X-Git-Url: http://git.meshlink.io/?a=blobdiff_plain;f=utcp.c;h=8ff9553de87f966a2d0e3d9b17b38ae7f79ec844;hb=aae57951f85ef517f85788ff7f66fe82cf8b2ad0;hp=f5875e2f58943523bc9853c68d191267e45d2d11;hpb=62409f6844ec25698a7344d4837a53285f043bc0;p=utcp

diff --git a/utcp.c b/utcp.c
index f5875e2..8ff9553 100644
--- a/utcp.c
+++ b/utcp.c
@@ -29,146 +29,66 @@
 #include <sys/time.h>
 #include <sys/socket.h>
 
-#define UTCP_INTERNAL
-#include "utcp.h"
-
-#define PREP(l) char pkt[(l) + sizeof struct hdr]; struct hdr *hdr = &pkt;
-
-#define SYN 1
-#define ACK 2
-#define FIN 4
-#define RST 8
-
-struct hdr {
-	uint16_t src; // Source port
-	uint16_t dst; // Destination port
-	uint32_t seq; // Sequence number
-	uint32_t ack; // Acknowledgement number
-	uint32_t wnd; // Window size
-	uint16_t ctl; // Flags (SYN, ACK, FIN, RST)
-	uint16_t aux; // other stuff
-};
-
-enum state {
-	CLOSED,
-	LISTEN,
-	SYN_SENT,
-	SYN_RECEIVED,
-	ESTABLISHED,
-	FIN_WAIT_1,
-	FIN_WAIT_2,
-	CLOSE_WAIT,
-	CLOSING,
-	LAST_ACK,
-	TIME_WAIT
-};
-
-const char *strstate[] = {
-	"CLOSED",
-	"LISTEN",
-	"SYN_SENT",
-	"SYN_RECEIVED",
-	"ESTABLISHED",
-	"FIN_WAIT_1",
-	"FIN_WAIT_2",
-	"CLOSE_WAIT",
-	"CLOSING",
-	"LAST_ACK",
-	"TIME_WAIT"
-};
-
-struct utcp_connection {
-	void *priv;
-	struct utcp *utcp;
-	bool reapable;
-
-	uint16_t src;
-	uint16_t dst;
-	enum state state;
-
-	// The following two structures form the TCB
+#include "utcp_priv.h"
 
-	struct {
-		uint32_t una;
-		uint32_t nxt;
-		uint32_t wnd;
-		uint32_t up;
-		uint32_t wl1;
-		uint32_t wl2;
-		uint32_t iss;
-	} snd;
-
-	struct {
-		uint32_t nxt;
-		uint32_t wnd;
-		uint32_t up;
-		uint32_t irs;
-	} rcv;
-
-	utcp_recv_t recv;
-
-	struct timeval conn_timeout;
-	struct timeval rtrx_timeout;
-
-	char *sndbuf;
-	uint32_t sndbufsize;
-};
-
-struct utcp {
-	void *priv;
-
-	utcp_accept_t accept;
-	utcp_pre_accept_t pre_accept;
-	utcp_send_t send;
-
-	uint16_t mtu;
-	int timeout;
+#ifdef UTCP_DEBUG
+#include <stdarg.h>
 
-	struct utcp_connection **connections;
-	int nconnections;
-	int nallocated;
-};
-
-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]);
+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);
 	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;
 }
 
 // Connections are stored in a sorted list.
@@ -236,16 +156,20 @@ static struct utcp_connection *allocate_connection(struct utcp *utcp, uint16_t s
 		else
 			utcp->nallocated *= 2;
 		struct utcp_connection **new_array = realloc(utcp->connections, utcp->nallocated * sizeof *utcp->connections);
-		if(!new_array) {
-			errno = ENOMEM;
+		if(!new_array)
 			return NULL;
-		}
 		utcp->connections = new_array;
 	}
 
 	struct utcp_connection *c = calloc(1, sizeof *c);
-	if(!c) {
-		errno = ENOMEM;
+	if(!c)
+		return NULL;
+
+	c->sndbufsize = DEFAULT_SNDBUFSIZE;
+	c->maxsndbufsize = DEFAULT_MAXSNDBUFSIZE;
+	c->sndbuf = malloc(c->sndbufsize);
+	if(!c->sndbuf) {
+		free(c);
 		return NULL;
 	}
 
