/*
 *
 *  Connection Manager
 *
 *  Copyright (C) 2007-2009  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 <string.h>
#include <stdint.h>
#include <arpa/inet.h>
#include <netinet/in.h>

#define CONNMAN_API_SUBJECT_TO_CHANGE
#include <connman/plugin.h>
#include <connman/device.h>
#include <connman/notifier.h>
#include <connman/resolver.h>
#include <connman/log.h>

#include <glib.h>

#define	_DBG_DNSPROXY(fmt, arg...)	DBG(DBG_DNSPROXY, fmt, ## arg)

#if __BYTE_ORDER == __LITTLE_ENDIAN
struct domain_hdr {
	uint16_t id;
	uint8_t rd:1;
	uint8_t tc:1;
	uint8_t aa:1;
	uint8_t opcode:4;
	uint8_t qr:1;
	uint8_t rcode:4;
	uint8_t z:3;
	uint8_t ra:1;
	uint16_t qdcount;
	uint16_t ancount;
	uint16_t nscount;
	uint16_t arcount;
} __attribute__ ((packed));
#elif __BYTE_ORDER == __BIG_ENDIAN
struct domain_hdr {
	uint16_t id;
	uint8_t qr:1;
	uint8_t opcode:4;
	uint8_t aa:1;
	uint8_t tc:1;
	uint8_t rd:1;
	uint8_t ra:1;
	uint8_t z:3;
	uint8_t rcode:4;
	uint16_t qdcount;
	uint16_t ancount;
	uint16_t nscount;
	uint16_t arcount;
} __attribute__ ((packed));
#else
#error "Unknown byte order"
#endif

struct server_data {
	char *interface;
	char *domain;
	char *server;
	GIOChannel *channel;
	guint watch;
	gboolean enabled;
};

struct request_data {
	struct sockaddr_in sin;
	socklen_t len;
	guint16 srcid;
	guint16 dstid;
	guint16 altid;
	guint timeout;
	guint numserv;
	guint numresp;
	gpointer resp;
	gsize resplen;
};

static GSList *server_list = NULL;
static GSList *request_list = NULL;
static guint16 request_id = 0x0000;

static GIOChannel *listener_channel = NULL;
static guint listener_watch = 0;

static struct request_data *find_request(guint16 id)
{
	GSList *list;

	for (list = request_list; list; list = list->next) {
		struct request_data *req = list->data;

		if (req->dstid == id || req->altid == id)
			return req;
	}

	return NULL;
}

static struct server_data *find_server(const char *interface,
					const char *domain, const char *server)
{
	GSList *list;

	_DBG_DNSPROXY("interface %s server %s", interface, server);

	for (list = server_list; list; list = list->next) {
		struct server_data *data = list->data;

		if (data->interface == NULL || data->server == NULL)
			continue;

		if (g_str_equal(data->interface, interface) == TRUE &&
				g_str_equal(data->server, server) == TRUE) {
			if (domain == NULL) {
				if (data->domain == NULL)
					return data;
				continue;
			}

			if (g_str_equal(data->domain, domain) == TRUE)
				return data;
		}
	}

	return NULL;
}

static gboolean server_event(GIOChannel *channel, GIOCondition condition,
							gpointer user_data)
{
	struct server_data *data = user_data;
	struct request_data *req;
	unsigned char buf[768];
	struct domain_hdr *hdr = (void *) &buf;
	struct sockaddr_in sin;
	socklen_t size = sizeof(sin);
	int sk, err, len;

	if (condition & (G_IO_NVAL | G_IO_ERR | G_IO_HUP)) {
		connman_error("Error with server channel");
		data->watch = 0;
		return FALSE;
	}

	sk = g_io_channel_unix_get_fd(channel);

	len = recvfrom(sk, buf, sizeof(buf), 0, (struct sockaddr *) &sin, &size);
	if (len < 12)
		return TRUE;

	_DBG_DNSPROXY("Received %d bytes (id 0x%04x) from %s", 
                len, buf[0] | buf[1] << 8, inet_ntoa(sin.sin_addr));

	req = find_request(buf[0] | buf[1] << 8);
	if (req == NULL)
		return TRUE;

