X-Git-Url: http://git.meshlink.io/?a=blobdiff_plain;f=utcp.c;h=ce056904169c6923baa95a0e5435626e5da75fd5;hb=f268b8518415a5cf896e1b3518c2a0141d1364d4;hp=74dfc015db89db1fd8e25cd891a1d16498110643;hpb=5737643dd1b17348e50e8eaafa58757be7827f37;p=utcp

diff --git a/utcp.c b/utcp.c
index 74dfc01..ce05690 100644
--- a/utcp.c
+++ b/utcp.c
@@ -103,6 +103,19 @@ static void set_state(struct utcp_connection *c, enum state state) {
 	debug("%p new state: %s\n", c->utcp, strstate[state]);
 }
 
+static bool fin_wanted(struct utcp_connection *c, uint32_t seq) {
+	if(seq != c->snd.last)
+		return false;
+	switch(c->state) {
+	case FIN_WAIT_1:
+	case CLOSING:
+	case LAST_ACK:
+		return true;
+	default:
+		return false;
+	}
+}
+
 static inline void list_connections(struct utcp *utcp) {
 	debug("%p has %d connections:\n", utcp, utcp->nconnections);
 	for(int i = 0; i < utcp->nconnections; i++)
@@ -113,13 +126,84 @@ static int32_t seqdiff(uint32_t a, uint32_t b) {
 	return a - b;
 }
 
+// Buffer functions
+// TODO: convert to ringbuffers to avoid memmove() operations.
+
+// Store data into the buffer
+static ssize_t buffer_put(struct buffer *buf, const void *data, size_t len) {
+	if(buf->maxsize <= buf->used)
+		return 0;
+	if(len > buf->maxsize - buf->used)
+		len = buf->maxsize - buf->used;
+	if(len > buf->size - buf->used) {
+		size_t newsize = buf->size;
+		do {
+			newsize *= 2;
+		} while(newsize < buf->used + len);
+		if(newsize > buf->maxsize)
+			newsize = buf->maxsize;
+		char *newdata = realloc(buf->data, newsize);
+		if(!newdata)
+			return -1;
+		buf->data = newdata;
+		buf->size = newsize;
+	}
+	memcpy(buf->data + buf->used, data, len);
+	buf->used += len;
+	return len;
+}
+
+// Get data from the buffer. data can be NULL.
+static ssize_t buffer_get(struct buffer *buf, void *data, size_t len) {
+	if(len > buf->used)
+		len = buf->used;
+	if(data)
+		memcpy(data, buf->data, len);
+	if(len < buf->used)
+		memmove(buf->data, buf->data + len, buf->used - len);
+	buf->used -= len;
+	return len;
+}
+
+// Copy data from the buffer without removing it.
+static ssize_t buffer_copy(struct buffer *buf, void *data, size_t offset, size_t len) {
+	if(offset >= buf->used)
+		return 0;
+	if(offset + len > buf->used)
+		len = buf->used - offset;
+	memcpy(data, buf->data + offset, len);
+	return len;
+}
+
+static bool buffer_init(struct buffer *buf, uint32_t len, uint32_t maxlen) {
+	memset(buf, 0, sizeof *buf);
+	buf->data = malloc(len);
+	if(!len)
+		return false;
+	buf->size = len;
+	buf->maxsize = maxlen;
+	return true;
+}
+
+static void buffer_exit(struct buffer *buf) {
+	free(buf->data);
+	memset(buf, 0, sizeof *buf);
+}
+
+static uint32_t buffer_free(const struct buffer *buf) {
+	return buf->maxsize - buf->used;
+}
+
 // Connections are stored in a sorted list.
 // This gives O(log(N)) lookup time, O(N log(N)) insertion time and O(N) deletion time.
 
 static int compare(const void *va, const void *vb) {
+	assert(va && vb);
+
 	const struct utcp_connection *a = *(struct utcp_connection **)va;
 	const struct utcp_connection *b = *(struct utcp_connection **)vb;
 
