X-Git-Url: http://git.meshlink.io/?p=utcp;a=blobdiff_plain;f=utcp.c;h=6aa985f72701ee2eb0f6e4f1a3f9497cc6ddedd0;hp=ac598ddae28667fd9a40c28ace29255b7dd22f66;hb=97f8b67ac77d0623e536d302eb1e08666be7d411;hpb=83f65f2eee2d5c7d58b27021770926d53f0f193e

diff --git a/utcp.c b/utcp.c
index ac598dd..6aa985f 100644
--- a/utcp.c
+++ b/utcp.c
@@ -27,8 +27,6 @@
 #include <stdbool.h>
 #include <string.h>
 #include <unistd.h>
-#include <sys/time.h>
-#include <sys/socket.h>
 #include <time.h>
 
 #include "utcp_priv.h"
@@ -45,15 +43,37 @@
 #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 += USEC_PER_SEC;\
-	} while (0)
-#endif
+static void timespec_sub(const struct timespec *a, const struct timespec *b, struct timespec *r) {
+	r->tv_sec = a->tv_sec - b->tv_sec;
+	r->tv_nsec = a->tv_nsec - b->tv_nsec;
+
+	if(r->tv_nsec < 0) {
+		r->tv_sec--, r->tv_nsec += NSEC_PER_SEC;
+	}
+}
+
+static int32_t timespec_diff_usec(const struct timespec *a, const struct timespec *b) {
+	int64_t diff = (a->tv_sec - b->tv_sec) * 1000000000 + a->tv_sec - b->tv_sec;
+	return diff / 1000;
+}
+
+static bool timespec_lt(const struct timespec *a, const struct timespec *b) {
+	if(a->tv_sec == b->tv_sec) {
+		return a->tv_nsec < b->tv_nsec;
+	} else {
+		return a->tv_sec < b->tv_sec;
+	}
+}
+
+static void timespec_clear(struct timespec *a) {
+	a->tv_sec = 0;
+}
+
+static bool timespec_isset(const struct timespec *a) {
+	return a->tv_sec;
+}
+
+static long CLOCK_GRANULARITY; // usec
 
 static inline size_t min(size_t a, size_t b) {
 	return a < b ? a : b;
@@ -70,6 +90,14 @@ static inline size_t max(size_t a, size_t b) {
 #define UTCP_DEBUG_DATALEN 20
 #endif
 
+#ifndef UTCP_CLOCK
+#if defined(CLOCK_MONOTONIC_RAW) && defined(__x86_64__)
+#define UTCP_CLOCK CLOCK_MONOTONIC_RAW
+#else
+#define UTCP_CLOCK CLOCK_MONOTONIC
+#endif
+#endif
+
 static void debug(struct utcp_connection *c, const char *format, ...) {
 	struct timespec tv;
 	char buf[1024];
@@ -140,7 +168,7 @@ static void set_state(struct utcp_connection *c, enum state state) {
 	c->state = state;
 
 	if(state == ESTABLISHED) {
-		timerclear(&c->conn_timeout);
+		timespec_clear(&c->conn_timeout);
 	}
 
 	debug(c, "state %s\n", strstate[state]);
@@ -171,12 +199,40 @@ static int32_t seqdiff(uint32_t a, uint32_t b) {
 }
 
 // Buffer functions
-// TODO: convert to ringbuffers to avoid memmove() operations.
+static bool buffer_wraps(struct buffer *buf) {
+	return buf->size - buf->offset < buf->used;
+}
+
+static bool buffer_resize(struct buffer *buf, uint32_t newsize) {
+	char *newdata = realloc(buf->data, newsize);
+
+	if(!newdata) {
+		return false;
+	}
+
+	buf->data = newdata;
+
+	if(buffer_wraps(buf)) {
+		// Shift the right part of the buffer until it hits the end of the new buffer.
+		// Old situation:
+		// [345......012]
+		// New situation:
+		// [345.........|........012]
+		uint32_t tailsize = buf->size - buf->offset;
+		uint32_t newoffset = newsize - tailsize;
+		memmove(buf + newoffset, buf + buf->offset, tailsize);
+		buf->offset = newoffset;
+	}
+
+	buf->size = newsize;
+	return true;
+}
 
