X-Git-Url: http://git.meshlink.io/?p=utcp;a=blobdiff_plain;f=utcp.c;h=d09b9e7d526e80c4ce39590c19c718904fe32590;hp=c93d4bb35bc476717fa9233b7c7a43e73d546a77;hb=f1035e971bb894203bdfba6cafbaf0bb30f197eb;hpb=09ee8ab4685761cf33ac4cbf37e171917565e000

diff --git a/utcp.c b/utcp.c
index c93d4bb..d09b9e7 100644
--- a/utcp.c
+++ b/utcp.c
@@ -1,6 +1,6 @@
 /*
     utcp.c -- Userspace TCP
-    Copyright (C) 2014 Guus Sliepen <guus@tinc-vpn.org>
+    Copyright (C) 2014-2017 Guus Sliepen <guus@tinc-vpn.org>
 
     This program is free software; you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
@@ -45,17 +45,18 @@
 #endif
 
 #ifndef timersub
-#define timersub(a, b, r) do {\
-	(r)->tv_sec = (a)->tv_sec - (b)->tv_sec;\
-	(r)->tv_usec = (a)->tv_usec - (b)->tv_usec;\
-	if((r)->tv_usec < 0)\
-		(r)->tv_sec--, (r)->tv_usec += 1000000;\
-} while (0)
+#define timersub(a, b, r)\
+	do {\
+		(r)->tv_sec = (a)->tv_sec - (b)->tv_sec;\
+		(r)->tv_usec = (a)->tv_usec - (b)->tv_usec;\
+		if((r)->tv_usec < 0)\
+			(r)->tv_sec--, (r)->tv_usec += USEC_PER_SEC;\
+	} while (0)
 #endif
 
-#ifndef max
-#define max(a, b) ((a) > (b) ? (a) : (b))
-#endif
+static inline size_t max(size_t a, size_t b) {
+	return a > b ? a : b;
+}
 
 #ifdef UTCP_DEBUG
 #include <stdarg.h>
@@ -69,74 +70,82 @@ static void debug(const char *format, ...) {
 
 static void print_packet(struct utcp *utcp, const char *dir, const void *pkt, size_t len) {
 	struct hdr hdr;
-	if(len < sizeof hdr) {
-		debug("%p %s: short packet (%zu bytes)\n", utcp, dir, len);
+
+	if(len < sizeof(hdr)) {
+		debug("%p %s: short packet (%lu bytes)\n", utcp, dir, (unsigned long)len);
 		return;
 	}
 
-	memcpy(&hdr, pkt, sizeof hdr);
-	fprintf (stderr, "%p %s: len=%zu, src=%u dst=%u seq=%u ack=%u wnd=%u ctl=", utcp, dir, len, hdr.src, hdr.dst, hdr.seq, hdr.ack, hdr.wnd);
-	if(hdr.ctl & SYN)
+	memcpy(&hdr, pkt, sizeof(hdr));
+	debug("%p %s: len=%lu, src=%u dst=%u seq=%u ack=%u wnd=%u aux=%x ctl=", utcp, dir, (unsigned long)len, hdr.src, hdr.dst, hdr.seq, hdr.ack, hdr.wnd, hdr.aux);
+
+	if(hdr.ctl & SYN) {
 		debug("SYN");
-	if(hdr.ctl & RST)
+	}
+
+	if(hdr.ctl & RST) {
 		debug("RST");
-	if(hdr.ctl & FIN)
+	}
+
+	if(hdr.ctl & FIN) {
 		debug("FIN");
-	if(hdr.ctl & ACK)
+	}
+
+	if(hdr.ctl & ACK) {
 		debug("ACK");
+	}
 
-	if(len > sizeof hdr) {
-		uint32_t datalen = len - sizeof hdr;
-		uint8_t *str = malloc((datalen << 1) + 7);
-		memcpy(str, " data=", 6);
-		uint8_t *strptr = str + 6;
-		const uint8_t *data = pkt;
-		const uint8_t *dataend = data + datalen;
-
-		while(data != dataend) {
-			*strptr = (*data >> 4) > 9? (*data >> 4) + 55 : (*data >> 4) + 48;
-			++strptr;
-			*strptr = (*data & 0xf) > 9? (*data & 0xf) + 55 : (*data & 0xf) + 48;
-			++strptr;
-			++data;
+	if(len > sizeof(hdr)) {
+		uint32_t datalen = len - sizeof(hdr);
+		const uint8_t *data = (uint8_t *)pkt + sizeof(hdr);
+		char str[datalen * 2 + 1];
+		char *p = str;
+
+		for(uint32_t i = 0; i < datalen; i++) {
+			*p++ = "0123456789ABCDEF"[data[i] >> 4];
+			*p++ = "0123456789ABCDEF"[data[i] & 15];
 		}
-		*strptr = 0;
 
-		debug(str);
-		free(str);
+		*p = 0;
+
+		debug(" data=%s", str);
 	}
 
 	debug("\n");
 }
 #else
-#define debug(...)
-#define print_packet(...)
+#define debug(...) do {} while(0)
+#define print_packet(...) do {} while(0)
 #endif
 
 static void set_state(struct utcp_connection *c, enum state state) {
 	c->state = state;
-	if(state == ESTABLISHED)
+
+	if(state == ESTABLISHED) {
 		timerclear(&c->conn_timeout);
+	}
+
 	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)
+	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++)
-		debug("  %u -> %u state %s\n", utcp->connections[i]->src, utcp->connections[i]->dst, strstate[utcp->connections[i]->state]);
+static bool is_reliable(struct utcp_connection *c) {
+	return c->flags & UTCP_RELIABLE;
 }
 
 static int32_t seqdiff(uint32_t a, uint32_t b) {
@@ -148,41 +157,50 @@ static int32_t seqdiff(uint32_t a, uint32_t b) {
 
 // Store data into the buffer
 static ssize_t buffer_put_at(struct buffer *buf, size_t offset, const void *data, size_t len) {
-	if(buf->maxsize <= buf->used)
-		return 0;
-
-	debug("buffer_put_at %zu %zu %zu\n", buf->used, offset, len);
+	debug("buffer_put_at %lu %lu %lu\n", (unsigned long)buf->used, (unsigned long)offset, (unsigned long)len);
 
 	size_t required = offset + len;
+
 	if(required > buf->maxsize) {
-		if(offset >= buf->maxsize)
+		if(offset >= buf->maxsize) {
 			return 0;
-		abort();
+		}
+
 		len = buf->maxsize - offset;
 		required = buf->maxsize;
 	}
 
 	if(required > buf->size) {
 		size_t newsize = buf->size;
+
 		if(!newsize) {
 			newsize = required;
 		} else {
 			do {
 				newsize *= 2;
-			} while(newsize < buf->used + len);
+			} while(newsize < required);
 		}
-		if(newsize > buf->maxsize)
+
+		if(newsize > buf->maxsize) {
 			newsize = buf->maxsize;
+		}
+
 		char *newdata = realloc(buf->data, newsize);
-		if(!newdata)
+
+		if(!newdata) {
 			return -1;
+		}
+
 		buf->data = newdata;
 		buf->size = newsize;
 	}
 
 	memcpy(buf->data + offset, data, len);
-	if(required > buf->used)
+
+	if(required > buf->used) {
 		buf->used = required;
+	}
+
 	return len;
 }
 
