Updated fragment timeouts to use timeval for better precision

src/window.c

@@ -17,6 +17,7 @@
 #include <unistd.h>
 #include <stdint.h>
 #include <time.h>
+#include <sys/time.h>
 #include <stdio.h>
 #include <err.h>
 #include <string.h>
@@ -51,6 +52,8 @@ window_buffer_init(size_t length, unsigned windowsize, unsigned fragsize, int di
 	buf->maxfraglen = fragsize;
 	buf->window_end = AFTER(buf, windowsize);
 	buf->direction = dir;
+	buf->timeout.tv_sec = 5;
+	buf->timeout.tv_usec = 0;
 
 	return buf;
 }
@@ -121,8 +124,9 @@ window_append_fragment(struct frag_buffer *w, fragment *src)
 }
 
 /* Handles fragment received from the sending side (RECV)
- * Returns seq ID of packet to be ACKed immediately */
-int
+ * Returns index of fragment in window or <0 if dropped
+ * The next ACK MUST be for this fragment */
+ssize_t
 window_process_incoming_fragment(struct frag_buffer *w, fragment *f)
 {
 	/* Check if packet is in window */
@@ -131,30 +135,31 @@ window_process_incoming_fragment(struct frag_buffer *w, fragment *f)
 	startid = w->start_seq_id;
 	endid = (w->start_seq_id + w->windowsize) % MAX_SEQ_ID;
 	if (!INWINDOW_SEQ(startid, endid, f->seqID)) {
-		WDEBUG("Dropping frag with seqID %u: not in window (%u-%u)\n",
-				  f->seqID, startid, endid);
+		WDEBUG("Dropping frag with seqID %u: not in window (%u-%u)\n", f->seqID, startid, endid);
 		w->oos++;
-		/* ACK duplicate so sender can move on ASAP */
-		return f->seqID;
+		return -1;
 	}
 	/* Place fragment into correct location in buffer */
-	size_t dest = WRAP(w->window_start + SEQ_OFFSET(startid, f->seqID));
-	WDEBUG("   Putting frag seq %u into frags[%lu + %u = %lu]", f->seqID, w->window_start, SEQ_OFFSET(startid, f->seqID), dest);
+	ssize_t dest = WRAP(w->window_start + SEQ_OFFSET(startid, f->seqID));
+	WDEBUG("   Putting frag seq %u into frags[%lu + %u = %lu]",
+		   f->seqID, w->window_start, SEQ_OFFSET(startid, f->seqID), dest);
 	/* Check if fragment already received */
 	fd = &w->frags[dest];
 	if (fd->len != 0) {
 		WDEBUG("Received duplicate frag, dropping. (prev %u/new %u)", fd->seqID, f->seqID);
 		if (f->seqID == fd->seqID)
-			return f->seqID;
+			return -1;
 	}
 	memcpy(fd, f, sizeof(fragment));
-	fd->retries = 0;
-	fd->ack_other = -1;
-	/* We assume this packet gets ACKed immediately on return of this function */
-	fd->acks = 1;
 	w->numitems ++;
 
-	return f->seqID;
+	fd->retries = 0;
+	fd->ack_other = -1;
+
+	/* We assume this packet gets ACKed immediately on return of this function */
+	fd->acks = 1;
+
+	return dest;
 }
 
