X-Git-Url: http://git.meshlink.io/?a=blobdiff_plain;f=utcp.c;h=f5484ab82b92e53e5365f7de75a822881218a7f4;hb=aef3cad25ea81f727608689ef97fce9e0dbe5285;hp=97c43637f4ce52ceb74efd978c278f3e0df1eafb;hpb=4368d8c9956242f0bdc00d43ebf32a72332522c1;p=utcp

diff --git a/utcp.c b/utcp.c
index 97c4363..f5484ab 100644
--- a/utcp.c
+++ b/utcp.c
@@ -19,6 +19,7 @@
 
 #define _GNU_SOURCE
 
+#include <assert.h>
 #include <errno.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -31,60 +32,167 @@
 
 #include "utcp_priv.h"
 
-static void set_state(struct utcp_connection *c, enum state state) {
-	c->state = state;
-	if(state == ESTABLISHED)
-		timerclear(&c->conn_timeout);
-	fprintf(stderr, "%p new state: %s\n", c->utcp, strstate[state]);
+#ifndef EBADMSG
+#define EBADMSG         104
+#endif
+
+#ifndef SHUT_RDWR
+#define SHUT_RDWR 2
+#endif
+
+#ifdef poll
+#undef poll
+#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)
+#endif
+
+#ifdef UTCP_DEBUG
+#include <stdarg.h>
+
+static void debug(const char *format, ...) {
+	va_list ap;
+	va_start(ap, format);
+	vfprintf(stderr, format, ap);
+	va_end(ap);
 }
 
 static void print_packet(struct utcp *utcp, const char *dir, const void *pkt, size_t len) {
 	struct hdr hdr;
 	if(len < sizeof hdr) {
-		fprintf(stderr, "%p %s: short packet (%zu bytes)\n", utcp, dir, len);
+		debug("%p %s: short packet (%zu bytes)\n", utcp, dir, len);
 		return;
 	}
 
 	memcpy(&hdr, pkt, sizeof hdr);
-	fprintf (stderr, "%p %s: src=%u dst=%u seq=%u ack=%u wnd=%u ctl=", utcp, dir, hdr.src, hdr.dst, hdr.seq, hdr.ack, hdr.wnd);
+	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)
-		fprintf(stderr, "SYN");
+		debug("SYN");
 	if(hdr.ctl & RST)
-		fprintf(stderr, "RST");
+		debug("RST");
 	if(hdr.ctl & FIN)
-		fprintf(stderr, "FIN");
+		debug("FIN");
 	if(hdr.ctl & ACK)
-		fprintf(stderr, "ACK");
+		debug("ACK");
 
 	if(len > sizeof hdr) {
-		fprintf(stderr, " data=");
+		debug(" data=");
 		for(int i = sizeof hdr; i < len; i++) {
 			const char *data = pkt;
-			fprintf(stderr, "%c", data[i] >= 32 ? data[i] : '.');
+			debug("%c", data[i] >= 32 ? data[i] : '.');
 		}
 	}
 
-	fprintf(stderr, "\n");
+	debug("\n");
+}
+#else
+#define debug(...)
+#define print_packet(...)
+#endif
+
+static void set_state(struct utcp_connection *c, enum state state) {
+	c->state = state;
+	if(state == ESTABLISHED)
+		timerclear(&c->conn_timeout);
+	debug("%p new state: %s\n", c->utcp, strstate[state]);
 }
 
 static inline void list_connections(struct utcp *utcp) {
-	fprintf(stderr, "%p has %d connections:\n", utcp, utcp->nconnections);
+	debug("%p has %d connections:\n", utcp, utcp->nconnections);
 	for(int i = 0; i < utcp->nconnections; i++)
-		fprintf(stderr, "  %u -> %u state %s\n", utcp->connections[i]->src, utcp->connections[i]->dst, strstate[utcp->connections[i]->state]);
+		debug("  %u -> %u state %s\n", utcp->connections[i]->src, utcp->connections[i]->dst, strstate[utcp->connections[i]->state]);
 }
 
 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;
-	if(!a->src || !b->src)
-		abort();
+
+	assert(a && b);
+	assert(a->src && b->src);
+
 	int c = (int)a->src - (int)b->src;
 	if(c)
 		return c;
@@ -106,13 +214,14 @@ static struct utcp_connection *find_connection(const struct utcp *utcp, uint16_t
 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);
-	if(!cp)
-		abort();
+
+	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--;
 
