lighttpd1.4/src/mod_extforward.c

#include "first.h"

#include "base.h"
#include "log.h"
#include "buffer.h"
#include "http_header.h"
#include "request.h"
#include "sock_addr.h"

#include "plugin.h"

#include <limits.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>

#include "sys-socket.h"

/**
 * mod_extforward.c for lighttpd, by comman.kang <at> gmail <dot> com
 *                  extended, modified by Lionel Elie Mamane (LEM), lionel <at> mamane <dot> lu
 *                  support chained proxies by glen@delfi.ee, #1528
 *
 * Config example:
 *
 *       Trust proxy 10.0.0.232 and 10.0.0.232
 *       extforward.forwarder = ( "10.0.0.232" => "trust",
 *                                "10.0.0.233" => "trust" )
 *
 *       Trust all proxies  (NOT RECOMMENDED!)
 *       extforward.forwarder = ( "all" => "trust")
 *
 *       Note that "all" has precedence over specific entries,
 *       so "all except" setups will not work.
 *
 *       In case you have chained proxies, you can add all their IP's to the
 *       config. However "all" has effect only on connecting IP, as the
 *       X-Forwarded-For header can not be trusted.
 *
 * Note: The effect of this module is variable on $HTTP["remotip"] directives and
 *       other module's remote ip dependent actions.
 *  Things done by modules before we change the remoteip or after we reset it will match on the proxy's IP.
 *  Things done in between these two moments will match on the real client's IP.
 *  The moment things are done by a module depends on in which hook it does things and within the same hook
 *  on whether they are before/after us in the module loading order
 *  (order in the server.modules directive in the config file).
 *
 * Tested behaviours:
 *
 *  mod_access: Will match on the real client.
 *
 *  mod_accesslog:
 *   In order to see the "real" ip address in access log ,
 *   you'll have to load mod_extforward after mod_accesslog.
 *   like this:
 *
 *    server.modules  = (
 *       .....
 *       mod_accesslog,
 *       mod_extforward
 *    )
 */


typedef enum {
	PROXY_FORWARDED_NONE         = 0x00,
	PROXY_FORWARDED_FOR          = 0x01,
	PROXY_FORWARDED_PROTO        = 0x02,
	PROXY_FORWARDED_HOST         = 0x04,
	PROXY_FORWARDED_BY           = 0x08,
	PROXY_FORWARDED_REMOTE_USER  = 0x10
} proxy_forwarded_t;

struct sock_addr_mask {
  sock_addr addr;
  int bits;
};

struct forwarder_cfg {
  const array *forwarder;
  int forward_all;
  uint32_t addrs_used;
 #if defined(__STDC_VERSION__) && __STDC_VERSION__-0 >= 199901L /* C99 */
  struct sock_addr_mask addrs[];
 #else
  struct sock_addr_mask addrs[1];
 #endif
};

typedef struct {
    const array *forwarder;
    int forward_all;
    uint32_t forward_masks_used;
    const struct sock_addr_mask *forward_masks;
    const array *headers;
    unsigned int opts;
    char hap_PROXY;
    char hap_PROXY_ssl_client_verify;
} plugin_config;

typedef struct {
    PLUGIN_DATA;
    plugin_config defaults;
    plugin_config conf;
    array *default_headers;
} plugin_data;

static plugin_data *mod_extforward_plugin_data_singleton;
static int extforward_check_proxy;


/* context , used for restore remote ip */

typedef struct {
	/* per-request state */
	sock_addr saved_remote_addr;
	buffer *saved_remote_addr_buf;

	/* hap-PROXY protocol prior to receiving first request */
	int(*saved_network_read)(connection *, chunkqueue *, off_t);