 /* Reassembles first complete sequence of fragments into data. (RECV)
@@ -235,14 +240,21 @@ window_reassemble_data(struct frag_buffer *w, uint8_t *data, size_t maxlen, int
 size_t
 window_sending(struct frag_buffer *w)
 {
+	struct timeval timeout, now;
 	fragment *f;
 	size_t tosend = 0;
+
 	if (w->numitems == 0)
 		return 0;
+
+	gettimeofday(&now, NULL);
+
 	for (size_t i = 0; i < w->windowsize; i++) {
 		f = &w->frags[WRAP(w->window_start + i)];
 		if (f->len == 0 || f->acks >= 1) continue;
-		if (f->retries < 1 || difftime(time(NULL), f->lastsent) >= ACK_TIMEOUT) {
+
+		timeradd(&w->timeout, &f->lastsent, &timeout);
+		if (f->retries < 1 || !timercmp(&now, &timeout, <)) {
 			/* Fragment not sent or timed out (to be re-sent) */
 			tosend++;
 		}
@@ -255,14 +267,21 @@ window_sending(struct frag_buffer *w)
 fragment *
 window_get_next_sending_fragment(struct frag_buffer *w, int *other_ack)
 {
+	struct timeval timeout, now;
 	fragment *f = NULL;
+
 	if (*other_ack >= MAX_SEQ_ID || *other_ack < 0)
 		*other_ack = -1;
+
+	gettimeofday(&now, NULL);
+
 	for (size_t i = 0; i < w->windowsize; i++) {
 		f = &w->frags[WRAP(w->window_start + i)];
 		if (f->acks >= 1) continue;
-		/* TODO: use timeval for more precise timeouts */
-		if (f->retries >= 1 && difftime(time(NULL), f->lastsent) >= ACK_TIMEOUT) {
+
+		timeradd(&w->timeout, &f->lastsent, &timeout);
+
+		if (f->retries >= 1 && !timercmp(&now, &timeout, <)) {
 			/* Fragment sent before, not ACK'd */
 			WDEBUG("Sending fragment %u again, %u retries so far, %u resent overall\n", f->seqID, f->retries, w->resends);
 			w->resends ++;
@@ -271,7 +290,6 @@ window_get_next_sending_fragment(struct frag_buffer *w, int *other_ack)
 			/* Fragment not sent */
 			goto found;
 		}
-
 	}
 	if (f)
 		WDEBUG("Not sending any fragments (last frag checked: retries %u, seqid %u, len %lu)",
@@ -286,7 +304,7 @@ window_get_next_sending_fragment(struct frag_buffer *w, int *other_ack)
 	f->start &= 1;
 	f->end &= 1;
 	f->retries++;
-	time(&f->lastsent);
+	gettimeofday(&f->lastsent, NULL);
 	return f;
 }
 

src/window.h

@@ -19,7 +19,6 @@
 
 #define MAX_SEQ_ID 256
 #define MAX_FRAGSIZE 4096
-#define ACK_TIMEOUT 5
 
 #define WINDOW_SENDING 1
 #define WINDOW_RECVING 0
@@ -37,7 +36,7 @@ typedef struct fragment {
 	uint8_t end;				/* end of chunk flag */
 	uint8_t data[MAX_FRAGSIZE];	/* fragment data */
 	unsigned retries;			/* number of times fragment has been sent */
-	time_t lastsent;	/* timestamp of most recent send attempt TODO: millisecond precision*/
+	struct timeval lastsent;	/* timestamp of most recent send attempt */
 	int acks;					/* number of times packet has been ack'd (should be <= 1) */
 } fragment;
 
@@ -56,6 +55,7 @@ struct frag_buffer {
 	unsigned resends;		/* number of fragments resent */
 	unsigned oos;			/* Number of out-of-sequence fragments received */
 	int direction;			/* Sending or recving */
+	struct timeval timeout;	/* Fragment timeout before resend */
 };
 
 extern int window_debug;
@@ -113,7 +113,7 @@ size_t window_buffer_available(struct frag_buffer *w);
 int window_append_fragment(struct frag_buffer *w, fragment *src);
 
 /* Handles fragment received from the sending side (RECV) */
-int window_process_incoming_fragment(struct frag_buffer *w, fragment *f);
+ssize_t window_process_incoming_fragment(struct frag_buffer *w, fragment *f);
 
 /* Reassembles first complete sequence of fragments into data. (RECV)
  * Returns length of data reassembled, or 0 if no data reassembled */