 // Store data into the buffer
 static ssize_t buffer_put_at(struct buffer *buf, size_t offset, const void *data, size_t len) {
 	debug(NULL, "buffer_put_at %lu %lu %lu\n", (unsigned long)buf->used, (unsigned long)offset, (unsigned long)len);
 
+	// Ensure we don't store more than maxsize bytes in total
 	size_t required = offset + len;
 
 	if(required > buf->maxsize) {
@@ -188,32 +244,41 @@ static ssize_t buffer_put_at(struct buffer *buf, size_t offset, const void *data
 		required = buf->maxsize;
 	}
 
+	// Check if we need to resize the buffer
 	if(required > buf->size) {
 		size_t newsize = buf->size;
 
 		if(!newsize) {
-			newsize = required;
-		} else {
-			do {
-				newsize *= 2;
-			} while(newsize < required);
+			newsize = 4096;
 		}
 
+		do {
+			newsize *= 2;
+		} while(newsize < required);
+
 		if(newsize > buf->maxsize) {
 			newsize = buf->maxsize;
 		}
 
-		char *newdata = realloc(buf->data, newsize);
-
-		if(!newdata) {
+		if(!buffer_resize(buf, newsize)) {
 			return -1;
 		}
+	}
+
+	uint32_t realoffset = buf->offset + offset;
 
-		buf->data = newdata;
-		buf->size = newsize;
+	if(buf->size - buf->offset < offset) {
+		// The offset wrapped
+		realoffset -= buf->size;
 	}
 
-	memcpy(buf->data + offset, data, len);
+	if(buf->size - realoffset < len) {
+		// The new chunk of data must be wrapped
+		memcpy(buf->data + realoffset, data, buf->size - realoffset);
+		memcpy(buf->data, (char *)data + buf->size - realoffset, len - (buf->size - realoffset));
+	} else {
+		memcpy(buf->data + realoffset, data, len);
+	}
 
 	if(required > buf->used) {
 		buf->used = required;
@@ -226,52 +291,59 @@ static ssize_t buffer_put(struct buffer *buf, const void *data, size_t len) {
 	return buffer_put_at(buf, buf->used, data, 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;
+// Copy data from the buffer without removing it.
+static ssize_t buffer_copy(struct buffer *buf, void *data, size_t offset, size_t len) {
+	// Ensure we don't copy more than is actually stored in the buffer
+	if(offset >= buf->used) {
+		return 0;
 	}
 
-	if(data) {
-		memcpy(data, buf->data, len);
+	if(buf->used - offset < len) {
+		len = buf->used - offset;
 	}
 
-	if(len < buf->used) {
-		memmove(buf->data, buf->data + len, buf->used - len);
+	uint32_t realoffset = buf->offset + offset;
+
+	if(buf->size - buf->offset < offset) {
+		// The offset wrapped
+		realoffset -= buf->size;
+	}
+
+	if(buf->size - realoffset < len) {
+		// The data is wrapped
+		memcpy(data, buf->data + realoffset, buf->size - realoffset);
+		memcpy((char *)data + buf->size - realoffset, buf->data, len - (buf->size - realoffset));
+	} else {
+		memcpy(data, buf->data + realoffset, 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;
+// Discard data from the buffer.
+static ssize_t buffer_discard(struct buffer *buf, size_t len) {
+	if(buf->used < len) {
+		len = buf->used;
 	}
 
-	if(offset + len > buf->used) {
-		len = buf->used - offset;
+	if(buf->size - buf->offset < len) {
+		buf->offset -= buf->size;
 	}
 
-	memcpy(data, buf->data + offset, len);
+	buf->offset += len;
+	buf->used -= len;
+
 	return len;
 }
 
