_status,
+        (cache_handle_t *h, request_rec *r,
+                apr_table_t *headers, ap_cache_status_e status,
+                const char *reason), (h, r, headers, status, reason),
+        OK, DECLINED)