/**
 * @file client.c  DNS Client
 *
 * Copyright (C) 2010 Creytiv.com
 */
#include <re.h> 
#include <string.h>

#define DEBUG_MODULE "dnsc"
#define DEBUG_LEVEL 5
#include <re_dbg.h>


enum {
	NTX_MAX = 20,
	QUERY_HASH_SIZE = 16,
	TCP_HASH_SIZE = 2,
	CONN_TIMEOUT = 10 * 1000,
	IDLE_TIMEOUT = 30 * 1000,
	SRVC_MAX = 32,
};


struct tcpconn {
	struct le le;
	struct list ql;
	struct tmr tmr;
	struct sa srv;
	struct tcp_conn *conn;
	struct mbuf *mb;
	bool connected;
	uint16_t flen;
	struct dnsc *dnsc; /* parent */
};


struct dns_query {
	struct le le;
	struct le le_tc;
	struct tmr tmr;
	struct mbuf mb;
	struct list rrlv[3];
	char *name;
	const struct sa *srvv;
	const uint32_t *srvc;
	struct tcpconn *tc;
	struct dnsc *dnsc;     /* parent  */
	struct dns_query **qp; /* app ref */
	uint32_t ntx;
	uint16_t id;
	uint16_t type;
	uint16_t dnsclass;
	uint8_t opcode;
	dns_query_h *qh;
	void *arg;
};


struct dnsquery {
	struct dnshdr hdr;
	char *name;
	uint16_t type;
	uint16_t dnsclass;
};


struct dnsc {
	struct dnsc_conf conf;
	struct hash *ht_query;
	struct hash *ht_tcpconn;
	struct udp_sock *us;
	struct sa srvv[SRVC_MAX];
	uint32_t srvc;
};


static const struct dnsc_conf default_conf = {
	QUERY_HASH_SIZE,
	TCP_HASH_SIZE,
	CONN_TIMEOUT,
	IDLE_TIMEOUT,
	false
};


static void tcpconn_close(struct tcpconn *tc, int err);
static int  send_tcp(struct dns_query *q);
static void udp_timeout_handler(void *arg);


static bool rr_unlink_handler(struct le *le, void *arg)
{
	struct dnsrr *rr = le->data;
	(void)arg;

	list_unlink(&rr->le_priv);
	mem_deref(rr);

	return false;
}


static void query_abort(struct dns_query *q)
{
	if (q->tc) {
		list_unlink(&q->le_tc);
		q->tc = mem_deref(q->tc);
	}

	tmr_cancel(&q->tmr);
	hash_unlink(&q->le);
}


static void query_destructor(void *data)
{
	struct dns_query *q = data;
	uint32_t i;

	query_abort(q);
	mbuf_reset(&q->mb);
	mem_deref(q->name);

	for (i=0; i<ARRAY_SIZE(q->rrlv); i++)
		(void)list_apply(&q->rrlv[i], true, rr_unlink_handler, NULL);
}


static void query_handler(struct dns_query *q, int err,
			  const struct dnshdr *hdr, struct list *ansl,
			  struct list *authl, struct list *addl)
{
	/* deref here - before calling handler */
	if (q->qp)
		*q->qp = NULL;

	/* The handler must only be called _once_ */
	if (q->qh) {
		q->qh(err, hdr, ansl, authl, addl, q->arg);
		q->qh = NULL;
	}