+	buffer_exit(&c->sndbuf);
 	free(c);
 }
 
@@ -151,10 +260,7 @@ 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;
 	}
@@ -167,6 +273,8 @@ static struct utcp_connection *allocate_connection(struct utcp *utcp, uint16_t s
 	c->snd.una = c->snd.iss;
 	c->snd.nxt = c->snd.iss + 1;
 	c->rcv.wnd = utcp->mtu;
+	c->snd.last = c->snd.nxt;
+	c->snd.cwnd = utcp->mtu;
 	c->utcp = utcp;
 
 	// Add it to the sorted list of connections
@@ -183,6 +291,7 @@ struct utcp_connection *utcp_connect(struct utcp *utcp, uint16_t dst, utcp_recv_
 		return NULL;
 
 	c->recv = recv;
+	c->priv = priv;
 
 	struct hdr hdr;
 
@@ -190,8 +299,9 @@ struct utcp_connection *utcp_connect(struct utcp *utcp, uint16_t dst, utcp_recv_
 	hdr.dst = c->dst;
 	hdr.seq = c->snd.iss;
 	hdr.ack = 0;
-	hdr.ctl = SYN;
 	hdr.wnd = c->rcv.wnd;
+	hdr.ctl = SYN;
+	hdr.aux = 0;
 
 	set_state(c, SYN_SENT);
 
@@ -206,19 +316,78 @@ struct utcp_connection *utcp_connect(struct utcp *utcp, uint16_t dst, utcp_recv_
 
 void utcp_accept(struct utcp_connection *c, utcp_recv_t recv, void *priv) {
 	if(c->reapable || c->state != SYN_RECEIVED) {
-		fprintf(stderr, "Error: accept() called on invalid connection %p in state %s\n", c, strstate[c->state]);
+		debug("Error: accept() called on invalid connection %p in state %s\n", c, strstate[c->state]);
 		return;
 	}
 
-	fprintf(stderr, "%p accepted, %p %p\n", c, recv, priv);
+	debug("%p accepted, %p %p\n", c, recv, priv);
 	c->recv = recv;
 	c->priv = priv;
 	set_state(c, ESTABLISHED);
 }
 
+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);
+
+	assert(left >= 0);
+
+	if(cwndleft <= 0)
+		cwndleft = 0;
+
+	if(cwndleft < left)
+		left = cwndleft;
+
+	if(!left && !sendatleastone)
+		return;
+
+	struct {
+		struct hdr hdr;
+		char data[];
+	} *pkt;
+
+	pkt = malloc(sizeof pkt->hdr + c->utcp->mtu);
+	if(!pkt->data)
+		return;
+
+	pkt->hdr.src = c->src;
+	pkt->hdr.dst = c->dst;
+	pkt->hdr.ack = c->rcv.nxt;
+	pkt->hdr.wnd = c->snd.wnd;
+	pkt->hdr.ctl = ACK;
+	pkt->hdr.aux = 0;
+
+	do {
+		uint32_t seglen = left > c->utcp->mtu ? c->utcp->mtu : left;
+		pkt->hdr.seq = c->snd.nxt;
+
+		buffer_copy(&c->sndbuf, pkt->data, seqdiff(c->snd.nxt, c->snd.una), seglen);
+
+		c->snd.nxt += 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;
+			}
+		}
+
+		print_packet(c->utcp, "send", pkt, sizeof pkt->hdr + seglen);
+		c->utcp->send(c->utcp, pkt, sizeof pkt->hdr + seglen);
+	} while(left);
+
+	free(pkt);
+}
+
 ssize_t utcp_send(struct utcp_connection *c, const void *data, size_t len) {
 	if(c->reapable) {
-		fprintf(stderr, "Error: send() called on closed connection %p\n", c);
+		debug("Error: send() called on closed connection %p\n", c);
 		errno = EBADF;
 		return -1;
 	}
@@ -228,7 +397,7 @@ ssize_t utcp_send(struct utcp_connection *c, const void *data, size_t len) {
 	case LISTEN:
 	case SYN_SENT:
 	case SYN_RECEIVED:
-		fprintf(stderr, "Error: send() called on unconnected connection %p\n", c);
+		debug("Error: send() called on unconnected connection %p\n", c);
 		errno = ENOTCONN;
 		return -1;
 	case ESTABLISHED:
@@ -239,7 +408,7 @@ ssize_t utcp_send(struct utcp_connection *c, const void *data, size_t len) {
 	case CLOSING:
 	case LAST_ACK:
 	case TIME_WAIT:
-		fprintf(stderr, "Error: send() called on closing connection %p\n", c);
+		debug("Error: send() called on closing connection %p\n", c);
 		errno = EPIPE;
 		return -1;
 	}
@@ -254,72 +423,92 @@ 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) {
-		if(c->sndbufsize > c->maxsndbufsize / 2)
-			c->sndbufsize = c->maxsndbufsize;
-		else
-			c->sndbufsize *= 2;
-		c->sndbuf = realloc(c->sndbuf, c->sndbufsize);
+	len = buffer_put(&c->sndbuf, data, len);
+	if(len <= 0) {
+		errno = EWOULDBLOCK;
+		return 0;
 	}
 
