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

#include "mod_cache.h"
#include "apr_file_io.h"
#include "apr_strings.h"
#include "util_filter.h"
#include "util_script.h"

#if APR_HAVE_UNISTD_H
#include <unistd.h> /* needed for unlink/link */
#endif

/*
 * disk_cache_object_t
 * Pointed to by cache_object_t::vobj
 */
typedef struct disk_cache_object {
    const char *root;        /* the location of the cache directory */
    char *tempfile;          /* temp file tohold the content */
#if 0
    int dirlevels;              /* Number of levels of subdirectories */
    int dirlength;            /* Length of subdirectory names */   
#endif
    char *datafile;          /* name of file where the data will go */
    char *hdrsfile;          /* name of file where the hdrs will go */
    char *name;
    apr_time_t version;      /* update count of the file */
    apr_file_t *fd;          /* data file */
    apr_file_t *hfd;         /* headers file */
    apr_off_t file_size;     /*  File size of the cached data file  */    
} disk_cache_object_t;

/*
 * mod_disk_cache configuration
 */
/* TODO: Make defaults OS specific */
#define CACHEFILE_LEN 20        /* must be less than HASH_LEN/2 */
#define DEFAULT_DIRLEVELS 3
#define DEFAULT_DIRLENGTH 2
#define DEFAULT_MIN_FILE_SIZE 1
#define DEFAULT_MAX_FILE_SIZE 1000000
#define DEFAULT_CACHE_SIZE 1000000
 
typedef struct {
    const char* cache_root;
    apr_size_t cache_root_len;
    off_t space;                 /* Maximum cache size (in 1024 bytes) */
    apr_time_t maxexpire;        /* Maximum time to keep cached files in msecs */
    apr_time_t defaultexpire;    /* default time to keep cached file in msecs */
    double lmfactor;             /* factor for estimating expires date */
    apr_time_t gcinterval;       /* garbage collection interval, in msec */
    int dirlevels;               /* Number of levels of subdirectories */
    int dirlength;               /* Length of subdirectory names */
    int	expirychk;               /* true if expiry time is observed for cached files */
    apr_size_t minfs;            /* minumum file size for cached files */
    apr_size_t maxfs;            /* maximum file size for cached files */
    apr_time_t mintm;            /* minimum time margin for caching files */
    /* dgc_time_t gcdt;            time of day for daily garbage collection */
    apr_array_header_t *gcclnun; /* gc_retain_t entries for unused files */
    apr_array_header_t *gcclean; /* gc_retain_t entries for all files */
    int maxgcmem;                /* maximum memory used by garbage collection */
} disk_cache_conf;

module AP_MODULE_DECLARE_DATA disk_cache_module;

/* Forward declarations */
static int remove_entity(cache_handle_t *h);
static apr_status_t write_headers(cache_handle_t *h, request_rec *r, cache_info *i);
static apr_status_t write_body(cache_handle_t *h, request_rec *r, apr_bucket_brigade *b);
static apr_status_t read_headers(cache_handle_t *h, request_rec *r);
static apr_status_t read_body(cache_handle_t *h, apr_pool_t *p, apr_bucket_brigade *bb);

/*
 * Local static functions
 */
#define CACHE_HEADER_SUFFIX ".header"
#define CACHE_DATA_SUFFIX   ".data"
static char *header_file(apr_pool_t *p, int dirlevels, int dirlength, 
                         const char *root, const char *name)
{
    char *hashfile;
    hashfile = generate_name(p, dirlevels, dirlength, name);
    return apr_pstrcat(p, root, "/", hashfile, CACHE_HEADER_SUFFIX, NULL);
}

static char *data_file(apr_pool_t *p, int dirlevels, int dirlength, 
                       const char *root, const char *name)
{
    char *hashfile;
    hashfile = generate_name(p, dirlevels, dirlength, name);
    return apr_pstrcat(p, root, "/", hashfile, CACHE_DATA_SUFFIX, NULL);
}

static void mkdir_structure(disk_cache_conf *conf, char *file, apr_pool_t *pool)
{
    apr_status_t rv;
    char *p;

    for (p = file + conf->cache_root_len + 1;;) {
        p = strchr(p, '/');
        if (!p)
            break;
        *p = '\0';

        rv = apr_dir_make(file, 
                          APR_UREAD|APR_UWRITE|APR_UEXECUTE, pool);
        if (rv != APR_SUCCESS && !APR_STATUS_IS_EEXIST(rv)) {
            /* XXX */
        }
        *p = '/';
        ++p;
    }
}

static apr_status_t file_cache_el_final(cache_handle_t *h, request_rec *r)
{
    apr_status_t rv;
    disk_cache_conf *conf = ap_get_module_config(r->server->module_config,
                                                 &disk_cache_module);
    disk_cache_object_t *dobj = (disk_cache_object_t *) h->cache_obj->vobj;