+	assert(a && b);
 	assert(a->src && b->src);
 
 	int c = (int)a->src - (int)b->src;
@@ -147,10 +231,10 @@ static void free_connection(struct utcp_connection *c) {
 	assert(cp);
 
 	int i = cp - utcp->connections;
-	memmove(cp + i, cp + i + 1, (utcp->nconnections - i - 1) * sizeof *cp);
+	memmove(cp, cp + 1, (utcp->nconnections - i - 1) * sizeof *cp);
 	utcp->nconnections--;
 
-	free(c->sndbuf);
+	buffer_exit(&c->sndbuf);
 	free(c);
 }
 
@@ -189,10 +273,7 @@ static struct utcp_connection *allocate_connection(struct utcp *utcp, uint16_t s
 	if(!c)
 		return NULL;
 
-	c->sndbufsize = DEFAULT_SNDBUFSIZE;
-	c->maxsndbufsize = DEFAULT_MAXSNDBUFSIZE;
-	c->sndbuf = malloc(c->sndbufsize);
-	if(!c->sndbuf) {
+	if(!buffer_init(&c->sndbuf, DEFAULT_SNDBUFSIZE, DEFAULT_MAXSNDBUFSIZE)) {
 		free(c);
 		return NULL;
 	}
@@ -201,7 +282,12 @@ static struct utcp_connection *allocate_connection(struct utcp *utcp, uint16_t s
 
 	c->src = src;
 	c->dst = dst;
+#ifdef UTCP_DEBUG
+#warning debugging
+	c->snd.iss = 0;
+#else
 	c->snd.iss = rand();
+#endif
 	c->snd.una = c->snd.iss;
 	c->snd.nxt = c->snd.iss + 1;
 	c->rcv.wnd = utcp->mtu;
@@ -261,7 +347,6 @@ void utcp_accept(struct utcp_connection *c, utcp_recv_t recv, void *priv) {
 static void ack(struct utcp_connection *c, bool sendatleastone) {
 	int32_t left = seqdiff(c->snd.last, c->snd.nxt);
 	int32_t cwndleft = c->snd.cwnd - seqdiff(c->snd.nxt, c->snd.una);
-	char *data = c->sndbuf + seqdiff(c->snd.nxt, c->snd.una);
 
 	assert(left >= 0);
 
@@ -280,7 +365,7 @@ static void ack(struct utcp_connection *c, bool sendatleastone) {
 	} *pkt;
 
 	pkt = malloc(sizeof pkt->hdr + c->utcp->mtu);
-	if(!pkt->data)
+	if(!pkt)
 		return;
 
 	pkt->hdr.src = c->src;
@@ -294,22 +379,14 @@ static void ack(struct utcp_connection *c, bool sendatleastone) {
 		uint32_t seglen = left > c->utcp->mtu ? c->utcp->mtu : left;
 		pkt->hdr.seq = c->snd.nxt;
 
-		memcpy(pkt->data, data, seglen);
+		buffer_copy(&c->sndbuf, pkt->data, seqdiff(c->snd.nxt, c->snd.una), seglen);
 
 		c->snd.nxt += seglen;
-		data += seglen;
 		left -= seglen;
 
-		if(c->state != ESTABLISHED && !left && seglen) {
-			switch(c->state) {
-			case FIN_WAIT_1:
-			case CLOSING:
-				seglen--;
-				pkt->hdr.ctl |= FIN;
-				break;
-			default:
-				break;
-			}
+		if(seglen && fin_wanted(c, c->snd.nxt)) {
+			seglen--;
+			pkt->hdr.ctl |= FIN;
 		}
 
 		print_packet(c->utcp, "send", pkt, sizeof pkt->hdr + seglen);
@@ -357,44 +434,13 @@ ssize_t utcp_send(struct utcp_connection *c, const void *data, size_t len) {
 		return -1;
 	}
 