-	if(len > c->sndbufsize - bufused)
-		len = c->sndbufsize - bufused;
+	c->snd.last += len;
+	ack(c, false);
+	return len;
+}
 
-	if(!len) {
-		errno == EWOULDBLOCK;
-		return 0;
-	}
+static void swap_ports(struct hdr *hdr) {
+	uint16_t tmp = hdr->src;
+	hdr->src = hdr->dst;
+	hdr->dst = tmp;
+}
 
-	memcpy(c->sndbuf + bufused, data, len);
+static void retransmit(struct utcp_connection *c) {
+	if(c->state == CLOSED || c->snd.nxt == c->snd.una)
+		return;
 
-	// Send segments
+	struct utcp *utcp = c->utcp;
 
 	struct {
 		struct hdr hdr;
-		char data[c->utcp->mtu];
-	} pkt;
+		char data[];
+	} *pkt;
 
-	pkt.hdr.src = c->src;
-	pkt.hdr.dst = c->dst;
-	pkt.hdr.ack = c->rcv.nxt;
-	pkt.hdr.wnd = c->snd.wnd;
-	pkt.hdr.ctl = ACK;
+	pkt = malloc(sizeof pkt->hdr + c->utcp->mtu);
+	if(!pkt)
+		return;
 
-	uint32_t left = len;
+	pkt->hdr.src = c->src;
+	pkt->hdr.dst = c->dst;
 
-	while(left) {
-		uint32_t seglen = left > c->utcp->mtu ? c->utcp->mtu : left;
-		pkt.hdr.seq = c->snd.nxt;
+	switch(c->state) {
+		case LISTEN:
+			// TODO: this should not happen
+			break;
 
-		memcpy(pkt.data, data, seglen);
+		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;
 
-		c->snd.nxt += seglen;
-		data += seglen;
-		left -= seglen;
+		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;
+			}
+			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;
 
-		print_packet(c->utcp, "send", &pkt, sizeof pkt.hdr + seglen);
-		c->utcp->send(c->utcp, &pkt, sizeof pkt.hdr + seglen);
+		default:
+			// TODO: implement
+			abort();
 	}
 
-	fprintf(stderr, "len=%zu\n", len);
-	return len;
+	free(pkt);
 }
 
-static void swap_ports(struct hdr *hdr) {
-	uint16_t tmp = hdr->src;
-	hdr->src = hdr->dst;
-	hdr->dst = tmp;
-}
 
-int utcp_recv(struct utcp *utcp, const void *data, size_t len) {
+ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 	if(!utcp) {
 		errno = EFAULT;
 		return -1;
@@ -406,7 +595,7 @@ int utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 		return 0;
 	}
 
-	fprintf(stderr, "%p state %s\n", c->utcp, strstate[c->state]);
+	debug("%p state %s\n", c->utcp, strstate[c->state]);
 
 	// In case this is for a CLOSED connection, ignore the packet.
 	// TODO: make it so incoming packets can never match a CLOSED connection.
@@ -416,6 +605,8 @@ int 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.
@@ -464,12 +655,13 @@ int utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 #endif
 
 	if(!acceptable) {
-		fprintf(stderr, "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
@@ -478,7 +670,7 @@ int utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 	// ackno should not roll back, and it should also not be bigger than snd.nxt.
 