@@ -192,33 +210,47 @@ static ssize_t buffer_put(struct buffer *buf, const void *data, size_t 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)
+	if(len > buf->used) {
 		len = buf->used;
-	if(data)
+	}
+
+	if(data) {
 		memcpy(data, buf->data, len);
-	if(len < buf->used)
+	}
+
+	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)
+	if(offset >= buf->used) {
 		return 0;
-	if(offset + len > buf->used)
+	}
+
+	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);
+	memset(buf, 0, sizeof(*buf));
+
 	if(len) {
 		buf->data = malloc(len);
-		if(!buf->data)
+
+		if(!buf->data) {
 			return false;
+		}
 	}
+
 	buf->size = len;
 	buf->maxsize = maxlen;
 	return true;
@@ -226,7 +258,7 @@ static bool buffer_init(struct buffer *buf, uint32_t len, uint32_t maxlen) {
 
 static void buffer_exit(struct buffer *buf) {
 	free(buf->data);
-	memset(buf, 0, sizeof *buf);
+	memset(buf, 0, sizeof(*buf));
 }
 
 static uint32_t buffer_free(const struct buffer *buf) {
@@ -246,31 +278,36 @@ static int compare(const void *va, const void *vb) {
 	assert(a->src && b->src);
 
 	int c = (int)a->src - (int)b->src;
-	if(c)
+
+	if(c) {
 		return c;
+	}
+
 	c = (int)a->dst - (int)b->dst;
 	return c;
 }
 
 static struct utcp_connection *find_connection(const struct utcp *utcp, uint16_t src, uint16_t dst) {
-	if(!utcp->nconnections)
+	if(!utcp->nconnections) {
 		return NULL;
+	}
+
 	struct utcp_connection key = {
 		.src = src,
 		.dst = dst,
 	}, *keyp = &key;
-	struct utcp_connection **match = bsearch(&keyp, utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
+	struct utcp_connection **match = bsearch(&keyp, utcp->connections, utcp->nconnections, sizeof(*utcp->connections), compare);
 	return match ? *match : NULL;
 }
 
 static void free_connection(struct utcp_connection *c) {
 	struct utcp *utcp = c->utcp;
-	struct utcp_connection **cp = bsearch(&c, utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
+	struct utcp_connection **cp = bsearch(&c, utcp->connections, utcp->nconnections, sizeof(*utcp->connections), compare);
 
 	assert(cp);
 
 	int i = cp - utcp->connections;
-	memmove(cp, cp + 1, (utcp->nconnections - i - 1) * sizeof *cp);
+	memmove(cp, cp + 1, (utcp->nconnections - i - 1) * sizeof(*cp));
 	utcp->nconnections--;
 
 	buffer_exit(&c->rcvbuf);
@@ -291,27 +328,37 @@ static struct utcp_connection *allocate_connection(struct utcp *utcp, uint16_t s
 			errno = ENOMEM;
 			return NULL;
 		}
+
 		src = rand() | 0x8000;
-		while(find_connection(utcp, src, dst))
+
+		while(find_connection(utcp, src, dst)) {
 			src++;
+		}
 	}
 
 	// Allocate memory for the new connection
 
 	if(utcp->nconnections >= utcp->nallocated) {
-		if(!utcp->nallocated)
+		if(!utcp->nallocated) {
 			utcp->nallocated = 4;
-		else
+		} else {
 			utcp->nallocated *= 2;
-		struct utcp_connection **new_array = realloc(utcp->connections, utcp->nallocated * sizeof *utcp->connections);
-		if(!new_array)
+		}
+
+		struct utcp_connection **new_array = realloc(utcp->connections, utcp->nallocated * sizeof(*utcp->connections));
+
+		if(!new_array) {
 			return NULL;
+		}
+
 		utcp->connections = new_array;
 	}
 
-	struct utcp_connection *c = calloc(1, sizeof *c);
-	if(!c)
+	struct utcp_connection *c = calloc(1, sizeof(*c));
+
+	if(!c) {
 		return NULL;
+	}
 
 	if(!buffer_init(&c->sndbuf, DEFAULT_SNDBUFSIZE, DEFAULT_MAXSNDBUFSIZE)) {
 		free(c);
@@ -343,11 +390,19 @@ static struct utcp_connection *allocate_connection(struct utcp *utcp, uint16_t s
 	// Add it to the sorted list of connections
 
 	utcp->connections[utcp->nconnections++] = c;
-	qsort(utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
+	qsort(utcp->connections, utcp->nconnections, sizeof(*utcp->connections), compare);
 
 	return c;
 }
 
+static inline uint32_t absdiff(uint32_t a, uint32_t b) {
+	if(a > b) {
+		return a - b;
+	} else {
+		return b - a;
+	}
+}
+
 // Update RTT variables. See RFC 6298.
 static void update_rtt(struct utcp_connection *c, uint32_t rtt) {
 	if(!rtt) {
@@ -362,13 +417,14 @@ static void update_rtt(struct utcp_connection *c, uint32_t rtt) {
 		utcp->rttvar = rtt / 2;
 		utcp->rto = rtt + max(2 * rtt, CLOCK_GRANULARITY);
 	} else {
-		utcp->rttvar = (utcp->rttvar * 3 + abs(utcp->srtt - rtt)) / 4;
+		utcp->rttvar = (utcp->rttvar * 3 + absdiff(utcp->srtt, rtt)) / 4;
 		utcp->srtt = (utcp->srtt * 7 + rtt) / 8;
 		utcp->rto = utcp->srtt + max(utcp->rttvar, CLOCK_GRANULARITY);
 	}
 
-	if(utcp->rto > MAX_RTO)
+	if(utcp->rto > MAX_RTO) {
 		utcp->rto = MAX_RTO;
+	}
 
 	debug("rtt %u srtt %u rttvar %u rto %u\n", rtt, utcp->srtt, utcp->rttvar, utcp->rto);
 }
@@ -376,10 +432,12 @@ static void update_rtt(struct utcp_connection *c, uint32_t rtt) {
 static void start_retransmit_timer(struct utcp_connection *c) {
 	gettimeofday(&c->rtrx_timeout, NULL);
 	c->rtrx_timeout.tv_usec += c->utcp->rto;
+
 	while(c->rtrx_timeout.tv_usec >= 1000000) {
 		c->rtrx_timeout.tv_usec -= 1000000;
 		c->rtrx_timeout.tv_sec++;
 	}
+
 	debug("timeout set to %lu.%06lu (%u)\n", c->rtrx_timeout.tv_sec, c->rtrx_timeout.tv_usec, c->utcp->rto);
 }
 
@@ -388,35 +446,53 @@ static void stop_retransmit_timer(struct utcp_connection *c) {
 	debug("timeout cleared\n");
 }
 
-struct utcp_connection *utcp_connect(struct utcp *utcp, uint16_t dst, utcp_recv_t recv, void *priv) {
+struct utcp_connection *utcp_connect_ex(struct utcp *utcp, uint16_t dst, utcp_recv_t recv, void *priv, uint32_t flags) {
 	struct utcp_connection *c = allocate_connection(utcp, 0, dst);
-	if(!c)
+
+	if(!c) {
 		return NULL;
+	}
 
+	assert((flags & ~0xf) == 0);
+
+	c->flags = flags;
 	c->recv = recv;
 	c->priv = priv;
 