@@ -258,10 +182,6 @@ static struct utcp_connection *allocate_connection(struct utcp *utcp, uint16_t s
 	c->snd.nxt = c->snd.iss + 1;
 	c->rcv.wnd = utcp->mtu;
 	c->utcp = utcp;
-	c->sndbufsize = 65536;
-	c->sndbuf = malloc(c->sndbufsize);
-	if(!c->sndbuf)
-		c->sndbufsize = 0;
 
 	// Add it to the sorted list of connections
 
@@ -300,11 +220,11 @@ 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);
@@ -312,7 +232,7 @@ void utcp_accept(struct utcp_connection *c, utcp_recv_t recv, void *priv) {
 
 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;
 	}
@@ -322,7 +242,7 @@ 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:
@@ -333,7 +253,7 @@ 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;
 	}
@@ -348,12 +268,31 @@ ssize_t utcp_send(struct utcp_connection *c, const void *data, size_t len) {
 		return -1;
 	}
 
-	uint32_t bufused = c->snd.nxt - c->snd.una;
+	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);
+	}
 
 	if(len > c->sndbufsize - bufused)
 		len = c->sndbufsize - bufused;
 
-	memcpy(c->sndbuf + (c->snd.nxt - c->snd.una), data, len);
+	if(!len) {
+		errno == EWOULDBLOCK;
+		return 0;
+	}
+
+	memcpy(c->sndbuf + bufused, data, len);
 
 	// Send segments
 
@@ -394,10 +333,6 @@ static void swap_ports(struct hdr *hdr) {
 	hdr->dst = tmp;
 }
 
-static int32_t seqdiff(uint32_t a, uint32_t b) {
-	return a - b;
-}
-
 int utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 	if(!utcp) {
 		errno = EFAULT;
@@ -414,33 +349,56 @@ int utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 
 	print_packet(utcp, "recv", data, len);
 
+	// Drop packets smaller than the header
+
 	struct hdr 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;
 
+	// Drop packets with an unknown CTL flag
+
 	if(hdr.ctl & ~(SYN | ACK | RST | FIN)) {
 		errno = EBADMSG;
 		return -1;
 	}
 
-	//list_connections(utcp);
+	// Try to match the packet to an existing connection
 
 	struct utcp_connection *c = find_connection(utcp, hdr.dst, hdr.src);
 
 	// Is it for a new connection?
 
 	if(!c) {
+		// Ignore RST packets
+
 		if(hdr.ctl & RST)
 			return 0;
 
-		if(hdr.ctl & SYN && !(hdr.ctl & ACK) && utcp->accept && (!utcp->pre_accept || utcp->pre_accept(utcp, hdr.dst)) && (c = allocate_connection(utcp, hdr.dst, hdr.src))) { // LISTEN
-			// Return SYN+ACK
+		// Is it a SYN packet and are we LISTENing?
+
+		if(hdr.ctl & SYN && !(hdr.ctl & ACK) && utcp->accept) {
+			// If we don't want to accept it, send a RST back
+			if((utcp->pre_accept && !utcp->pre_accept(utcp, hdr.dst))) {
+				len = 1;
+				goto reset;
+			}
+
+			// Try to allocate memory, otherwise send a RST back
+			c = allocate_connection(utcp, hdr.dst, hdr.src);
+			if(!c) {
+				len = 1;
+				goto reset;
+			}
+
+			// 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;
@@ -453,123 +411,179 @@ int utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 			hdr.ctl = SYN | ACK;
 			print_packet(c->utcp, "send", &hdr, sizeof hdr);
 			utcp->send(utcp, &hdr, sizeof hdr);
-			return 0;
-		} else { // CLOSED
+		} else {
+			// No, we don't want your packets, send a RST back
 			len = 1;
 			goto reset;
 		}
+
+		return 0;
 	}
 
-	fprintf(stderr, "%p state %s\n", c->utcp, strstate[c->state]);
+	debug("%p state %s\n", c->utcp, strstate[c->state]);
 
-	if(c->state == CLOSED) {
-		fprintf(stderr, "Error: packet recv()d on closed connection %p\n", c);
-		errno = EBADF;
-		return -1;
-	}
+	// 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)
+		return 0;
 
 	// It is for an existing connection.
 
