/* ====================================================================
 * Copyright (c) 1995 The Apache Group.  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. All advertising materials mentioning features or use of this
 *    software must display the following acknowledgment:
 *    "This product includes software developed by the Apache Group
 *    for use in the Apache HTTP server project (http://www.apache.org/)."
 *
 * 4. The names "Apache Server" and "Apache Group" must not be used to
 *    endorse or promote products derived from this software without
 *    prior written permission.
 *
 * 5. Redistributions of any form whatsoever must retain the following
 *    acknowledgment:
 *    "This product includes software developed by the Apache Group
 *    for use in the Apache HTTP server project (http://www.apache.org/)."
 *
 * THIS SOFTWARE IS PROVIDED BY THE APACHE GROUP ``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 GROUP OR
 * IT'S 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 Group and was originally based
 * on public domain software written at the National Center for
 * Supercomputing Applications, University of Illinois, Urbana-Champaign.
 * For more information on the Apache Group and the Apache HTTP server
 * project, please see <http://www.apache.org/>.
 *
 */

/*
 * $Id: mod_rpaf-2.0.c 18 2008-01-01 03:05:40Z thomas $
 *
 * Author: Thomas Eibner, <thomas@stderr.net>
 * URL: http://stderr.net/apache/rpaf/
 * rpaf is short for reverse proxy add forward 
 *
 * This module does the opposite of mod_proxy_add_forward written by
 * Ask Bjørn Hansen. http://develooper.com/code/mpaf/ or mod_proxy
 * in 1.3.25 and above and mod_proxy from Apache 2.0
 * 
 */ 

#include "httpd.h"
#include "http_config.h"
#include "http_core.h"
#include "http_log.h"
#include "http_protocol.h"
#include "http_vhost.h"
#include "apr_strings.h"
#include "arpa/inet.h"
#include <ctype.h> // isspace

module AP_MODULE_DECLARE_DATA rpaf_module;

typedef struct {
    int                enable;
    int                sethostname;
    const char         *headername;
    apr_array_header_t *proxy_ips;
    int                recursive;
} rpaf_server_cfg;

typedef struct {
    const char  *old_ip;
    int         old_family;
    request_rec *r;
} rpaf_cleanup_rec;

static void *rpaf_create_server_cfg(apr_pool_t *p, server_rec *s) {
    rpaf_server_cfg *cfg = (rpaf_server_cfg *)apr_pcalloc(p, sizeof(rpaf_server_cfg));
    if (!cfg)
        return NULL;

    cfg->proxy_ips = apr_array_make(p, 0, sizeof(char *));
    cfg->enable = 0;
    cfg->sethostname = 0;

    return (void *)cfg;
}

/* It was ported from https://github.com/gnif/mod_rpaf */
/* quick check for ipv4/6 likelihood; similar to Apache2.4 mod_remoteip check */
static int rpaf_looks_like_ip(const char *ip) {
    static const char ipv4_set[] = "0123456789./";
    static const char ipv6_set[] = "0123456789abcdef:/.";

    /* zero length value is not valid */
    if (!*ip)
      return 0;

    const char *ptr    = ip;

    /* determine if this could be a IPv6 or IPv4 address */
    if (strchr(ip, ':'))
    {
        while(*ptr && strchr(ipv6_set, *ptr) != NULL)
            ++ptr;
    }
    else
    {
        while(*ptr && strchr(ipv4_set, *ptr) != NULL)
            ++ptr;
    }

    return (*ptr == '\0');
}

static const char *rpaf_set_proxy_ip(cmd_parms *cmd, void *dummy, const char *proxy_ip) {
    server_rec *s = cmd->server;
    rpaf_server_cfg *cfg = (rpaf_server_cfg *)ap_get_module_config(s->module_config, 
                                                                   &rpaf_module);

    /* check for valid syntax of ip */
    *(char **)apr_array_push(cfg->proxy_ips) = apr_pstrdup(cmd->pool, proxy_ip);
    return NULL;
}

static const char *rpaf_set_headername(cmd_parms *cmd, void *dummy, const char *headername) {
    server_rec *s = cmd->server;
    rpaf_server_cfg *cfg = (rpaf_server_cfg *)ap_get_module_config(s->module_config, 
                                                                   &rpaf_module);

    cfg->headername = headername; 
    return NULL;
}

static const char *rpaf_enable(cmd_parms *cmd, void *dummy, int flag) {
    server_rec *s = cmd->server;
    rpaf_server_cfg *cfg = (rpaf_server_cfg *)ap_get_module_config(s->module_config, 
                                                                   &rpaf_module);

    cfg->enable = flag;
    return NULL;
}

static const char *rpaf_sethostname(cmd_parms *cmd, void *dummy, int flag) {
    server_rec *s = cmd->server;
    rpaf_server_cfg *cfg = (rpaf_server_cfg *)ap_get_module_config(s->module_config, 
                                                                   &rpaf_module);

    cfg->sethostname = flag;
    return NULL;
}

static const char *rpaf_set_recursive(cmd_parms *cmd, void *dummy, int flag) {
    server_rec *s = cmd->server;
    rpaf_server_cfg *cfg = (rpaf_server_cfg *)ap_get_module_config(s->module_config, 
                                                                   &rpaf_module);

    cfg->recursive = flag;
    return NULL;
}

static int is_in_array(const char *remote_ip, apr_array_header_t *proxy_ips) {
    int i;
    char **list = (char**)proxy_ips->elts;
    for (i = 0; i < proxy_ips->nelts; i++) {
        if (strncmp(remote_ip, list[i], strlen(list[i])) == 0)
            return 1;
    }
    return 0;
}

