/* 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 "ap_config.h"
#include "ap_mmn.h"
#include "httpd.h"
#include "http_config.h"
#include "http_connection.h"
#include "http_protocol.h"
#include "http_log.h"
#include "apr_strings.h"
#include "apr_lib.h"
#define APR_WANT_BYTEFUNC
#include "apr_want.h"
#include "apr_network_io.h"

module AP_MODULE_DECLARE_DATA remoteip_module;

typedef struct {
    /** A proxy IP mask to match */
    apr_ipsubnet_t *ip;
    /** Flagged if internal, otherwise an external trusted proxy */
    void  *internal;
} remoteip_proxymatch_t;

typedef struct {
    /** The header to retrieve a proxy-via IP list */
    const char *remoteip_header_name;
    /** A header to record the proxied IP's
     * (removed as the physical connection and
     * from the proxy-via IP header value list)
     */
    const char *proxies_header_name;
    /** A header that may indicate user is using a
     * HTTPS connection to the reverse-proxy, and
     * the value that it must match for it to do so.
     */
    const char *secure_header_name;
    const char *secure_header_value;
    /** A list of trusted proxies, ideally configured
     *  with the most commonly encountered listed first
     */
    apr_array_header_t *proxymatch_ip;
    /** The fixed scheme names http (derived from
      * original server configuration) and https
      * (set statically).
      */
    const char *orig_scheme;
    const char *secure_scheme;
    /** The configured ports for http (derived from
      * server configuration) and https (defaults to
      * 443 and may be overwritten by the user.
      */
    int orig_port;
    int secure_port;	
    /** A buffer holding the current port number as
      * string and thus not longer than 5 digits.
      * This prevents the buffer to be malloc'ed 
      * for each request.
      */
    char buffer[6];
} remoteip_config_t;

typedef struct {
    apr_sockaddr_t *useragent_addr;
    char *useragent_ip;
    /** The list of proxy IP's ignored as remote IP's */
    const char *proxy_ips;
    /** The remaining list of untrusted proxied remote IP's */
    const char *proxied_remote;
} remoteip_req_t;

static void *create_remoteip_server_config(apr_pool_t *p, server_rec *s)
{
    remoteip_config_t *config = apr_pcalloc(p, sizeof *config);
    /* config->header_name = NULL;
     * config->proxies_header_name = NULL;
     */

    config->secure_port = 443;
    config->orig_port = s->port;

    config->secure_scheme = apr_pstrdup(p, "https");
    config->orig_scheme = s->server_scheme;

    return config;
}

static void *merge_remoteip_server_config(apr_pool_t *p, void *globalv,
                                          void *serverv)
{
    remoteip_config_t *global = (remoteip_config_t *) globalv;
    remoteip_config_t *server = (remoteip_config_t *) serverv;
    remoteip_config_t *config;

    config = (remoteip_config_t *) apr_palloc(p, sizeof(*config));
    config->remoteip_header_name = server->remoteip_header_name
                        ? server->remoteip_header_name
                        : global->remoteip_header_name;
    config->proxies_header_name = server->proxies_header_name
                                ? server->proxies_header_name
                                : global->proxies_header_name;
    config->proxymatch_ip = server->proxymatch_ip
                          ? server->proxymatch_ip
                          : global->proxymatch_ip;
    config->secure_header_name = server->secure_header_name
                                ? server->secure_header_name
                                : global->secure_header_name;
    config->secure_header_value = server->secure_header_value
                                ? server->secure_header_value
                                : global->secure_header_value;
    config->secure_port = server->secure_port
                        ? server->secure_port
                        : global->secure_port;
    return config;
}

static const char *header_name_set(cmd_parms *cmd, void *dummy,
                                   const char *arg)
{
    remoteip_config_t *config = ap_get_module_config(cmd->server->module_config,
                                                     &remoteip_module);
    config->remoteip_header_name = arg;
    return NULL;
}

static const char *proxies_header_name_set(cmd_parms *cmd, void *dummy,
                                           const char *arg)
{
    remoteip_config_t *config = ap_get_module_config(cmd->server->module_config,
                                                     &remoteip_module);
    config->proxies_header_name = arg;
    return NULL;
}