-	uint32_t bufused = seqdiff(c->snd.nxt, c->snd.una);
-
-	/* Check our send buffer.
-	 * - If it's big enough, just put the data in there.
-	 * - If not, decide whether to enlarge if possible.
-	 * - Cap len so it doesn't overflow our buffer.
-	 */
-
-	if(len > c->sndbufsize - bufused && c->sndbufsize < c->maxsndbufsize) {
-		uint32_t newbufsize;
-		if(c->sndbufsize > c->maxsndbufsize / 2)
-			newbufsize = c->maxsndbufsize;
-		else
-			newbufsize = c->sndbufsize * 2;
-		if(bufused + len > newbufsize) {
-			if(bufused + len > c->maxsndbufsize)
-				newbufsize = c->maxsndbufsize;
-			else
-				newbufsize = bufused + len;
-		}
-		char *newbuf = realloc(c->sndbuf, newbufsize);
-		if(newbuf) {
-			c->sndbuf = newbuf;
-			c->sndbufsize = newbufsize;
-		}
-	}
-
-	if(len > c->sndbufsize - bufused)
-		len = c->sndbufsize - bufused;
-
-	if(!len) {
-		errno == EWOULDBLOCK;
+	len = buffer_put(&c->sndbuf, data, len);
+	if(len <= 0) {
+		errno = EWOULDBLOCK;
 		return 0;
 	}
 
-	memcpy(c->sndbuf + bufused, data, len);
 	c->snd.last += len;
-
 	ack(c, false);
 	return len;
 }
@@ -405,6 +451,82 @@ static void swap_ports(struct hdr *hdr) {
 	hdr->dst = tmp;
 }
 
+static void retransmit(struct utcp_connection *c) {
+	if(c->state == CLOSED || c->snd.nxt == c->snd.una)
+		return;
+
+	struct utcp *utcp = c->utcp;
+
+	struct {
+		struct hdr hdr;
+		char data[];
+	} *pkt;
+
+	pkt = malloc(sizeof pkt->hdr + c->utcp->mtu);
+	if(!pkt)
+		return;
+
+	pkt->hdr.src = c->src;
+	pkt->hdr.dst = c->dst;
+
+	switch(c->state) {
+		case SYN_SENT:
+			// Send our SYN again
+			pkt->hdr.seq = c->snd.iss;
+			pkt->hdr.ack = 0;
+			pkt->hdr.wnd = c->rcv.wnd;
+			pkt->hdr.ctl = SYN;
+			print_packet(c->utcp, "rtrx", pkt, sizeof pkt->hdr);
+			utcp->send(utcp, pkt, sizeof pkt->hdr);
+			break;
+
+		case SYN_RECEIVED:
+			// Send SYNACK again
+			pkt->hdr.seq = c->snd.nxt;
+			pkt->hdr.ack = c->rcv.nxt;
+			pkt->hdr.ctl = SYN | ACK;
+			print_packet(c->utcp, "rtrx", pkt, sizeof pkt->hdr);
+			utcp->send(utcp, pkt, sizeof pkt->hdr);
+			break;
+
+		case ESTABLISHED:
+		case FIN_WAIT_1:
+		case CLOSE_WAIT:
+		case CLOSING:
+		case LAST_ACK:
+			// Send unacked data again.
+			pkt->hdr.seq = c->snd.una;
+			pkt->hdr.ack = c->rcv.nxt;
+			pkt->hdr.ctl = ACK;
+			uint32_t len = seqdiff(c->snd.last, c->snd.una);
+			if(len > utcp->mtu)
+				len = utcp->mtu;
+			if(fin_wanted(c, c->snd.una + len)) {
+				len--;
+				pkt->hdr.ctl |= FIN;
+			}
+			c->snd.nxt = c->snd.una + len;
+			buffer_copy(&c->sndbuf, pkt->data, 0, len);
+			print_packet(c->utcp, "rtrx", pkt, sizeof pkt->hdr + len);
+			utcp->send(utcp, pkt, sizeof pkt->hdr + len);
+			break;
+
+		case CLOSED:
+		case LISTEN:
+		case TIME_WAIT:
+		case FIN_WAIT_2:
+			// We shouldn't need to retransmit anything in this state.
+#ifdef UTCP_DEBUG
+			abort();
+#endif
+			timerclear(&c->rtrx_timeout);
+			break;
+	}
+
+	free(pkt);
+}
+
+
 ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 	if(!utcp) {
 		errno = EFAULT;
@@ -502,6 +624,8 @@ ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 
 	// It is for an existing connection.
 