    /* move the data over */
    if (dobj->fd) {
        apr_file_flush(dobj->fd);
        if (!dobj->datafile) {
            dobj->datafile = data_file(r->pool, conf->dirlevels, conf->dirlength,
                                       conf->cache_root, h->cache_obj->key);
        }
        /* Remove old file with the same name. If remove fails, then
         * perhaps we need to create the directory tree where we are
         * about to write the new file.
         */
        rv = apr_file_remove(dobj->datafile, r->pool);
        if (rv != APR_SUCCESS) {
            mkdir_structure(conf, dobj->datafile, r->pool);
        }

        /*
         * This assumes that the tempfile is on the same file system
         * as the cache_root. If not, then we need a file copy/move
         * rather than a rename.
         */
        rv = apr_file_rename(dobj->tempfile, dobj->datafile, r->pool);
        if (rv != APR_SUCCESS) {
            /* XXX log */
        }

        apr_file_close(dobj->fd);
        dobj->fd = NULL;
       /* XXX log */
   }

   return APR_SUCCESS;
}


/* These two functions get and put state information into the data 
 * file for an ap_cache_el, this state information will be read 
 * and written transparent to clients of this module 
 */
static int file_cache_read_mydata(apr_file_t *fd, cache_info *info, 
                                  disk_cache_object_t *dobj)
{
    apr_status_t rv;
    char urlbuff[1034]; /* XXX FIXME... THIS IS A POTENTIAL SECURITY HOLE */
    int urllen = sizeof(urlbuff);
    int offset=0;
    char * temp;

    /* read the data from the cache file */
    /* format
     * date SP expire SP count CRLF
     * dates are stored as a hex representation of apr_time_t (number of
     * microseconds since 00:00:00 january 1, 1970 UTC)
     */
    rv = apr_file_gets(&urlbuff[0], urllen, fd);
    if (rv != APR_SUCCESS) {
        return rv;
    }

    if ((temp = strchr(&urlbuff[0], '\n')) != NULL) /* trim off new line character */
        *temp = '\0';      /* overlay it with the null terminator */

    if (!apr_date_checkmask(urlbuff, "&&&&&&&&&&&&&&&& &&&&&&&&&&&&&&&& &&&&&&&&&&&&&&&&")) {
        return APR_EGENERAL;
    }

    info->date = ap_cache_hex2usec(urlbuff + offset);
    offset += (sizeof(info->date)*2) + 1;
    info->expire = ap_cache_hex2usec(urlbuff + offset);
    offset += (sizeof(info->expire)*2) + 1;
    dobj->version = ap_cache_hex2usec(urlbuff + offset);
    
    /* check that we have the same URL */
    rv = apr_file_gets(&urlbuff[0], urllen, fd);
    if (rv != APR_SUCCESS) {
        return rv;
    }

    if ((temp = strchr(&urlbuff[0], '\n')) != NULL) { /* trim off new line character */
        *temp = '\0';      /* overlay it with the null terminator */
    }

    if (strncmp(urlbuff, "X-NAME: ", 7) != 0) {
        return APR_EGENERAL;
    }
    if (strcmp(urlbuff + 8, dobj->name) != 0) {
        return APR_EGENERAL;
    }
    
    return APR_SUCCESS;
}

static int file_cache_write_mydata(apr_file_t *fd , cache_handle_t *h, request_rec *r)
{
    apr_status_t rc;
    char *buf;
    apr_size_t amt;

    char	dateHexS[sizeof(apr_time_t) * 2 + 1];
    char	expireHexS[sizeof(apr_time_t) * 2 + 1];
    char	verHexS[sizeof(apr_time_t) * 2 + 1];
    cache_info *info = &(h->cache_obj->info);
    disk_cache_object_t *dobj = (disk_cache_object_t *) h->cache_obj->vobj;
    