-	struct hdr hdr;
-
-	hdr.src = c->src;
-	hdr.dst = c->dst;
-	hdr.seq = c->snd.iss;
-	hdr.ack = 0;
-	hdr.wnd = c->rcv.wnd;
-	hdr.ctl = SYN;
-	hdr.aux = 0;
+	struct {
+		struct hdr hdr;
+		uint8_t init[4];
+	} pkt;
+
+	pkt.hdr.src = c->src;
+	pkt.hdr.dst = c->dst;
+	pkt.hdr.seq = c->snd.iss;
+	pkt.hdr.ack = 0;
+	pkt.hdr.wnd = c->rcv.wnd;
+	pkt.hdr.ctl = SYN;
+	pkt.hdr.aux = 0x0101;
+	pkt.init[0] = 1;
+	pkt.init[1] = 0;
+	pkt.init[2] = 0;
+	pkt.init[3] = flags & 0x7;
 
 	set_state(c, SYN_SENT);
 
-	print_packet(utcp, "send", &hdr, sizeof hdr);
-	utcp->send(utcp, &hdr, sizeof hdr);
+	print_packet(utcp, "send", &pkt, sizeof(pkt));
+	utcp->send(utcp, &pkt, sizeof(pkt));
 
 	gettimeofday(&c->conn_timeout, NULL);
 	c->conn_timeout.tv_sec += utcp->timeout;
 
+	start_retransmit_timer(c);
+
 	return c;
 }
 
+struct utcp_connection *utcp_connect(struct utcp *utcp, uint16_t dst, utcp_recv_t recv, void *priv) {
+	return utcp_connect_ex(utcp, dst, recv, priv, UTCP_TCP);
+}
+
 void utcp_accept(struct utcp_connection *c, utcp_recv_t recv, void *priv) {
 	if(c->reapable || c->state != SYN_RECEIVED) {
 		debug("Error: accept() called on invalid connection %p in state %s\n", c, strstate[c->state]);
@@ -436,23 +512,28 @@ static void ack(struct utcp_connection *c, bool sendatleastone) {
 
 	assert(left >= 0);
 
-	if(cwndleft <= 0)
+	if(cwndleft <= 0) {
 		cwndleft = 0;
+	}
 
-	if(cwndleft < left)
+	if(cwndleft < left) {
 		left = cwndleft;
+	}
 
-	if(!left && !sendatleastone)
+	if(!left && !sendatleastone) {
 		return;
+	}
 
 	struct {
 		struct hdr hdr;
-		char data[];
+		uint8_t data[];
 	} *pkt;
 
-	pkt = malloc(sizeof pkt->hdr + c->utcp->mtu);
-	if(!pkt)
+	pkt = malloc(sizeof(pkt->hdr) + c->utcp->mtu);
+
+	if(!pkt) {
 		return;
+	}
 
 	pkt->hdr.src = c->src;
 	pkt->hdr.dst = c->dst;
@@ -482,8 +563,8 @@ static void ack(struct utcp_connection *c, bool sendatleastone) {
 			debug("Starting RTT measurement, expecting ack %u\n", c->rtt_seq);
 		}
 
-		print_packet(c->utcp, "send", pkt, sizeof pkt->hdr + seglen);
-		c->utcp->send(c->utcp, pkt, sizeof pkt->hdr + seglen);
+		print_packet(c->utcp, "send", pkt, sizeof(pkt->hdr) + seglen);
+		c->utcp->send(c->utcp, pkt, sizeof(pkt->hdr) + seglen);
 	} while(left);
 
 	free(pkt);
@@ -499,14 +580,16 @@ ssize_t utcp_send(struct utcp_connection *c, const void *data, size_t len) {
 	switch(c->state) {
 	case CLOSED:
 	case LISTEN:
-	case SYN_SENT:
-	case SYN_RECEIVED:
 		debug("Error: send() called on unconnected connection %p\n", c);
 		errno = ENOTCONN;
 		return -1;
+
+	case SYN_SENT:
+	case SYN_RECEIVED:
 	case ESTABLISHED:
 	case CLOSE_WAIT:
 		break;
+
 	case FIN_WAIT_1:
 	case FIN_WAIT_2:
 	case CLOSING:
@@ -517,26 +600,45 @@ ssize_t utcp_send(struct utcp_connection *c, const void *data, size_t len) {
 		return -1;
 	}
 
-	// Add data to send buffer
+	// Exit early if we have nothing to send.
 
-	if(!len)
+	if(!len) {
 		return 0;
+	}
 
 	if(!data) {
 		errno = EFAULT;
 		return -1;
 	}
 
+	// Add data to send buffer.
+
 	len = buffer_put(&c->sndbuf, data, len);
+
 	if(len <= 0) {
 		errno = EWOULDBLOCK;
 		return 0;
 	}
 
 	c->snd.last += len;
+
+	// Don't send anything yet if the connection has not fully established yet
+
+	if(c->state == SYN_SENT || c->state == SYN_RECEIVED) {
+		return len;
+	}
+
 	ack(c, false);
-	if(!timerisset(&c->rtrx_timeout))
+
+	if(!is_reliable(c)) {
+		c->snd.una = c->snd.nxt = c->snd.last;
+		buffer_get(&c->sndbuf, NULL, c->sndbuf.used);
+	}
+
+	if(is_reliable(c) && !timerisset(&c->rtrx_timeout)) {
 		start_retransmit_timer(c);
+	}
+
 	return len;
 }
 
@@ -547,19 +649,24 @@ static void swap_ports(struct hdr *hdr) {
 }
 
 static void retransmit(struct utcp_connection *c) {
-	if(c->state == CLOSED || c->snd.nxt == c->snd.una)
+	if(c->state == CLOSED || c->snd.last == c->snd.una) {
+		debug("Retransmit() called but nothing to retransmit!\n");
+		stop_retransmit_timer(c);
 		return;
+	}
 
 	struct utcp *utcp = c->utcp;
 
 	struct {
 		struct hdr hdr;
-		char data[];
+		uint8_t data[];
 	} *pkt;
 
-	pkt = malloc(sizeof pkt->hdr + c->utcp->mtu);
-	if(!pkt)
+	pkt = malloc(sizeof(pkt->hdr) + c->utcp->mtu);
+
+	if(!pkt) {
 		return;
+	}
 
 	pkt->hdr.src = c->src;
 	pkt->hdr.dst = c->dst;
@@ -567,89 +674,122 @@ static void retransmit(struct utcp_connection *c) {
 	pkt->hdr.aux = 0;
 
 	switch(c->state) {
-		case SYN_SENT:
-			// Send our SYN again
-			pkt->hdr.seq = c->snd.iss;
-			pkt->hdr.ack = 0;
-			pkt->hdr.ctl = SYN;
-			print_packet(c->utcp, "rtrx", pkt, sizeof pkt->hdr);
-			utcp->send(utcp, pkt, sizeof pkt->hdr);
-			break;
+	case SYN_SENT:
+		// Send our SYN again
+		pkt->hdr.seq = c->snd.iss;
+		pkt->hdr.ack = 0;
+		pkt->hdr.ctl = SYN;
+		pkt->hdr.aux = 0x0101;
+		pkt->data[0] = 1;
+		pkt->data[1] = 0;
+		pkt->data[2] = 0;
+		pkt->data[3] = c->flags & 0x7;
+		print_packet(c->utcp, "rtrx", pkt, sizeof(pkt->hdr) + 4);
+		utcp->send(utcp, pkt, sizeof(pkt->hdr) + 4);
+		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 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;
-			c->snd.cwnd = utcp->mtu; // reduce cwnd on retransmit
-			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 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;
+		}
 