-static bool buffer_init(struct buffer *buf, uint32_t len, uint32_t maxlen) {
-	memset(buf, 0, sizeof(*buf));
-
-	if(len) {
-		buf->data = malloc(len);
-
-		if(!buf->data) {
-			return false;
-		}
+static bool buffer_set_size(struct buffer *buf, uint32_t minsize, uint32_t maxsize) {
+	if(maxsize < minsize) {
+		maxsize = minsize;
 	}
 
-	buf->size = len;
-	buf->maxsize = maxlen;
-	return true;
+	buf->maxsize = maxsize;
+
+	return buf->size >= minsize || buffer_resize(buf, minsize);
 }
 
 static void buffer_exit(struct buffer *buf) {
@@ -378,12 +450,12 @@ static struct utcp_connection *allocate_connection(struct utcp *utcp, uint16_t s
 		return NULL;
 	}
 
-	if(!buffer_init(&c->sndbuf, DEFAULT_SNDBUFSIZE, DEFAULT_MAXSNDBUFSIZE)) {
+	if(!buffer_set_size(&c->sndbuf, DEFAULT_SNDBUFSIZE, DEFAULT_MAXSNDBUFSIZE)) {
 		free(c);
 		return NULL;
 	}
 
-	if(!buffer_init(&c->rcvbuf, DEFAULT_RCVBUFSIZE, DEFAULT_MAXRCVBUFSIZE)) {
+	if(!buffer_set_size(&c->rcvbuf, DEFAULT_RCVBUFSIZE, DEFAULT_MAXRCVBUFSIZE)) {
 		buffer_exit(&c->sndbuf);
 		free(c);
 		return NULL;
@@ -401,7 +473,7 @@ 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->snd.last = c->snd.nxt;
-	c->snd.cwnd = (utcp->mtu > 2190 ? 2 : utcp->mtu > 1095 ? 3 : 4) * utcp->mtu;
+	c->snd.cwnd = (utcp->mss > 2190 ? 2 : utcp->mss > 1095 ? 3 : 4) * utcp->mss;
 	c->snd.ssthresh = ~0;
 	debug_cwnd(c);
 	c->utcp = utcp;
@@ -449,19 +521,27 @@ 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;
+	clock_gettime(UTCP_CLOCK, &c->rtrx_timeout);
+
+	uint32_t rto = c->utcp->rto;
 
-	while(c->rtrx_timeout.tv_usec >= 1000000) {
-		c->rtrx_timeout.tv_usec -= 1000000;
+	while(rto > USEC_PER_SEC) {
 		c->rtrx_timeout.tv_sec++;
+		rto -= USEC_PER_SEC;
 	}
 
-	debug(c, "rtrx_timeout %ld.%06lu\n", c->rtrx_timeout.tv_sec, c->rtrx_timeout.tv_usec);
+	c->rtrx_timeout.tv_nsec += c->utcp->rto * 1000;
+
+	if(c->rtrx_timeout.tv_nsec >= NSEC_PER_SEC) {
+		c->rtrx_timeout.tv_nsec -= NSEC_PER_SEC;
+		c->rtrx_timeout.tv_sec++;
+	}
+
+	debug(c, "rtrx_timeout %ld.%06lu\n", c->rtrx_timeout.tv_sec, c->rtrx_timeout.tv_nsec);
 }
 
 static void stop_retransmit_timer(struct utcp_connection *c) {
-	timerclear(&c->rtrx_timeout);
+	timespec_clear(&c->rtrx_timeout);
 	debug(c, "rtrx_timeout cleared\n");
 }
 
@@ -500,7 +580,7 @@ struct utcp_connection *utcp_connect_ex(struct utcp *utcp, uint16_t dst, utcp_re
 	print_packet(c, "send", &pkt, sizeof(pkt));
 	utcp->send(utcp, &pkt, sizeof(pkt));
 
-	gettimeofday(&c->conn_timeout, NULL);
+	clock_gettime(UTCP_CLOCK, &c->conn_timeout);
 	c->conn_timeout.tv_sec += utcp->timeout;
 
 	start_retransmit_timer(c);
@@ -535,8 +615,8 @@ static void ack(struct utcp_connection *c, bool sendatleastone) {
 	} else if(cwndleft < left) {
 		left = cwndleft;
 