	/* connection-level state applied to requests in handle_request_env */
	array *env;
	int ssl_client_verify;
} handler_ctx;


static handler_ctx * handler_ctx_init(void) {
	handler_ctx * hctx;
	hctx = calloc(1, sizeof(*hctx));
	force_assert(hctx);
	return hctx;
}

static void handler_ctx_free(handler_ctx *hctx) {
	free(hctx);
}

INIT_FUNC(mod_extforward_init) {
	return calloc(1, sizeof(plugin_data));
}

FREE_FUNC(mod_extforward_free) {
    plugin_data * const p = p_d;
    array_free(p->default_headers);
    if (NULL == p->cvlist) return;
    /* (init i to 0 if global context; to 1 to skip empty global context) */
    for (int i = !p->cvlist[0].v.u2[1], used = p->nconfig; i < used; ++i) {
        config_plugin_value_t *cpv = p->cvlist + p->cvlist[i].v.u2[0];
        for (; -1 != cpv->k_id; ++cpv) {
            switch (cpv->k_id) {
              case 0: /* extforward.forwarder */
                if (cpv->vtype == T_CONFIG_LOCAL) free(cpv->v.v);
                break;
              default:
                break;
            }
        }
    }
}

static void mod_extforward_merge_config_cpv(plugin_config * const pconf, const config_plugin_value_t * const cpv) {
    switch (cpv->k_id) { /* index into static config_plugin_keys_t cpk[] */
      case 0: /* extforward.forwarder */
        if (cpv->vtype == T_CONFIG_LOCAL) {
            const struct forwarder_cfg * const fwd = cpv->v.v;
            pconf->forwarder = fwd->forwarder;
            pconf->forward_all = fwd->forward_all;
            pconf->forward_masks_used = fwd->addrs_used;
            pconf->forward_masks = fwd->addrs;
        }
        break;
      case 1: /* extforward.headers */
        pconf->headers = cpv->v.a;
        break;
      case 2: /* extforward.params */
        if (cpv->vtype == T_CONFIG_LOCAL)
            pconf->opts = cpv->v.u;
        break;
      case 3: /* extforward.hap-PROXY */
        pconf->hap_PROXY = (char)cpv->v.u;
        break;
      case 4: /* extforward.hap-PROXY-ssl-client-verify */
        pconf->hap_PROXY_ssl_client_verify = (char)cpv->v.u;
        break;
      default:/* should not happen */
        return;
    }
}

static void mod_extforward_merge_config(plugin_config * const pconf, const config_plugin_value_t *cpv) {
    do {
        mod_extforward_merge_config_cpv(pconf, cpv);
    } while ((++cpv)->k_id != -1);
}

static void mod_extforward_patch_config(connection * const con, plugin_data * const p) {
    memcpy(&p->conf, &p->defaults, sizeof(plugin_config));
    for (int i = 1, used = p->nconfig; i < used; ++i) {
        if (config_check_cond(con, (uint32_t)p->cvlist[i].k_id))
            mod_extforward_merge_config(&p->conf, p->cvlist + p->cvlist[i].v.u2[0]);
    }
}

static void * mod_extforward_parse_forwarder(server *srv, const array *forwarder) {
    const data_string * const allds = (const data_string *)
      array_get_element_klen(forwarder, CONST_STR_LEN("all"));
    const int forward_all = (NULL == allds)
      ? 0
      : buffer_eq_icase_slen(&allds->value, CONST_STR_LEN("trust")) ? 1 : -1;
    uint32_t nmasks = 0;
    for (uint32_t j = 0; j < forwarder->used; ++j) {
        data_string * const ds = (data_string *)forwarder->data[j];
        char * const nm_slash = strchr(ds->key.ptr, '/');
        if (NULL != nm_slash) ++nmasks;
        if (!buffer_eq_icase_slen(&ds->value, CONST_STR_LEN("trust"))) {
            if (!buffer_eq_icase_slen(&ds->value, CONST_STR_LEN("untrusted")))
                log_error(srv->errh, __FILE__, __LINE__,
                  "ERROR: expect \"trust\", not \"%s\" => \"%s\"; "
                  "treating as untrusted", ds->key.ptr, ds->value.ptr);
            if (NULL != nm_slash) {
                /* future: consider adding member next to bits in sock_addr_mask
                 *         with bool trusted/untrusted member */
                --nmasks;
                log_error(srv->errh, __FILE__, __LINE__,
                  "ERROR: untrusted CIDR masks are ignored (\"%s\" => \"%s\")",
                  ds->key.ptr, ds->value.ptr);
            }
            buffer_clear(&ds->value); /* empty is untrusted */
            continue;
        }
    }