	/* in case we have more (than one) q refs */
	query_abort(q);
}


static bool query_close_handler(struct le *le, void *arg)
{
	struct dns_query *q = le->data;
	(void)arg;

	query_handler(q, ECONNABORTED, NULL, NULL, NULL, NULL);
	mem_deref(q);

	return false;
}


static bool query_cmp_handler(struct le *le, void *arg)
{
	struct dns_query *q = le->data;
	struct dnsquery *dq = arg;

	if (q->id != dq->hdr.id)
		return false;

	if (q->opcode != dq->hdr.opcode)
		return false;

	if (q->type != dq->type)
		return false;

	if (q->dnsclass != dq->dnsclass)
		return false;

	if (str_casecmp(q->name, dq->name))
		return false;

	return true;
}


static int reply_recv(struct dnsc *dnsc, struct mbuf *mb)
{
	struct dns_query *q = NULL;
	uint32_t i, j, nv[3];
	struct dnsquery dq;
	int err = 0;

	if (!dnsc || !mb)
		return EINVAL;

	dq.name = NULL;

	if (dns_hdr_decode(mb, &dq.hdr) || !dq.hdr.qr) {
		err = EBADMSG;
		goto out;
	}

	err = dns_dname_decode(mb, &dq.name, 0);
	if (err)
		goto out;

	if (mbuf_get_left(mb) < 4) {
		err = EBADMSG;
		goto out;
	}

	dq.type     = ntohs(mbuf_read_u16(mb));
	dq.dnsclass = ntohs(mbuf_read_u16(mb));

	q = list_ledata(hash_lookup(dnsc->ht_query, hash_joaat_str_ci(dq.name),
				    query_cmp_handler, &dq));
	if (!q) {
		err = ENOENT;
		goto out;
	}

	/* try next server */
	if (dq.hdr.rcode == DNS_RCODE_SRV_FAIL && q->ntx < *q->srvc) {

		if (!q->tc) /* try next UDP server immediately */
			tmr_start(&q->tmr, 0, udp_timeout_handler, q);

		err = EPROTO;
		goto out;
	}

	nv[0] = dq.hdr.nans;
	nv[1] = dq.hdr.nauth;
	nv[2] = dq.hdr.nadd;

	for (i=0; i<ARRAY_SIZE(nv); i++) {

		for (j=0; j<nv[i]; j++) {

			struct dnsrr *rr = NULL;

			err = dns_rr_decode(mb, &rr, 0);
			if (err) {
				query_handler(q, err, NULL, NULL, NULL, NULL);
				mem_deref(q);
				goto out;
			}

			list_append(&q->rrlv[i], &rr->le_priv, rr);
		}
	}

	if (q->type == DNS_QTYPE_AXFR) {

		struct dnsrr *rrh, *rrt;

		rrh = list_ledata(list_head(&q->rrlv[0]));
		rrt = list_ledata(list_tail(&q->rrlv[0]));

		/* Wait for last AXFR reply with terminating SOA record */
		if (dq.hdr.rcode == DNS_RCODE_OK && dq.hdr.nans > 0 &&
		    (!rrt || rrt->type != DNS_TYPE_SOA || rrh == rrt)) {
			DEBUG_INFO("waiting for last SOA record in reply\n");
			goto out;
		}
	}

	query_handler(q, 0, &dq.hdr, &q->rrlv[0], &q->rrlv[1], &q->rrlv[2]);
	mem_deref(q);

 out:
	mem_deref(dq.name);

	return err;
}


static void udp_recv_handler(const struct sa *src, struct mbuf *mb, void *arg)
{
	(void)src;
	(void)reply_recv(arg, mb);
}


static void tcp_recv_handler(struct mbuf *mbrx, void *arg)
{
	struct tcpconn *tc = arg;
	struct mbuf *mb = tc->mb;
	int err = 0;
	size_t n;

 next:
	/* frame length */
	if (!tc->flen) {

		n = min(2 - mb->end, mbuf_get_left(mbrx));

		err = mbuf_write_mem(mb, mbuf_buf(mbrx), n);
		if (err)
			goto error;

		mbrx->pos += n;

		if (mb->end < 2)
			return;

		mb->pos = 0;
		tc->flen = ntohs(mbuf_read_u16(mb));
		mb->pos = 0;
		mb->end = 0;
	}