static const char *secure_header_set(cmd_parms *cmd, void *dummy,
                                           const char *name, const char *value)
{
    remoteip_config_t *config = ap_get_module_config(cmd->server->module_config,
                                                     &remoteip_module);
    config->secure_header_name = name;
    config->secure_header_value = value;
    return NULL;
}

static const char *secure_port_set(cmd_parms *cmd, void *dummy, const char *value)
{
    remoteip_config_t *config = ap_get_module_config(cmd->server->module_config,
                                                     &remoteip_module);
    config->secure_port = atoi(value);
    return NULL;
}

/* Would be quite nice if APR exported this */
/* apr:network_io/unix/sockaddr.c */
static int looks_like_ip(const char *ipstr)
{
    if (ap_strchr_c(ipstr, ':')) {
        /* definitely not a hostname; assume it is intended to be an IPv6 address */
        return 1;
    }

    /* simple IPv4 address string check */
    while ((*ipstr == '.') || apr_isdigit(*ipstr))
        ipstr++;
    return (*ipstr == '\0');
}

static const char *proxies_set(cmd_parms *cmd, void *cfg,
                               const char *arg)
{
    remoteip_config_t *config = ap_get_module_config(cmd->server->module_config,
                                                     &remoteip_module);
    remoteip_proxymatch_t *match;
    apr_status_t rv;
    char *ip = apr_pstrdup(cmd->temp_pool, arg);
    char *s = ap_strchr(ip, '/');
    if (s) {
        *s++ = '\0';
    }

    if (!config->proxymatch_ip) {
        config->proxymatch_ip = apr_array_make(cmd->pool, 1, sizeof(*match));
    }
    match = (remoteip_proxymatch_t *) apr_array_push(config->proxymatch_ip);
    match->internal = cmd->info;

    if (looks_like_ip(ip)) {
        /* Note s may be null, that's fine (explicit host) */
        rv = apr_ipsubnet_create(&match->ip, ip, s, cmd->pool);
    }
    else
    {
        apr_sockaddr_t *temp_sa;

        if (s) {
            return apr_pstrcat(cmd->pool, "RemoteIP: Error parsing IP ", arg,
                               " the subnet /", s, " is invalid for ",
                               cmd->cmd->name, NULL);
        }

        rv = apr_sockaddr_info_get(&temp_sa,  ip, APR_UNSPEC, 0,
                                   APR_IPV4_ADDR_OK, cmd->temp_pool);
        while (rv == APR_SUCCESS)
        {
            apr_sockaddr_ip_get(&ip, temp_sa);
            rv = apr_ipsubnet_create(&match->ip, ip, NULL, cmd->pool);
            if (!(temp_sa = temp_sa->next)) {
                break;
            }
            match = (remoteip_proxymatch_t *)
                    apr_array_push(config->proxymatch_ip);
            match->internal = cmd->info;
        }
    }

    if (rv != APR_SUCCESS) {
        return apr_psprintf(cmd->pool,
                            "RemoteIP: Error parsing IP %s (%pm error) for %s",
                            arg, &rv, cmd->cmd->name);
    }

    return NULL;
}

static const char *proxylist_read(cmd_parms *cmd, void *cfg,
                                  const char *filename)
{
    char lbuf[MAX_STRING_LEN];
    char *arg;
    const char *args;
    const char *errmsg;
    ap_configfile_t *cfp;
    apr_status_t rv;

    filename = ap_server_root_relative(cmd->temp_pool, filename);
    rv = ap_pcfg_openfile(&cfp, cmd->temp_pool, filename);
    if (rv != APR_SUCCESS) {
        return apr_psprintf(cmd->pool, "%s: Could not open file %s: %pm",
                            cmd->cmd->name, filename, &rv);
    }