 	if(hdr.ctl & ACK && (seqdiff(hdr.ack, c->snd.nxt) > 0 || seqdiff(hdr.ack, c->snd.una) < 0)) {
-		fprintf(stderr, "Packet ack seqno out of range, %u %u %u\n", hdr.ack, c->snd.una, c->snd.nxt);
+		debug("Packet ack seqno out of range, %u %u %u\n", hdr.ack, c->snd.una, c->snd.nxt);
 		// Ignore unacceptable RST packets.
 		if(hdr.ctl & RST)
 			return 0;
@@ -538,21 +730,70 @@ int utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 	// 3. Advance snd.una
 
 	uint32_t advanced = seqdiff(hdr.ack, c->snd.una);
-	c->snd.una = hdr.ack;
+	prevrcvnxt = c->rcv.nxt;
 
 	if(advanced) {
-		fprintf(stderr, "%p advanced %u\n", utcp, advanced);
-		// Make room in the send buffer.
-		// TODO: try to avoid memmoving too much. Circular buffer?
-		uint32_t left = seqdiff(c->snd.nxt, hdr.ack);
-		if(left)
-			memmove(c->sndbuf, c->sndbuf + advanced, left);
+		int32_t data_acked = advanced;
+
+		switch(c->state) {
+			case SYN_SENT:
+			case SYN_RECEIVED:
+				data_acked--;
+				break;
+			// TODO: handle FIN as well.
+			default:
+				break;
+		}
+
+		assert(data_acked >= 0);
+
+		int32_t bufused = seqdiff(c->snd.last, c->snd.una);
+		assert(data_acked <= bufused);
+
+		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->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)
+				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) {
+			c->dupack++;
+			if(c->dupack == 3) {
+				debug("Triplicate ACK\n");
+				//TODO: Resend one packet and go to fast recovery mode. See RFC 6582.
+				//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;
+			}
+		}
 	}
 
 	// 4. Update timers
 
 	if(advanced) {
-		timerclear(&c->conn_timeout); // It should be set anew in utcp_timeout() if c->snd.una != c->snd.nxt.
+		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.nxt)
 			timerclear(&c->rtrx_timeout);
 	}
@@ -626,10 +867,14 @@ int utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 			abort();
 		}
 
-		int rxd;
+		ssize_t rxd;
 
 		if(c->recv) {
 			rxd = c->recv(c, data, len);
+			if(rxd != len) {
+				// TODO: once we have a receive buffer, handle the application not accepting all data.
+				abort();
+			}
 			if(rxd < 0)
 				rxd = 0;
 			else if(rxd > len)
@@ -656,6 +901,8 @@ int utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 			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:
@@ -670,6 +917,7 @@ int utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 
 		// FIN counts as one sequence number
 		c->rcv.nxt++;
+		len++;
 
 		// Inform the application that the peer closed the connection.
 		if(c->recv) {
@@ -678,20 +926,14 @@ int utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 		}
 	}
 
-	if(!len && !advanced)
-		return 0;
-
-	if(!len && !(hdr.ctl & SYN) && !(hdr.ctl & FIN))
-		return 0;
+	// Now we send something back if:
+	// - we advanced rcv.nxt (ie, we got some data that needs to be ACKed)
+	//   -> sendatleastone = true
+	// - or we got an ack, so we should maybe send a bit more data
+	//   -> sendatleastone = false
 
 ack:
-	hdr.src = c->src;
-	hdr.dst = c->dst;
-	hdr.seq = c->snd.nxt;
-	hdr.ack = c->rcv.nxt;
-	hdr.ctl = ACK;
-	print_packet(c->utcp, "send", &hdr, sizeof hdr);
-	utcp->send(utcp, &hdr, sizeof hdr);
+	ack(c, prevrcvnxt != c->rcv.nxt);
 	return 0;
 
 reset:
@@ -712,14 +954,14 @@ reset:
 }
 
 int utcp_shutdown(struct utcp_connection *c, int dir) {
-	fprintf(stderr, "%p shutdown %d\n", c->utcp, dir);
+	debug("%p shutdown %d\n", c ? c->utcp : NULL, dir);
 	if(!c) {
 		errno = EFAULT;
 		return -1;
 	}
 
 	if(c->reapable) {
-		fprintf(stderr, "Error: shutdown() called on closed connection %p\n", c);
+		debug("Error: shutdown() called on closed connection %p\n", c);
 		errno = EBADF;
 		return -1;
 	}
@@ -751,27 +993,17 @@ int utcp_shutdown(struct utcp_connection *c, int dir) {
 		return 0;
 	}
 