	/* content */
	n = min(tc->flen - mb->end, mbuf_get_left(mbrx));

	err = mbuf_write_mem(mb, mbuf_buf(mbrx), n);
	if (err)
		goto error;

	mbrx->pos += n;

	if (mb->end < tc->flen)
		return;

	mb->pos = 0;

	err = reply_recv(tc->dnsc, mb);
	if (err)
		goto error;

	/* reset tcp buffer */
	tc->flen = 0;
	mb->pos = 0;
	mb->end = 0;

	/* more data ? */
	if (mbuf_get_left(mbrx) > 0) {
		DEBUG_INFO("%u bytes of tcp data left\n", mbuf_get_left(mbrx));
		goto next;
	}

	return;

 error:
	tcpconn_close(tc, err);
}


static void tcpconn_timeout_handler(void *arg)
{
	struct tcpconn *tc = arg;

	DEBUG_NOTICE("tcp (%J) %s timeout \n", &tc->srv,
		     tc->connected ? "idle" : "connect");

	tcpconn_close(tc, ETIMEDOUT);
}


static void tcp_estab_handler(void *arg)
{
	struct tcpconn *tc = arg;
	struct le *le = list_head(&tc->ql);
	int err = 0;

	DEBUG_INFO("connection (%J) established\n", &tc->srv);

	while (le) {
		struct dns_query *q = le->data;

		le = le->next;

		q->mb.pos = 0;
		err = tcp_send(tc->conn, &q->mb);
		if (err)
			break;

		DEBUG_INFO("tcp send %J\n", &tc->srv);
	}

	if (err) {
		tcpconn_close(tc, err);
		return;
	}

	tmr_start(&tc->tmr, tc->dnsc->conf.idle_timeout,
		  tcpconn_timeout_handler, tc);
	tc->connected = true;
}


static void tcp_close_handler(int err, void *arg)
{
	struct tcpconn *tc = arg;

	DEBUG_NOTICE("connection (%J) closed: %m\n", &tc->srv, err);
	tcpconn_close(tc, err);
}


static bool tcpconn_cmp_handler(struct le *le, void *arg)
{
	const struct tcpconn *tc = le->data;

	/* avoid trying this connection if dead */
	if (!tc->conn)
		return false;

	return sa_cmp(&tc->srv, arg, SA_ALL);
}


static bool tcpconn_fail_handler(struct le *le, void *arg)
{
	struct dns_query *q = le->data;
	int err = *((int *)arg);

	list_unlink(&q->le_tc);
	q->tc = mem_deref(q->tc);

	if (q->ntx >= *q->srvc) {
		DEBUG_WARNING("all servers failed, giving up!!\n");
		err = err ? err : ECONNREFUSED;
		goto out;
	}

	/* try next server(s) */
	err = send_tcp(q);
	if (err) {
		DEBUG_WARNING("all servers failed, giving up\n");
		goto out;
	}

 out:
	if (err) {
		query_handler(q, err, NULL, NULL, NULL, NULL);
		mem_deref(q);
	}

	return false;
}


static void tcpconn_close(struct tcpconn *tc, int err)
{
	if (!tc)
		return;

	/* avoid trying this connection again (e.g. same address) */
	tc->conn = mem_deref(tc->conn);
	(void)list_apply(&tc->ql, true, tcpconn_fail_handler, &err);
	mem_deref(tc);
}


static void tcpconn_destructor(void *arg)
{
	struct tcpconn *tc = arg;

	hash_unlink(&tc->le);
	tmr_cancel(&tc->tmr);
	mem_deref(tc->conn);
	mem_deref(tc->mb);
}


static int tcpconn_alloc(struct tcpconn **tcpp, struct dnsc *dnsc,
			 const struct sa *srv)
{
	struct tcpconn *tc;
	int err = ENOMEM;

	if (!tcpp || !dnsc || !srv)
		return EINVAL;

	tc = mem_zalloc(sizeof(struct tcpconn), tcpconn_destructor);
	if (!tc)
		goto out;