    while (!(ap_cfg_getline(lbuf, MAX_STRING_LEN, cfp))) {
        args = lbuf;
        while (*(arg = ap_getword_conf(cmd->temp_pool, &args)) != '\0') {
            if (*arg == '#') {
                break;
            }
            errmsg = proxies_set(cmd, cfg, arg);
            if (errmsg) {
                ap_cfg_closefile(cfp);
                errmsg = apr_psprintf(cmd->pool, "%s at line %d of %s",
                                      errmsg, cfp->line_number, filename);
                return errmsg;
            }
        }
    }

    ap_cfg_closefile(cfp);
    return NULL;
}

static int is_trusted_proxy(remoteip_config_t *config, apr_sockaddr_t *sa, void *internal) {
    int i;

    if (config->proxymatch_ip) {
        remoteip_proxymatch_t *match;
        match = (remoteip_proxymatch_t *)config->proxymatch_ip->elts;
        for (i = 0; i < config->proxymatch_ip->nelts; ++i) {
            if (apr_ipsubnet_test(match[i].ip, sa)) {
                if (internal) {
                    /* Allow an internal proxy to present an external proxy,
                       but do not allow an external proxy to present an internal proxy.
                       In this case, the presented internal proxy will be considered external.
                     */
                    internal = match[i].internal;
                }
                return 1;
            }
        }
    }

    return 0;
}

static int remoteip_modify_request(request_rec *r)
{
    conn_rec *c = r->connection;
    remoteip_config_t *config = (remoteip_config_t *)
        ap_get_module_config(r->server->module_config, &remoteip_module);
    remoteip_req_t *req = NULL;

    apr_sockaddr_t *temp_sa;

    apr_status_t rv;
    char *remote;
    char *proxy_ips = NULL;
    char *parse_remote;
    char *eos;
    char *pchar = NULL;
    /* The protocol to be set: http(0), https(1). */
    int secure = 0;
    /* Flag whether allowed to change the request, here: the protocol. */
    int trusted_proxy = 0;
    unsigned char *addrbyte;

    /* If no RemoteIPInternalProxy, RemoteIPInternalProxyList, RemoteIPTrustedProxy 
       or RemoteIPTrustedProxyList directive is configured, 
       all proxies will be considered as external trusted proxies. 
     */ 
    void *internal = NULL;

    if (!config->remoteip_header_name && !config->secure_header_name) {
        return DECLINED;
    }

    if (config->proxymatch_ip) { 
        /* This indicates that a RemoteIPInternalProxy, RemoteIPInternalProxyList, RemoteIPTrustedProxy 
           or RemoteIPTrustedProxyList directive is configured. 
           In this case, default to internal proxy. 
         */ 
        internal = (void *) 1; 
    }
  
    temp_sa = c->client_addr;
    remote = (char *) apr_table_get(r->headers_in, config->remoteip_header_name);
    if (remote) {
        remote = apr_pstrdup(r->pool, remote);
    }

    /* Loop through all entries the remoteip_header.
     * For further use, flag the car trusted_proxy if a trusted proxy was seen.
     */
    while ((trusted_proxy|=is_trusted_proxy(config, temp_sa, internal))==1 && remote) {

        /* verify user agent IP against the trusted proxy list
         */
        if (config->proxymatch_ip) {
            int i;
            remoteip_proxymatch_t *match;
            match = (remoteip_proxymatch_t *)config->proxymatch_ip->elts;
            for (i = 0; i < config->proxymatch_ip->nelts; ++i) {
                if (apr_ipsubnet_test(match[i].ip, temp_sa)) {
                    if (internal) { 
                        /* Allow an internal proxy to present an external proxy, 
                           but do not allow an external proxy to present an internal proxy. 
                           In this case, the presented internal proxy will be considered external. 
                         */ 
                        internal = match[i].internal; 
                    }
                    trusted_proxy = 1;
                    break;
                }
            }
            if (i && i >= config->proxymatch_ip->nelts) {
                break;
            }
        }

        if ((parse_remote = strrchr(remote, ',')) == NULL) {
            parse_remote = remote;
            remote = NULL;
        }
        else {
            *(parse_remote++) = '\0';
        }

        while (*parse_remote == ' ') {
            ++parse_remote;
        }

        eos = parse_remote + strlen(parse_remote) - 1;
        while (eos >= parse_remote && *eos == ' ') {
            *(eos--) = '\0';
        }

        if (eos < parse_remote) {
            if (remote) {
                *(remote + strlen(remote)) = ',';
            }
            else {
                remote = parse_remote;
            }
            break;
        }