-		case CLOSED:
-		case LISTEN:
-		case TIME_WAIT:
-		case FIN_WAIT_2:
-			// We shouldn't need to retransmit anything in this state.
+		if(fin_wanted(c, c->snd.una + len)) {
+			len--;
+			pkt->hdr.ctl |= FIN;
+		}
+
+		c->snd.nxt = c->snd.una + len;
+		c->snd.cwnd = utcp->mtu; // reduce cwnd on retransmit
+		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();
+		abort();
 #endif
-			stop_retransmit_timer(c);
-			goto cleanup;
+		stop_retransmit_timer(c);
+		goto cleanup;
 	}
 
 	start_retransmit_timer(c);
 	utcp->rto *= 2;
-	if(utcp->rto > MAX_RTO)
+
+	if(utcp->rto > MAX_RTO) {
 		utcp->rto = MAX_RTO;
+	}
+
 	c->rtt_start.tv_sec = 0; // invalidate RTT timer
 
 cleanup:
 	free(pkt);
 }
 
-// Update receive buffer and SACK entries after consuming data.
+/* Update receive buffer and SACK entries after consuming data.
+ *
+ * Situation:
+ *
+ * |.....0000..1111111111.....22222......3333|
+ * |---------------^
+ *
+ * 0..3 represent the SACK entries. The ^ indicates up to which point we want
+ * to remove data from the receive buffer. The idea is to substract "len"
+ * from the offset of all the SACK entries, and then remove/cut down entries
+ * that are shifted to before the start of the receive buffer.
+ *
+ * There are three cases:
+ * - the SACK entry is after ^, in that case just change the offset.
+ * - the SACK entry starts before and ends after ^, so we have to
+ *   change both its offset and size.
+ * - the SACK entry is completely before ^, in that case delete it.
+ */
 static void sack_consume(struct utcp_connection *c, size_t len) {
-	debug("sack_consume %zu\n", len);
-	if(len > c->rcvbuf.used)
-		abort();
+	debug("sack_consume %lu\n", (unsigned long)len);
+
+	if(len > c->rcvbuf.used) {
+		debug("All SACK entries consumed");
+		c->sacks[0].len = 0;
+		return;
+	}
 
 	buffer_get(&c->rcvbuf, NULL, len);
 
-	for(int i = 0; i < NSACKS && c->sacks[i].len; ) {
+	for(int i = 0; i < NSACKS && c->sacks[i].len;) {
 		if(len < c->sacks[i].offset) {
 			c->sacks[i].offset -= len;
 			i++;
 		} else if(len < c->sacks[i].offset + c->sacks[i].len) {
-			c->sacks[i].offset = 0;
 			c->sacks[i].len -= len - c->sacks[i].offset;
+			c->sacks[i].offset = 0;
 			i++;
 		} else {
 			if(i < NSACKS - 1) {
-				memmove(&c->sacks[i], &c->sacks[i + 1], (NSACKS - 1 - i) * sizeof c->sacks[i]);
-				c->sacks[i + 1].len = 0;
+				memmove(&c->sacks[i], &c->sacks[i + 1], (NSACKS - 1 - i) * sizeof(c->sacks)[i]);
+				c->sacks[NSACKS - 1].len = 0;
 			} else {
 				c->sacks[i].len = 0;
 				break;
@@ -657,16 +797,19 @@ static void sack_consume(struct utcp_connection *c, size_t len) {
 		}
 	}
 
-	for(int i = 0; i < NSACKS && c->sacks[i].len; i++)
+	for(int i = 0; i < NSACKS && c->sacks[i].len; i++) {
 		debug("SACK[%d] offset %u len %u\n", i, c->sacks[i].offset, c->sacks[i].len);
+	}
 }
 
 static void handle_out_of_order(struct utcp_connection *c, uint32_t offset, const void *data, size_t len) {
 	debug("out of order packet, offset %u\n", offset);
 	// Packet loss or reordering occured. Store the data in the buffer.
 	ssize_t rxd = buffer_put_at(&c->rcvbuf, offset, data, len);
-	if(rxd < len)
+
+	if(rxd < 0 || (size_t)rxd < len) {
 		abort();
+	}
 
 	// Make note of where we put it.
 	for(int i = 0; i < NSACKS; i++) {
@@ -679,10 +822,13 @@ static void handle_out_of_order(struct utcp_connection *c, uint32_t offset, cons
 			if(offset + rxd < c->sacks[i].offset) { // insert before
 				if(!c->sacks[NSACKS - 1].len) { // only if room left
 					debug("Insert SACK entry at %d\n", i);
-					memmove(&c->sacks[i + 1], &c->sacks[i], (NSACKS - i - 1) * sizeof c->sacks[i]);
+					memmove(&c->sacks[i + 1], &c->sacks[i], (NSACKS - i - 1) * sizeof(c->sacks)[i]);
 					c->sacks[i].offset = offset;
 					c->sacks[i].len = rxd;
+				} else {
+					debug("SACK entries full, dropping packet\n");
 				}
+
 				break;
 			} else { // merge
 				debug("Merge with start of SACK entry at %d\n", i);
@@ -695,18 +841,20 @@ static void handle_out_of_order(struct utcp_connection *c, uint32_t offset, cons
 				c->sacks[i].len = offset + rxd - c->sacks[i].offset;
 				// TODO: handle potential merge with next entry
 			}
+
 			break;
 		}
 	}
 
-	for(int i = 0; i < NSACKS && c->sacks[i].len; i++)
+	for(int i = 0; i < NSACKS && c->sacks[i].len; i++) {
 		debug("SACK[%d] offset %u len %u\n", i, c->sacks[i].offset, c->sacks[i].len);
+	}
 }
 
 static void handle_in_order(struct utcp_connection *c, const void *data, size_t len) {
 	// Check if we can process out-of-order data now.
 	if(c->sacks[0].len && len >= c->sacks[0].offset) { // TODO: handle overlap with second SACK
-		debug("incoming packet len %zu connected with SACK at %u\n", len, c->sacks[0].offset);
+		debug("incoming packet len %lu connected with SACK at %u\n", (unsigned long)len, c->sacks[0].offset);
 		buffer_put_at(&c->rcvbuf, 0, data, len); // TODO: handle return value
 		len = max(len, c->sacks[0].offset + c->sacks[0].len);
 		data = c->rcvbuf.data;
@@ -714,39 +862,53 @@ static void handle_in_order(struct utcp_connection *c, const void *data, size_t
 
 	if(c->recv) {
 		ssize_t rxd = c->recv(c, data, len);
-		if(rxd != len) {
+
+		if(rxd < 0 || (size_t)rxd != len) {
 			// TODO: handle the application not accepting all data.
 			abort();
 		}
 	}
 
-	if(c->rcvbuf.used)
+	if(c->rcvbuf.used) {
 		sack_consume(c, len);
+	}
 
 	c->rcv.nxt += len;
 }
 
 
 static void handle_incoming_data(struct utcp_connection *c, uint32_t seq, const void *data, size_t len) {
+	if(!is_reliable(c)) {
+		c->recv(c, data, len);
+		c->rcv.nxt = seq + len;
+		return;
+	}
+
 	uint32_t offset = seqdiff(seq, c->rcv.nxt);
-	if(offset + len > c->rcvbuf.maxsize)
+
+	if(offset + len > c->rcvbuf.maxsize) {
 		abort();
+	}
 
-	if(offset)
+	if(offset) {
 		handle_out_of_order(c, offset, data, len);
-	else
+	} else {
 		handle_in_order(c, data, len);
+	}
 }
 