-	if(c->state == SYN_SENT) {
-		if(hdr.ctl & ACK) {
-			if(seqdiff(hdr.ack, c->snd.iss) <= 0 || seqdiff(hdr.ack, c->snd.nxt) > 0) {
-				fprintf(stderr, "Invalid ACK, %u %u %u\n", hdr.ack, c->snd.iss, c->snd.nxt);
-				goto reset;
-			}
-		}
-		if(hdr.ctl & RST) {
-			if(!(hdr.ctl & ACK))
-				return 0;
-			set_state(c, CLOSED);
-			errno = ECONNREFUSED;
-			if(c->recv)
-				c->recv(c, NULL, 0);
-			return 0;
-		}
-		if(hdr.ctl & SYN) {
-			c->dst = hdr.src;
-			c->rcv.nxt = hdr.seq + 1;
-			c->rcv.irs = hdr.seq;
-			c->snd.wnd = hdr.wnd;
+	// 1. Drop invalid packets.
 
-			if(hdr.ctl & ACK)
-				c->snd.una = hdr.ack;
-			if(seqdiff(c->snd.una, c->snd.iss) > 0) {
-				set_state(c, ESTABLISHED);
-				// TODO: signal app?
-				swap_ports(&hdr);
-				hdr.seq = c->snd.nxt;
-				hdr.ack = c->rcv.nxt;
-				hdr.ctl = ACK;
-			} else {
-				set_state(c, SYN_RECEIVED);
-				swap_ports(&hdr);
-				hdr.seq = c->snd.iss;
-				hdr.ack = c->rcv.nxt;
-				hdr.ctl = SYN | ACK;
-			}
-			print_packet(c->utcp, "send", &hdr, sizeof hdr);
-			utcp->send(utcp, &hdr, sizeof hdr);
-			// TODO: queue any data?
-		}
+	// 1a. Drop packets that should not happen in our current state.
 
-		return 0;
+	switch(c->state) {
+	case SYN_SENT:
+	case SYN_RECEIVED:
+	case ESTABLISHED:
+	case FIN_WAIT_1:
+	case FIN_WAIT_2:
+	case CLOSE_WAIT:
+	case CLOSING:
+	case LAST_ACK:
+	case TIME_WAIT:
+		break;
+	default:
+		abort();
 	}
 
+	// 1b. Drop packets with a sequence number not in our receive window.
+
 	bool acceptable;
 
-	if(len == 0)
+	if(c->state == SYN_SENT)
+		acceptable = true;
+
+	// TODO: handle packets overlapping c->rcv.nxt.
+#if 0
+	// Only use this when accepting out-of-order packets.
+	else if(len == 0)
 		if(c->rcv.wnd == 0)
 			acceptable = hdr.seq == c->rcv.nxt;
 		else
-			acceptable = (hdr.seq >= c->rcv.nxt && hdr.seq < c->rcv.nxt + c->rcv.wnd);
+			acceptable = (seqdiff(hdr.seq, c->rcv.nxt) >= 0 && seqdiff(hdr.seq, c->rcv.nxt + c->rcv.wnd) < 0);
 	else
 		if(c->rcv.wnd == 0)
+			// We don't accept data when the receive window is zero.
 			acceptable = false;
 		else
-			acceptable = (hdr.seq >= c->rcv.nxt && hdr.seq < c->rcv.nxt + c->rcv.wnd)
-				|| (hdr.seq + len - 1 >= c->rcv.nxt && hdr.seq + len - 1 < c->rcv.nxt + c->rcv.wnd);
+			// Both start and end of packet must be within the receive window
+			acceptable = (seqdiff(hdr.seq, c->rcv.nxt) >= 0 && seqdiff(hdr.seq, c->rcv.nxt + c->rcv.wnd) < 0)
+				|| (seqdiff(hdr.seq + len + 1, c->rcv.nxt) >= 0 && seqdiff(hdr.seq + len - 1, c->rcv.nxt + c->rcv.wnd) < 0);
+#else
+	if(c->state != SYN_SENT)
+		acceptable = hdr.seq == c->rcv.nxt;
+#endif
 
