/*
 *
 *  Resolver library with GLib integration
 *
 *  Copyright (C) 2009-2010  Intel Corporation. All rights reserved.
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License version 2 as
 *  published by the Free Software Foundation.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 *
 */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <errno.h>
#include <unistd.h>
#include <stdarg.h>
#include <string.h>
#include <stdlib.h>
#include <resolv.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <arpa/nameser.h>

#include "gresolv.h"

struct sort_result {
	int precedence;
	int src_scope;
	int dst_scope;
	int src_label;
	int dst_label;
	gboolean reachable;
	union {
		struct sockaddr sa;
		struct sockaddr_in sin;
		struct sockaddr_in6 sin6;
	} src;
	union {
		struct sockaddr sa;
		struct sockaddr_in sin;
		struct sockaddr_in6 sin6;
	} dst;
};

struct resolv_query;

struct resolv_lookup {
	GResolv *resolv;
	guint id;

	int nr_results;
	struct sort_result *results;

	struct resolv_query *ipv4_query;
	struct resolv_query *ipv6_query;

	guint ipv4_status;
	guint ipv6_status;

	GResolvResultFunc result_func;
	gpointer result_data;
};

struct resolv_query {
	GResolv *resolv;

	guint timeout;

	uint16_t msgid;

	struct resolv_lookup *lookup;
};

struct resolv_nameserver {
	GResolv *resolv;

	char *address;
	uint16_t port;
	unsigned long flags;

	GIOChannel *udp_channel;
	guint udp_watch;
};

struct _GResolv {
	gint ref_count;

	guint next_lookup_id;
	GQueue *lookup_queue;
	GQueue *query_queue;

	int index;
	GList *nameserver_list;

	struct __res_state res;

	GResolvDebugFunc debug_func;
	gpointer debug_data;
};

static void sort_and_return_results(struct resolv_lookup *lookup);
static void rfc3484_sort_results(struct resolv_lookup *lookup);

static inline void debug(GResolv *resolv, const char *format, ...)
{
	char str[256];
	va_list ap;

	if (resolv->debug_func == NULL)
		return;

	va_start(ap, format);

	if (vsnprintf(str, sizeof(str), format, ap) > 0)
		resolv->debug_func(str, resolv->debug_data);

	va_end(ap);
}

static void destroy_query(struct resolv_query *query)
{
	if (query->timeout > 0)
		g_source_remove(query->timeout);

	g_free(query);
}

static void destroy_lookup(struct resolv_lookup *lookup)
{
	if (lookup->ipv4_query) {
		g_queue_remove(lookup->resolv->query_queue, lookup->ipv4_query);
		destroy_query(lookup->ipv4_query);
	}
	if (lookup->ipv6_query) {
		g_queue_remove(lookup->resolv->query_queue, lookup->ipv6_query);
		destroy_query(lookup->ipv6_query);
	}
	g_free(lookup->results);
	g_free(lookup);
}

static gboolean query_timeout(gpointer user_data)
{
	struct resolv_query *query = user_data;
	struct resolv_lookup *lookup = query->lookup;
	GResolv *resolv = query->resolv;

	query->timeout = 0;

	if (query == lookup->ipv4_query) {
		lookup->ipv4_status = G_RESOLV_RESULT_STATUS_NO_RESPONSE;
		lookup->ipv4_query = NULL;
	} else if (query == lookup->ipv6_query) {
		lookup->ipv6_status = G_RESOLV_RESULT_STATUS_NO_RESPONSE;
		lookup->ipv6_query = NULL;
	}
	if (!lookup->ipv4_query && !lookup->ipv4_query)
		sort_and_return_results(lookup);

	destroy_query(query);
	g_queue_remove(resolv->query_queue, query);

	return FALSE;
}

static void free_nameserver(struct resolv_nameserver *nameserver)
{
	if (nameserver == NULL)
		return;