    struct forwarder_cfg * const fwd =
      malloc(sizeof(struct forwarder_cfg)+sizeof(struct sock_addr_mask)*nmasks);
    force_assert(fwd);
    memset(fwd, 0,
           sizeof(struct forwarder_cfg) + sizeof(struct sock_addr_mask)*nmasks);
    fwd->forwarder = forwarder;
    fwd->forward_all = forward_all;
    fwd->addrs_used = 0;
    for (uint32_t j = 0; j < forwarder->used; ++j) {
        data_string * const ds = (data_string *)forwarder->data[j];
        char * const nm_slash = strchr(ds->key.ptr, '/');
        if (NULL == nm_slash) continue;
        if (buffer_string_is_empty(&ds->value)) continue; /* ignored */

        char *err;
        const int nm_bits = strtol(nm_slash + 1, &err, 10);
        int rc;
        if (*err || nm_bits <= 0) {
            log_error(srv->errh, __FILE__, __LINE__,
              "ERROR: invalid netmask: %s %s", ds->key.ptr, err);
            free(fwd);
            return NULL;
        }
        struct sock_addr_mask * const sm = fwd->addrs + fwd->addrs_used++;
        sm->bits = nm_bits;
        *nm_slash = '\0';
        rc = sock_addr_from_str_numeric(&sm->addr, ds->key.ptr, srv->errh);
        *nm_slash = '/';
        if (1 != rc) {
            free(fwd);
            return NULL;
        }
        buffer_clear(&ds->value);
        /* empty is untrusted,
         * e.g. if subnet (incorrectly) appears in X-Forwarded-For */
    }

    return fwd;
}

static unsigned int mod_extforward_parse_opts(server *srv, const array *opts_params) {
    unsigned int opts = 0;
    for (uint32_t j = 0, used = opts_params->used; j < used; ++j) {
        proxy_forwarded_t param;
        data_unset *du = opts_params->data[j];
      #if 0  /*("for" and "proto" historical behavior: always enabled)*/
        if (buffer_eq_slen(&du->key, CONST_STR_LEN("by")))
            param = PROXY_FORWARDED_BY;
        else if (buffer_eq_slen(&du->key, CONST_STR_LEN("for")))
            param = PROXY_FORWARDED_FOR;
        else
      #endif
        if (buffer_eq_slen(&du->key, CONST_STR_LEN("host")))
            param = PROXY_FORWARDED_HOST;
      #if 0
        else if (buffer_eq_slen(&du->key, CONST_STR_LEN("proto")))
            param = PROXY_FORWARDED_PROTO;
      #endif
        else if (buffer_eq_slen(&du->key, CONST_STR_LEN("remote_user")))
            param = PROXY_FORWARDED_REMOTE_USER;
        else {
            log_error(srv->errh, __FILE__, __LINE__,
              "extforward.params keys must be one of: "
              "host, remote_user, but not: %s", du->key.ptr);
            return HANDLER_ERROR;
        }

        if (du->type == TYPE_STRING) {
            data_string *ds = (data_string *)du;
            if (buffer_eq_slen(&ds->value, CONST_STR_LEN("enable"))) {
                opts |= param;
            }
            else if (!buffer_eq_slen(&ds->value, CONST_STR_LEN("disable"))) {
                log_error(srv->errh, __FILE__, __LINE__,
                  "extforward.params values must be one of: "
                  "0, 1, enable, disable; error for key: %s", du->key.ptr);
                return UINT_MAX;
            }
        }
        else if (du->type == TYPE_INTEGER) {
            data_integer *di = (data_integer *)du;
            if (di->value) opts |= param;
        }
        else {
            log_error(srv->errh, __FILE__, __LINE__,
              "extforward.params values must be one of: "
              "0, 1, enable, disable; error for key: %s", du->key.ptr);
            return UINT_MAX;
        }
    }
    return opts;
}