-		if(!sendatleastone || cwndleft > c->utcp->mtu) {
-			left -= left % c->utcp->mtu;
+		if(!sendatleastone || cwndleft > c->utcp->mss) {
+			left -= left % c->utcp->mss;
 		}
 	}
 
@@ -549,13 +629,7 @@ static void ack(struct utcp_connection *c, bool sendatleastone) {
 	struct {
 		struct hdr hdr;
 		uint8_t data[];
-	} *pkt;
-
-	pkt = malloc(sizeof(pkt->hdr) + c->utcp->mtu);
-
-	if(!pkt) {
-		return;
-	}
+	} *pkt = c->utcp->pkt;
 
 	pkt->hdr.src = c->src;
 	pkt->hdr.dst = c->dst;
@@ -565,7 +639,7 @@ static void ack(struct utcp_connection *c, bool sendatleastone) {
 	pkt->hdr.aux = 0;
 
 	do {
-		uint32_t seglen = left > c->utcp->mtu ? c->utcp->mtu : left;
+		uint32_t seglen = left > c->utcp->mss ? c->utcp->mss : left;
 		pkt->hdr.seq = c->snd.nxt;
 
 		buffer_copy(&c->sndbuf, pkt->data, seqdiff(c->snd.nxt, c->snd.una), seglen);
@@ -580,7 +654,7 @@ static void ack(struct utcp_connection *c, bool sendatleastone) {
 
 		if(!c->rtt_start.tv_sec) {
 			// Start RTT measurement
-			gettimeofday(&c->rtt_start, NULL);
+			clock_gettime(UTCP_CLOCK, &c->rtt_start);
 			c->rtt_seq = pkt->hdr.seq + seglen;
 			debug(c, "starting RTT measurement, expecting ack %u\n", c->rtt_seq);
 		}
@@ -588,8 +662,6 @@ static void ack(struct utcp_connection *c, bool sendatleastone) {
 		print_packet(c, "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) {
@@ -676,15 +748,16 @@ ssize_t utcp_send(struct utcp_connection *c, const void *data, size_t len) {
 
 	if(!is_reliable(c)) {
 		c->snd.una = c->snd.nxt = c->snd.last;
-		buffer_get(&c->sndbuf, NULL, c->sndbuf.used);
+		buffer_discard(&c->sndbuf, c->sndbuf.used);
+		c->do_poll = true;
 	}
 
-	if(is_reliable(c) && !timerisset(&c->rtrx_timeout)) {
+	if(is_reliable(c) && !timespec_isset(&c->rtrx_timeout)) {
 		start_retransmit_timer(c);
 	}
 
-	if(is_reliable(c) && !timerisset(&c->conn_timeout)) {
-		gettimeofday(&c->conn_timeout, NULL);
+	if(is_reliable(c) && !timespec_isset(&c->conn_timeout)) {
+		clock_gettime(UTCP_CLOCK, &c->conn_timeout);
 		c->conn_timeout.tv_sec += c->utcp->timeout;
 	}
 
@@ -710,7 +783,7 @@ static void fast_retransmit(struct utcp_connection *c) {
 		uint8_t data[];
 	} *pkt;
 
-	pkt = malloc(sizeof(pkt->hdr) + c->utcp->mtu);
+	pkt = malloc(c->utcp->mtu);
 
 	if(!pkt) {
 		return;
@@ -731,7 +804,7 @@ static void fast_retransmit(struct utcp_connection *c) {
 		pkt->hdr.seq = c->snd.una;
 		pkt->hdr.ack = c->rcv.nxt;
 		pkt->hdr.ctl = ACK;
-		uint32_t len = min(seqdiff(c->snd.last, c->snd.una), utcp->mtu);
+		uint32_t len = min(seqdiff(c->snd.last, c->snd.una), utcp->mss);
 