+	uint32_t prevrcvnxt = c->rcv.nxt;
+
 	// 1. Drop invalid packets.
 
 	// 1a. Drop packets that should not happen in our current state.
@@ -518,7 +642,10 @@ ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 	case TIME_WAIT:
 		break;
 	default:
+#ifdef UTCP_DEBUG
 		abort();
+#endif
+		break;
 	}
 
 	// 1b. Drop packets with a sequence number not in our receive window.
@@ -550,12 +677,13 @@ ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 #endif
 
 	if(!acceptable) {
-		debug("Packet not acceptable, %u  <= %u + %zu < %u\n", c->rcv.nxt, hdr.seq, len, c->rcv.nxt + c->rcv.wnd);
+		debug("Packet not acceptable, %u <= %u + %zu < %u\n", c->rcv.nxt, hdr.seq, len, c->rcv.nxt + c->rcv.wnd);
 		// Ignore unacceptable RST packets.
 		if(hdr.ctl & RST)
 			return 0;
 		// Otherwise, send an ACK back in the hope things improve.
-		goto ack;
+		ack(c, true);
+		return 0;
 	}
 
 	c->snd.wnd = hdr.wnd; // TODO: move below
@@ -617,14 +745,17 @@ ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 			set_state(c, CLOSED);
 			return 0;
 		default:
+#ifdef UTCP_DEBUG
 			abort();
+#endif
+			break;
 		}
 	}
 
 	// 3. Advance snd.una
 
 	uint32_t advanced = seqdiff(hdr.ack, c->snd.una);
-	uint32_t prevrcvnxt = c->rcv.nxt;
+	prevrcvnxt = c->rcv.nxt;
 
 	if(advanced) {
 		int32_t data_acked = advanced;
@@ -644,18 +775,15 @@ ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 		int32_t bufused = seqdiff(c->snd.last, c->snd.una);
 		assert(data_acked <= bufused);
 
-		// Make room in the send buffer.
-		// TODO: try to avoid memmoving too much. Circular buffer?
-		uint32_t left = bufused - data_acked;
-		if(data_acked && left)
-			memmove(c->sndbuf, c->sndbuf + data_acked, left);
+		if(data_acked)
+			buffer_get(&c->sndbuf, NULL, data_acked);
 
 		c->snd.una = hdr.ack;
 
 		c->dupack = 0;
 		c->snd.cwnd += utcp->mtu;
-		if(c->snd.cwnd > c->maxsndbufsize)
-			c->snd.cwnd = c->maxsndbufsize;
+		if(c->snd.cwnd > c->sndbuf.maxsize)
+			c->snd.cwnd = c->sndbuf.maxsize;
 
 		// Check if we have sent a FIN that is now ACKed.
 		switch(c->state) {
@@ -676,10 +804,13 @@ ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 	} else {
 		if(!len) {
 			c->dupack++;
-			if(c->dupack >= 3) {
+			if(c->dupack == 3) {
 				debug("Triplicate ACK\n");
 				//TODO: Resend one packet and go to fast recovery mode. See RFC 6582.
-				//abort();
+				//We do a very simple variant here; reset the nxt pointer to the last acknowledged packet from the peer.
+				//This will cause us to start retransmitting, but at the same speed as the incoming ACKs arrive,
+				//thus preventing a drop in speed.
+				c->snd.nxt = c->snd.una;
 			}
 		}
 	}
@@ -716,7 +847,10 @@ ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 			// Ehm, no. We should never receive a second SYN.
 			goto reset;
 		default:
+#ifdef UTCP_DEBUG
 			abort();
+#endif
+			return 0;
 		}
 