 
 ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
+	const uint8_t *ptr = data;
+
 	if(!utcp) {
 		errno = EFAULT;
 		return -1;
 	}
 
-	if(!len)
+	if(!len) {
 		return 0;
+	}
 
 	if(!data) {
 		errno = EFAULT;
@@ -758,16 +920,17 @@ ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 	// Drop packets smaller than the header
 
 	struct hdr hdr;
-	if(len < sizeof hdr) {
+
+	if(len < sizeof(hdr)) {
 		errno = EBADMSG;
 		return -1;
 	}
 
 	// Make a copy from the potentially unaligned data to a struct hdr
 
-	memcpy(&hdr, data, sizeof hdr);
-	data += sizeof hdr;
-	len -= sizeof hdr;
+	memcpy(&hdr, ptr, sizeof(hdr));
+	ptr += sizeof(hdr);
+	len -= sizeof(hdr);
 
 	// Drop packets with an unknown CTL flag
 
@@ -776,6 +939,53 @@ ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 		return -1;
 	}
 
+	// Check for auxiliary headers
+
+	const uint8_t *init = NULL;
+
+	uint16_t aux = hdr.aux;
+
+	while(aux) {
+		size_t auxlen = 4 * (aux >> 8) & 0xf;
+		uint8_t auxtype = aux & 0xff;
+
+		if(len < auxlen) {
+			errno = EBADMSG;
+			return -1;
+		}
+
+		switch(auxtype) {
+		case AUX_INIT:
+			if(!(hdr.ctl & SYN) || auxlen != 4) {
+				errno = EBADMSG;
+				return -1;
+			}
+
+			init = ptr;
+			break;
+
+		default:
+			errno = EBADMSG;
+			return -1;
+		}
+
+		len -= auxlen;
+		ptr += auxlen;
+
+		if(!(aux & 0x800)) {
+			break;
+		}
+
+		if(len < 2) {
+			errno = EBADMSG;
+			return -1;
+		}
+
+		memcpy(&aux, ptr, 2);
+		len -= 2;
+		ptr += 2;
+	}
+
 	// Try to match the packet to an existing connection
 
 	struct utcp_connection *c = find_connection(utcp, hdr.dst, hdr.src);
@@ -785,8 +995,9 @@ ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 	if(!c) {
 		// Ignore RST packets
 
-		if(hdr.ctl & RST)
+		if(hdr.ctl & RST) {
 			return 0;
+		}
 
 		// Is it a SYN packet and are we LISTENing?
 
@@ -799,24 +1010,55 @@ ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 
 			// Try to allocate memory, otherwise send a RST back
 			c = allocate_connection(utcp, hdr.dst, hdr.src);
+
 			if(!c) {
 				len = 1;
 				goto reset;
 			}
 
+			// Parse auxilliary information
+			if(init) {
+				if(init[0] < 1) {
+					len = 1;
+					goto reset;
+				}
+
+				c->flags = init[3] & 0x7;
+			} else {
+				c->flags = UTCP_TCP;
+			}
+
 			// Return SYN+ACK, go to SYN_RECEIVED state
 			c->snd.wnd = hdr.wnd;
 			c->rcv.irs = hdr.seq;
 			c->rcv.nxt = c->rcv.irs + 1;
 			set_state(c, SYN_RECEIVED);
 
-			hdr.dst = c->dst;
-			hdr.src = c->src;
-			hdr.ack = c->rcv.irs + 1;
-			hdr.seq = c->snd.iss;
-			hdr.ctl = SYN | ACK;
-			print_packet(c->utcp, "send", &hdr, sizeof hdr);
-			utcp->send(utcp, &hdr, sizeof hdr);
+			struct {
+				struct hdr hdr;
+				uint8_t data[4];
+			} pkt;
+
+			pkt.hdr.src = c->src;
+			pkt.hdr.dst = c->dst;
+			pkt.hdr.ack = c->rcv.irs + 1;
+			pkt.hdr.seq = c->snd.iss;
+			pkt.hdr.wnd = c->rcv.wnd;
+			pkt.hdr.ctl = SYN | ACK;
+
+			if(init) {
+				pkt.hdr.aux = 0x0101;
+				pkt.data[0] = 1;
+				pkt.data[1] = 0;
+				pkt.data[2] = 0;
+				pkt.data[3] = c->flags & 0x7;
+				print_packet(c->utcp, "send", &pkt, sizeof(hdr) + 4);
+				utcp->send(utcp, &pkt, sizeof(hdr) + 4);
+			} else {
+				pkt.hdr.aux = 0;
+				print_packet(c->utcp, "send", &pkt, sizeof(hdr));
+				utcp->send(utcp, &pkt, sizeof(hdr));
+			}
 		} else {
 			// No, we don't want your packets, send a RST back
 			len = 1;
@@ -831,8 +1073,10 @@ ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 	// In case this is for a CLOSED connection, ignore the packet.
 	// TODO: make it so incoming packets can never match a CLOSED connection.
 
-	if(c->state == CLOSED)
+	if(c->state == CLOSED) {
+		debug("Got packet for closed connection\n");
 		return 0;
+	}
 
 	// It is for an existing connection.
 
@@ -853,6 +1097,7 @@ ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 	case LAST_ACK:
 	case TIME_WAIT:
 		break;
+
 	default:
 #ifdef UTCP_DEBUG
 		abort();
@@ -864,33 +1109,37 @@ ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 
 	bool acceptable;
 
-	if(c->state == SYN_SENT)
+	if(c->state == SYN_SENT) {
 		acceptable = true;
-	else if(len == 0)
+	} else if(len == 0) {
 		acceptable = seqdiff(hdr.seq, c->rcv.nxt) >= 0;
-	else {
+	} else {
 		int32_t rcv_offset = seqdiff(hdr.seq, c->rcv.nxt);
 
 		// cut already accepted front overlapping
 		if(rcv_offset < 0) {
-			acceptable = rcv_offset + len >= 0;
+			acceptable = len > (size_t) - rcv_offset;
+
 			if(acceptable) {
-				data -= rcv_offset;
+				ptr -= rcv_offset;
 				len += rcv_offset;
+				hdr.seq -= rcv_offset;
 			}
+		} else {
+			acceptable = seqdiff(hdr.seq, c->rcv.nxt) >= 0 && seqdiff(hdr.seq, c->rcv.nxt) + len <= c->rcvbuf.maxsize;
 		}
-
-		acceptable = seqdiff(hdr.seq, c->rcv.nxt) >= 0 && seqdiff(hdr.seq, c->rcv.nxt) + len <= c->rcvbuf.maxsize;
 	}
 
 	if(!acceptable) {
-		debug("Packet not acceptable, %u <= %u + %zu < %u\n", c->rcv.nxt, hdr.seq, len, c->rcv.nxt + c->rcvbuf.maxsize);
+		debug("Packet not acceptable, %u <= %u + %lu < %u\n", c->rcv.nxt, hdr.seq, (unsigned long)len, c->rcv.nxt + c->rcvbuf.maxsize);
+
 		// Ignore unacceptable RST packets.
-		if(hdr.ctl & RST)
+		if(hdr.ctl & RST) {
 			return 0;
-		// Otherwise, send an ACK back in the hope things improve.
-		ack(c, true);
-		return 0;
+		}
+
+		// Otherwise, continue processing.
+		len = 0;
 	}
 
 	c->snd.wnd = hdr.wnd; // TODO: move below
@@ -901,9 +1150,12 @@ ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 
 	if(hdr.ctl & ACK && (seqdiff(hdr.ack, c->snd.last) > 0 || seqdiff(hdr.ack, c->snd.una) < 0)) {
 		debug("Packet ack seqno out of range, %u <= %u < %u\n", c->snd.una, hdr.ack, c->snd.una + c->sndbuf.used);
+
 		// Ignore unacceptable RST packets.
-		if(hdr.ctl & RST)
+		if(hdr.ctl & RST) {
 			return 0;
+		}
+
 		goto reset;
 	}
 