SETDEFAULTS_FUNC(mod_extforward_set_defaults) {
    static const config_plugin_keys_t cpk[] = {
      { CONST_STR_LEN("extforward.forwarder"),
        T_CONFIG_ARRAY,
        T_CONFIG_SCOPE_CONNECTION }
     ,{ CONST_STR_LEN("extforward.headers"),
        T_CONFIG_ARRAY,
        T_CONFIG_SCOPE_CONNECTION }
     ,{ CONST_STR_LEN("extforward.params"),
        T_CONFIG_ARRAY,
        T_CONFIG_SCOPE_CONNECTION }
     ,{ CONST_STR_LEN("extforward.hap-PROXY"),
        T_CONFIG_BOOL,
        T_CONFIG_SCOPE_CONNECTION }
     ,{ CONST_STR_LEN("extforward.hap-PROXY-ssl-client-verify"),
        T_CONFIG_BOOL,
        T_CONFIG_SCOPE_CONNECTION }
     ,{ NULL, 0,
        T_CONFIG_UNSET,
        T_CONFIG_SCOPE_UNSET }
    };

    plugin_data * const p = p_d;
    if (!config_plugin_values_init(srv, p, cpk, "mod_extforward"))
        return HANDLER_ERROR;

    int hap_PROXY = 0;

    /* process and validate config directives
     * (init i to 0 if global context; to 1 to skip empty global context) */
    for (int i = !p->cvlist[0].v.u2[1]; i < p->nconfig; ++i) {
        config_plugin_value_t *cpv = p->cvlist + p->cvlist[i].v.u2[0];
        for (; -1 != cpv->k_id; ++cpv) {
            switch (cpv->k_id) {
              case 0: /* extforward.forwarder */
                if (!array_is_kvstring(cpv->v.a)) {
                    log_error(srv->errh, __FILE__, __LINE__,
                      "unexpected value for %s; "
                      "expected list of \"IPaddr\" => \"trust\"",
                      cpk[cpv->k_id].k);
                    return HANDLER_ERROR;
                }
                cpv->v.v = mod_extforward_parse_forwarder(srv, cpv->v.a);
                if (NULL == cpv->v.v) {
                    log_error(srv->errh, __FILE__, __LINE__,
                      "unexpected value for %s", cpk[cpv->k_id].k);
                    return HANDLER_ERROR;
                }
                cpv->vtype = T_CONFIG_LOCAL;
                break;
              case 1: /* extforward.headers */
                if (!array_is_vlist(cpv->v.a)) {
                    log_error(srv->errh, __FILE__, __LINE__,
                      "unexpected value for %s; "
                      "expected list of \"headername\"", cpk[cpv->k_id].k);
                    return HANDLER_ERROR;
                }
                break;
              case 2: /* extforward.params */
                if (!array_is_kvany(cpv->v.a)) {
                    log_error(srv->errh, __FILE__, __LINE__,
                      "unexpected value for %s; "
                      "expected list of \"param\" => \"value\"",
                      cpk[cpv->k_id].k);
                    return HANDLER_ERROR;
                }
                cpv->v.u = mod_extforward_parse_opts(srv, cpv->v.a);
                if (UINT_MAX == cpv->v.u)
                    return HANDLER_ERROR;
                break;
              case 3: /* extforward.hap-PROXY */
                if (cpv->v.u) hap_PROXY = 1;
                break;
              case 4: /* extforward.hap-PROXY-ssl-client-verify */
                break;
              default:/* should not happen */
                break;
            }
        }
    }

    mod_extforward_plugin_data_singleton = p;
    p->defaults.opts = PROXY_FORWARDED_NONE;