 		// SYN counts as one sequence number
@@ -746,7 +880,10 @@ ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 		case SYN_SENT:
 		case SYN_RECEIVED:
 			// This should never happen.
+#ifdef UTCP_DEBUG
 			abort();
+#endif
+			return 0;
 		case ESTABLISHED:
 		case FIN_WAIT_1:
 		case FIN_WAIT_2:
@@ -758,7 +895,10 @@ ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 			// Ehm no, We should never receive more data after a FIN.
 			goto reset;
 		default:
+#ifdef UTCP_DEBUG
 			abort();
+#endif
+			return 0;
 		}
 
 		ssize_t rxd;
@@ -767,7 +907,6 @@ ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 			rxd = c->recv(c, data, len);
 			if(rxd != len) {
 				// TODO: once we have a receive buffer, handle the application not accepting all data.
-				fprintf(stderr, "c->recv(%p, %p, %zu) returned %zd\n", c, data, len, rxd);
 				abort();
 			}
 			if(rxd < 0)
@@ -788,7 +927,10 @@ ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 		case SYN_SENT:
 		case SYN_RECEIVED:
 			// This should never happen.
+#ifdef UTCP_DEBUG
 			abort();
+#endif
+			break;
 		case ESTABLISHED:
 			set_state(c, CLOSE_WAIT);
 			break;
@@ -807,7 +949,10 @@ ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 			// Ehm, no. We should never receive a second FIN.
 			goto reset;
 		default:
+#ifdef UTCP_DEBUG
 			abort();
+#endif
+			break;
 		}
 
 		// FIN counts as one sequence number
@@ -849,7 +994,7 @@ reset:
 }
 
 int utcp_shutdown(struct utcp_connection *c, int dir) {
-	debug("%p shutdown %d\n", c ? c->utcp : NULL, dir);
+	debug("%p shutdown %d at %u\n", c ? c->utcp : NULL, dir, c ? c->snd.last : 0);
 	if(!c) {
 		errno = EFAULT;
 		return -1;
@@ -861,12 +1006,26 @@ int utcp_shutdown(struct utcp_connection *c, int dir) {
 		return -1;
 	}
 
-	// TODO: handle dir
+	if(!(dir == UTCP_SHUT_RD || dir == UTCP_SHUT_WR || dir == UTCP_SHUT_RDWR)) {
+		errno = EINVAL;
+		return -1;
+	}
+
+	// TCP does not have a provision for stopping incoming packets.
+	// The best we can do is to just ignore them.
+	if(dir == UTCP_SHUT_RD || dir == UTCP_SHUT_RDWR)
+		c->recv = NULL;
+
+	// The rest of the code deals with shutting down writes.
+	if(dir == UTCP_SHUT_RD)
+		return 0;
 
 	switch(c->state) {
 	case CLOSED:
-		return 0;
 	case LISTEN:
+		errno = ENOTCONN;
+		return -1;
+
 	case SYN_SENT:
 		set_state(c, CLOSED);
 		return 0;
@@ -897,6 +1056,8 @@ int utcp_shutdown(struct utcp_connection *c, int dir) {
 int utcp_close(struct utcp_connection *c) {
 	if(utcp_shutdown(c, SHUT_RDWR))
 		return -1;
+	c->recv = NULL;
+	c->poll = NULL;
 	c->reapable = true;
 	return 0;
 }
@@ -913,6 +1074,8 @@ int utcp_abort(struct utcp_connection *c) {
 		return -1;
 	}
 
+	c->recv = NULL;
+	c->poll = NULL;
 	c->reapable = true;
 
 	switch(c->state) {
@@ -951,80 +1114,13 @@ int utcp_abort(struct utcp_connection *c) {
 	return 0;
 }
 
