Increased bad fragment tolerance to keep data flowing

src/window.c

@@ -24,6 +24,7 @@
 #include <stdlib.h>
 
 #include "common.h"
+#include "util.h"
 #include "window.h"
 
 int window_debug = 0;
@@ -123,33 +124,49 @@ window_append_fragment(struct frag_buffer *w, fragment *src)
 	return 1;
 }
 
+
+ssize_t
+window_process_incoming_fragment(struct frag_buffer *w, fragment *f)
 /* Handles fragment received from the sending side (RECV)
  * 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 */
-	unsigned startid, endid;
+	unsigned startid, endid, offset;
 	fragment *fd;
 	startid = w->start_seq_id;
 	endid = (w->start_seq_id + w->windowsize) % MAX_SEQ_ID;
+	offset = SEQ_OFFSET(startid, f->seqID);
+
 	if (!INWINDOW_SEQ(startid, endid, f->seqID)) {
-		WDEBUG("Dropping frag with seqID %u: not in window (%u-%u)\n", f->seqID, startid, endid);
 		w->oos++;
+		if (offset > MIN(w->length - w->numitems, MAX_SEQ_ID / 2)) {
+			/* Only drop the fragment if it is ancient */
+			WDEBUG("Dropping frag with seqID %u: not in window (%u-%u)", f->seqID, startid, endid);
 			return -1;
+		} else {
+			/* Save "new" fragments to avoid causing other end to advance
+			 * when this fragment is ACK'd despite being dropped */
+			WDEBUG("WARNING: Got future fragment (%u), offset %u from start %u (wsize %u).",
+				   f->seqID, offset, startid, w->windowsize);
+		}
 	}
 	/* Place fragment into correct location in buffer */
 	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)
+		if (f->seqID == fd->seqID) {
+			/* use retries as counter for dupes */
+			fd->retries ++;
 			return -1;
 		}
+	}
+
 	memcpy(fd, f, sizeof(fragment));
 	w->numitems ++;
 
@@ -173,22 +190,24 @@ window_reassemble_data(struct frag_buffer *w, uint8_t *data, size_t maxlen, int
 	if (w->direction != WINDOW_RECVING)
 		return 0;
 	if (w->frags[w->chunk_start].start == 0 && w->numitems > 0) {
-		WDEBUG("chunk_start (%lu)pointing to non-start fragment (seq %u, len %lu)!",
+		WDEBUG("chunk_start (%lu) pointing to non-start fragment (seq %u, len %lu)!",
 			  w->chunk_start, w->frags[w->chunk_start].seqID, w->frags[w->chunk_start].len);
 		return 0;
 	}
 	if (compression) *compression = 1;
 
 	fragment *f;
-	size_t i, curseq;
+	size_t i;
+	unsigned curseq;
 	int end = 0;
 	curseq = w->frags[w->chunk_start].seqID;
 	for (i = 0; i < w->numitems; ++i) {
 		woffs = WRAP(w->chunk_start + i);
 		f = &w->frags[woffs];
 		fraglen = f->len;
-		if (fraglen == 0 || !f->data || f->seqID != curseq) {
-			WDEBUG("data missing! Not reassembling!");
+		if (fraglen == 0 || f->seqID != curseq) {
+			WDEBUG("Missing next frag %u [%lu], got seq %u (%lu bytes) instead! Not reassembling!",
+				   curseq, woffs, f->seqID, fraglen);
 			return 0;
 		}
 
@@ -200,8 +219,7 @@ window_reassemble_data(struct frag_buffer *w, uint8_t *data, size_t maxlen, int
 		if (compression) {
 			*compression &= f->compressed & 1;
 			if (f->compressed != *compression) {
-				WDEBUG("Inconsistent compression flags in chunk. Not reassembling!");
-				return 0;
+				WDEBUG("Inconsistent compression flags in chunk. Will reassemble anyway!");
 			}
 		}
 		if (fraglen > maxlen) {
@@ -218,13 +236,18 @@ window_reassemble_data(struct frag_buffer *w, uint8_t *data, size_t maxlen, int
 			break;
 		}
 