 		if(fin_wanted(c, c->snd.una + len)) {
 			len--;
@@ -762,13 +835,7 @@ static void retransmit(struct utcp_connection *c) {
 	struct {
 		struct hdr hdr;
 		uint8_t data[];
-	} *pkt;
-
-	pkt = malloc(sizeof(pkt->hdr) + c->utcp->mtu);
-
-	if(!pkt) {
-		return;
-	}
+	} *pkt = c->utcp->pkt;
 
 	pkt->hdr.src = c->src;
 	pkt->hdr.dst = c->dst;
@@ -808,7 +875,7 @@ static void retransmit(struct utcp_connection *c) {
 		pkt->hdr.seq = c->snd.una;
 		pkt->hdr.ack = c->rcv.nxt;
 		pkt->hdr.ctl = ACK;
-		uint32_t len = min(seqdiff(c->snd.last, c->snd.una), utcp->mtu);
+		uint32_t len = min(seqdiff(c->snd.last, c->snd.una), utcp->mss);
 
 		if(fin_wanted(c, c->snd.una + len)) {
 			len--;
@@ -817,8 +884,8 @@ static void retransmit(struct utcp_connection *c) {
 
 		// RFC 5681 slow start after timeout
 		uint32_t flightsize = seqdiff(c->snd.nxt, c->snd.una);
-		c->snd.ssthresh = max(flightsize / 2, utcp->mtu * 2); // eq. 4
-		c->snd.cwnd = utcp->mtu;
+		c->snd.ssthresh = max(flightsize / 2, utcp->mss * 2); // eq. 4
+		c->snd.cwnd = utcp->mss;
 		debug_cwnd(c);
 
 		buffer_copy(&c->sndbuf, pkt->data, 0, len);
@@ -851,7 +918,7 @@ static void retransmit(struct utcp_connection *c) {
 	c->dupack = 0; // cancel any ongoing fast recovery
 
 cleanup:
-	free(pkt);
+	return;
 }
 
 /* Update receive buffer and SACK entries after consuming data.
@@ -881,7 +948,7 @@ static void sack_consume(struct utcp_connection *c, size_t len) {
 		return;
 	}
 
-	buffer_get(&c->rcvbuf, NULL, len);
+	buffer_discard(&c->rcvbuf, len);
 
 	for(int i = 0; i < NSACKS && c->sacks[i].len;) {
 		if(len < c->sacks[i].offset) {
@@ -1252,6 +1319,19 @@ synack:
 			// Otherwise, continue processing.
 			len = 0;
 		}
+	} else {
+#if UTCP_DEBUG
+		int32_t rcv_offset = seqdiff(hdr.seq, c->rcv.nxt);
+
+		if(rcv_offset) {
+			debug(c, "packet out of order, offset %u bytes", rcv_offset);
+		}
+
+		if(rcv_offset >= 0) {
+			c->rcv.nxt = hdr.seq + len;
+		}
+
+#endif
 	}
 
 	c->snd.wnd = hdr.wnd; // TODO: move below
@@ -1372,10 +1452,10 @@ synack:
 		// RTT measurement
 		if(c->rtt_start.tv_sec) {
 			if(c->rtt_seq == hdr.ack) {
-				struct timeval now, diff;
-				gettimeofday(&now, NULL);
-				timersub(&now, &c->rtt_start, &diff);
-				update_rtt(c, diff.tv_sec * 1000000 + diff.tv_usec);
+				struct timespec now;
+				clock_gettime(UTCP_CLOCK, &now);
+				int32_t diff = timespec_diff_usec(&now, &c->rtt_start);
+				update_rtt(c, diff);
 				c->rtt_start.tv_sec = 0;
 			} else if(c->rtt_seq < hdr.ack) {
 				debug(c, "cancelling RTT measurement: %u < %u\n", c->rtt_seq, hdr.ack);
@@ -1404,7 +1484,8 @@ synack:
 #endif
 
 		if(data_acked) {
-			buffer_get(&c->sndbuf, NULL, data_acked);
+			buffer_discard(&c->sndbuf, data_acked);
+			c->do_poll = true;
 		}
 