	if (nameserver->udp_watch > 0)
		g_source_remove(nameserver->udp_watch);

	if (nameserver->udp_channel != NULL)
		g_io_channel_unref(nameserver->udp_channel);

	g_free(nameserver->address);
	g_free(nameserver);
}

static void flush_nameservers(GResolv *resolv)
{
	GList *list;

	for (list = g_list_first(resolv->nameserver_list);
					list; list = g_list_next(list))
		free_nameserver(list->data);

	g_list_free(resolv->nameserver_list);
	resolv->nameserver_list = NULL;
}

static int send_query(GResolv *resolv, const unsigned char *buf, int len)
{
	GList *list;

	if (resolv->nameserver_list == NULL)
		return -ENOENT;

	for (list = g_list_first(resolv->nameserver_list);
					list; list = g_list_next(list)) {
		struct resolv_nameserver *nameserver = list->data;
		int sk, sent;

		if (nameserver->udp_channel == NULL)
			continue;

		sk = g_io_channel_unix_get_fd(nameserver->udp_channel);

		sent = send(sk, buf, len, 0);
	}

	return 0;
}

static gint compare_lookup_id(gconstpointer a, gconstpointer b)
{
	const struct resolv_lookup *lookup = a;
	guint id = GPOINTER_TO_UINT(b);

	if (lookup->id < id)
		return -1;

	if (lookup->id > id)
		return 1;

	return 0;
}

static gint compare_query_msgid(gconstpointer a, gconstpointer b)
{
	const struct resolv_query *query = a;
	uint16_t msgid = GPOINTER_TO_UINT(b);

	if (query->msgid < msgid)
		return -1;

	if (query->msgid > msgid)
		return 1;

	return 0;
}

static void add_result(struct resolv_lookup *lookup, int family, const void *data)
{
	int n = lookup->nr_results++;
	lookup->results = g_realloc(lookup->results,
				    sizeof(struct sort_result) * (n+1));

	memset(&lookup->results[n], 0, sizeof(struct sort_result));

	lookup->results[n].dst.sa.sa_family = family;
	if (family == AF_INET)
		memcpy(&lookup->results[n].dst.sin.sin_addr, data, NS_INADDRSZ);
	else
		memcpy(&lookup->results[n].dst.sin6.sin6_addr, data, NS_IN6ADDRSZ);
}

static void parse_response(struct resolv_nameserver *nameserver,
					const unsigned char *buf, int len)
{
	GResolv *resolv = nameserver->resolv;
	GResolvResultStatus status;
	struct resolv_query *query;
	struct resolv_lookup *lookup;
	GList *list;
	ns_msg msg;
	ns_rr rr;
	int i, n, rcode, count;

	debug(resolv, "response from %s", nameserver->address);

	ns_initparse(buf, len, &msg);

	rcode = ns_msg_getflag(msg, ns_f_rcode);
	count = ns_msg_count(msg, ns_s_an);

	debug(resolv, "msg id: 0x%04x rcode: %d count: %d",
					ns_msg_id(msg), rcode, count);

	switch (rcode) {
	case 0:
		status = G_RESOLV_RESULT_STATUS_SUCCESS;
		break;
	case 1:
		status = G_RESOLV_RESULT_STATUS_FORMAT_ERROR;
		break;
	case 2:
		status = G_RESOLV_RESULT_STATUS_SERVER_FAILURE;
		break;
	case 3:
		status = G_RESOLV_RESULT_STATUS_NAME_ERROR;
		break;
	case 4:
		status = G_RESOLV_RESULT_STATUS_NOT_IMPLEMENTED;
		break;
	case 5:
		status = G_RESOLV_RESULT_STATUS_REFUSED;
		break;
	default:
		status = G_RESOLV_RESULT_STATUS_ERROR;
		break;
	}

	list = g_queue_find_custom(resolv->query_queue,
			GUINT_TO_POINTER(ns_msg_id(msg)), compare_query_msgid);
	if (!list)
		return;