	_DBG_DNSPROXY("id 0x%04x rcode %d", hdr->id, hdr->rcode);

	buf[0] = req->srcid & 0xff;
	buf[1] = req->srcid >> 8;

	req->numresp++;

	if (hdr->rcode == 0 || req->resp == NULL) {
		g_free(req->resp);
		req->resplen = 0;

		req->resp = g_try_malloc(len);
		if (req->resp == NULL)
			return TRUE;

		memcpy(req->resp, buf, len);
		req->resplen = len;
	}

	if (hdr->rcode > 0 && req->numresp < req->numserv)
		return TRUE;

	if (req->timeout > 0)
		g_source_remove(req->timeout);

	request_list = g_slist_remove(request_list, req);

	sk = g_io_channel_unix_get_fd(listener_channel);

	err = sendto(sk, req->resp, req->resplen, 0,
				(struct sockaddr *) &req->sin, req->len);

	g_free(req->resp);
	g_free(req);

	return TRUE;
}

static gboolean parse_server(struct sockaddr_in *sin, const char *server)
{
	char *addr, *port;

	/* NB: must create writable copy to deal with port syntax */
	addr = g_strdup(server);

	memset(sin, 0, sizeof(*sin));
	sin->sin_family = AF_INET;
	port = strchr(addr, ':');
	if (port != NULL) {
		int portid;

		*port++ = '\0';		/* NB: inet_aton fails otherwise */

		errno = 0;
		sin->sin_port = htons((int) strtol(port, NULL, 10));
		if (sin->sin_port == 0 || errno != 0)
			goto bad;
	} else
		sin->sin_port = htons(53);
	if (inet_aton(addr, &sin->sin_addr) != 0) {
		g_free(addr);
		return TRUE;
	}
	/* fall thru... */
bad:
	connman_error("Invalid DNS server address %s", server);
	g_free(addr);
	return FALSE;
}

static struct server_data *create_server(const char *interface,
					const char *domain, const char *server)
{
	struct server_data *data;
	struct sockaddr_in sin;
	int sk;

	_DBG_DNSPROXY("interface %s server %s", interface, server);

	if (!parse_server(&sin, server))
		return NULL;

	sk = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
	if (sk < 0) {
		connman_error("Failed to create server %s socket", server);
		return NULL;
	}
	/* NB: we depend on host routes being installed for each dns server */

	if (connect(sk, (struct sockaddr *) &sin, sizeof(sin)) < 0) {
		connman_error("Failed to connect server %s: %s", server, strerror(errno));
		close(sk);
		return NULL;
	}

	data = g_try_new0(struct server_data, 1);
	if (data == NULL) {
		connman_error("Failed to allocate server %s data", server);
		close(sk);
		return NULL;
	}

	data->channel = g_io_channel_unix_new(sk);
	if (data->channel == NULL) {
		connman_error("Failed to create server %s channel", server);
		close(sk);
		g_free(data);
		return NULL;
	}

	g_io_channel_set_close_on_unref(data->channel, TRUE);

	data->watch = g_io_add_watch(data->channel, G_IO_IN,
							server_event, data);

	data->interface = g_strdup(interface);
	data->domain = g_strdup(domain);
	data->server = g_strdup(server);
	data->enabled = TRUE;		/* NB: we know this is correct */

	return data;
}

static void destroy_server(struct server_data *data)
{
	_DBG_DNSPROXY("interface %s server %s", data->interface, data->server);

	if (data->watch > 0)
		g_source_remove(data->watch);

	g_io_channel_unref(data->channel);

	g_free(data->server);
	g_free(data->domain);
	g_free(data->interface);
	g_free(data);
}

static int dnsproxy_set(const struct connman_resolver_state *entry)
{
	struct server_data *data;
	char **serverp;

	for (serverp = entry->servers; *serverp != NULL; serverp++) {

		DBG(DBG_DNSPROXY | DBG_CONNECTION,
		    "interface %s server %s domain %s",
		    entry->interface, *serverp, entry->domain);

		if (g_str_equal(*serverp, "127.0.0.1") == TRUE)
			return -ENODEV;

		data = create_server(entry->interface, entry->domain, *serverp);
		if (data == NULL)
			return -EIO;

		server_list = g_slist_append(server_list, data);