    if (!r->headers_out) {
        /* XXX log message */
        return 0;
    }

    ap_cache_usec2hex(info->date, dateHexS);
    ap_cache_usec2hex(info->expire, expireHexS);
    ap_cache_usec2hex(dobj->version++, verHexS);
    buf = apr_pstrcat(r->pool, dateHexS, " ", expireHexS, " ", verHexS, "\n", NULL);
    amt = strlen(buf);
    rc = apr_file_write(fd, buf, &amt);
    if (rc != APR_SUCCESS) {
        /* XXX log message */
        return 0;
    }

    buf = apr_pstrcat(r->pool, "X-NAME: ", dobj->name, "\n", NULL);
    amt = strlen(buf);
    rc = apr_file_write(fd, buf, &amt);
    if (rc != APR_SUCCESS) {
        /* XXX log message */
        return 0;
    }
    return 1;
}

/*
 * Hook and mod_cache callback functions
 */
#define AP_TEMPFILE "/aptmpXXXXXX"
static int create_entity(cache_handle_t *h, request_rec *r,
                         const char *type, 
                         const char *key, 
                         apr_size_t len)
{ 
    disk_cache_conf *conf = ap_get_module_config(r->server->module_config, 
                                                 &disk_cache_module);
    apr_status_t rv;
    cache_object_t *obj;
    disk_cache_object_t *dobj;
    apr_file_t *tmpfile;

    if (strcasecmp(type, "disk")) {
	return DECLINED;
    }

    /* Allocate and initialize cache_object_t and disk_cache_object_t */
    obj = apr_pcalloc(r->pool, sizeof(*obj));
    obj->vobj = dobj = apr_pcalloc(r->pool, sizeof(*dobj));

    obj->key = apr_pstrdup(r->pool, key);
    obj->info.len = len;
    obj->complete = 0;   /* Cache object is not complete */

    dobj->name = obj->key;

    /* open temporary file */
    dobj->tempfile = apr_pstrcat(r->pool, conf->cache_root, AP_TEMPFILE, NULL);
    rv = apr_file_mktemp(&tmpfile, dobj->tempfile,  
                         APR_CREATE | APR_READ | APR_WRITE | APR_EXCL, r->pool);

    /* Populate the cache handle */
    h->cache_obj = obj;
    h->read_body = &read_body;
    h->read_headers = &read_headers;
    h->write_body = &write_body;
    h->write_headers = &write_headers;
    h->remove_entity = &remove_entity;

    ap_log_error(APLOG_MARK, APLOG_INFO|APLOG_NOERRNO, 0, r->server,
                 "disk_cache: Caching URL %s",  key);

    return OK;
}

static int open_entity(cache_handle_t *h, request_rec *r, const char *type, const char *key)
{
    apr_status_t rc;
    disk_cache_conf *conf = ap_get_module_config(r->server->module_config, 
                                                 &disk_cache_module);
    char *data = data_file(r->pool, conf->dirlevels, conf->dirlength, 
                           conf->cache_root, key);
    char *headers = header_file(r->pool, conf->dirlevels, conf->dirlength, 
                                conf->cache_root, key);
    apr_file_t *fd;
    apr_file_t *hfd;
    apr_finfo_t finfo;
    cache_object_t *obj;
    cache_info *info;
    disk_cache_object_t *dobj;

    h->cache_obj = NULL;

    /* Look up entity keyed to 'url' */
    if (strcasecmp(type, "disk")) {
	return DECLINED;
    }

    /* Open the data file */
    rc = apr_file_open(&fd, data, APR_READ|APR_BINARY, 0, r->pool);
    if (rc != APR_SUCCESS) {
        /* XXX: Log message */
        return DECLINED;
    }

    /* Open the headers file */
    rc = apr_file_open(&hfd, headers, APR_READ|APR_BINARY, 0, r->pool);
    if (rc != APR_SUCCESS) {
        /* XXX: Log message */
        return DECLINED;
    }