	hash_append(dnsc->ht_tcpconn, sa_hash(srv, SA_ALL), &tc->le, tc);
	tc->srv = *srv;
	tc->dnsc = dnsc;

	tc->mb = mbuf_alloc(1500);
	if (!tc->mb)
		goto out;

	err = tcp_connect(&tc->conn, srv, tcp_estab_handler,
			  tcp_recv_handler, tcp_close_handler, tc);
	if (err)
		goto out;

	tmr_start(&tc->tmr, tc->dnsc->conf.conn_timeout,
		  tcpconn_timeout_handler, tc);
 out:
	if (err)
		mem_deref(tc);
	else
		*tcpp = tc;

	return err;
}


static int send_tcp(struct dns_query *q)
{
	const struct sa *srv;
	struct tcpconn *tc;
	int err = 0;

	if (!q)
		return EINVAL;

	while (q->ntx < *q->srvc) {

		srv = &q->srvv[q->ntx++];

		DEBUG_NOTICE("trying tcp server#%u: %J\n", q->ntx-1, srv);

		tc = list_ledata(hash_lookup(q->dnsc->ht_tcpconn,
					     sa_hash(srv, SA_ALL),
					     tcpconn_cmp_handler,
					     (void *)srv));
		if (!tc) {
			err = tcpconn_alloc(&tc, q->dnsc, srv);
			if (err)
				continue;
		}

		if (tc->connected) {
			q->mb.pos = 0;
			err = tcp_send(tc->conn, &q->mb);
			if (err) {
				tcpconn_close(tc, err);
				continue;
			}

			tmr_start(&tc->tmr, tc->dnsc->conf.idle_timeout,
				  tcpconn_timeout_handler, tc);
			DEBUG_NOTICE("tcp send %J\n", srv);
		}

		list_append(&tc->ql, &q->le_tc, q);
		q->tc = mem_ref(tc);
		break;
	}

	return err;
}


static void tcp_timeout_handler(void *arg)
{
	struct dns_query *q = arg;

	query_handler(q, ETIMEDOUT, NULL, NULL, NULL, NULL);
	mem_deref(q);
}


static int send_udp(struct dns_query *q)
{
	const struct sa *srv;
	int err = ETIMEDOUT;
	uint32_t i;

	if (!q)
		return EINVAL;

	for (i=0; i<*q->srvc; i++) {

		srv = &q->srvv[q->ntx++%*q->srvc];

		DEBUG_INFO("trying udp server#%u: %J\n", i, srv);

		q->mb.pos = 0;
		err = udp_send(q->dnsc->us, srv, &q->mb);
		if (!err)
			break;
	}

	return err;
}


static void udp_timeout_handler(void *arg)
{
	struct dns_query *q = arg;
	int err = ETIMEDOUT;

	if (q->ntx >= NTX_MAX)
		goto out;

	err = send_udp(q);
	if (err)
		goto out;

	tmr_start(&q->tmr, 1000<<MIN(2, q->ntx - 2),
		  udp_timeout_handler, q);

 out:
	if (err) {
		query_handler(q, err, NULL, NULL, NULL, NULL);
		mem_deref(q);
	}
}


static int query(struct dns_query **qp, struct dnsc *dnsc, uint8_t opcode,
		 const char *name, uint16_t type, uint16_t dnsclass,
		 const struct dnsrr *ans_rr, int proto,
		 const struct sa *srvv, const uint32_t *srvc,
		 bool aa, bool rd, dns_query_h *qh, void *arg)
{
	struct dns_query *q = NULL;
	struct dnshdr hdr;
	int err = 0;
	uint32_t i;

	if (!dnsc || !name || !srvv || !srvc || !(*srvc))
		return EINVAL;

	if (DNS_QTYPE_AXFR == type)
		proto = IPPROTO_TCP;

	q = mem_zalloc(sizeof(*q), query_destructor);
	if (!q)
		goto nmerr;

	hash_append(dnsc->ht_query, hash_joaat_str_ci(name), &q->le, q);
	tmr_init(&q->tmr);
	mbuf_init(&q->mb);