	query = list->data;
	lookup = query->lookup;

	if (query == lookup->ipv6_query) {
		lookup->ipv6_status = status;
		lookup->ipv6_query = NULL;
	} else if (query == lookup->ipv4_query) {
		lookup->ipv4_status = status;
		lookup->ipv4_query = NULL;
	}

	for (i = 0, n = 0; i < count; i++) {
		ns_parserr(&msg, ns_s_an, i, &rr);

		if (ns_rr_class(rr) != ns_c_in)
			continue;

		g_assert(offsetof(struct sockaddr_in, sin_addr) ==
			 offsetof(struct sockaddr_in6, sin6_flowinfo));

		if (ns_rr_type(rr) == ns_t_a &&
		    ns_rr_rdlen(rr) == NS_INADDRSZ) {
			add_result(lookup, AF_INET, ns_rr_rdata(rr));
		} else if (ns_rr_type(rr) == ns_t_aaaa &&
			   ns_rr_rdlen(rr) == NS_IN6ADDRSZ) {
			add_result(lookup, AF_INET6, ns_rr_rdata(rr));
		}
	}

	if (!lookup->ipv4_query && !lookup->ipv6_query)
		sort_and_return_results(lookup);

	destroy_query(query);
	g_queue_remove(resolv->query_queue, query);
}

static gboolean received_udp_data(GIOChannel *channel, GIOCondition cond,
							gpointer user_data)
{
	struct resolv_nameserver *nameserver = user_data;
	unsigned char buf[4096];
	int sk, len;

	if (cond & (G_IO_NVAL | G_IO_ERR | G_IO_HUP)) {
		nameserver->udp_watch = 0;
		return FALSE;
	}

	sk = g_io_channel_unix_get_fd(nameserver->udp_channel);

	len = recv(sk, buf, sizeof(buf), 0);
	if (len < 12)
		return TRUE;

	parse_response(nameserver, buf, len);

	return TRUE;
}

static int connect_udp_channel(struct resolv_nameserver *nameserver)
{
	struct addrinfo hints, *rp;
	char portnr[6];
	int err, sk;

	memset(&hints, 0, sizeof(hints));
	hints.ai_family = AF_UNSPEC;
	hints.ai_socktype = SOCK_DGRAM;
	hints.ai_flags = AI_PASSIVE | AI_NUMERICSERV | AI_NUMERICHOST;

	sprintf(portnr, "%d", nameserver->port);
	err = getaddrinfo(nameserver->address, portnr, &hints, &rp);
	if (err)
		return -EINVAL;

	/* Do not blindly copy this code elsewhere; it doesn't loop over the
	   results using ->ai_next as it should. That's OK in *this* case
	   because it was a numeric lookup; we *know* there's only one. */
	if (!rp)
		return -EINVAL;

	sk = socket(rp->ai_family, rp->ai_socktype, rp->ai_protocol);
	if (sk < 0) {
		freeaddrinfo(rp);
		return -EIO;
	}

	if (connect(sk, rp->ai_addr, rp->ai_addrlen) < 0) {
		close(sk);
		freeaddrinfo(rp);
		return -EIO;
	}

	freeaddrinfo(rp);

	nameserver->udp_channel = g_io_channel_unix_new(sk);
	if (nameserver->udp_channel == NULL) {
		close(sk);
		return -ENOMEM;
	}

	g_io_channel_set_close_on_unref(nameserver->udp_channel, TRUE);

	nameserver->udp_watch = g_io_add_watch(nameserver->udp_channel,
			       G_IO_IN | G_IO_NVAL | G_IO_ERR | G_IO_HUP,
			       received_udp_data, nameserver);

	return 0;
}

GResolv *g_resolv_new(int index)
{
	GResolv *resolv;

	if (index < 0)
		return NULL;

	resolv = g_try_new0(GResolv, 1);
	if (resolv == NULL)
		return NULL;