    /* Create and init the cache object */
    h->cache_obj = obj = apr_pcalloc(r->pool, sizeof(cache_object_t));
    obj->vobj = dobj = apr_pcalloc(r->pool, sizeof(disk_cache_object_t));

    info = &(obj->info);
    obj->key = (char *) key;
    dobj->name = (char *) key;
    dobj->fd = fd;
    dobj->hfd = hfd;
    dobj->datafile = data;
    dobj->hdrsfile = headers;

    rc = apr_file_info_get(&finfo, APR_FINFO_SIZE, fd);
    if (rc == APR_SUCCESS) {
        dobj->file_size = finfo.size;
    }
    
    /* Read the bytes to setup the cache_info fields */
    rc = file_cache_read_mydata(hfd, info, dobj);
    if (rc != APR_SUCCESS) {
        /* XXX log message */
        return DECLINED;
    }

    /* Initialize the cache_handle callback functions */
    h->read_body = &read_body;
    h->read_headers = &read_headers;
    h->write_body = &write_body;
    h->write_headers = &write_headers;
    h->remove_entity = &remove_entity;

    ap_log_error(APLOG_MARK, APLOG_INFO|APLOG_NOERRNO, 0, r->server,
                 "disk_cache: Serving Cached URL %s",  dobj->name);
    return OK;
}

static int remove_url(const char *type, char *key) 
{
  return OK;
}

static int remove_entity(cache_handle_t *h) 
{
    cache_object_t *obj = h->cache_obj;

    /* Null out the cache object pointer so next time we start from scratch  */
    h->cache_obj = NULL;
    return OK;
}

/*
 * Reads headers from a buffer and returns an array of headers.
 * Returns NULL on file error
 * This routine tries to deal with too long lines and continuation lines.
 * @@@: XXX: FIXME: currently the headers are passed thru un-merged. 
 * Is that okay, or should they be collapsed where possible?
 */
static apr_status_t read_headers(cache_handle_t *h, request_rec *r) 
{
    apr_status_t rv;
    char *temp;
    char urlbuff[1034];
    int urllen = sizeof(urlbuff);
    disk_cache_object_t *dobj = (disk_cache_object_t *) h->cache_obj->vobj;

    /* This case should not happen... */
    if (!dobj->fd || !dobj->hfd) {
        /* XXX log message */
        return APR_NOTFOUND; 
    }

    if(!r->headers_out) {
        r->headers_out = apr_table_make(r->pool, 20);
    }
    
    /*
     * Call routine to read the header lines/status line 
     */
    ap_scan_script_header_err(r, dobj->hfd, NULL);
 
    apr_table_setn(r->headers_out, "Content-Type", 
                   ap_make_content_type(r, r->content_type));

    rv = apr_file_gets(&urlbuff[0], urllen, dobj->hfd);           /* Read status  */
    if (rv != APR_SUCCESS) {
        /* XXX log message */
	return rv;
    }

    r->status = atoi(urlbuff);                           /* Save status line into request rec  */

    rv = apr_file_gets(&urlbuff[0], urllen, dobj->hfd);               /* Read status line */
    if (rv != APR_SUCCESS) {
        /* XXX log message */
	return rv;
    }

    if ((temp = strchr(&urlbuff[0], '\n')) != NULL)       /* trim off new line character */
	*temp = '\0';              /* overlay it with the null terminator */

    r->status_line = apr_pstrdup(r->pool, urlbuff);            /* Save status line into request rec  */

    apr_file_close(dobj->hfd);

    ap_log_error(APLOG_MARK, APLOG_INFO|APLOG_NOERRNO, 0, r->server,
                 "disk_cache: Served headers for URL %s",  dobj->name);
    return APR_SUCCESS;
}

static apr_status_t read_body(cache_handle_t *h, apr_pool_t *p, apr_bucket_brigade *bb) 
{
    apr_bucket *e;
    disk_cache_object_t *dobj = (disk_cache_object_t*) h->cache_obj->vobj;

    e = apr_bucket_file_create(dobj->fd, 0, (apr_size_t) dobj->file_size, p,
                               bb->bucket_alloc);
    APR_BRIGADE_INSERT_HEAD(bb, e);
    e = apr_bucket_eos_create(bb->bucket_alloc);
    APR_BRIGADE_INSERT_TAIL(bb, e);

    return APR_SUCCESS;
}

static apr_status_t write_headers(cache_handle_t *h, request_rec *r, cache_info *info)
{
    disk_cache_conf *conf = ap_get_module_config(r->server->module_config, 
                                                 &disk_cache_module);
    apr_status_t rv;
    char *buf;
    char statusbuf[8];
    apr_size_t amt;
    disk_cache_object_t *dobj = (disk_cache_object_t*) h->cache_obj->vobj;
    apr_file_t *hfd = dobj->hfd;

    if (!hfd)  {
        if (!dobj->hdrsfile) {
            dobj->hdrsfile = header_file(r->pool, 
                                         conf->dirlevels, 
                                         conf->dirlength, 
                                         conf->cache_root,
                                         h->cache_obj->key);
        }
        
