/* 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.
 */

/*
 * mod_version.c
 * Allow conditional configuration depending on the httpd version
 *
 * André Malo (nd/perlig.de), January 2004
 *
 * Some stuff coded here is heavily based on the core <IfModule>
 * containers.
 *
 * The module makes the following confgurations possible:
 *
 * <IfVersion op major.minor.patch>
 *     # conditional config here ...
 *</IfVersion>
 *
 * where "op" is one of:
 * = / ==       equal
 * >            greater than
 * >=           greater or equal
 * <            less than
 * <=           less or equal
 *
 * If minor version and patch level are omitted they are assumed to be 0.
 *
 * Alternatively you can match the whole version (including some vendor-added
 * string of the CORE version, see ap_release.h) against a regular expression:
 *
 * <IfVersion op regex>
 *     # conditional config here ...
 *</IfVersion>
 *
 * where "op" is one of:
 * = / ==       match; regex must be surrounded by slashes
 * ~            match; regex MAY NOT be surrounded by slashes
 *
 * Note that all operators may be preceeded by an exclamation mark
 * (without spaces) in order to reverse their meaning.
 *
 */

#include "apr.h"
#include "apr_strings.h"
#include "apr_lib.h"

#include "httpd.h"
#include "http_config.h"
#include "http_log.h"


/* module structure */
module AP_MODULE_DECLARE_DATA version_module;

/* queried httpd version */
static ap_version_t httpd_version;


/*
 * compare the supplied version with the core one
 */
static int compare_version(char *version_string, const char **error)
{
    char *p = version_string, *ep;
    int version[3] = {0, 0, 0};
    int c = 0;

    *error = "Version appears to be invalid. It must have the format "
             "major[.minor[.patch]] where major, minor and patch are "
             "numbers.";

    if (!apr_isdigit(*p)) {
        return 0;
    }

    /* parse supplied version */
    ep = version_string + strlen(version_string);
    while (p <= ep && c < 3) {
        if (*p == '.') {
            *p = '\0';
        }

        if (!*p) {
            version[c++] = atoi(version_string);
            version_string = ++p;
            continue;
        }

        if (!apr_isdigit(*p)) {
            break;
        }

        ++p;
    }

    if (p < ep) { /* syntax error */
        return 0;
    }

    *error = NULL;

    if      (httpd_version.major > version[0]) {
        return 1;
    }
    else if (httpd_version.major < version[0]) {
        return -1;
    }
    else if (httpd_version.minor > version[1]) {
        return 1;
    }
    else if (httpd_version.minor < version[1]) {
        return -1;
    }
    else if (httpd_version.patch > version[2]) {
        return 1;
    }
    else if (httpd_version.patch < version[2]) {
        return -1;
    }

    /* seems to be the same */
    return 0;
}

/*
 * match version against a regular expression
 */
static int match_version(apr_pool_t *pool, char *version_string,
                         const char **error)
{
    ap_regex_t *compiled;
    const char *to_match;
    int rc;

    compiled = ap_pregcomp(pool, version_string, AP_REG_EXTENDED);
    if (!compiled) {
        *error = "Unable to compile regular expression";
        return 0;
    }

    *error = NULL;

    to_match = apr_psprintf(pool, "%d.%d.%d%s",
                            httpd_version.major,
                            httpd_version.minor,
                            httpd_version.patch,
                            httpd_version.add_string);

    rc = !ap_regexec(compiled, to_match, 0, NULL, 0);

    ap_pregfree(pool, compiled);
    return rc;
}

/*
 * Implements the <IfVersion> container
 */
static const char *start_ifversion(cmd_parms *cmd, void *mconfig,
                                   const char *arg1, const char *arg2,
                                   const char *arg3)
{
    const char *endp;
    int reverse = 0, done = 0, match = 0, compare;
    const char *p, *error;
    char c;

    /* supplying one argument is possible, we assume an equality check then */
    if (!arg2) {
        arg2 = arg1;
        arg1 = "=";
    }

    /* surrounding quotes without operator */
    if (!arg3 && *arg2 == '>' && !arg2[1]) {
        arg3 = ">";
        arg2 = arg1;
        arg1 = "=";
    }

    /* the third argument makes version surrounding quotes plus operator
     * possible.
     */
    endp = arg2 + strlen(arg2);
    if (   endp == arg2
        || (!(arg3 && *arg3 == '>' && !arg3[1]) && *--endp != '>')) {
        return apr_pstrcat(cmd->pool, cmd->cmd->name,
                           "> directive missing closing '>'", NULL);
    }

    p = arg1;
    if (*p == '!') {
        reverse = 1;
        if (p[1]) {
            ++p;
        }
    }

    c = *p++;
    if (!*p || (*p == '=' && !p[1] && c != '~')) {
        if (!httpd_version.major) {
            ap_get_server_revision(&httpd_version);
        }

        done = 1;
        switch (c) {
        case '=':
            /* normal comparison */
            if (*arg2 != '/') {
                compare = compare_version(apr_pstrmemdup(cmd->pool, arg2,
                                                         endp-arg2),
                                          &error);
                if (error) {
                    return error;
                }

                match = !compare;
                break;
            }

            /* regexp otherwise */
            if (endp == ++arg2 || *--endp != '/') {
                return "Missing delimiting / of regular expression.";
            }

        case '~':
            /* regular expression */
            match = match_version(cmd->pool, apr_pstrmemdup(cmd->pool, arg2,
                                                            endp-arg2),
                                  &error);
            if (error) {
                return error;
            }
            break;

        case '<':
            compare = compare_version(apr_pstrmemdup(cmd->pool, arg2,
                                                     endp-arg2),
                                      &error);
            if (error) {
                return error;
            }

            match = ((-1 == compare) || (*p && !compare));
            break;

        case '>':
            compare = compare_version(apr_pstrmemdup(cmd->pool, arg2,
                                                     endp-arg2),
                                      &error);
            if (error) {
                return error;
            }

            match = ((1 == compare) || (*p && !compare));
            break;

        default:
            done = 0;
            break;
        }
    }

    if (!done) {
        return apr_pstrcat(cmd->pool, "unrecognized operator '", arg1, "'",
                           NULL);
    }

    if ((!reverse && match) || (reverse && !match)) {
        ap_directive_t *parent = NULL;
        ap_directive_t *current = NULL;
        const char *retval;

        retval = ap_build_cont_config(cmd->pool, cmd->temp_pool, cmd,
                                      &current, &parent, "<IfVersion");
        *(ap_directive_t **)mconfig = current;
        return retval;
    }

    *(ap_directive_t **)mconfig = NULL;
    return ap_soak_end_container(cmd, "<IfVersion");
}

static const command_rec version_cmds[] = {
    AP_INIT_TAKE123("<IfVersion", start_ifversion, NULL, EXEC_ON_READ | OR_ALL,
                    "a comparison operator, a version (and a delimiter)"),
    { NULL }
};

module AP_MODULE_DECLARE_DATA version_module =
{
    STANDARD20_MODULE_STUFF,
    NULL,             /* dir config creater */
    NULL,             /* dir merger --- default is to override */
    NULL,             /* server config */
    NULL,             /* merge server configs */
    version_cmds,     /* command apr_table_t */
    NULL,             /* register hooks */
};