    /* initialize p->defaults from global config context */
    if (p->nconfig > 0 && p->cvlist->v.u2[1]) {
        const config_plugin_value_t *cpv = p->cvlist + p->cvlist->v.u2[0];
        if (-1 != cpv->k_id)
            mod_extforward_merge_config(&p->defaults, cpv);
    }

    /* default to "X-Forwarded-For" or "Forwarded-For" if extforward.headers
     * is not specified or is empty (and not using hap_PROXY) */
    if (!p->defaults.hap_PROXY
        && (NULL == p->defaults.headers || 0 == p->defaults.headers->used)) {
        p->defaults.headers = p->default_headers = array_init(2);
        array_insert_value(p->default_headers,CONST_STR_LEN("X-Forwarded-For"));
        array_insert_value(p->default_headers,CONST_STR_LEN("Forwarded-For"));
    }

    /* attempt to warn if mod_extforward is not last module loaded to hook
     * handle_connection_accept.  (Nice to have, but remove this check if
     * it reaches too far into internals and prevents other code changes.)
     * While it would be nice to check connection_handle_accept plugin slot
     * to make sure mod_extforward is last, that info is private to plugin.c
     * so merely warn if mod_openssl is loaded after mod_extforward, though
     * future modules which hook connection_handle_accept might be missed.*/
    if (hap_PROXY) {
        uint32_t i;
        for (i = 0; i < srv->srvconf.modules->used; ++i) {
            data_string *ds = (data_string *)srv->srvconf.modules->data[i];
            if (buffer_eq_slen(&ds->value, CONST_STR_LEN("mod_extforward")))
                break;
        }
        for (; i < srv->srvconf.modules->used; ++i) {
            data_string *ds = (data_string *)srv->srvconf.modules->data[i];
            if (buffer_eq_slen(&ds->value, CONST_STR_LEN("mod_openssl"))) {
                log_error(srv->errh, __FILE__, __LINE__,
                  "mod_extforward must be loaded after mod_openssl in "
                  "server.modules when extforward.hap-PROXY = \"enable\"");
                break;
            }
        }
    }

    for (uint32_t i = 0; i < srv->srvconf.modules->used; ++i) {
        data_string *ds = (data_string *)srv->srvconf.modules->data[i];
        if (buffer_is_equal_string(&ds->value, CONST_STR_LEN("mod_proxy"))) {
            extforward_check_proxy = 1;
            break;
        }
    }

    return HANDLER_GO_ON;
}


/*
   extract a forward array from the environment
*/
static array *extract_forward_array(const buffer *pbuffer)
{
	array *result = array_init(8);
	if (!buffer_string_is_empty(pbuffer)) {
		const char *base, *curr;
		/* state variable, 0 means not in string, 1 means in string */
		int in_str = 0;
		for (base = pbuffer->ptr, curr = pbuffer->ptr; *curr; curr++) {
			int hex_or_colon = (light_isxdigit(*curr) || *curr == ':');
			if (in_str) {
				if (!hex_or_colon && *curr != '.') {
					/* found an separator , insert value into result array */
					array_insert_value(result, base, curr - base);
					/* change state to not in string */
					in_str = 0;
				}
			} else {
				if (hex_or_colon) {
					/* found leading char of an IP address, move base pointer and change state */
					base = curr;
					in_str = 1;
				}
			}
		}
		/* if breaking out while in str, we got to the end of string, so add it */
		if (in_str) {
			array_insert_value(result, base, curr - base);
		}
	}
	return result;
}

/*
 * check whether ip is trusted, return 1 for trusted , 0 for untrusted
 */
static int is_proxy_trusted(plugin_data *p, const char * const ip, size_t iplen)
{
    const data_string *ds =
      (const data_string *)array_get_element_klen(p->conf.forwarder, ip, iplen);
    if (NULL != ds) return !buffer_string_is_empty(&ds->value);