        /* This is flaky... we need to manage the cache_info differently */
        h->cache_obj->info = *info;
        
        /* Remove old file with the same name. If remove fails, then
         * perhaps we need to create the directory tree where we are
         * about to write the new headers file.
         */
        rv = apr_file_remove(dobj->hdrsfile, r->pool);
        if (rv != APR_SUCCESS) {
            mkdir_structure(conf, dobj->hdrsfile, r->pool);
        }

        rv = apr_file_open(&dobj->hfd, dobj->hdrsfile,
                           APR_WRITE | APR_CREATE | APR_EXCL,
                           0, r->pool);
        if (rv != APR_SUCCESS) {
            return rv;
        }
        hfd = dobj->hfd;
        dobj->name = h->cache_obj->key;

        file_cache_write_mydata(dobj->hfd, h, r);

        if (r->headers_out) {
            int i;
            apr_table_entry_t *elts = (apr_table_entry_t *) apr_table_elts(r->headers_out)->elts;
            for (i = 0; i < apr_table_elts(r->headers_out)->nelts; ++i) {
                if (elts[i].key != NULL) {
                    buf = apr_pstrcat(r->pool, elts[i].key, ": ",  elts[i].val, CRLF, NULL);
                    amt = strlen(buf);
                    apr_file_write(hfd, buf, &amt);
                }
            }
            buf = apr_pstrcat(r->pool, CRLF, NULL);
            amt = strlen(buf);
            apr_file_write(hfd, buf, &amt);
            
            /* This case only occurs when the content is generated locally */
            if (!apr_table_get(r->headers_out, "Content-Type") && r->content_type) {
                apr_table_setn(r->headers_out, "Content-Type", 
                               ap_make_content_type(r, r->content_type));
            }
        }
        sprintf(statusbuf,"%d", r->status);
        buf = apr_pstrcat(r->pool, statusbuf, CRLF, NULL);
        amt = strlen(buf);
        apr_file_write(hfd, buf, &amt);

        /* This case only occurs when the content is generated locally */
        if (!r->status_line) {
            r->status_line = ap_get_status_line(r->status);
        }
        buf = apr_pstrcat(r->pool, r->status_line, "\n", NULL);
        amt = strlen(buf);
        apr_file_write(hfd, buf, &amt);
        buf = apr_pstrcat(r->pool, CRLF, NULL);
        amt = strlen(buf);
        apr_file_write(hfd, buf, &amt);
        apr_file_close(hfd); /* flush and close */
    }
    else {
        /* XXX log message */
    }

    ap_log_error(APLOG_MARK, APLOG_INFO|APLOG_NOERRNO, 0, r->server,
                 "disk_cache: Caching headers for URL %s",  dobj->name);
    return APR_SUCCESS;
}
static apr_status_t write_body(cache_handle_t *h, request_rec *r, apr_bucket_brigade *b) 
{
    apr_bucket *e;
    apr_status_t rv;
    disk_cache_object_t *dobj = (disk_cache_object_t *) h->cache_obj->vobj;
    cache_info *info = &(h->cache_obj->info);

    if (!dobj->fd) {
        rv = apr_file_open(&dobj->fd, dobj->tempfile, 
                           APR_WRITE | APR_CREATE | APR_BINARY| APR_TRUNCATE | APR_BUFFERED,
                           APR_UREAD | APR_UWRITE, r->pool);
        if (rv != APR_SUCCESS) {
            return rv;
        }
    }
    APR_BRIGADE_FOREACH(e, b) {
        const char *str;
        apr_size_t length;
        apr_bucket_read(e, &str, &length, APR_BLOCK_READ);
        apr_file_write(dobj->fd, str, &length);
    }
    if (APR_BUCKET_IS_EOS(APR_BRIGADE_LAST(b))) {
        file_cache_el_final(h, r);    /* Link to the perm file, and close the descriptor  */
        ap_log_error(APLOG_MARK, APLOG_INFO|APLOG_NOERRNO, 0, r->server,
                     "disk_cache: Cached body for URL %s",  dobj->name);
    }

    return APR_SUCCESS;	
}

static void *create_config(apr_pool_t *p, server_rec *s)
{
    disk_cache_conf *conf = apr_pcalloc(p, sizeof(disk_cache_conf));