        /* We map as IPv4 rather than IPv6 for equivalent host names
         * or IPV4OVERIPV6
         */
        rv = apr_sockaddr_info_get(&temp_sa,  parse_remote,
                                   APR_UNSPEC, temp_sa->port,
                                   APR_IPV4_ADDR_OK, r->pool);
        if (rv != APR_SUCCESS) {
            ap_log_rerror(APLOG_MARK, APLOG_DEBUG,  rv, r, APLOGNO(01568)
                          "RemoteIP: Header %s value of %s cannot be parsed "
                          "as a client IP",
                          config->remoteip_header_name, parse_remote);

            if (remote) {
                *(remote + strlen(remote)) = ',';
            }
            else {
                remote = parse_remote;
            }
            break;
        }

        addrbyte = (unsigned char *) &temp_sa->sa.sin.sin_addr;

        /* For intranet (Internal proxies) ignore all restrictions below */
        if (!internal
              && ((temp_sa->family == APR_INET
                   /* For internet (non-Internal proxies) deny all
                    * RFC3330 designated local/private subnets:
                    * 10.0.0.0/8   169.254.0.0/16  192.168.0.0/16
                    * 127.0.0.0/8  172.16.0.0/12
                    */
                      && (addrbyte[0] == 10
                       || addrbyte[0] == 127
                       || (addrbyte[0] == 169 && addrbyte[1] == 254)
                       || (addrbyte[0] == 172 && (addrbyte[1] & 0xf0) == 16)
                       || (addrbyte[0] == 192 && addrbyte[1] == 168)))
#if APR_HAVE_IPV6
               || (temp_sa->family == APR_INET6
                   /* For internet (non-Internal proxies) we translated
                    * IPv4-over-IPv6-mapped addresses as IPv4, above.
                    * Accept only Global Unicast 2000::/3 defined by RFC4291
                    */
                      && ((temp_sa->sa.sin6.sin6_addr.s6_addr[0] & 0xe0) != 0x20))
#endif
        )) {
            ap_log_rerror(APLOG_MARK, APLOG_DEBUG,  rv, r, APLOGNO(01569)
                          "RemoteIP: Header %s value of %s appears to be "
                          "a private IP or nonsensical.  Ignored",
                          config->remoteip_header_name, parse_remote);
            if (remote) {
                *(remote + strlen(remote)) = ',';
            }
            else {
                remote = parse_remote;
            }

            break;
        }

        /* save away our results */
        if (!req) {
            req = (remoteip_req_t *) apr_palloc(r->pool, sizeof(remoteip_req_t));
            req->useragent_ip = r->useragent_ip;
        }

        /* Set useragent_ip string */
        if (!internal) {
            if (proxy_ips) {
                proxy_ips = apr_pstrcat(r->pool, proxy_ips, ", ",
                                        req->useragent_ip, NULL);
            }
            else {
                proxy_ips = req->useragent_ip;
            }
        }

        req->useragent_addr = temp_sa;
        apr_sockaddr_ip_get(&req->useragent_ip, req->useragent_addr);
    }

    /* Is there a client IP to be set? */
    if (req) {
        req->proxied_remote = remote;
        req->proxy_ips = proxy_ips;

        if (req->proxied_remote) {
            apr_table_setn(r->headers_in, config->remoteip_header_name,
                            req->proxied_remote);
        }
        else {
            apr_table_unset(r->headers_in, config->remoteip_header_name);
        }
        if (req->proxy_ips) {
            apr_table_setn(r->notes, "remoteip-proxy-ip-list", req->proxy_ips);
            if (config->proxies_header_name) {
                apr_table_setn(r->headers_in, config->proxies_header_name,
                               req->proxy_ips);
            }
        }

        r->useragent_addr = req->useragent_addr;
        r->useragent_ip = req->useragent_ip;

        ap_log_rerror(APLOG_MARK, APLOG_TRACE1, 0, r,
                      req->proxy_ips
                          ? "Using %s as client's IP by proxies %s via"
                          : "Using %s as client's IP by internal proxies %s",
                      req->useragent_ip,
                      (req->proxy_ips ? req->proxy_ips : ""));
    }