    if (p->conf.forward_masks_used) {
        const struct sock_addr_mask * const addrs = p->conf.forward_masks;
        const uint32_t aused = p->conf.forward_masks_used;
        sock_addr addr;
        /* C funcs inet_aton(), inet_pton() require '\0'-terminated IP str */
        char addrstr[64]; /*(larger than INET_ADDRSTRLEN and INET6_ADDRSTRLEN)*/
        if (iplen >= sizeof(addrstr)) return 0;
        memcpy(addrstr, ip, iplen);
        addrstr[iplen] = '\0';

        if (1 != sock_addr_inet_pton(&addr, addrstr, AF_INET,  0)
         && 1 != sock_addr_inet_pton(&addr, addrstr, AF_INET6, 0)) return 0;

        for (uint32_t i = 0; i < aused; ++i) {
            if (sock_addr_is_addr_eq_bits(&addr, &addrs[i].addr, addrs[i].bits))
                return 1;
        }
    }

    return 0;
}

static int is_connection_trusted(connection * const con, plugin_data *p)
{
    if (p->conf.forward_all) return (1 == p->conf.forward_all);
    return is_proxy_trusted(p, CONST_BUF_LEN(con->dst_addr_buf));
}

/*
 * Return last address of proxy that is not trusted.
 * Do not accept "all" keyword here.
 */
static const char *last_not_in_array(array *a, plugin_data *p)
{
	int i;

	for (i = a->used - 1; i >= 0; i--) {
		data_string *ds = (data_string *)a->data[i];
		if (!is_proxy_trusted(p, CONST_BUF_LEN(&ds->value))) {
			return ds->value.ptr;
		}
	}
	return NULL;
}

static int mod_extforward_set_addr(connection *con, plugin_data *p, const char *addr) {
	sock_addr sock;
	handler_ctx *hctx = con->plugin_ctx[p->id];

	if (con->conf.log_request_handling) {
		log_error(con->conf.errh, __FILE__, __LINE__, "using address: %s", addr);
	}

	sock.plain.sa_family = AF_UNSPEC;
	if (1 != sock_addr_from_str_numeric(&sock, addr, con->conf.errh)) return 0;
	if (sock.plain.sa_family == AF_UNSPEC) return 0;

	/* we found the remote address, modify current connection and save the old address */
	if (hctx) {
		if (hctx->saved_remote_addr_buf) {
			if (con->conf.log_request_handling) {
				log_error(con->conf.errh, __FILE__, __LINE__,
				  "-- mod_extforward_uri_handler already patched this connection, resetting state");
			}
			con->dst_addr = hctx->saved_remote_addr;
			buffer_free(con->dst_addr_buf);
			con->dst_addr_buf = hctx->saved_remote_addr_buf;
			hctx->saved_remote_addr_buf = NULL;
		}
	} else {
		con->plugin_ctx[p->id] = hctx = handler_ctx_init();
	}
	/* save old address */
	if (extforward_check_proxy) {
		http_header_env_set(con, CONST_STR_LEN("_L_EXTFORWARD_ACTUAL_FOR"), CONST_BUF_LEN(con->dst_addr_buf));
	}
	hctx->saved_remote_addr = con->dst_addr;
	hctx->saved_remote_addr_buf = con->dst_addr_buf;
	/* patch connection address */
	con->dst_addr = sock;
	con->dst_addr_buf = buffer_init_string(addr);

	if (con->conf.log_request_handling) {
		log_error(con->conf.errh, __FILE__, __LINE__,
		  "patching con->dst_addr_buf for the accesslog: %s", addr);
	}

	/* Now, clean the conf_cond cache, because we may have changed the results of tests */
	config_cond_cache_reset_item(con, COMP_HTTP_REMOTE_IP);