+		/* Move position counters and expected next seqID */
 		maxlen -= fraglen;
 		curseq = (curseq + 1) % MAX_SEQ_ID;
 	}
-	if (end == 0) { /* no end of chunk found but reached end of data */
+
+	if (end == 0) {
+		/* no end of chunk found because the window buffer has no more frags
+		 * meaning they haven't been received yet. */
 		return 0;
 	}
-	WDEBUG("Reassembling %lu bytes of data from %lu frags; compression %d!", datalen, i + 1, *compression);
+
+	WDEBUG("Reassembled %lu bytes from %lu frags; %scompressed!", datalen, i + 1, *compression ? "" : "un");
 	/* Clear all used fragments */
 	size_t p;
 	ITER_FORWARD(w->chunk_start, WRAP(w->chunk_start + i + 1), w->length, p,
@@ -235,15 +258,19 @@ window_reassemble_data(struct frag_buffer *w, uint8_t *data, size_t maxlen, int
 	return datalen;
 }
 
-/* Returns number of fragments that can be sent immediately; effectively
- * the same as window_get_next_sending_fragment but without changing anything. */
 size_t
-window_sending(struct frag_buffer *w)
+window_sending(struct frag_buffer *w, struct timeval *nextresend)
+/* Returns number of fragments that can be sent immediately; effectively
+   the same as window_get_next_sending_fragment but without doing anything.
+   *nextresend is time before the next frag will be resent */
 {
-	struct timeval timeout, now;
+	struct timeval age, now, oldest;
 	fragment *f;
 	size_t tosend = 0;
 
+	oldest.tv_sec = 0;
+	oldest.tv_usec = 0;
+
 	if (w->numitems == 0)
 		return 0;
 
@@ -253,12 +280,30 @@ window_sending(struct frag_buffer *w)
 		f = &w->frags[WRAP(w->window_start + i)];
 		if (f->len == 0 || f->acks >= 1) continue;
 
-		timeradd(&w->timeout, &f->lastsent, &timeout);
-		if (f->retries < 1 || !timercmp(&now, &timeout, <)) {
-			/* Fragment not sent or timed out (to be re-sent) */
+		if (f->retries < 1 || f->lastsent.tv_sec == 0) {
+			/* Sending frag for first time
+			 * Note: if retries==0 then lastsent MUST also be 0 */
 			tosend++;
+		} else {
+			/* Frag has been sent before so lastsent is a valid timestamp */
+			timersub(&now, &f->lastsent, &age);
+
+			if (!timercmp(&age, &w->timeout, <)) {
+				/* ACK timeout: Frag will be resent */
+				tosend++;
+			} else if (timercmp(&age, &oldest, >)) {
+				/* Hasn't timed out yet and is oldest so far */
+				oldest = age;
 			}
 		}
+	}
+
+	if (nextresend) {
+		/* nextresend = time before oldest fragment (not being sent now)
+		 * will be re-sent = timeout - age */
+		timersub(&w->timeout, &oldest, nextresend);
+	}
+
 	return tosend;
 }
 
@@ -267,7 +312,7 @@ window_sending(struct frag_buffer *w)
 fragment *
 window_get_next_sending_fragment(struct frag_buffer *w, int *other_ack)
 {
-	struct timeval timeout, now;
+	struct timeval age, now;
 	fragment *f = NULL;
 
 	if (*other_ack >= MAX_SEQ_ID || *other_ack < 0)
@@ -277,13 +322,14 @@ window_get_next_sending_fragment(struct frag_buffer *w, int *other_ack)
 
 	for (size_t i = 0; i < w->windowsize; i++) {
 		f = &w->frags[WRAP(w->window_start + i)];
-		if (f->acks >= 1) continue;
+		if (f->acks >= 1 || f->len == 0) continue;
 
-		timeradd(&w->timeout, &f->lastsent, &timeout);
+		timersub(&now, &f->lastsent, &age);
 
-		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);
+		if (f->retries >= 1 && !timercmp(&age, &w->timeout, <)) {
+			/* Resending fragment due to ACK timeout */
+			WDEBUG("Retrying frag %u (%ld ms old/timeout %ld ms), retries: %u/total %u",
+				   f->seqID, timeval_to_ms(&age), timeval_to_ms(&w->timeout), f->retries, w->resends);
 			w->resends ++;
 			goto found;
 		} else if (f->retries == 0 && f->len > 0) {