		_DBG_DNSPROXY("added dns %s for interface %s in domain %s",
			      *serverp, entry->interface, entry->domain);
	}
	return 0;
}

static int dnsproxy_unset(const struct connman_resolver_state *entry)
{
	struct server_data *data;
	GSList *list, *next;

	DBG(DBG_DNSPROXY | DBG_CONNECTION, "interface %s", entry->interface);

	for (list = server_list; list != NULL; list = next) {
		struct server_data *data = list->data;
		next = list->next;
		if (g_str_equal(data->interface, entry->interface) == TRUE) {
			DBG(DBG_DNSPROXY | DBG_CONNECTION,
			    "removing server %s", data->server);
			server_list = g_slist_remove(server_list, data);
			destroy_server(data);
		}
	}

	return 0;
}

static struct connman_resolver dnsproxy_resolver = {
	.name		= "dnsproxy",
	.priority	= CONNMAN_RESOLVER_PRIORITY_HIGH,
	.set		= dnsproxy_set,
	.unset		= dnsproxy_unset,
};

static int parse_request(unsigned char *buf, int len,
					char *name, unsigned int size)
{
	struct domain_hdr *hdr = (void *) buf;
	uint16_t qdcount = ntohs(hdr->qdcount);
	unsigned char *ptr;
	char *last_label = NULL;
	int label_count = 0;
	unsigned int remain, used = 0;

	if (len < 12)
		return -EINVAL;

	_DBG_DNSPROXY("id 0x%04x qr %d opcode %d qdcount %d",
				hdr->id, hdr->qr, hdr->opcode, qdcount);

	if (hdr->qr != 0 || qdcount != 1)
		return -EINVAL;

	memset(name, 0, size);

	ptr = buf + 12;
	remain = len - 12;

	while (remain > 0) {
		uint8_t len = *ptr;

		if (len == 0x00) {
			if (label_count > 0)
				last_label = (char *) (ptr + 1);
			break;
		}

		label_count++;

		if (used + len + 1 > size)
			return -ENOBUFS;

		strncat(name, (char *) (ptr + 1), len);
		strcat(name, ".");

		used += len + 1;

		ptr += len + 1;
		remain -= len + 1;
	}

	_DBG_DNSPROXY("query %s (%d labels)", name, label_count);

	return 0;
}

static void send_response(int sk, unsigned char *buf, int len,
				const struct sockaddr *to, socklen_t tolen)
{
	struct domain_hdr *hdr = (void *) buf;
	int err;

	if (len < 12)
		return;

	_DBG_DNSPROXY("id 0x%04x qr %d opcode %d", hdr->id, hdr->qr, hdr->opcode);

	hdr->qr = 1;
	hdr->rcode = 2;

	hdr->ancount = 0;
	hdr->nscount = 0;
	hdr->arcount = 0;

	err = sendto(sk, buf, len, 0, to, tolen);
}

static int append_query(unsigned char *buf, unsigned int size,
				const char *query, const char *domain)
{
	unsigned char *ptr = buf;
	char *offset;

	_DBG_DNSPROXY("query %s domain %s", query, domain);

	offset = (char *) query;
	while (offset != NULL) {
		char *tmp;

		tmp = strchr(offset, '.');
		if (tmp == NULL) {
			if (strlen(offset) == 0)
				break;
			*ptr = strlen(offset);
			memcpy(ptr + 1, offset, strlen(offset));
			ptr += strlen(offset) + 1;
			break;
		}

		*ptr = tmp - offset;
		memcpy(ptr + 1, offset, tmp - offset);
		ptr += tmp - offset + 1;

		offset = tmp + 1;
	}

	offset = (char *) domain;
	while (offset != NULL) {
		char *tmp;

		tmp = strchr(offset, '.');
		if (tmp == NULL) {
			if (strlen(offset) == 0)
				break;
			*ptr = strlen(offset);
			memcpy(ptr + 1, offset, strlen(offset));
			ptr += strlen(offset) + 1;
			break;
		}

		*ptr = tmp - offset;
		memcpy(ptr + 1, offset, tmp - offset);
		ptr += tmp - offset + 1;

		offset = tmp + 1;
	}

	*ptr++ = 0x00;

	return ptr - buf;
}

static gboolean request_timeout(gpointer user_data)
{
	struct request_data *req = user_data;