@@ -912,46 +1164,65 @@ ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 	if(hdr.ctl & RST) {
 		switch(c->state) {
 		case SYN_SENT:
-			if(!(hdr.ctl & ACK))
+			if(!(hdr.ctl & ACK)) {
 				return 0;
+			}
+
 			// The peer has refused our connection.
 			set_state(c, CLOSED);
 			errno = ECONNREFUSED;
-			if(c->recv)
+
+			if(c->recv) {
 				c->recv(c, NULL, 0);
+			}
+
 			return 0;
+
 		case SYN_RECEIVED:
-			if(hdr.ctl & ACK)
+			if(hdr.ctl & ACK) {
 				return 0;
+			}
+
 			// We haven't told the application about this connection yet. Silently delete.
 			free_connection(c);
 			return 0;
+
 		case ESTABLISHED:
 		case FIN_WAIT_1:
 		case FIN_WAIT_2:
 		case CLOSE_WAIT:
-			if(hdr.ctl & ACK)
+			if(hdr.ctl & ACK) {
 				return 0;
+			}
+
 			// The peer has aborted our connection.
 			set_state(c, CLOSED);
 			errno = ECONNRESET;
-			if(c->recv)
+
+			if(c->recv) {
 				c->recv(c, NULL, 0);
+			}
+
 			return 0;
+
 		case CLOSING:
 		case LAST_ACK:
 		case TIME_WAIT:
-			if(hdr.ctl & ACK)
+			if(hdr.ctl & ACK) {
 				return 0;
+			}
+
 			// As far as the application is concerned, the connection has already been closed.
 			// If it has called utcp_close() already, we can immediately free this connection.
 			if(c->reapable) {
 				free_connection(c);
 				return 0;
 			}
+
 			// Otherwise, immediately move to the CLOSED state.
 			set_state(c, CLOSED);
 			return 0;
+
 		default:
 #ifdef UTCP_DEBUG
 			abort();
@@ -960,9 +1231,16 @@ ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 		}
 	}
 
+	uint32_t advanced;
+
+	if(!(hdr.ctl & ACK)) {
+		advanced = 0;
+		goto skip_ack;
+	}
+
 	// 3. Advance snd.una
 
-	uint32_t advanced = seqdiff(hdr.ack, c->snd.una);
+	advanced = seqdiff(hdr.ack, c->snd.una);
 	prevrcvnxt = c->rcv.nxt;
 
 	if(advanced) {
@@ -983,13 +1261,14 @@ ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 		int32_t data_acked = advanced;
 
 		switch(c->state) {
-			case SYN_SENT:
-			case SYN_RECEIVED:
-				data_acked--;
-				break;
-			// TODO: handle FIN as well.
-			default:
-				break;
+		case SYN_SENT:
+		case SYN_RECEIVED:
+			data_acked--;
+			break;
+
+		// TODO: handle FIN as well.
+		default:
+			break;
 		}
 
 		assert(data_acked >= 0);
@@ -997,39 +1276,49 @@ 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);
 
-		if(data_acked)
+		if(data_acked) {
 			buffer_get(&c->sndbuf, NULL, data_acked);
+		}
 
 		// Also advance snd.nxt if possible
-		if(seqdiff(c->snd.nxt, hdr.ack) < 0)
+		if(seqdiff(c->snd.nxt, hdr.ack) < 0) {
 			c->snd.nxt = hdr.ack;
+		}
 
 		c->snd.una = hdr.ack;
 
 		c->dupack = 0;
 		c->snd.cwnd += utcp->mtu;
-		if(c->snd.cwnd > c->sndbuf.maxsize)
+
+		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) {
 		case FIN_WAIT_1:
-			if(c->snd.una == c->snd.last)
+			if(c->snd.una == c->snd.last) {
 				set_state(c, FIN_WAIT_2);
+			}
+
 			break;
+
 		case CLOSING:
 			if(c->snd.una == c->snd.last) {
 				gettimeofday(&c->conn_timeout, NULL);
 				c->conn_timeout.tv_sec += 60;
 				set_state(c, TIME_WAIT);
 			}
+
 			break;
+
 		default:
 			break;
 		}
 	} else {
-		if(!len) {
+		if(!len && is_reliable(c)) {
 			c->dupack++;
+
 			if(c->dupack == 3) {
 				debug("Triplicate ACK\n");
 				//TODO: Resend one packet and go to fast recovery mode. See RFC 6582.
@@ -1046,25 +1335,39 @@ ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 
 	if(advanced) {
 		timerclear(&c->conn_timeout); // It will be set anew in utcp_timeout() if c->snd.una != c->snd.nxt.
-		if(c->snd.una == c->snd.last)
+
+		if(c->snd.una == c->snd.last) {
 			stop_retransmit_timer(c);
-		else
+		} else if(is_reliable(c)) {
 			start_retransmit_timer(c);
+		}
 	}
 
+skip_ack:
 	// 5. Process SYN stuff
 
 	if(hdr.ctl & SYN) {
 		switch(c->state) {
 		case SYN_SENT:
+
 			// This is a SYNACK. It should always have ACKed the SYN.
-			if(!advanced)
+			if(!advanced) {
 				goto reset;
+			}
+
 			c->rcv.irs = hdr.seq;
 			c->rcv.nxt = hdr.seq;
-			set_state(c, ESTABLISHED);
+
+			if(c->shut_wr) {
+				c->snd.last++;
+				set_state(c, FIN_WAIT_1);
+			} else {
+				set_state(c, ESTABLISHED);
+			}
+
 			// TODO: notify application of this somehow.
 			break;
+
 		case SYN_RECEIVED:
 		case ESTABLISHED:
 		case FIN_WAIT_1:
@@ -1074,7 +1377,8 @@ ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 		case LAST_ACK:
 		case TIME_WAIT:
 			// Ehm, no. We should never receive a second SYN.
-			goto reset;
+			return 0;
+
 		default:
 #ifdef UTCP_DEBUG
 			abort();
@@ -1090,12 +1394,14 @@ ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 
 	if(c->state == SYN_RECEIVED) {
 		// This is the ACK after the SYNACK. It should always have ACKed the SYNACK.
-		if(!advanced)
+		if(!advanced) {
 			goto reset;
+		}
 
 		// Are we still LISTENing?
-		if(utcp->accept)
+		if(utcp->accept) {
 			utcp->accept(c, c->src);
+		}
 
 		if(c->state != ESTABLISHED) {
 			set_state(c, CLOSED);
@@ -1113,16 +1419,19 @@ ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 			abort();
 #endif
 			return 0;
+
 		case ESTABLISHED:
 		case FIN_WAIT_1:
 		case FIN_WAIT_2:
 			break;
+
 		case CLOSE_WAIT:
 		case CLOSING:
 		case LAST_ACK:
 		case TIME_WAIT:
 			// Ehm no, We should never receive more data after a FIN.
 			goto reset;
+
 		default:
 #ifdef UTCP_DEBUG
 			abort();
@@ -1130,7 +1439,7 @@ ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 			return 0;
 		}
 