    /* Handle the secure_header_name if the request was sent via a trusted proxy.
     * As the request object may be reused without resetting the scheme and
     * server port, we'll always have to set port and scheme.
     */
    if (config->secure_header_name && trusted_proxy == 1) {
        pchar = (char *) apr_table_get(r->headers_in, config->secure_header_name);
        if (pchar && 0 == strcmp(pchar, config->secure_header_value)) {
           secure = 1;
        }
    }

    if (secure) {
        apr_table_setn(r->subprocess_env, "HTTPS", "on");
        r->server->port = config->secure_port;
        r->server->server_scheme = config->secure_scheme;
        r->parsed_uri.port = r->server->port;
        
        /* Header available, matched and processed. May be unset now. */
        apr_table_unset(r->headers_in, config->secure_header_name);

        ap_log_rerror(APLOG_MARK, APLOG_TRACE1, 0, r,
                      "Setting scheme https and server's port %d",
                      r->server->port);
    }
    else {
        r->server->port = config->orig_port;
        r->server->server_scheme = config->orig_scheme;
    }

    /* In order not to malloc on each request, the config*
     * holds a buffer for taking the server port number.
     */
    snprintf(config->buffer, 5, "%d", r->server->port);
    apr_table_setn(r->subprocess_env, "SERVER_PORT", config->buffer);

    return OK;
}

static const command_rec remoteip_cmds[] =
{
    AP_INIT_TAKE1("RemoteIPHeader", header_name_set, NULL, RSRC_CONF,
                  "Specifies a request header to trust as the client IP, "
                  "e.g. X-Forwarded-For"),
    AP_INIT_TAKE1("RemoteIPProxiesHeader", proxies_header_name_set,
                  NULL, RSRC_CONF,
                  "Specifies a request header to record proxy IP's, "
                  "e.g. X-Forwarded-By; if not given then do not record"),
    AP_INIT_ITERATE("RemoteIPTrustedProxy", proxies_set, 0, RSRC_CONF,
                    "Specifies one or more proxies which are trusted "
                    "to present IP headers"),
    AP_INIT_ITERATE("RemoteIPInternalProxy", proxies_set, (void*)1, RSRC_CONF,
                    "Specifies one or more internal (transparent) proxies "
                    "which are trusted to present IP headers"),
    AP_INIT_TAKE1("RemoteIPTrustedProxyList", proxylist_read, 0,
                  RSRC_CONF | EXEC_ON_READ,
                  "The filename to read the list of trusted proxies, "
                  "see the RemoteIPTrustedProxy directive"),
    AP_INIT_TAKE1("RemoteIPInternalProxyList", proxylist_read, (void*)1,
                  RSRC_CONF | EXEC_ON_READ,
                  "The filename to read the list of internal proxies, "
                  "see the RemoteIPInternalProxy directive"),
    AP_INIT_TAKE2("SecureIndicatorHeader", secure_header_set, NULL, RSRC_CONF,
                  "Specifies a request header and value that indicates a secure connection, "
                  "e.g. \"X-Forwarded-Proto https\" or \"X-Secure-Connection on\""),
    AP_INIT_TAKE1("SecureIndicatorSSLPort", secure_port_set, NULL, RSRC_CONF,
                  "Port to be used for redirections if SecureIndicatorHeader is set, "
                  "Default is \"SecureInidcatorSSLPort 443\" "),
    { NULL }
};

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

AP_DECLARE_MODULE(remoteip) = {
    STANDARD20_MODULE_STUFF,
    NULL,                          /* create per-directory config structure */
    NULL,                          /* merge per-directory config structures */
    create_remoteip_server_config, /* create per-server config structure */
    merge_remoteip_server_config,  /* merge per-server config structures */
    remoteip_cmds,                 /* command apr_table_t */
    register_hooks                 /* register hooks */
};