 		// Also advance snd.nxt if possible
@@ -1425,9 +1506,9 @@ synack:
 
 		// Increase the congestion window according to RFC 5681
 		if(c->snd.cwnd < c->snd.ssthresh) {
-			c->snd.cwnd += min(advanced, utcp->mtu); // eq. 2
+			c->snd.cwnd += min(advanced, utcp->mss); // eq. 2
 		} else {
-			c->snd.cwnd += max(1, (utcp->mtu * utcp->mtu) / c->snd.cwnd); // eq. 3
+			c->snd.cwnd += max(1, (utcp->mss * utcp->mss) / c->snd.cwnd); // eq. 3
 		}
 
 		if(c->snd.cwnd > c->sndbuf.maxsize) {
@@ -1447,7 +1528,7 @@ synack:
 
 		case CLOSING:
 			if(c->snd.una == c->snd.last) {
-				gettimeofday(&c->conn_timeout, NULL);
+				clock_gettime(UTCP_CLOCK, &c->conn_timeout);
 				c->conn_timeout.tv_sec += utcp->timeout;
 				set_state(c, TIME_WAIT);
 			}
@@ -1466,8 +1547,8 @@ synack:
 				// RFC 5681 fast recovery
 				debug(c, "fast recovery started\n", c->dupack);
 				uint32_t flightsize = seqdiff(c->snd.nxt, c->snd.una);
-				c->snd.ssthresh = max(flightsize / 2, utcp->mtu * 2); // eq. 4
-				c->snd.cwnd = min(c->snd.ssthresh + 3 * utcp->mtu, c->sndbuf.maxsize);
+				c->snd.ssthresh = max(flightsize / 2, utcp->mss * 2); // eq. 4
+				c->snd.cwnd = min(c->snd.ssthresh + 3 * utcp->mss, c->sndbuf.maxsize);
 
 				if(c->snd.cwnd > c->sndbuf.maxsize) {
 					c->snd.cwnd = c->sndbuf.maxsize;
@@ -1477,7 +1558,7 @@ synack:
 
 				fast_retransmit(c);
 			} else if(c->dupack > 3) {
-				c->snd.cwnd += utcp->mtu;
+				c->snd.cwnd += utcp->mss;
 
 				if(c->snd.cwnd > c->sndbuf.maxsize) {
 					c->snd.cwnd = c->sndbuf.maxsize;
@@ -1498,10 +1579,10 @@ synack:
 	if(advanced) {
 		if(c->snd.una == c->snd.last) {
 			stop_retransmit_timer(c);
-			timerclear(&c->conn_timeout);
+			timespec_clear(&c->conn_timeout);
 		} else if(is_reliable(c)) {
 			start_retransmit_timer(c);
-			gettimeofday(&c->conn_timeout, NULL);
+			clock_gettime(UTCP_CLOCK, &c->conn_timeout);
 			c->conn_timeout.tv_sec += utcp->timeout;
 		}
 	}
@@ -1629,7 +1710,7 @@ skip_ack:
 			break;
 
 		case FIN_WAIT_2:
-			gettimeofday(&c->conn_timeout, NULL);
+			clock_gettime(UTCP_CLOCK, &c->conn_timeout);
 			c->conn_timeout.tv_sec += utcp->timeout;
 			set_state(c, TIME_WAIT);
 			break;
@@ -1760,7 +1841,7 @@ int utcp_shutdown(struct utcp_connection *c, int dir) {
 
 	ack(c, false);
 
-	if(!timerisset(&c->rtrx_timeout)) {
+	if(!timespec_isset(&c->rtrx_timeout)) {
 		start_retransmit_timer(c);
 	}
 