	_DBG_DNSPROXY("id 0x%04x", req->srcid);

	request_list = g_slist_remove(request_list, req);

	if (req->resplen > 0 && req->resp != NULL) {
		int sk, err;

		sk = g_io_channel_unix_get_fd(listener_channel);

		err = sendto(sk, req->resp, req->resplen, 0,
				(struct sockaddr *) &req->sin, req->len);
	}

	g_free(req->resp);
	g_free(req);

	return FALSE;
}

static gboolean listener_event(GIOChannel *channel, GIOCondition condition,
							gpointer user_data)
{
	GSList *list;
	unsigned char buf[768];
	char query[512];
	struct request_data *req;
	struct sockaddr_in sin;
	socklen_t size = sizeof(sin);
	int sk, err, len;

	if (condition & (G_IO_NVAL | G_IO_ERR | G_IO_HUP)) {
		connman_error("Error with listener channel");
		listener_watch = 0;
		return FALSE;
	}

	sk = g_io_channel_unix_get_fd(channel);

	memset(&sin, 0, sizeof(sin));
	len = recvfrom(sk, buf, sizeof(buf), 0,
					(struct sockaddr *) &sin, &size);
	if (len < 2)
		return TRUE;

	_DBG_DNSPROXY("Received %d bytes (id 0x%04x)", len, buf[0] | buf[1] << 8);

	err = parse_request(buf, len, query, sizeof(query));
	if (err < 0 || g_slist_length(server_list) == 0) {
		_DBG_DNSPROXY("FAIL: err %d server_list length %d", err,
		    g_slist_length(server_list));
		send_response(sk, buf, len, (struct sockaddr *) &sin, size);
		return TRUE;
	}

	req = g_try_new0(struct request_data, 1);
	if (req == NULL) {
		_DBG_DNSPROXY("no memory for request");
		return TRUE;
	}

	memcpy(&req->sin, &sin, sizeof(sin));
	req->len = size;

	request_id += 2;
	if (request_id == 0x0000 || request_id == 0xffff)
		request_id += 2;

	req->srcid = buf[0] | (buf[1] << 8);
	req->dstid = request_id;
	req->altid = request_id + 1;

	buf[0] = req->dstid & 0xff;
	buf[1] = req->dstid >> 8;

	request_list = g_slist_append(request_list, req);

	req->numserv = 0;
	req->timeout = g_timeout_add_seconds(5, request_timeout, req);

	for (list = server_list; list; list = list->next) {
		struct server_data *data = list->data;

		_DBG_DNSPROXY("server %s domain %s enabled %d",
			data->server, data->domain, data->enabled);

		if (data->enabled == FALSE)
			continue;

		sk = g_io_channel_unix_get_fd(data->channel);

		err = send(sk, buf, len, 0);
		if (err < 0)
			_DBG_DNSPROXY("failed to send to DNS server %s: %s",
				      data->server, strerror(errno));

		req->numserv++;

		if (data->domain != NULL) {
			unsigned char alt[1024];
			struct domain_hdr *hdr = (void *) &alt;
			int altlen;

			alt[0] = req->altid & 0xff;
			alt[1] = req->altid >> 8;

			memcpy(alt + 2, buf + 2, 10);
			hdr->qdcount = htons(1);

			altlen = append_query(alt + 12, sizeof(alt) - 12,
							query, data->domain);
			if (altlen < 0)
				continue;

			alt[altlen + 12] = 0x00;
			alt[altlen + 13] = 0x01;
			alt[altlen + 14] = 0x00;
			alt[altlen + 15] = 0x01;

			err = send(sk, alt, altlen + 12 + 4, 0);
			if (err < 0)
				_DBG_DNSPROXY("failed sending to DNS server %s: %s",
				      data->server, strerror(errno));

			req->numserv++;
		}
	}

	return TRUE;
}

static int create_listener(void)
{
	static char *localservers[] = {"127.0.0.1", NULL};
	const char *ifname = "lo";
	struct sockaddr_in sin;
	int sk;

	_DBG_DNSPROXY("");

	sk = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
	if (sk < 0) {
		connman_error("Failed to create listener socket");
		return -EIO;
	}