-static void retransmit(struct utcp_connection *c) {
-	if(c->state == CLOSED || c->snd.nxt == c->snd.una)
-		return;
-
-	struct utcp *utcp = c->utcp;
-
-	struct {
-		struct hdr hdr;
-		char *data;
-	} pkt;
-
-	pkt.data = malloc(c->utcp->mtu);
-	if(!pkt.data)
-		return;
-
-	pkt.hdr.src = c->src;
-	pkt.hdr.dst = c->dst;
-
-	switch(c->state) {
-		case LISTEN:
-			// TODO: this should not happen
-			break;
-
-		case SYN_SENT:
-			pkt.hdr.seq = c->snd.iss;
-			pkt.hdr.ack = 0;
-			pkt.hdr.wnd = c->rcv.wnd;
-			pkt.hdr.ctl = SYN;
-			print_packet(c->utcp, "rtrx", &pkt, sizeof pkt.hdr);
-			utcp->send(utcp, &pkt, sizeof pkt.hdr);
-			break;
-
-		case SYN_RECEIVED:
-			pkt.hdr.seq = c->snd.nxt;
-			pkt.hdr.ack = c->rcv.nxt;
-			pkt.hdr.ctl = SYN | ACK;
-			print_packet(c->utcp, "rtrx", &pkt, sizeof pkt.hdr);
-			utcp->send(utcp, &pkt, sizeof pkt.hdr);
-			break;
-
-		case ESTABLISHED:
-		case FIN_WAIT_1:
-			pkt.hdr.seq = c->snd.una;
-			pkt.hdr.ack = c->rcv.nxt;
-			pkt.hdr.ctl = ACK;
-			uint32_t len = seqdiff(c->snd.nxt, c->snd.una);
-			if(c->state == FIN_WAIT_1)
-				len--;
-			if(len > utcp->mtu)
-				len = utcp->mtu;
-			else {
-				if(c->state == FIN_WAIT_1)
-					pkt.hdr.ctl |= FIN;
-			}
-			memcpy(pkt.data, c->sndbuf, len);
-			print_packet(c->utcp, "rtrx", &pkt, sizeof pkt.hdr + len);
-			utcp->send(utcp, &pkt, sizeof pkt.hdr + len);
-			break;
-
-		default:
-			// TODO: implement
-			abort();
-	}
-
-	free(pkt.data);
-}
-
 /* Handle timeouts.
  * One call to this function will loop through all connections,
  * checking if something needs to be resent or not.
  * The return value is the time to the next timeout in milliseconds,
  * or maybe a negative value if the timeout is infinite.
  */
-int utcp_timeout(struct utcp *utcp) {
+struct timeval utcp_timeout(struct utcp *utcp) {
 	struct timeval now;
 	gettimeofday(&now, NULL);
 	struct timeval next = {now.tv_sec + 3600, now.tv_usec};
@@ -1055,8 +1151,8 @@ int utcp_timeout(struct utcp *utcp) {
 			retransmit(c);
 		}
 
-		if(c->poll && c->sndbufsize < c->maxsndbufsize / 2)
-			c->poll(c, c->maxsndbufsize - c->sndbufsize);
+		if(c->poll && buffer_free(&c->sndbuf) && (c->state == ESTABLISHED || c->state == CLOSE_WAIT))
+			c->poll(c, buffer_free(&c->sndbuf));
 
 		if(timerisset(&c->conn_timeout) && timercmp(&c->conn_timeout, &next, <))
 			next = c->conn_timeout;
@@ -1074,9 +1170,18 @@ int utcp_timeout(struct utcp *utcp) {
 
 	struct timeval diff;
 	timersub(&next, &now, &diff);
-	if(diff.tv_sec < 0)
-		return 0;
-	return diff.tv_sec * 1000 + diff.tv_usec / 1000;
+	return diff;
+}
+
+bool utcp_is_active(struct utcp *utcp) {
+	if(!utcp)
+		return false;
+
+	for(int i = 0; i < utcp->nconnections; i++)
+		if(utcp->connections[i]->state != CLOSED && utcp->connections[i]->state != TIME_WAIT)
+			return true;
+
+	return false;
 }
 