@@ -1878,10 +1959,10 @@ int utcp_abort(struct utcp_connection *c) {
  * The return value is the time to the next timeout in milliseconds,
  * or maybe a negative value if the timeout is infinite.
  */
-struct timeval utcp_timeout(struct utcp *utcp) {
-	struct timeval now;
-	gettimeofday(&now, NULL);
-	struct timeval next = {now.tv_sec + 3600, now.tv_usec};
+struct timespec utcp_timeout(struct utcp *utcp) {
+	struct timespec now;
+	clock_gettime(UTCP_CLOCK, &now);
+	struct timespec next = {now.tv_sec + 3600, now.tv_nsec};
 
 	for(int i = 0; i < utcp->nconnections; i++) {
 		struct utcp_connection *c = utcp->connections[i];
@@ -1901,7 +1982,7 @@ struct timeval utcp_timeout(struct utcp *utcp) {
 			continue;
 		}
 
-		if(timerisset(&c->conn_timeout) && timercmp(&c->conn_timeout, &now, <)) {
+		if(timespec_isset(&c->conn_timeout) && timespec_lt(&c->conn_timeout, &now)) {
 			errno = ETIMEDOUT;
 			c->state = CLOSED;
 
@@ -1916,14 +1997,15 @@ struct timeval utcp_timeout(struct utcp *utcp) {
 			continue;
 		}
 
-		if(timerisset(&c->rtrx_timeout) && timercmp(&c->rtrx_timeout, &now, <)) {
+		if(timespec_isset(&c->rtrx_timeout) && timespec_lt(&c->rtrx_timeout, &now)) {
 			debug(c, "retransmitting after timeout\n");
 			retransmit(c);
 		}
 
 		if(c->poll) {
-			if((c->state == ESTABLISHED || c->state == CLOSE_WAIT)) {
-				uint32_t len =  buffer_free(&c->sndbuf);
+			if((c->state == ESTABLISHED || c->state == CLOSE_WAIT) && c->do_poll) {
+				c->do_poll = false;
+				uint32_t len = buffer_free(&c->sndbuf);
 
 				if(len) {
 					c->poll(c, len);
@@ -1933,18 +2015,18 @@ struct timeval utcp_timeout(struct utcp *utcp) {
 			}
 		}
 
-		if(timerisset(&c->conn_timeout) && timercmp(&c->conn_timeout, &next, <)) {
+		if(timespec_isset(&c->conn_timeout) && timespec_lt(&c->conn_timeout, &next)) {
 			next = c->conn_timeout;
 		}
 
-		if(timerisset(&c->rtrx_timeout) && timercmp(&c->rtrx_timeout, &next, <)) {
+		if(timespec_isset(&c->rtrx_timeout) && timespec_lt(&c->rtrx_timeout, &next)) {
 			next = c->rtrx_timeout;
 		}
 	}
 
-	struct timeval diff;
+	struct timespec diff;
 
-	timersub(&next, &now, &diff);
+	timespec_sub(&next, &now, &diff);
 
 	return diff;
 }
@@ -1974,11 +2056,17 @@ struct utcp *utcp_init(utcp_accept_t accept, utcp_pre_accept_t pre_accept, utcp_
 		return NULL;
 	}
 
+	if(!CLOCK_GRANULARITY) {
+		struct timespec res;
+		clock_getres(UTCP_CLOCK, &res);
+		CLOCK_GRANULARITY = res.tv_sec * USEC_PER_SEC + res.tv_nsec / 1000;
+	}
+
 	utcp->accept = accept;
 	utcp->pre_accept = pre_accept;
 	utcp->send = send;
 	utcp->priv = priv;
-	utcp->mtu = DEFAULT_MTU;
+	utcp_set_mtu(utcp, DEFAULT_MTU);
 	utcp->timeout = DEFAULT_USER_TIMEOUT; // sec
 	utcp->rto = START_RTO; // usec
 
@@ -2016,11 +2104,31 @@ uint16_t utcp_get_mtu(struct utcp *utcp) {
 	return utcp ? utcp->mtu : 0;
 }
 