	return 1;
}

static void mod_extforward_set_proto(connection *con, const char *proto, size_t protolen) {
	if (0 != protolen && !buffer_is_equal_caseless_string(con->uri.scheme, proto, protolen)) {
		/* update scheme if X-Forwarded-Proto is set
		 * Limitations:
		 * - Only "http" or "https" are currently accepted since the request to lighttpd currently has to
		 *   be HTTP/1.0 or HTTP/1.1 using http or https.  If this is changed, then the scheme from this
		 *   untrusted header must be checked to contain only alphanumeric characters, and to be a
		 *   reasonable length, e.g. < 256 chars.
		 * - con->uri.scheme is not reset in mod_extforward_restore() but is currently not an issues since
		 *   con->uri.scheme will be reset by next request.  If a new module uses con->uri.scheme in the
		 *   handle_request_done hook, then should evaluate if that module should use the forwarded value
		 *   (probably) or the original value.
		 */
		if (extforward_check_proxy) {
			http_header_env_set(con, CONST_STR_LEN("_L_EXTFORWARD_ACTUAL_PROTO"), CONST_BUF_LEN(con->uri.scheme));
		}
		if (buffer_eq_icase_ss(proto, protolen, CONST_STR_LEN("https"))) {
			buffer_copy_string_len(con->uri.scheme, CONST_STR_LEN("https"));
			config_cond_cache_reset_item(con, COMP_HTTP_SCHEME);
		} else if (buffer_eq_icase_ss(proto, protolen, CONST_STR_LEN("http"))) {
			buffer_copy_string_len(con->uri.scheme, CONST_STR_LEN("http"));
			config_cond_cache_reset_item(con, COMP_HTTP_SCHEME);
		}
	}
}

static handler_t mod_extforward_X_Forwarded_For(connection *con, plugin_data *p, const buffer *x_forwarded_for) {
	/* build forward_array from forwarded data_string */
	array *forward_array = extract_forward_array(x_forwarded_for);
	const char *real_remote_addr = last_not_in_array(forward_array, p);
	if (real_remote_addr != NULL) { /* parsed */
		/* get scheme if X-Forwarded-Proto is set
		 * Limitations:
		 * - X-Forwarded-Proto may or may not be set by proxies, even if X-Forwarded-For is set
		 * - X-Forwarded-Proto may be a comma-separated list if there are multiple proxies,
		 *   but the historical behavior of the code below only honored it if there was exactly one value
		 *   (not done: walking backwards in X-Forwarded-Proto the same num of steps
		 *    as in X-Forwarded-For to find proto set by last trusted proxy)
		 */
		const buffer *x_forwarded_proto = http_header_request_get(con, HTTP_HEADER_X_FORWARDED_PROTO, CONST_STR_LEN("X-Forwarded-Proto"));
		if (mod_extforward_set_addr(con, p, real_remote_addr) && NULL != x_forwarded_proto) {
			mod_extforward_set_proto(con, CONST_BUF_LEN(x_forwarded_proto));
		}
	}
	array_free(forward_array);
	return HANDLER_GO_ON;
}

static int find_end_quoted_string (const char * const s, int i) {
    do {
        ++i;
    } while (s[i] != '"' && s[i] != '\0' && (s[i] != '\\' || s[++i] != '\0'));
    return i;
}

static int find_next_semicolon_or_comma_or_eq (const char * const s, int i) {
    for (; s[i] != '=' && s[i] != ';' && s[i] != ',' && s[i] != '\0'; ++i) {
        if (s[i] == '"') {
            i = find_end_quoted_string(s, i);
            if (s[i] == '\0') return -1;
        }
    }
    return i;
}

static int find_next_semicolon_or_comma (const char * const s, int i) {
    for (; s[i] != ';' && s[i] != ',' && s[i] != '\0'; ++i) {
        if (s[i] == '"') {
            i = find_end_quoted_string(s, i);
            if (s[i] == '\0') return -1;
        }
    }
    return i;
}

static int buffer_backslash_unescape (buffer * const b) {
    /* (future: might move to buffer.c) */
    size_t j = 0;
    size_t len = buffer_string_length(b);
    char *p = memchr(b->ptr, '\\', len);

    if (NULL == p) return 1; /*(nothing to do)*/

    len -= (size_t)(p - b->ptr);
    for (size_t i = 0; i < len; ++i) {
        if (p[i] == '\\') {
            if (++i == len) return 0; /*(invalid trailing backslash)*/
        }
        p[j++] = p[i];
    }
    buffer_string_set_length(b, (size_t)(p+j - b->ptr));
    return 1;
}