	//setsockopt(sk, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt));
	//setsockopt(sk, SOL_IP, IP_PKTINFO, &opt, sizeof(opt));

	if (setsockopt(sk, SOL_SOCKET, SO_BINDTODEVICE,
					ifname, strlen(ifname) + 1) < 0) {
		connman_error("Failed to bind listener interface");
		close(sk);
		return -EIO;
	}

	memset(&sin, 0, sizeof(sin));
	sin.sin_family = AF_INET;
	sin.sin_port = htons(53);
	sin.sin_addr.s_addr = inet_addr("127.0.0.1");
	//sin.sin_addr.s_addr = INADDR_ANY;

	if (bind(sk, (struct sockaddr *) &sin, sizeof(sin)) < 0) {
		connman_error("Failed to bind listener socket");
		close(sk);
		return -EIO;
	}

	listener_channel = g_io_channel_unix_new(sk);
	if (listener_channel == NULL) {
		connman_error("Failed to create listener channel");
		close(sk);
		return -EIO;
	}

	g_io_channel_set_close_on_unref(listener_channel, TRUE);

	listener_watch = g_io_add_watch(listener_channel, G_IO_IN,
							listener_event, NULL);

	connman_resolver_set("lo", NULL, NULL, localservers);

	return 0;
}

static void destroy_listener(void)
{
	GSList *list;

	_DBG_DNSPROXY("");

	connman_resolver_unset("lo");

	if (listener_watch > 0)
		g_source_remove(listener_watch);

	for (list = request_list; list; list = list->next) {
		struct request_data *req = list->data;

		_DBG_DNSPROXY("Dropping request (id 0x%04x -> 0x%04x)",
						req->srcid, req->dstid);

		g_free(req->resp);
		g_free(req);
		list->data = NULL;
	}

	g_slist_free(request_list);
	request_list = NULL;

	g_io_channel_unref(listener_channel);
}

static void dnsproxy_offline_mode(connman_bool_t isoffline)
{
	GSList *list;

	DBG(DBG_DNSPROXY | DBG_CONNECTION, "offline %d", isoffline);

	for (list = server_list; list; list = list->next) {
		struct server_data *data = list->data;

		data->enabled = !isoffline;

		DBG(DBG_DNSPROXY | DBG_CONNECTION,
		    "server %s on %s (%senabled)",
		    data->server, data->interface,
		    data->enabled ? "" : "!");
	}
}

static void dnsproxy_default_changed(struct connman_service *service)
{
	const char *interface;
	GSList *list;

	DBG(DBG_DNSPROXY | DBG_CONNECTION, "service %p", service);

	if (service == NULL) {
		/*
		 * There is no default; this can happen when no
		 * devices are operational (e.g. wired unplugged
		 * and wireless down).  Be paranoid here: there
		 * should be no servers as everything should be
		 * torn down; this is just in case.
		 */
		dnsproxy_offline_mode(TRUE);
		return;
	}

	interface = connman_service_get_interface(service);
	if (interface == NULL) {
		connman_error("%s: no interface for service %p", __func__,
		    service);
		return;
	}

	for (list = server_list; list; list = list->next) {
		struct server_data *data = list->data;

		data->enabled = (g_strcmp0(data->interface, interface) == 0);

		DBG(DBG_DNSPROXY | DBG_CONNECTION,
		    "server %s on %s device %s (%senabled)",
		    data->server, data->interface, interface,
		    data->enabled ? "" : "!");
	}
}

static struct connman_notifier dnsproxy_notifier = {
	.name		= "dnsproxy",
	.priority	= CONNMAN_NOTIFIER_PRIORITY_DEFAULT,
	.offline_mode	= dnsproxy_offline_mode,
	.default_changed= dnsproxy_default_changed,
};

static int dnsproxy_init(void)
{
	int err;

	err = create_listener();
	if (err < 0)
		return err;

	err = connman_resolver_register(&dnsproxy_resolver);
	if (err < 0) {
		destroy_listener();
		return err;
	}

	return connman_notifier_register(&dnsproxy_notifier);
}

static void dnsproxy_exit(void)
{
	destroy_listener();

	connman_resolver_unregister(&dnsproxy_resolver);

	connman_notifier_unregister(&dnsproxy_notifier);
}

CONNMAN_PLUGIN_DEFINE(dnsproxy, "DNS proxy resolver plugin", VERSION,
		 CONNMAN_PLUGIN_PRIORITY_DEFAULT, dnsproxy_init, dnsproxy_exit)