    /* XXX: Set default values */
    conf->dirlevels = DEFAULT_DIRLEVELS;
    conf->dirlength = DEFAULT_DIRLENGTH;
    conf->space = DEFAULT_CACHE_SIZE;
    conf->maxfs = DEFAULT_MAX_FILE_SIZE;
    conf->minfs = DEFAULT_MIN_FILE_SIZE;

    conf->cache_root = NULL;
    conf->cache_root_len = 0;

    return conf;
}

/*
 * mod_disk_cache configuration directives handlers.
 */
static const char
*set_cache_root(cmd_parms *parms, void *in_struct_ptr, const char *arg)
{
    disk_cache_conf *conf = ap_get_module_config(parms->server->module_config, 
                                                 &disk_cache_module);
    conf->cache_root = arg;
    conf->cache_root_len = strlen(arg);
    /* TODO: canonicalize cache_root and strip off any trailing slashes */

    return NULL;
}
static const char
*set_cache_size(cmd_parms *parms, void *in_struct_ptr, const char *arg)
{
    disk_cache_conf *conf = ap_get_module_config(parms->server->module_config, 
                                                 &disk_cache_module);
    conf->space = atoi(arg);
    return NULL;
}
static const char
*set_cache_gcint(cmd_parms *parms, void *in_struct_ptr, const char *arg)
{
    disk_cache_conf *conf = ap_get_module_config(parms->server->module_config, 
                                                 &disk_cache_module);
    /* XXX */
    return NULL;
}
/*
 * Consider eliminating the next two directives in favor of
 * Ian's prime number hash...
 * key = hash_fn( r->uri) 
 * filename = "/key % prime1 /key %prime2/key %prime3" 
 */
static const char
*set_cache_dirlevels(cmd_parms *parms, void *in_struct_ptr, const char *arg)
{
    disk_cache_conf *conf = ap_get_module_config(parms->server->module_config, 
                                                 &disk_cache_module);
    int val = atoi(arg);
    if (val < 1)
        return "CacheDirLevels value must be an integer greater than 0";
    if (val * conf->dirlength > CACHEFILE_LEN)
        return "CacheDirLevels*CacheDirLength value must not be higher than 20";
    conf->dirlevels = val;
    return NULL;
}
static const char
*set_cache_dirlength(cmd_parms *parms, void *in_struct_ptr, const char *arg)
{
    disk_cache_conf *conf = ap_get_module_config(parms->server->module_config, 
                                                 &disk_cache_module);
    int val = atoi(arg);
    if (val < 1)
        return "CacheDirLength value must be an integer greater than 0";
    if (val * conf->dirlevels > CACHEFILE_LEN)
        return "CacheDirLevels*CacheDirLength value must not be higher than 20";