	resolv->ref_count = 1;

	resolv->next_lookup_id = 1;

	resolv->query_queue = g_queue_new();
	if (resolv->query_queue == NULL) {
		g_free(resolv);
		return NULL;
	}

	resolv->lookup_queue = g_queue_new();
	if (resolv->lookup_queue == NULL) {
		g_queue_free(resolv->query_queue);
		g_free(resolv);
		return NULL;
	}

	resolv->index = index;
	resolv->nameserver_list = NULL;

	res_ninit(&resolv->res);

	return resolv;
}

GResolv *g_resolv_ref(GResolv *resolv)
{
	if (resolv == NULL)
		return NULL;

	g_atomic_int_inc(&resolv->ref_count);

	return resolv;
}

void g_resolv_unref(GResolv *resolv)
{
	struct resolv_query *query;

	if (resolv == NULL)
		return;

	if (g_atomic_int_dec_and_test(&resolv->ref_count) == FALSE)
		return;

	while ((query = g_queue_pop_head(resolv->query_queue)))
		destroy_query(query);

	g_queue_free(resolv->query_queue);
	g_queue_free(resolv->lookup_queue);

	flush_nameservers(resolv);

	res_nclose(&resolv->res);

	g_free(resolv);
}

void g_resolv_set_debug(GResolv *resolv,
                                GResolvDebugFunc func, gpointer user_data)
{
	if (resolv == NULL)
		return;

	resolv->debug_func = func;
	resolv->debug_data = user_data;
}

gboolean g_resolv_add_nameserver(GResolv *resolv, const char *address,
					uint16_t port, unsigned long flags)
{
	struct resolv_nameserver *nameserver;

	if (resolv == NULL)
		return FALSE;

	nameserver = g_try_new0(struct resolv_nameserver, 1);
	if (nameserver == NULL)
		return FALSE;

	nameserver->address = g_strdup(address);
	nameserver->port = port;
	nameserver->flags = flags;

	if (connect_udp_channel(nameserver) < 0) {
		free_nameserver(nameserver);
		return FALSE;
	}

	nameserver->resolv = resolv;

	resolv->nameserver_list = g_list_append(resolv->nameserver_list,
								nameserver);

	debug(resolv, "setting nameserver %s", address);

	return TRUE;
}

void g_resolv_flush_nameservers(GResolv *resolv)
{
	if (resolv == NULL)
		return;

	flush_nameservers(resolv);
}

static void sort_and_return_results(struct resolv_lookup *lookup)
{
	char buf[100];
	GResolvResultStatus status;
	char **results = g_try_new0(char *, lookup->nr_results + 1);
	int i, n = 0;

	if (!results)
		return;

	rfc3484_sort_results(lookup);

	for (i = 0; i < lookup->nr_results; i++) {
		if (lookup->results[i].dst.sa.sa_family == AF_INET) {
			if (!inet_ntop(AF_INET, &lookup->results[i].dst.sin.sin_addr,
				       buf, sizeof(buf)))
				continue;
		} else if (lookup->results[i].dst.sa.sa_family == AF_INET6) {
			if (!inet_ntop(AF_INET6, &lookup->results[i].dst.sin6.sin6_addr,
				       buf, sizeof(buf)))
				continue;
		} else
			continue;

		results[n++] = strdup(buf);
	}
	results[n++] = NULL;

	status = lookup->ipv4_status;
	if (status == G_RESOLV_RESULT_STATUS_SUCCESS)
		status = lookup->ipv6_status;

	lookup->result_func(status, results, lookup->result_data);

	g_strfreev(results);
	g_queue_remove(lookup->resolv->lookup_queue, lookup);
	destroy_lookup(lookup);
}

static gint add_query(struct resolv_lookup *lookup, const char *hostname, int type)
{
	struct resolv_query *query = g_try_new0(struct resolv_query, 1);
	unsigned char buf[4096];
	int len;