	for (i=0; i<ARRAY_SIZE(q->rrlv); i++)
		list_init(&q->rrlv[i]);

	err = str_dup(&q->name, name);
	if (err)
		goto error;

	q->srvv = srvv;
	q->srvc = srvc;
	q->id   = rand_u16();
	q->type = type;
	q->opcode = opcode;
	q->dnsclass = dnsclass;
	q->dnsc = dnsc;

	memset(&hdr, 0, sizeof(hdr));

	hdr.id = q->id;
	hdr.opcode = q->opcode;
	hdr.aa = aa;
	hdr.rd = rd;
	hdr.nq = 1;
	hdr.nans = ans_rr ? 1 : 0;

	if (proto == IPPROTO_TCP)
		q->mb.pos += 2;

	err = dns_hdr_encode(&q->mb, &hdr);
	if (err)
		goto error;

	err = dns_dname_encode(&q->mb, name, NULL, 0, false);
	if (err)
		goto error;

	err |= mbuf_write_u16(&q->mb, htons(type));
	err |= mbuf_write_u16(&q->mb, htons(dnsclass));
	if (err)
		goto error;

	if (ans_rr) {
		err = dns_rr_encode(&q->mb, ans_rr, 0, NULL, 0);
		if (err)
			goto error;
	}

	q->qh  = qh;
	q->arg = arg;

	switch (proto) {

	case IPPROTO_TCP:
		q->mb.pos = 0;
		(void)mbuf_write_u16(&q->mb, htons(q->mb.end - 2));

		err = send_tcp(q);
		if (err)
			goto error;

		tmr_start(&q->tmr, 60 * 1000, tcp_timeout_handler, q);
		break;

	case IPPROTO_UDP:
		err = send_udp(q);
		if (err)
			goto error;

		tmr_start(&q->tmr, 500, udp_timeout_handler, q);
		break;

	default:
		err = EPROTONOSUPPORT;
		goto error;
	}

	if (qp) {
		q->qp = qp;
		*qp = q;
	}

	return 0;

 nmerr:
	err = ENOMEM;
 error:
	mem_deref(q);

	return err;
}


/**
 * Query a DNS name
 *
 * @param qp       Pointer to allocated DNS query
 * @param dnsc     DNS Client
 * @param name     DNS name
 * @param type     DNS Resource Record type
 * @param dnsclass DNS Class
 * @param rd       Recursion Desired (RD) flag
 * @param qh       Query handler
 * @param arg      Handler argument
 *
 * @return 0 if success, otherwise errorcode
 */
int dnsc_query(struct dns_query **qp, struct dnsc *dnsc, const char *name,
	       uint16_t type, uint16_t dnsclass,
	       bool rd, dns_query_h *qh, void *arg)
{
	if (!dnsc)
		return EINVAL;

	return query(qp, dnsc, DNS_OPCODE_QUERY, name, type, dnsclass, NULL,
		     IPPROTO_UDP, dnsc->srvv, &dnsc->srvc, false, rd, qh, arg);
}


/**
 * Query a DNS name SRV record
 *
 * @param qp       Pointer to allocated DNS query
 * @param dnsc     DNS Client
 * @param name     DNS name
 * @param type     DNS Resource Record type
 * @param dnsclass DNS Class
 * @param proto    Protocol
 * @param srvv     DNS Nameservers
 * @param srvc     Number of DNS nameservers
 * @param rd       Recursion Desired (RD) flag
 * @param qh       Query handler
 * @param arg      Handler argument
 *
 * @return 0 if success, otherwise errorcode
 */
int dnsc_query_srv(struct dns_query **qp, struct dnsc *dnsc, const char *name,
		   uint16_t type, uint16_t dnsclass, int proto,
		   const struct sa *srvv, const uint32_t *srvc,
		   bool rd, dns_query_h *qh, void *arg)
{
	return query(qp, dnsc, DNS_OPCODE_QUERY, name, type, dnsclass,
		     NULL, proto, srvv, srvc, false, rd, qh, arg);
}


