mod_expires.c

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/*
 * mod_expires.c
 * version 0.0.11
 * status beta
 * 
 * Andrew Wilson <[e-mail]> 26.Jan.96
 *
 * This module allows you to control the form of the Expires: header
 * that Apache issues for each access.  Directives can appear in
 * configuration files or in .htaccess files so expiry semantics can
 * be defined on a per-directory basis.  
 *
 * DIRECTIVE SYNTAX
 *
 * Valid directives are:
 *
 *     ExpiresActive on | off
 *     ExpiresDefault <code><seconds>
 *     ExpiresByType type/encoding <code><seconds>
 *
 * Valid values for <code> are:
 *
 *     'M'      expires header shows file modification date + <seconds>
 *     'A'      expires header shows access time + <seconds>
 *
 *              [I'm not sure which of these is best under different
 *              circumstances, I guess it's for other people to explore.
 *              The effects may be indistinguishable for a number of cases]
 *
 * <seconds> should be an integer value [acceptable to atoi()]
 *
 * There is NO space between the <code> and <seconds>.
 *
 * For example, a directory which contains information which changes
 * frequently might contain:
 *
 *     # reports generated by cron every hour.  don't let caches
 *     # hold onto stale information
 *     ExpiresDefault M3600
 *
 * Another example, our html pages can change all the time, the gifs
 * tend not to change often:
 * 
 *     # pages are hot (1 week), images are cold (1 month)
 *     ExpiresByType text/html A604800
 *     ExpiresByType image/gif A2592000
 *
 * Expires can be turned on for all URLs on the server by placing the
 * following directive in a conf file:
 *
 *     ExpiresActive on
 *
 * ExpiresActive can also appear in .htaccess files, enabling the
 * behaviour to be turned on or off for each chosen directory.
 *
 *     # turn off Expires behaviour in this directory
 *     # and subdirectories
 *     ExpiresActive off
 *
 * Directives defined for a directory are valid in subdirectories
 * unless explicitly overridden by new directives in the subdirectory
 * .htaccess files.
 *
 * ALTERNATIVE DIRECTIVE SYNTAX
 *
 * Directives can also be defined in a more readable syntax of the form:
 *
 *     ExpiresDefault "<base> [plus] {<num> <type>}*"
 *     ExpiresByType type/encoding "<base> [plus] {<num> <type>}*"
 *
 * where <base> is one of:
 *      access  
 *      now             equivalent to 'access'
 *      modification
 *
 * where the 'plus' keyword is optional
 *
 * where <num> should be an integer value [acceptable to atoi()]
 *
 * where <type> is one of:
 *      years
 *      months
 *      weeks
 *      days
 *      hours
 *      minutes
 *      seconds
 *
 * For example, any of the following directives can be used to make
 * documents expire 1 month after being accessed, by default:
 *
 *      ExpiresDefault "access plus 1 month"
 *      ExpiresDefault "access plus 4 weeks"
 *      ExpiresDefault "access plus 30 days"
 *
 * The expiry time can be fine-tuned by adding several '<num> <type>'
 * clauses:
 *
 *      ExpiresByType text/html "access plus 1 month 15 days 2 hours"
 *      ExpiresByType image/gif "modification plus 5 hours 3 minutes"
 *
 * ---
 *
 * Change-log:
 * 29.Jan.96    Hardened the add_* functions.  Server will now bail out
 *              if bad directives are given in the conf files.
 * 02.Feb.96    Returns DECLINED if not 'ExpiresActive on', giving other
 *              expires-aware modules a chance to play with the same
 *              directives. [Michael Rutman]
 * 03.Feb.96    Call tzset() before localtime().  Trying to get the module
 *              to work properly in non GMT timezones.
 * 12.Feb.96    Modified directive syntax to allow more readable commands:
 *                ExpiresDefault "now plus 10 days 20 seconds"
 *                ExpiresDefault "access plus 30 days"
 *                ExpiresDefault "modification plus 1 year 10 months 30 days"
 * 13.Feb.96    Fix call to table_get() with NULL 2nd parameter [Rob Hartill]
 * 19.Feb.96    Call gm_timestr_822() to get time formatted correctly, can't
 *              rely on presence of HTTP_TIME_FORMAT in Apache 1.1+.
 * 21.Feb.96    This version (0.0.9) reverses assumptions made in 0.0.8
 *              about star/star handlers.  Reverting to 0.0.7 behaviour.
 * 08.Jun.96    allows ExpiresDefault to be used with responses that use 
 *              the DefaultType by not DECLINING, but instead skipping 
 *              the table_get check and then looking for an ExpiresDefault.
 *              [Rob Hartill]
 * 04.Nov.96    'const' definitions added.
 *
 * TODO
 * add support for Cache-Control: max-age=20 from the HTTP/1.1
 * proposal (in this case, a ttl of 20 seconds) [ask roy]
 * add per-file expiry and explicit expiry times - duplicates some
 * of the mod_cern_meta.c functionality.  eg:
 *              ExpiresExplicit index.html "modification plus 30 days"
 *
 * BUGS
 * Hi, welcome to the internet.
 */

#include <ctype.h>
#include "httpd.h"
#include "http_config.h"
#include "http_log.h"

typedef struct {
    int active;
    char *expiresdefault;
    table *expiresbytype;
} expires_dir_config;

/* from mod_dir, why is this alias used?
 */
#define DIR_CMD_PERMS OR_INDEXES

#define ACTIVE_ON       1
#define ACTIVE_OFF      0
#define ACTIVE_DONTCARE 2

module MODULE_VAR_EXPORT expires_module;

static void *create_dir_expires_config(pool *p, char *dummy)
{
    expires_dir_config *new =
    (expires_dir_config *) ap_pcalloc(p, sizeof(expires_dir_config));
    new->active = ACTIVE_DONTCARE;
    new->expiresdefault = "";
    new->expiresbytype = ap_make_table(p, 4);
    return (void *) new;
}

static const char *set_expiresactive(cmd_parms *cmd, expires_dir_config * dir_config, int arg)
{
    /* if we're here at all it's because someone explicitly
     * set the active flag
     */
    dir_config->active = ACTIVE_ON;
    if (arg == 0) {
        dir_config->active = ACTIVE_OFF;
    };
    return NULL;
}

/* check_code() parse 'code' and return NULL or an error response
 * string.  If we return NULL then real_code contains code converted
 * to the cnnnn format.
 */
static char *check_code(pool *p, const char *code, char **real_code)
{
    char *word;
    char base = 'X';
    int modifier = 0;
    int num = 0;
    int factor = 0;

    /* 0.0.4 compatibility?
     */
    if ((code[0] == 'A') || (code[0] == 'M')) {
        *real_code = (char *)code;
        return NULL;
    };