-		handle_incoming_data(c, hdr.seq, data, len);
+		handle_incoming_data(c, hdr.seq, ptr, len);
 	}
 
 	// 7. Process FIN stuff
@@ -1144,23 +1453,28 @@ ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 			abort();
 #endif
 			break;
+
 		case ESTABLISHED:
 			set_state(c, CLOSE_WAIT);
 			break;
+
 		case FIN_WAIT_1:
 			set_state(c, CLOSING);
 			break;
+
 		case FIN_WAIT_2:
 			gettimeofday(&c->conn_timeout, NULL);
 			c->conn_timeout.tv_sec += 60;
 			set_state(c, TIME_WAIT);
 			break;
+
 		case CLOSE_WAIT:
 		case CLOSING:
 		case LAST_ACK:
 		case TIME_WAIT:
 			// Ehm, no. We should never receive a second FIN.
 			goto reset;
+
 		default:
 #ifdef UTCP_DEBUG
 			abort();
@@ -1191,6 +1505,8 @@ ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 reset:
 	swap_ports(&hdr);
 	hdr.wnd = 0;
+	hdr.aux = 0;
+
 	if(hdr.ctl & ACK) {
 		hdr.seq = hdr.ack;
 		hdr.ctl = RST;
@@ -1199,14 +1515,16 @@ reset:
 		hdr.seq = 0;
 		hdr.ctl = RST | ACK;
 	}
-	print_packet(utcp, "send", &hdr, sizeof hdr);
-	utcp->send(utcp, &hdr, sizeof hdr);
+
+	print_packet(utcp, "send", &hdr, sizeof(hdr));
+	utcp->send(utcp, &hdr, sizeof(hdr));
 	return 0;
 
 }
 
 int utcp_shutdown(struct utcp_connection *c, int dir) {
 	debug("%p shutdown %d at %u\n", c ? c->utcp : NULL, dir, c ? c->snd.last : 0);
+
 	if(!c) {
 		errno = EFAULT;
 		return -1;
@@ -1225,12 +1543,21 @@ int utcp_shutdown(struct utcp_connection *c, int dir) {
 
 	// 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)
+	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)
+	if(dir == UTCP_SHUT_RD) {
 		return 0;
+	}
+
+	// Only process shutting down writes once.
+	if(c->shut_wr) {
+		return 0;
+	}
+
+	c->shut_wr = true;
 
 	switch(c->state) {
 	case CLOSED:
@@ -1239,16 +1566,17 @@ int utcp_shutdown(struct utcp_connection *c, int dir) {
 		return -1;
 
 	case SYN_SENT:
-		set_state(c, CLOSED);
 		return 0;
 
 	case SYN_RECEIVED:
 	case ESTABLISHED:
 		set_state(c, FIN_WAIT_1);
 		break;
+
 	case FIN_WAIT_1:
 	case FIN_WAIT_2:
 		return 0;
+
 	case CLOSE_WAIT:
 		set_state(c, CLOSING);
 		break;
@@ -1262,44 +1590,40 @@ int utcp_shutdown(struct utcp_connection *c, int dir) {
 	c->snd.last++;
 
 	ack(c, false);
-	return 0;
-}
 
-int utcp_close(struct utcp_connection *c) {
-	if(utcp_shutdown(c, SHUT_RDWR))
-		return -1;
-	c->recv = NULL;
-	c->poll = NULL;
-	c->reapable = true;
+	if(!timerisset(&c->rtrx_timeout)) {
+		start_retransmit_timer(c);
+	}
+
 	return 0;
 }
 
-int utcp_abort(struct utcp_connection *c) {
+static bool reset_connection(struct utcp_connection *c) {
 	if(!c) {
 		errno = EFAULT;
-		return -1;
+		return false;
 	}
 
 	if(c->reapable) {
 		debug("Error: abort() called on closed connection %p\n", c);
 		errno = EBADF;
-		return -1;
+		return false;
 	}
 
 	c->recv = NULL;
 	c->poll = NULL;
-	c->reapable = true;
 
 	switch(c->state) {
 	case CLOSED:
-		return 0;
+		return true;
+
 	case LISTEN:
 	case SYN_SENT:
 	case CLOSING:
 	case LAST_ACK:
 	case TIME_WAIT:
 		set_state(c, CLOSED);
-		return 0;
+		return true;
 
 	case SYN_RECEIVED:
 	case ESTABLISHED:
@@ -1321,8 +1645,53 @@ int utcp_abort(struct utcp_connection *c) {
 	hdr.wnd = 0;
 	hdr.ctl = RST;
 
-	print_packet(c->utcp, "send", &hdr, sizeof hdr);
-	c->utcp->send(c->utcp, &hdr, sizeof hdr);
+	print_packet(c->utcp, "send", &hdr, sizeof(hdr));
+	c->utcp->send(c->utcp, &hdr, sizeof(hdr));
+	return true;
+}
+
+// Closes all the opened connections
+void utcp_abort_all_connections(struct utcp *utcp) {
+	if(!utcp) {
+		errno = EINVAL;
+		return;
+	}
+
+	for(int i = 0; i < utcp->nconnections; i++) {
+		struct utcp_connection *c = utcp->connections[i];
+
+		if(c->reapable || c->state == CLOSED) {
+			continue;
+		}
+
+		reset_connection(c);
+
+		if(c->recv) {
+			errno = 0;
+			c->recv(c, NULL, 0);
+		}
+	}
+
+	return;
+}
+
+int utcp_close(struct utcp_connection *c) {
+	if(utcp_shutdown(c, SHUT_RDWR) && errno != ENOTCONN) {
+		return -1;
+	}
+
+	c->recv = NULL;
+	c->poll = NULL;
+	c->reapable = true;
+	return 0;
+}
+
+int utcp_abort(struct utcp_connection *c) {
+	if(!reset_connection(c)) {
+		return -1;
+	}
+
+	c->reapable = true;
 	return 0;
 }
 
@@ -1339,8 +1708,10 @@ struct timeval utcp_timeout(struct utcp *utcp) {
 
 	for(int i = 0; i < utcp->nconnections; i++) {
 		struct utcp_connection *c = utcp->connections[i];
-		if(!c)
+
+		if(!c) {
 			continue;
+		}
 
 		// delete connections that have been utcp_close()d.
 		if(c->state == CLOSED) {
@@ -1349,14 +1720,18 @@ struct timeval utcp_timeout(struct utcp *utcp) {
 				free_connection(c);
 				i--;
 			}
+
 			continue;
 		}
 
 		if(timerisset(&c->conn_timeout) && timercmp(&c->conn_timeout, &now, <)) {
 			errno = ETIMEDOUT;
 			c->state = CLOSED;
-			if(c->recv)
+
+			if(c->recv) {
 				c->recv(c, NULL, 0);
+			}
+
 			continue;
 		}
 
@@ -1365,28 +1740,43 @@ struct timeval utcp_timeout(struct utcp *utcp) {
 			retransmit(c);
 		}
 
-		if(c->poll && buffer_free(&c->sndbuf) && (c->state == ESTABLISHED || c->state == CLOSE_WAIT))
-			c->poll(c, buffer_free(&c->sndbuf));
+		if(c->poll) {
+			if((c->state == ESTABLISHED || c->state == CLOSE_WAIT)) {
+				uint32_t len =  buffer_free(&c->sndbuf);
+
+				if(len) {
+					c->poll(c, len);
+				}
+			} else if(c->state == CLOSED) {
+				c->poll(c, 0);
+			}
+		}
 