	if (query == NULL)
		return -ENOMEM;

	len = res_mkquery(ns_o_query, hostname, ns_c_in, type,
					NULL, 0, NULL, buf, sizeof(buf));

	query->msgid = buf[0] << 8 | buf[1];

	if (send_query(lookup->resolv, buf, len) < 0)
		return -EIO;

	query->resolv = lookup->resolv;
	query->lookup = lookup;

	g_queue_push_tail(lookup->resolv->query_queue, query);

	query->timeout = g_timeout_add_seconds(5, query_timeout, query);

	if (type == ns_t_aaaa)
		lookup->ipv6_query = query;
	else
		lookup->ipv4_query = query;

	return 0;
}

guint g_resolv_lookup_hostname(GResolv *resolv, const char *hostname,
				GResolvResultFunc func, gpointer user_data)
{
	struct resolv_lookup *lookup;

	debug(resolv, "lookup hostname %s", hostname);

	if (resolv == NULL)
		return 0;

	if (resolv->nameserver_list == NULL) {
		int i;

		for (i = 0; i < resolv->res.nscount; i++) {
			char buf[100];
			int family = resolv->res.nsaddr_list[i].sin_family;
			void *sa_addr = &resolv->res.nsaddr_list[i].sin_addr;

			if (family != AF_INET && resolv->res._u._ext.nsaddrs[i]) {
				family = AF_INET6;
				sa_addr = &resolv->res._u._ext.nsaddrs[i]->sin6_addr;
			}
			if (family != AF_INET && family != AF_INET6)
				continue;

			if (inet_ntop(family, sa_addr, buf, sizeof(buf)))
				g_resolv_add_nameserver(resolv, buf, 53, 0);
		}

		if (resolv->nameserver_list == NULL)
			g_resolv_add_nameserver(resolv, "127.0.0.1", 53, 0);
	}

	lookup = g_try_new0(struct resolv_lookup, 1);
	if (!lookup)
		return 0;

	lookup->resolv = resolv;
	lookup->result_func = func;
	lookup->result_data = user_data;
	lookup->id = resolv->next_lookup_id++;

	if (add_query(lookup, hostname, ns_t_a)) {
		g_free(lookup);
		return -EIO;
	}
	if (add_query(lookup, hostname, ns_t_aaaa)) {
		destroy_query(lookup->ipv4_query);
		g_queue_remove(resolv->query_queue, lookup->ipv4_query);
		g_free(lookup);
		return -EIO;
	}

	g_queue_push_tail(resolv->lookup_queue, lookup);
	return lookup->id;
}

gboolean g_resolv_cancel_lookup(GResolv *resolv, guint id)
{
	GList *list;

	list = g_queue_find_custom(resolv->lookup_queue,
				GUINT_TO_POINTER(id), compare_lookup_id);

	if (list == NULL)
		return FALSE;

	destroy_lookup(list->data);
	g_queue_remove(resolv->query_queue, list->data);

	return TRUE;
}

static void find_srcaddr(struct sort_result *res)
{
	int fd;
	socklen_t sl = sizeof(res->src);

	fd = socket(res->dst.sa.sa_family, SOCK_DGRAM, IPPROTO_IP);
	if (fd < 0)
		return;

	if (connect(fd, &res->dst.sa, sizeof(res->dst))) {
		close(fd);
		return;
	}
	if (getsockname(fd, &res->src.sa, &sl)) {
		close(fd);
		return;
	}
	res->reachable = TRUE;
	close(fd);
}

struct gai_table
{
	unsigned char addr[NS_IN6ADDRSZ];
	int mask;
	int value;
};