static handler_t mod_extforward_Forwarded (connection *con, plugin_data *p, const buffer *forwarded) {
    /* HTTP list need not consist of param=value tokens,
     * but this routine expect such for HTTP Forwarded header
     * Since info in each set of params is only used if from
     * admin-specified trusted proxy:
     * - invalid param=value tokens are ignored and skipped
     * - not checking "for" exists in each set of params
     * - not checking for duplicated params in each set of params
     * - not checking canonical form of addr (also might be obfuscated)
     * - obfuscated tokens permitted in chain, though end of trust is expected
     *   to be non-obfuscated IP for mod_extforward to masquerade as remote IP
     * future: since (potentially) trusted proxies begin at end of string,
     *   it might be better to parse from end of string rather than parsing from
     *   beginning.  Doing so would also allow reducing arbitrary param limit
     *   to number of params permitted per proxy.
     */
    char * const s = forwarded->ptr;
    int i = 0, j = -1, v, vlen, k, klen;
    int used = (int)buffer_string_length(forwarded);
    int ofor = -1, oproto, ohost, oby, oremote_user;
    int offsets[256];/*(~50 params is more than reasonably expected to handle)*/
    while (i < used) {
        while (s[i] == ' ' || s[i] == '\t') ++i;
        if (s[i] == ';') { ++i; continue; }
        if (s[i] == ',') {
            if (j >= (int)(sizeof(offsets)/sizeof(int))) break;
            offsets[++j] = -1; /*("offset" separating params from next proxy)*/
            ++i;
            continue;
        }
        if (s[i] == '\0') break;

        k = i;
        i = find_next_semicolon_or_comma_or_eq(s, i);
        if (i < 0) {
            /*(reject IP spoofing if attacker sets improper quoted-string)*/
            log_error(con->conf.errh, __FILE__, __LINE__,
              "invalid quoted-string in Forwarded header");
            con->http_status = 400; /* Bad Request */
            con->mode = DIRECT;
            return HANDLER_FINISHED;
        }
        if (s[i] != '=') continue;
        klen = i - k;
        v = ++i;
        i = find_next_semicolon_or_comma(s, i);
        if (i < 0) {
            /*(reject IP spoofing if attacker sets improper quoted-string)*/
            log_error(con->conf.errh, __FILE__, __LINE__,
              "invalid quoted-string in Forwarded header");
            con->http_status = 400; /* Bad Request */
            con->mode = DIRECT;
            return HANDLER_FINISHED;
        }
        vlen = i - v;              /* might be 0 */

        /* have k, klen, v, vlen
         * (might contain quoted string) (contents not validated or decoded)
         * (might be repeated k)
         */
        if (0 == klen) continue;   /* invalid k */
        if (j >= (int)(sizeof(offsets)/sizeof(int))-4) break;
        offsets[j+1] = k;
        offsets[j+2] = klen;
        offsets[j+3] = v;
        offsets[j+4] = vlen;
        j += 4;
    }

    if (j >= (int)(sizeof(offsets)/sizeof(int))-4) {
        /* error processing Forwarded; too many params; fail closed */
        log_error(con->conf.errh, __FILE__, __LINE__,
          "Too many params in Forwarded header");
        con->http_status = 400; /* Bad Request */
        con->mode = DIRECT;
        return HANDLER_FINISHED;
    }

    if (-1 == j) return HANDLER_GO_ON;  /* make no changes */
    used = j+1;
    offsets[used] = -1; /* mark end of last set of params */

    while (j >= 4) { /*(param=value pairs)*/
        if (-1 == offsets[j]) { --j; continue; }
        do {
            j -= 3; /*(k, klen, v, vlen come in sets of 4)*/
        } while ((3 != offsets[j+1]  /* 3 == sizeof("for")-1 */
                  || !buffer_eq_icase_ssn(s+offsets[j], "for", 3))