 	if(!acceptable) {
-		fprintf(stderr, "Packet not acceptable, %u %u %u %zu\n", hdr.seq, c->rcv.nxt, c->rcv.wnd, len);
+		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;
-		goto ack_and_drop;
+		// Otherwise, send an ACK back in the hope things improve.
+		goto ack;
 	}
 
-	c->snd.wnd = hdr.wnd;
+	c->snd.wnd = hdr.wnd; // TODO: move below
+
+	// 1c. Drop packets with an invalid ACK.
+	// ackno should not roll back, and it should also not be bigger than snd.nxt.
 
-	// TODO: check whether segment really starts at rcv.nxt, otherwise trim it.
+	if(hdr.ctl & ACK && (seqdiff(hdr.ack, c->snd.nxt) > 0 || seqdiff(hdr.ack, c->snd.una) < 0)) {
+		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;
+		goto reset;
+	}
+
+	// 2. Handle RST packets
 
 	if(hdr.ctl & RST) {
 		switch(c->state) {
+		case SYN_SENT:
+			if(!(hdr.ctl & ACK))
+				return 0;
+			// The peer has refused our connection.
+			set_state(c, CLOSED);
+			errno = ECONNREFUSED;
+			if(c->recv)
+				c->recv(c, NULL, 0);
+			return 0;
 		case SYN_RECEIVED:
-			// TODO: delete connection?
-			break;
+			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)
+				return 0;
+			// The peer has aborted our connection.
 			set_state(c, CLOSED);
 			errno = ECONNRESET;
 			if(c->recv)
 				c->recv(c, NULL, 0);
-			break;
+			return 0;
 		case CLOSING:
 		case LAST_ACK:
 		case TIME_WAIT:
-			// TODO: delete connection?
-			break;
-		default:
-			// TODO: wtf?
+			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:
+			abort();
 		}
-		set_state(c, CLOSED);
-		return 0;
 	}
 
+	// 3. Advance snd.una
+
+	uint32_t advanced = seqdiff(hdr.ack, c->snd.una);
+	c->snd.una = hdr.ack;
+
+	if(advanced) {
+		debug("%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);
+	}
+
+	// 4. Update timers
+
+	if(advanced) {
+		timerclear(&c->conn_timeout); // It should be set anew in utcp_timeout() if c->snd.una != c->snd.nxt.
+		if(c->snd.una == c->snd.nxt)
+			timerclear(&c->rtrx_timeout);
+	}
+
+	// 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)
+				goto reset;
+			c->rcv.irs = hdr.seq;
+			c->rcv.nxt = hdr.seq;
+			set_state(c, ESTABLISHED);
+			// TODO: notify application of this somehow.
+			break;
 		case SYN_RECEIVED:
 		case ESTABLISHED:
 		case FIN_WAIT_1:
@@ -578,124 +592,120 @@ int utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 		case CLOSING:
 		case LAST_ACK:
 		case TIME_WAIT:
-			set_state(c, CLOSED);
-			errno = ECONNRESET;
-			if(c->recv)
-				c->recv(c, NULL, 0);
+			// Ehm, no. We should never receive a second SYN.
 			goto reset;
-			break;
 		default:
-			// TODO: wtf?
-			return 0;
+			abort();
 		}
+
+		// SYN counts as one sequence number
+		c->rcv.nxt++;
 	}
 
