UDT: Fix critical bugs: congestion window size was not set on senders side; sentAck was not set in case ACK threshold wasn't reached, which caused resendACKTimer to fail to send

udt/config.go

@@ -29,6 +29,7 @@ func DefaultConfig() *Config {
 		ListenReplayWindow: 5 * time.Minute,
 		LingerTime:         10 * time.Second,
 		MaxFlowWinSize:     64,
+		MaxBandwidth:       0,
 		MaxPacketSize:      65535,
 		SynTime:            10000 * time.Microsecond,
 		CongestionForSocket: func(sock *udtSocket) CongestionControl {

udt/congestion_native.go

@@ -29,7 +29,7 @@ func (ncc NativeCongestionControl) Init(parms CongestionControlParms, synTime ti
 	ncc.lastRCTime = time.Now()
 	parms.SetACKPeriod(ncc.rcInterval)
 
-	// TODO: Once packet loss is reported, the ACK interval should fall back to 1, and increased if a stable connection is detected.
+	// This value should be adjusted at runtime according to congestion.
 	parms.SetACKInterval(4)
 
 	ncc.slowStart = true
@@ -83,6 +83,7 @@ func (ncc NativeCongestionControl) OnACK(parms CongestionControlParms, ack packe
 	} else {
 		// Set the congestion window size (CWND) to: CWND = A * (RTT + SYN) + 16.
 		cWndSize = uint((float64(recvRate)/float64(time.Second))*float64(rtt+ncc.rcInterval) + 16)
+		parms.SetCongestionWindowSize(cWndSize)
 	}
 	if ncc.loss {
 		ncc.loss = false

udt/udtsocket_recv.go

@@ -88,6 +88,7 @@ func (s *udtSocketRecv) goReceiveEvent() {
 		case <-s.resendACKTimer: // handles both resending ACKs and NAKs
 			if s.recvAck2.IsLess(s.sentAck) {
 				s.sendACK(s.sentAck)
+				s.unackPktCount = 0
 			}
 			if first, valid := s.recvLossList.FirstSequence(); valid {
 				s.sendNAK(first, 1)
@@ -467,12 +468,6 @@ func (s *udtSocketRecv) ingestError(p *packet.ErrPacket) {
 func (s *udtSocketRecv) ackEvent() {
 	s.unackPktCount++
 
-	// Check if the threshold to send is reached, if used. Note that sendACK is called revery SynTime.
-	ackInterval := uint(s.ackInterval.get())
-	if (ackInterval > 0) && (ackInterval > s.unackPktCount) {
-		return
-	}
-
 	// The ack number is excluding.
 	ack := s.lastSequence.Add(1)
 
@@ -481,6 +476,13 @@ func (s *udtSocketRecv) ackEvent() {
 		return
 	}
 
+	// Check if the threshold to send is reached, if used. Note that sendACK is called revery SynTime.
+	ackInterval := uint(s.ackInterval.get())
+	if (ackInterval > 0) && (ackInterval > s.unackPktCount) {
+		s.sentAck = ack // This is needed for resendACKTimer to pick it up in case no ackInterval count of packets are immediately sent.
+		return
+	}
+
 	s.sendACK(ack)
 	s.unackPktCount = 0
 }