/**
 * Send a DNS query with NOTIFY opcode
 *
 * @param qp       Pointer to allocated DNS query
 * @param dnsc     DNS Client
 * @param name     DNS name
 * @param type     DNS Resource Record type
 * @param dnsclass DNS Class
 * @param ans_rr   Answer Resource Record
 * @param proto    Protocol
 * @param srvv     DNS Nameservers
 * @param srvc     Number of DNS nameservers
 * @param qh       Query handler
 * @param arg      Handler argument
 *
 * @return 0 if success, otherwise errorcode
 */
int dnsc_notify(struct dns_query **qp, struct dnsc *dnsc, const char *name,
		uint16_t type, uint16_t dnsclass, const struct dnsrr *ans_rr,
		int proto, const struct sa *srvv, const uint32_t *srvc,
		dns_query_h *qh, void *arg)
{
	return query(qp, dnsc, DNS_OPCODE_NOTIFY, name, type, dnsclass,
		     ans_rr, proto, srvv, srvc, true, false, qh, arg);
}


static void dnsc_destructor(void *data)
{
	struct dnsc *dnsc = data;

	(void)hash_apply(dnsc->ht_query, query_close_handler, NULL);
	hash_flush(dnsc->ht_tcpconn);

	mem_deref(dnsc->ht_tcpconn);
	mem_deref(dnsc->ht_query);
	mem_deref(dnsc->us);
}


/**
 * Allocate a DNS Client
 *
 * @param dcpp Pointer to allocated DNS Client
 * @param conf Optional DNS configuration, NULL for default
 * @param srvv DNS servers
 * @param srvc Number of DNS Servers
 *
 * @return 0 if success, otherwise errorcode
 */
int dnsc_alloc(struct dnsc **dcpp, const struct dnsc_conf *conf,
	       const struct sa *srvv, uint32_t srvc)
{
	struct dnsc *dnsc;
	int err;

	if (!dcpp)
		return EINVAL;

	dnsc = mem_zalloc(sizeof(*dnsc), dnsc_destructor);
	if (!dnsc)
		return ENOMEM;

	if (conf)
		dnsc->conf = *conf;
	else
		dnsc->conf = default_conf;

	err = dnsc_srv_set(dnsc, srvv, srvc);
	if (err)
		goto out;

	err = udp_listen(&dnsc->us, NULL, udp_recv_handler, dnsc);
	if (err)
		goto out;

	/* Experimental code:
	 *   Connected UDP sockets will only work if we have one UDP socket
	 *   per UDP server. Connected UDP socket is used to get ICMP
	 *   messages for unreachable DNS Servers.
	 */
	if (dnsc->conf.udp_conn)
		udp_connect(dnsc->us, true);

	err = hash_alloc(&dnsc->ht_query, dnsc->conf.query_hash_size);
	if (err)
		goto out;

	err = hash_alloc(&dnsc->ht_tcpconn, dnsc->conf.tcp_hash_size);
	if (err)
		goto out;

 out:
	if (err)
		mem_deref(dnsc);
	else
		*dcpp = dnsc;

	return err;
}


/**
 * Set the DNS Servers on a DNS Client
 *
 * @param dnsc DNS Client
 * @param srvv DNS Nameservers
 * @param srvc Number of nameservers
 *
 * @return 0 if success, otherwise errorcode
 */
int dnsc_srv_set(struct dnsc *dnsc, const struct sa *srvv, uint32_t srvc)
{
	uint32_t i;

	if (!dnsc)
		return EINVAL;

	dnsc->srvc = min((uint32_t)ARRAY_SIZE(dnsc->srvv), srvc);

	if (srvv) {
		for (i=0; i<dnsc->srvc; i++)
			dnsc->srvv[i] = srvv[i];
	}

	return 0;
}