-	if(!(hdr.ctl & ACK))
-		return 0;
+	// 6. Process new data
 
-	switch(c->state) {
-	case SYN_RECEIVED:
-		if(seqdiff(hdr.ack, c->snd.una) >= 0 && seqdiff(hdr.ack, c->snd.nxt) <= 0)
-			c->utcp->accept(c, hdr.dst);
-		
-		if(c->state != ESTABLISHED)
+	if(c->state == SYN_RECEIVED) {
+		// This is the ACK after the SYNACK. It should always have ACKed the SYNACK.
+		if(!advanced)
 			goto reset;
 
-		c->snd.una = hdr.ack;
-		break;
-	case ESTABLISHED:
-	case CLOSE_WAIT:
-		if(seqdiff(hdr.ack, c->snd.una) < 0)
-			return 0;
-		if(seqdiff(hdr.ack, c->snd.nxt) > 0)
-			goto ack_and_drop;
-		if(seqdiff(hdr.ack, c->snd.una) > 0 && seqdiff(hdr.ack, c->snd.nxt) <= 0) {
-			c->snd.una = hdr.ack;
-			if(seqdiff(c->snd.wl1, hdr.seq) < 0 || (c->snd.wl1 == hdr.seq && seqdiff(c->snd.wl2, hdr.ack) <= 0)) {
-				c->snd.wnd = hdr.wnd;
-				c->snd.wl1 = hdr.seq;
-				c->snd.wl2 = hdr.ack;
-			}
-		}
-		break;
-	case FIN_WAIT_1:
-		if(hdr.ack == c->snd.nxt)
-			set_state(c, FIN_WAIT_2);
-		break;
-	case FIN_WAIT_2:
-		// TODO: If nothing left to send, close.
-		break;
-	case CLOSING:
-		if(hdr.ack == c->snd.nxt) {
-			set_state(c, TIME_WAIT);
-		}
-		break;
-	case LAST_ACK:
-		if(hdr.ack == c->snd.nxt) {
+		// Are we still LISTENing?
+		if(utcp->accept)
+			utcp->accept(c, c->src);
+
+		if(c->state != ESTABLISHED) {
 			set_state(c, CLOSED);
+			c->reapable = true;
+			goto reset;
 		}
-		return 0;
-	case TIME_WAIT:
-		// TODO: retransmission of remote FIN, ACK and restart 2 MSL timeout
-		break;
-	default:
-		goto reset;
 	}
 
-	// Process data
+	if(len) {
+		switch(c->state) {
+		case SYN_SENT:
+		case SYN_RECEIVED:
+			// This should never happen.
+			abort();
+		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:
+			abort();
+		}
 
-	switch(c->state) {
-	case ESTABLISHED:
-	case FIN_WAIT_1:
-	case FIN_WAIT_2:
-		// TODO: process the data, see page 74
-		break;
-	case CLOSE_WAIT:
-	case CLOSING:
-	case LAST_ACK:
-	case TIME_WAIT:
-		break;
-	default:
-		abort();
+		int rxd;
+
+		if(c->recv) {
+			rxd = c->recv(c, data, len);
+			if(rxd < 0)
+				rxd = 0;
+			else if(rxd > len)
+				rxd = len; // Bad application, bad!
+		} else {
+			rxd = len;
+		}
+
+		c->rcv.nxt += len;
 	}
 
+	// 7. Process FIN stuff
+
 	if(hdr.ctl & FIN) {
 		switch(c->state) {
-		case CLOSED:
-		case LISTEN:
 		case SYN_SENT:
-			return 0;
 		case SYN_RECEIVED:
+			// This should never happen.
+			abort();
 		case ESTABLISHED:
 			set_state(c, CLOSE_WAIT);
-			c->rcv.nxt++;
-			goto ack_and_drop;
+			break;
 		case FIN_WAIT_1:
 			set_state(c, CLOSING);
-			c->rcv.nxt++;
-			goto ack_and_drop;
+			break;
 		case FIN_WAIT_2:
 			set_state(c, TIME_WAIT);
-			c->rcv.nxt++;
-			goto ack_and_drop;
+			break;
 		case CLOSE_WAIT:
 		case CLOSING:
 		case LAST_ACK:
 		case TIME_WAIT:
-			break;
+			// Ehm, no. We should never receive a second FIN.
+			goto reset;
 		default:
 			abort();
 		}
-	}
 