static const struct gai_table gai_labels[] = {
	{
		.addr = { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
			  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01 },
		.mask = 128,
		.value = 0,
	}, {
		.addr = { 0x20, 0x02, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
			  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 },
		.mask = 16,
		.value = 2,
	}, {
		.addr = { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
			  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 },
		.mask = 96,
		.value = 3,
	}, {
		.addr = { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
			  0x00, 0x00, 0xff, 0xff, 0x00, 0x00, 0x00, 0x00 },
		.mask = 96,
		.value = 4,
	}, {
		/* Variations from RFC 3484, matching glibc behaviour */
		.addr = { 0xfe, 0xc0, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
			  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 },
		.mask = 10,
		.value = 5,
	}, {
		.addr = { 0xfc, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
			  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 },
		.mask = 7,
		.value = 6,
	}, {
		.addr = { 0x20, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
			  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 },
		.mask = 32,
		.value = 7,
	}, {
		/* catch-all */
		.addr = { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
			  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 },
		.mask = 0,
		.value = 1,
	}
};

static const struct gai_table gai_precedences[] = {
	{
		.addr = { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
			  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01 },
		.mask = 128,
		.value = 50,
	}, {
		.addr = { 0x20, 0x02, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
			  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 },
		.mask = 16,
		.value = 30,
	}, {
		.addr = { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
			  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 },
		.mask = 96,
		.value = 20,
	}, {
		.addr = { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
			  0x00, 0x00, 0xff, 0xff, 0x00, 0x00, 0x00, 0x00 },
		.mask = 96,
		.value = 10,
	}, {
		.addr = { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
			  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 },
		.mask = 0,
		.value = 40,
	}
};

static unsigned char v4mapped[] = { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
				    0x00, 0x00, 0xff, 0xff, 0x00, 0x00, 0x00, 0x00 };

static gboolean mask_compare(const unsigned char *one, const unsigned char *two, int mask)
{
	if (mask > 8) {
		if (memcmp(one, two, mask / 8))
			return FALSE;
		one += mask / 8;
		two += mask / 8;
		mask %= 8;
	}
	if (mask && ((*one ^ *two) >> (8-mask)))
	    return FALSE;

	return TRUE;
}

static int match_gai_table(struct sockaddr *sa, const struct gai_table *tbl)
{
	struct sockaddr_in *sin = (void *)sa;
	struct sockaddr_in6 *sin6 = (void *)sa;
	void *addr;

	if (sa->sa_family == AF_INET) {
		addr = v4mapped;
		memcpy(v4mapped+12, &sin->sin_addr, NS_INADDRSZ);
	} else
		addr = &sin6->sin6_addr;

	while (1) {
		if (mask_compare(addr, tbl->addr, tbl->mask))
			return tbl->value;
		tbl++;
	}
}

#define DQUAD(_a,_b,_c,_d) ( ((_a)<<24) | ((_b)<<16) | ((_c)<<8) | (_d) )
#define V4MATCH(addr, a,b,c,d, m) ( ((addr) ^ DQUAD(a,b,c,d)) >> (32 - (m)) )

#define RFC3484_SCOPE_LINK	2
#define RFC3484_SCOPE_SITE	5
#define RFC3484_SCOPE_GLOBAL	14

static int addr_scope(struct sockaddr *sa)
{
	if (sa->sa_family == AF_INET) {
		struct sockaddr_in *sin = (void *)sa;
		guint32 addr = ntohl(sin->sin_addr.s_addr);

		if (V4MATCH(addr, 169,254,0,0, 16) ||
		    V4MATCH(addr, 127,0,0,0,   8))
			return RFC3484_SCOPE_LINK;

		/* Site-local */
		if (V4MATCH(addr, 10,0,0,0,    8) ||
		    V4MATCH(addr, 172,16,0,0,  12) ||
		    V4MATCH(addr, 192,168,0,0, 16))
			return RFC3484_SCOPE_SITE;

		/* Global */
		return RFC3484_SCOPE_GLOBAL;
	} else {
		struct sockaddr_in6 *sin6 = (void *)sa;