+uint16_t utcp_get_mss(struct utcp *utcp) {
+	return utcp ? utcp->mss : 0;
+}
+
 void utcp_set_mtu(struct utcp *utcp, uint16_t mtu) {
-	// TODO: handle overhead of the header
-	if(utcp) {
-		utcp->mtu = mtu;
+	if(!utcp) {
+		return;
+	}
+
+	if(mtu <= sizeof(struct hdr)) {
+		return;
 	}
+
+	if(mtu > utcp->mtu) {
+		char *new = realloc(utcp->pkt, mtu + sizeof(struct hdr));
+
+		if(!new) {
+			return;
+		}
+
+		utcp->pkt = new;
+	}
+
+	utcp->mtu = mtu;
+	utcp->mss = mtu - sizeof(struct hdr);
 }
 
 void utcp_reset_timers(struct utcp *utcp) {
@@ -2028,9 +2136,9 @@ void utcp_reset_timers(struct utcp *utcp) {
 		return;
 	}
 
-	struct timeval now, then;
+	struct timespec now, then;
 
-	gettimeofday(&now, NULL);
+	clock_gettime(UTCP_CLOCK, &now);
 
 	then = now;
 
@@ -2043,11 +2151,11 @@ void utcp_reset_timers(struct utcp *utcp) {
 			continue;
 		}
 
-		if(timerisset(&c->rtrx_timeout)) {
+		if(timespec_isset(&c->rtrx_timeout)) {
 			c->rtrx_timeout = now;
 		}
 
-		if(timerisset(&c->conn_timeout)) {
+		if(timespec_isset(&c->conn_timeout)) {
 			c->conn_timeout = then;
 		}
 
@@ -2100,6 +2208,8 @@ void utcp_set_sndbuf(struct utcp_connection *c, size_t size) {
 	if(c->sndbuf.maxsize != size) {
 		c->sndbuf.maxsize = -1;
 	}
+
+	c->do_poll = buffer_free(&c->sndbuf);
 }
 
 size_t utcp_get_rcvbuf(struct utcp_connection *c) {
@@ -2167,6 +2277,7 @@ void utcp_set_recv_cb(struct utcp_connection *c, utcp_recv_t recv) {
 void utcp_set_poll_cb(struct utcp_connection *c, utcp_poll_t poll) {
 	if(c) {
 		c->poll = poll;
+		c->do_poll = buffer_free(&c->sndbuf);
 	}
 }
 
@@ -2188,21 +2299,21 @@ void utcp_expect_data(struct utcp_connection *c, bool expect) {
 
 	if(expect) {
 		// If we expect data, start the connection timer.
-		if(!timerisset(&c->conn_timeout)) {
-			gettimeofday(&c->conn_timeout, NULL);
+		if(!timespec_isset(&c->conn_timeout)) {
+			clock_gettime(UTCP_CLOCK, &c->conn_timeout);
 			c->conn_timeout.tv_sec += c->utcp->timeout;
 		}
 	} else {
 		// If we want to cancel expecting data, only clear the timer when there is no unACKed data.
 		if(c->snd.una == c->snd.last) {
-			timerclear(&c->conn_timeout);
+			timespec_clear(&c->conn_timeout);
 		}
 	}
 }
 
 void utcp_offline(struct utcp *utcp, bool offline) {
-	struct timeval now;
-	gettimeofday(&now, NULL);
+	struct timespec now;
+	clock_gettime(UTCP_CLOCK, &now);
 
 	for(int i = 0; i < utcp->nconnections; i++) {
 		struct utcp_connection *c = utcp->connections[i];
@@ -2214,7 +2325,7 @@ void utcp_offline(struct utcp *utcp, bool offline) {
 		utcp_expect_data(c, offline);
 
 		if(!offline) {
-			if(timerisset(&c->rtrx_timeout)) {
+			if(timespec_isset(&c->rtrx_timeout)) {
 				c->rtrx_timeout = now;
 			}
 
@@ -2226,3 +2337,7 @@ void utcp_offline(struct utcp *utcp, bool offline) {
 		utcp->rto = START_RTO;
 	}
 }
+
+void utcp_set_clock_granularity(long granularity) {
+	CLOCK_GRANULARITY = granularity;
+}