-	// Process the data
+		// FIN counts as one sequence number
+		c->rcv.nxt++;
 
-	if(len && c->recv) {
-		c->recv(c, data, len);
-		c->rcv.nxt += len;
-		goto ack_and_drop;
+		// Inform the application that the peer closed the connection.
+		if(c->recv) {
+			errno = 0;
+			c->recv(c, NULL, 0);
+		}
 	}
 
+	if(!len && !advanced)
+		return 0;
+
+	if(!len && !(hdr.ctl & SYN) && !(hdr.ctl & FIN))
+		return 0;
+
+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);
 	return 0;
 
 reset:
@@ -709,33 +719,21 @@ reset:
 		hdr.seq = 0;
 		hdr.ctl = RST | ACK;
 	}
-	print_packet(c->utcp, "send", &hdr, sizeof hdr);
+	print_packet(utcp, "send", &hdr, sizeof hdr);
 	utcp->send(utcp, &hdr, sizeof hdr);
 	return 0;
 
-ack_and_drop:
-	swap_ports(&hdr);
-	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);
-	if(c->state == CLOSE_WAIT || c->state == TIME_WAIT) {
-		errno = 0;
-		if(c->recv)
-			c->recv(c, NULL, 0);
-	}
-	return 0;
 }
 
 int utcp_shutdown(struct utcp_connection *c, int dir) {
+	debug("%p shutdown %d\n", c->utcp, 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;
 	}
@@ -758,7 +756,7 @@ int utcp_shutdown(struct utcp_connection *c, int dir) {
 	case FIN_WAIT_2:
 		return 0;
 	case CLOSE_WAIT:
-		set_state(c, LAST_ACK);
+		set_state(c, CLOSING);
 		break;
 
 	case CLOSING:
@@ -799,7 +797,7 @@ 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;
 	}
@@ -879,12 +877,19 @@ static void retransmit(struct utcp_connection *c) {
 			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);
@@ -914,7 +919,7 @@ 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--;
 			}
@@ -982,8 +987,49 @@ void utcp_exit(struct utcp *utcp) {
 	free(utcp);
 }
 
-int utcp_set_connection_timeout(struct utcp *u, int timeout) {
-	int prev = u->timeout;
+uint16_t utcp_get_mtu(struct utcp *utcp) {
+	return utcp->mtu;
+}
+
+void utcp_set_mtu(struct utcp *utcp, uint16_t mtu) {
+	// TODO: handle overhead of the header
+	utcp->mtu = mtu;
+}
+
+int utcp_get_user_timeout(struct utcp *u) {
+	return u->timeout;
+}
+
+void utcp_set_user_timeout(struct utcp *u, int timeout) {
 	u->timeout = timeout;
-	return prev;
+}
+
+size_t utcp_get_sndbuf(struct utcp_connection *c) {
+	return c->maxsndbufsize;
+}
+
+void utcp_set_sndbuf(struct utcp_connection *c, size_t size) {
+	c->maxsndbufsize = size;
+	if(c->maxsndbufsize != size)
+		c->maxsndbufsize = -1;
+}
+
+bool utcp_get_nodelay(struct utcp_connection *c) {
+	return c->nodelay;
+}
+
+void utcp_set_nodelay(struct utcp_connection *c, bool nodelay) {
+	c->nodelay = nodelay;
+}
+
+bool utcp_get_keepalive(struct utcp_connection *c) {
+	return c->keepalive;
+}
+
+void utcp_set_keepalive(struct utcp_connection *c, bool keepalive) {
+	c->keepalive = keepalive;
+}
+
+size_t utcp_get_outq(struct utcp_connection *c) {
+	return seqdiff(c->snd.nxt, c->snd.una);
 }