 struct utcp *utcp_init(utcp_accept_t accept, utcp_pre_accept_t pre_accept, utcp_send_t send, void *priv) {
@@ -1105,7 +1210,7 @@ void utcp_exit(struct utcp *utcp) {
 	for(int i = 0; i < utcp->nconnections; i++) {
 		if(!utcp->connections[i]->reapable)
 			debug("Warning, freeing unclosed connection %p\n", utcp->connections[i]);
-		free(utcp->connections[i]->sndbuf);
+		buffer_exit(&utcp->connections[i]->sndbuf);
 		free(utcp->connections[i]);
 	}
 	free(utcp->connections);
@@ -1113,60 +1218,78 @@ void utcp_exit(struct utcp *utcp) {
 }
 
 uint16_t utcp_get_mtu(struct utcp *utcp) {
-	return utcp->mtu;
+	return utcp ? utcp->mtu : 0;
 }
 
 void utcp_set_mtu(struct utcp *utcp, uint16_t mtu) {
 	// TODO: handle overhead of the header
-	utcp->mtu = mtu;
+	if(utcp)
+		utcp->mtu = mtu;
 }
 
 int utcp_get_user_timeout(struct utcp *u) {
-	return u->timeout;
+	return u ? u->timeout : 0;
 }
 
 void utcp_set_user_timeout(struct utcp *u, int timeout) {
-	u->timeout = timeout;
+	if(u)
+		u->timeout = timeout;
 }
 
 size_t utcp_get_sndbuf(struct utcp_connection *c) {
-	return c->maxsndbufsize;
+	return c ? c->sndbuf.maxsize : 0;
 }
 
 size_t utcp_get_sndbuf_free(struct utcp_connection *c) {
-	return c->maxsndbufsize - c->sndbufsize;
+	if(c && (c->state == ESTABLISHED || c->state == CLOSE_WAIT))
+		return buffer_free(&c->sndbuf);
+	else
+		return 0;
 }
 
 void utcp_set_sndbuf(struct utcp_connection *c, size_t size) {
-	c->maxsndbufsize = size;
-	if(c->maxsndbufsize != size)
-		c->maxsndbufsize = -1;
+	if(!c)
+		return;
+	c->sndbuf.maxsize = size;
+	if(c->sndbuf.maxsize != size)
+		c->sndbuf.maxsize = -1;
 }
 
 bool utcp_get_nodelay(struct utcp_connection *c) {
-	return c->nodelay;
+	return c ? c->nodelay : false;
 }
 
 void utcp_set_nodelay(struct utcp_connection *c, bool nodelay) {
-	c->nodelay = nodelay;
+	if(c)
+		c->nodelay = nodelay;
 }
 
 bool utcp_get_keepalive(struct utcp_connection *c) {
-	return c->keepalive;
+	return c ? c->keepalive : false;
 }
 
 void utcp_set_keepalive(struct utcp_connection *c, bool keepalive) {
-	c->keepalive = keepalive;
+	if(c)
+		c->keepalive = keepalive;
 }
 
 size_t utcp_get_outq(struct utcp_connection *c) {
-	return seqdiff(c->snd.nxt, c->snd.una);
+	return c ? seqdiff(c->snd.nxt, c->snd.una) : 0;
 }
 
 void utcp_set_recv_cb(struct utcp_connection *c, utcp_recv_t recv) {
-	c->recv = recv;
+	if(c)
+		c->recv = recv;
 }
 
 void utcp_set_poll_cb(struct utcp_connection *c, utcp_poll_t poll) {
-	c->poll = poll;
+	if(c)
+		c->poll = poll;
+}
+
+void utcp_set_accept_cb(struct utcp *utcp, utcp_accept_t accept, utcp_pre_accept_t pre_accept) {
+	if(utcp) {
+		utcp->accept = accept;
+		utcp->pre_accept = pre_accept;
+	}
 }