		/* Multicast addresses have a 4-bit scope field */
		if (IN6_IS_ADDR_MULTICAST(&sin6->sin6_addr))
			return sin6->sin6_addr.s6_addr[1] & 0xf;

		if (IN6_IS_ADDR_LINKLOCAL(&sin6->sin6_addr) ||
		    IN6_IS_ADDR_LOOPBACK(&sin6->sin6_addr))
			return RFC3484_SCOPE_LINK;

		if (IN6_IS_ADDR_SITELOCAL(&sin6->sin6_addr))
			return RFC3484_SCOPE_SITE;

		return RFC3484_SCOPE_GLOBAL;
	}
}

static int rfc3484_compare(const void *__one, const void *__two)
{
	const struct sort_result *one = __one;
	const struct sort_result *two = __two;

	/* Rule 1: Avoid unusable destinations */
	if (one->reachable && !two->reachable)
		return -1;
	else if (two->reachable && !one->reachable)
		return 1;

	/* Rule 2: Prefer matching scope */
	if (one->dst_scope == one->src_scope &&
	    two->dst_scope != two->src_scope)
		return -1;
	else if (two->dst_scope == two->src_scope &&
		 one->dst_scope != one->src_scope)
		return 1;

	/* Rule 3: Avoid deprecated addresses */

	/* Rule 4: Prefer home addresses */

	/* Rule 5: Prefer matching label */
	if (one->dst_label == one->src_label &&
	    two->dst_label != two->src_label)
		return -1;
	else if (two->dst_label == two->src_label &&
		 one->dst_label != one->src_label)
		return 1;

	/* Rule 6: Prefer higher precedence */
	if (one->precedence > two->precedence)
		return -1;
	else if (two->precedence > one->precedence)
		return 1;

	/* Rule 7: Prefer native transport */

	/* Rule 8: Prefer smaller scope */
	if (one->dst_scope != two->dst_scope)
		return one->dst_scope - two->dst_scope;

	/* Rule 9: Use longest matching prefix */
	if (one->dst.sa.sa_family == AF_INET) {
		/* Rule 9 is meaningless and counterproductive for Legacy IP
		   unless perhaps we can tell that it's actually on the local
		   subnet. But we don't (yet) have local interface config
		   information, so do nothing here for Legacy IP for now. */
	} else {
		int i;

		for (i = 0; i < 4; i++) {
			guint32 cmp_one, cmp_two;

			cmp_one = one->src.sin6.sin6_addr.s6_addr32[i] ^
				one->dst.sin6.sin6_addr.s6_addr32[i];
			cmp_two = two->src.sin6.sin6_addr.s6_addr32[i] ^
				two->dst.sin6.sin6_addr.s6_addr32[i];

			if (!cmp_two && !cmp_one)
				continue;

			if (cmp_one && !cmp_two)
				return 1;
			if (cmp_two && !cmp_one)
				return -1;

			/* g_bit_storage() is effectively fls() */
			cmp_one = g_bit_storage(ntohl(cmp_one));
			cmp_two = g_bit_storage(ntohl(cmp_two));

			if (cmp_one == cmp_two)
				break;

			return cmp_one - cmp_two;
		}
	}


	/* Rule 10: Otherwise, leave the order unchanged */
	if (one < two)
		return -1;
	else
		return 1;
}

static void rfc3484_sort_results(struct resolv_lookup *lookup)
{
	int i;

	for (i = 0; i < lookup->nr_results; i++) {
		struct sort_result *res = &lookup->results[i];
		find_srcaddr(res);
		res->precedence = match_gai_table(&res->dst.sa, gai_precedences);
		res->dst_label = match_gai_table(&res->dst.sa, gai_labels);
		res->src_label = match_gai_table(&res->src.sa, gai_labels);
		res->dst_scope = addr_scope(&res->dst.sa);
		res->src_scope = addr_scope(&res->src.sa);
	}

	qsort(lookup->results, lookup->nr_results, sizeof(struct sort_result),
	      rfc3484_compare);
}