-	// Send FIN
-
-	struct hdr hdr;
-
-	hdr.src = c->src;
-	hdr.dst = c->dst;
-	hdr.seq = c->snd.nxt;
-	hdr.ack = c->rcv.nxt;
-	hdr.wnd = c->snd.wnd;
-	hdr.ctl = FIN | ACK;
-
-	c->snd.nxt += 1;
+	c->snd.last++;
 
-	print_packet(c->utcp, "send", &hdr, sizeof hdr);
-	c->utcp->send(c->utcp, &hdr, sizeof hdr);
+	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;
 	return 0;
 }
@@ -783,11 +1015,13 @@ int utcp_abort(struct utcp_connection *c) {
 	}
 
 	if(c->reapable) {
-		fprintf(stderr, "Error: abort() called on closed connection %p\n", c);
+		debug("Error: abort() called on closed connection %p\n", c);
 		errno = EBADF;
 		return -1;
 	}
 
+	c->recv = NULL;
+	c->poll = NULL;
 	c->reapable = true;
 
 	switch(c->state) {
@@ -826,74 +1060,13 @@ 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[c->utcp->mtu];
-	} pkt;
-
-	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();
-	}
-}
-
 /* 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};
@@ -905,7 +1078,7 @@ int utcp_timeout(struct utcp *utcp) {
 
 		if(c->state == CLOSED) {
 			if(c->reapable) {
-				fprintf(stderr, "Reaping %p\n", c);
+				debug("Reaping %p\n", c);
 				free_connection(c);
 				i--;
 			}
@@ -924,6 +1097,9 @@ int 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(timerisset(&c->conn_timeout) && timercmp(&c->conn_timeout, &next, <))
 			next = c->conn_timeout;
 
@@ -940,9 +1116,7 @@ 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;
 }
 
 struct utcp *utcp_init(utcp_accept_t accept, utcp_pre_accept_t pre_accept, utcp_send_t send, void *priv) {
@@ -968,8 +1142,13 @@ struct utcp *utcp_init(utcp_accept_t accept, utcp_pre_accept_t pre_accept, utcp_
 void utcp_exit(struct utcp *utcp) {
 	if(!utcp)
 		return;
-	for(int i = 0; i < utcp->nconnections; i++)
-		free_connection(utcp->connections[i]);
+	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]->sndbuf);
+		free(utcp->connections[i]);
+	}
+	free(utcp->connections);
 	free(utcp);
 }
 
@@ -991,13 +1170,17 @@ void utcp_set_user_timeout(struct utcp *u, int timeout) {
 }
 
 size_t utcp_get_sndbuf(struct utcp_connection *c) {
-	return c->maxsndbufsize;
+	return c->sndbuf.maxsize;
+}
+
+size_t utcp_get_sndbuf_free(struct utcp_connection *c) {
+	return buffer_free(&c->sndbuf);
 }
 
 void utcp_set_sndbuf(struct utcp_connection *c, size_t size) {
-	c->maxsndbufsize = size;
-	if(c->maxsndbufsize != size)
-		c->maxsndbufsize = -1;
+	c->sndbuf.maxsize = size;
+	if(c->sndbuf.maxsize != size)
+		c->sndbuf.maxsize = -1;
 }
 
 bool utcp_get_nodelay(struct utcp_connection *c) {
@@ -1019,3 +1202,11 @@ void utcp_set_keepalive(struct utcp_connection *c, bool keepalive) {
 size_t utcp_get_outq(struct utcp_connection *c) {
 	return seqdiff(c->snd.nxt, c->snd.una);
 }
+
+void utcp_set_recv_cb(struct utcp_connection *c, utcp_recv_t recv) {
+	c->recv = recv;
+}
+
+void utcp_set_poll_cb(struct utcp_connection *c, utcp_poll_t poll) {
+	c->poll = poll;
+}