    conf->dirlength = val;
    return NULL;
}
static const char
*set_cache_exchk(cmd_parms *parms, void *in_struct_ptr, int flag)
{
    disk_cache_conf *conf = ap_get_module_config(parms->server->module_config, 
                                                 &disk_cache_module);
    /* XXX */
    return NULL;
}
static const char
*set_cache_minfs(cmd_parms *parms, void *in_struct_ptr, const char *arg)
{
    disk_cache_conf *conf = ap_get_module_config(parms->server->module_config, 
                                                 &disk_cache_module);
    conf->minfs = atoi(arg);
    return NULL;
}
static const char
*set_cache_maxfs(cmd_parms *parms, void *in_struct_ptr, const char *arg)
{
    disk_cache_conf *conf = ap_get_module_config(parms->server->module_config, 
                                                 &disk_cache_module);
    conf->maxfs = atoi(arg);
    return NULL;
}
static const char
*set_cache_minetm(cmd_parms *parms, void *in_struct_ptr, const char *arg)
{
    disk_cache_conf *conf = ap_get_module_config(parms->server->module_config, 
                                                 &disk_cache_module);
    /* XXX */
    return NULL;
}
static const char
*set_cache_gctime(cmd_parms *parms, void *in_struct_ptr, const char *arg)
{
    disk_cache_conf *conf = ap_get_module_config(parms->server->module_config, 
                                                 &disk_cache_module);
    /* XXX */
    return NULL;
}
static const char
*add_cache_gcclean(cmd_parms *parms, void *in_struct_ptr, const char *arg, const char *arg1)
{
    disk_cache_conf *conf = ap_get_module_config(parms->server->module_config, 
                                                 &disk_cache_module);
    /* XXX */
    return NULL;
}
static const char
*add_cache_gcclnun(cmd_parms *parms, void *in_struct_ptr, const char *arg, const char *arg1)
{
    disk_cache_conf *conf = ap_get_module_config(parms->server->module_config, 
                                                 &disk_cache_module);
    /* XXX */
    return NULL;
}
static const char
*set_cache_maxgcmem(cmd_parms *parms, void *in_struct_ptr, const char *arg)
{
    disk_cache_conf *conf = ap_get_module_config(parms->server->module_config, 
                                                 &disk_cache_module);
    /* XXX */
    return NULL;
}
static const command_rec disk_cache_cmds[] =
{
    AP_INIT_TAKE1("CacheRoot", set_cache_root, NULL, RSRC_CONF,
                 "The directory to store cache files"),
    AP_INIT_TAKE1("CacheSize", set_cache_size, NULL, RSRC_CONF,
                  "The maximum disk space used by the cache in KB"),
    AP_INIT_TAKE1("CacheGcInterval", set_cache_gcint, NULL, RSRC_CONF,
                  "The interval between garbage collections, in hours"),
    AP_INIT_TAKE1("CacheDirLevels", set_cache_dirlevels, NULL, RSRC_CONF,
                  "The number of levels of subdirectories in the cache"),
    AP_INIT_TAKE1("CacheDirLength", set_cache_dirlength, NULL, RSRC_CONF,
                  "The number of characters in subdirectory names"),
    AP_INIT_FLAG("CacheExpiryCheck", set_cache_exchk, NULL, RSRC_CONF,
                 "on if cache observes Expires date when seeking files"),
    AP_INIT_TAKE1("CacheMinFileSize", set_cache_minfs, NULL, RSRC_CONF,
                  "The minimum file size to cache a document"),
    AP_INIT_TAKE1("CacheMaxFileSize", set_cache_maxfs, NULL, RSRC_CONF,
                  "The maximum file size to cache a document"),
    AP_INIT_TAKE1("CacheTimeMargin", set_cache_minetm, NULL, RSRC_CONF,
                  "The minimum time margin to cache a document"),
    AP_INIT_TAKE1("CacheGcDaily", set_cache_gctime, NULL, RSRC_CONF,
                  "The time of day for garbage collection (24 hour clock)"),
    AP_INIT_TAKE2("CacheGcUnused", add_cache_gcclnun, NULL, RSRC_CONF,
                  "The time in hours to retain unused file that match a url"),
    AP_INIT_TAKE2("CacheGcClean", add_cache_gcclean, NULL, RSRC_CONF,
                  "The time in hours to retain unchanged files that match a url"),
    AP_INIT_TAKE1("CacheGcMemUsage", set_cache_maxgcmem, NULL, RSRC_CONF,
                  "The maximum kilobytes of memory used for garbage collection"),
    {NULL}
};

static void disk_cache_register_hook(apr_pool_t *p)
{
    /* cache initializer */
    cache_hook_create_entity(create_entity, NULL, NULL, APR_HOOK_MIDDLE);
    cache_hook_open_entity(open_entity,  NULL, NULL, APR_HOOK_MIDDLE);
/*    cache_hook_remove_entity(remove_entity, NULL, NULL, APR_HOOK_MIDDLE); */
}

module AP_MODULE_DECLARE_DATA disk_cache_module = {
    STANDARD20_MODULE_STUFF,
    NULL,                       /* create per-directory config structure */
    NULL,                       /* merge per-directory config structures */
    create_config,              /* create per-server config structure */
    NULL,                       /* merge per-server config structures */
    disk_cache_cmds,	        /* command apr_table_t */
    disk_cache_register_hook	/* register hooks */
};