static char *extract_ip(apr_array_header_t *arr, apr_array_header_t *proxy_ips, int recursive) {
    int i;
    char **ips = (char **)arr->elts;
    int len = arr->nelts;
    ap_assert(len >= 0);

    if (!recursive) return ips[len-1];
    for (i = len-1; i >= 0; i--) {
        if (!is_in_array(ips[i], proxy_ips)) {
            return ips[i];
        }
    }
    return ips[0];
}

static apr_status_t rpaf_cleanup(void *data) {
    rpaf_cleanup_rec *rcr = (rpaf_cleanup_rec *)data;
    rcr->r->connection->remote_ip   = apr_pstrdup(rcr->r->connection->pool, rcr->old_ip);
    rcr->r->connection->remote_addr->sa.sin.sin_addr.s_addr = apr_inet_addr(rcr->r->connection->remote_ip);
    rcr->r->connection->remote_addr->sa.sin.sin_family = rcr->old_family;
    return APR_SUCCESS;
}

static int change_remote_ip(request_rec *r) {
    const char *fwdvalue;
    const char *fwdvalue_temp;
    int i;
    char *val;
    rpaf_server_cfg *cfg = (rpaf_server_cfg *)ap_get_module_config(r->server->module_config,
                                                                   &rpaf_module);

    if (!cfg->enable)
        return DECLINED;

    if (is_in_array(r->connection->remote_ip, cfg->proxy_ips) == 1) {
        /* check if cfg->headername is set and if it is use
           that instead of X-Forwarded-For by default */
        if (cfg->headername && (fwdvalue = apr_table_get(r->headers_in, cfg->headername))) {
            //
        } else if ((fwdvalue = apr_table_get(r->headers_in, "X-Forwarded-For"))) {
            //
        } else {
            return DECLINED;
        }

        if (fwdvalue) {
            rpaf_cleanup_rec *rcr = (rpaf_cleanup_rec *)apr_pcalloc(r->pool, sizeof(rpaf_cleanup_rec));
            apr_array_header_t *arr = apr_array_make(r->pool, 4, sizeof(char *));

            fwdvalue_temp = apr_pstrdup(r->pool, fwdvalue);
            while ((val = strsep((char **)&fwdvalue_temp, ",")) != NULL) {
                /* strip leading and trailing whitespace */
                while(isspace(*val))
                    ++val;
                for (i = strlen(val) - 1; i > 0 && isspace(val[i]); i--)
                    val[i] = '\0';
                if (rpaf_looks_like_ip(val))
                    *(char **)apr_array_push(arr) = apr_pstrdup(r->pool, val);
            }

            if (arr->nelts > 0) {
                rcr->old_ip = apr_pstrdup(r->connection->pool, r->connection->remote_ip);
                rcr->old_family = r->connection->remote_addr->sa.sin.sin_family;
                rcr->r = r;
                apr_pool_cleanup_register(r->pool, (void *)rcr, rpaf_cleanup, apr_pool_cleanup_null);
                r->connection->remote_ip = apr_pstrdup(r->connection->pool, extract_ip(arr, cfg->proxy_ips, cfg->recursive));
                r->connection->remote_addr->sa.sin.sin_addr.s_addr = apr_inet_addr(r->connection->remote_ip);
                r->connection->remote_addr->sa.sin.sin_family = AF_INET;
                if (cfg->sethostname) {
                    const char *hostvalue;
                    if ((hostvalue = apr_table_get(r->headers_in, "X-Forwarded-Host"))) {
                        /* 2.0 proxy frontend or 1.3 => 1.3.25 proxy frontend */
                        apr_table_set(r->headers_in, "Host", apr_pstrdup(r->pool, hostvalue));
                        r->hostname = apr_pstrdup(r->pool, hostvalue);
                        ap_update_vhost_from_headers(r);
                    } else if ((hostvalue = apr_table_get(r->headers_in, "X-Host"))) {
                        /* 1.3 proxy frontend with mod_proxy_add_forward */
                        apr_table_set(r->headers_in, "Host", apr_pstrdup(r->pool, hostvalue));
                        r->hostname = apr_pstrdup(r->pool, hostvalue);
                        ap_update_vhost_from_headers(r);
                    }
                }
            }
        }
    }
    return DECLINED;
}

static const command_rec rpaf_cmds[] = {
    AP_INIT_FLAG(
                 "RPAFenable",
                 rpaf_enable,
                 NULL,
                 RSRC_CONF,
                 "Enable mod_rpaf"
                 ),
    AP_INIT_FLAG(
                 "RPAFsethostname",
                 rpaf_sethostname,
                 NULL,
                 RSRC_CONF,
                 "Let mod_rpaf set the hostname from X-Host header and update vhosts"
                 ),
    AP_INIT_ITERATE(
                    "RPAFproxy_ips",
                    rpaf_set_proxy_ip,
                    NULL,
                    RSRC_CONF,
                    "IP(s) of Proxy server setting X-Forwarded-For header"
                    ),
    AP_INIT_TAKE1(
                    "RPAFheader",
                    rpaf_set_headername,
                    NULL,
                    RSRC_CONF,
                    "Which header to look for when trying to find the real ip of the client in a proxy setup"
                    ),
    AP_INIT_FLAG(
                 "RPAFrecursive",
                 rpaf_set_recursive,
                 NULL,
                 RSRC_CONF,
                 "Enable to support recursive ip extraction."
                 ),
    { NULL }
};

static void register_hooks(apr_pool_t *p) {
    ap_hook_post_read_request(change_remote_ip, NULL, NULL, APR_HOOK_FIRST);
}

module AP_MODULE_DECLARE_DATA rpaf_module = {
    STANDARD20_MODULE_STUFF,
    NULL,
    NULL,
    rpaf_create_server_cfg,
    NULL,
    rpaf_cmds,
    register_hooks,
};