-		if(timerisset(&c->conn_timeout) && timercmp(&c->conn_timeout, &next, <))
+		if(timerisset(&c->conn_timeout) && timercmp(&c->conn_timeout, &next, <)) {
 			next = c->conn_timeout;
+		}
 
-		if(timerisset(&c->rtrx_timeout) && timercmp(&c->rtrx_timeout, &next, <))
+		if(timerisset(&c->rtrx_timeout) && timercmp(&c->rtrx_timeout, &next, <)) {
 			next = c->rtrx_timeout;
+		}
 	}
 
 	struct timeval diff;
+
 	timersub(&next, &now, &diff);
+
 	return diff;
 }
 
 bool utcp_is_active(struct utcp *utcp) {
-	if(!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)
+		if(utcp->connections[i]->state != CLOSED && utcp->connections[i]->state != TIME_WAIT) {
 			return true;
+		}
 
 	return false;
 }
@@ -1397,31 +1787,41 @@ struct utcp *utcp_init(utcp_accept_t accept, utcp_pre_accept_t pre_accept, utcp_
 		return NULL;
 	}
 
-	struct utcp *utcp = calloc(1, sizeof *utcp);
-	if(!utcp)
+	struct utcp *utcp = calloc(1, sizeof(*utcp));
+
+	if(!utcp) {
 		return NULL;
+	}
 
 	utcp->accept = accept;
 	utcp->pre_accept = pre_accept;
 	utcp->send = send;
 	utcp->priv = priv;
 	utcp->mtu = DEFAULT_MTU;
-	utcp->timeout = DEFAULT_USER_TIMEOUT; // s
-	utcp->rto = START_RTO; // us
+	utcp->timeout = DEFAULT_USER_TIMEOUT; // sec
+	utcp->rto = START_RTO; // usec
 
 	return utcp;
 }
 
 void utcp_exit(struct utcp *utcp) {
-	if(!utcp)
+	if(!utcp) {
 		return;
+	}
+
 	for(int i = 0; i < utcp->nconnections; i++) {
-		if(!utcp->connections[i]->reapable)
-			debug("Warning, freeing unclosed connection %p\n", utcp->connections[i]);
-		buffer_exit(&utcp->connections[i]->rcvbuf);
-		buffer_exit(&utcp->connections[i]->sndbuf);
-		free(utcp->connections[i]);
+		struct utcp_connection *c = utcp->connections[i];
+
+		if(!c->reapable)
+			if(c->recv) {
+				c->recv(c, NULL, 0);
+			}
+
+		buffer_exit(&c->rcvbuf);
+		buffer_exit(&c->sndbuf);
+		free(c);
 	}
+
 	free(utcp->connections);
 	free(utcp);
 }
@@ -1432,8 +1832,33 @@ uint16_t utcp_get_mtu(struct utcp *utcp) {
 
 void utcp_set_mtu(struct utcp *utcp, uint16_t mtu) {
 	// TODO: handle overhead of the header
-	if(utcp)
+	if(utcp) {
 		utcp->mtu = mtu;
+	}
+}
+
+void utcp_reset_timers(struct utcp *utcp) {
+	if(!utcp) {
+		return;
+	}
+
+	struct timeval now, then;
+
+	gettimeofday(&now, NULL);
+
+	then = now;
+
+	then.tv_sec += utcp->timeout;
+
+	for(int i = 0; i < utcp->nconnections; i++) {
+		utcp->connections[i]->rtrx_timeout = now;
+		utcp->connections[i]->conn_timeout = then;
+		utcp->connections[i]->rtt_start.tv_sec = 0;
+	}
+
+	if(utcp->rto > START_RTO) {
+		utcp->rto = START_RTO;
+	}
 }
 
 int utcp_get_user_timeout(struct utcp *u) {
@@ -1441,8 +1866,9 @@ int utcp_get_user_timeout(struct utcp *u) {
 }
 
 void utcp_set_user_timeout(struct utcp *u, int timeout) {
-	if(u)
+	if(u) {
 		u->timeout = timeout;
+	}
 }
 
 size_t utcp_get_sndbuf(struct utcp_connection *c) {
@@ -1450,18 +1876,32 @@ size_t utcp_get_sndbuf(struct utcp_connection *c) {
 }
 
 size_t utcp_get_sndbuf_free(struct utcp_connection *c) {
-	if(c && (c->state == ESTABLISHED || c->state == CLOSE_WAIT))
+	if(!c) {
+		return 0;
+	}
+
+	switch(c->state) {
+	case SYN_SENT:
+	case SYN_RECEIVED:
+	case ESTABLISHED:
+	case CLOSE_WAIT:
 		return buffer_free(&c->sndbuf);
-	else
+
+	default:
 		return 0;
+	}
 }
 
 void utcp_set_sndbuf(struct utcp_connection *c, size_t size) {
-	if(!c)
+	if(!c) {
 		return;
+	}
+
 	c->sndbuf.maxsize = size;
-	if(c->sndbuf.maxsize != size)
+
+	if(c->sndbuf.maxsize != size) {
 		c->sndbuf.maxsize = -1;
+	}
 }
 
 size_t utcp_get_rcvbuf(struct utcp_connection *c) {
@@ -1469,18 +1909,23 @@ size_t utcp_get_rcvbuf(struct utcp_connection *c) {
 }
 
 size_t utcp_get_rcvbuf_free(struct utcp_connection *c) {
-	if(c && (c->state == ESTABLISHED || c->state == CLOSE_WAIT))
+	if(c && (c->state == ESTABLISHED || c->state == CLOSE_WAIT)) {
 		return buffer_free(&c->rcvbuf);
-	else
+	} else {
 		return 0;
+	}
 }
 
 void utcp_set_rcvbuf(struct utcp_connection *c, size_t size) {
-	if(!c)
+	if(!c) {
 		return;
+	}
+
 	c->rcvbuf.maxsize = size;
-	if(c->rcvbuf.maxsize != size)
+
+	if(c->rcvbuf.maxsize != size) {
 		c->rcvbuf.maxsize = -1;
+	}
 }
 
 bool utcp_get_nodelay(struct utcp_connection *c) {
@@ -1488,8 +1933,9 @@ bool utcp_get_nodelay(struct utcp_connection *c) {
 }
 
 void utcp_set_nodelay(struct utcp_connection *c, bool nodelay) {
-	if(c)
+	if(c) {
 		c->nodelay = nodelay;
+	}
 }
 
 bool utcp_get_keepalive(struct utcp_connection *c) {
@@ -1497,8 +1943,9 @@ bool utcp_get_keepalive(struct utcp_connection *c) {
 }
 
 void utcp_set_keepalive(struct utcp_connection *c, bool keepalive) {
-	if(c)
+	if(c) {
 		c->keepalive = keepalive;
+	}
 }
 
 size_t utcp_get_outq(struct utcp_connection *c) {
@@ -1506,13 +1953,15 @@ size_t utcp_get_outq(struct utcp_connection *c) {
 }
 
 void utcp_set_recv_cb(struct utcp_connection *c, utcp_recv_t recv) {
-	if(c)
+	if(c) {
 		c->recv = recv;
+	}
 }
 
 void utcp_set_poll_cb(struct utcp_connection *c, utcp_poll_t poll) {
-	if(c)
+	if(c) {
 		c->poll = poll;
+	}
 }
 
 void utcp_set_accept_cb(struct utcp *utcp, utcp_accept_t accept, utcp_pre_accept_t pre_accept) {