Rename HandleNDupAcks in TCP.

Rename HandleNDupAcks() to HandleLossDetected() as it will enter this when
is detected after:
- reorder window expires and TLP (in case of RACK)
- dupAckCount >= 3

PiperOrigin-RevId: 355237858

pkg/tcpip/transport/tcp/cubic.go

@@ -178,8 +178,8 @@ func (c *cubicState) getCwnd(packetsAcked, sndCwnd int, srtt time.Duration) int
 	return int(cwnd)
 }
 
-// HandleNDupAcks implements congestionControl.HandleNDupAcks.
-func (c *cubicState) HandleNDupAcks() {
+// HandleLossDetected implements congestionControl.HandleLossDetected.
+func (c *cubicState) HandleLossDetected() {
 	// See: https://tools.ietf.org/html/rfc8312#section-4.5
 	c.numCongestionEvents++
 	c.t = time.Now()

pkg/tcpip/transport/tcp/rack.go

@@ -301,7 +301,7 @@ func (s *sender) detectTLPRecovery(ack seqnum.Value, rcvdSeg *segment) {
 			// Step 2. Either the original packet or the retransmission (in the
 			// form of a probe) was lost. Invoke a congestion control response
 			// equivalent to fast recovery.
-			s.cc.HandleNDupAcks()
+			s.cc.HandleLossDetected()
 			s.enterRecovery()
 			s.leaveRecovery()
 		}

pkg/tcpip/transport/tcp/reno.go

@@ -79,10 +79,10 @@ func (r *renoState) Update(packetsAcked int) {
 	r.updateCongestionAvoidance(packetsAcked)
 }
 
-// HandleNDupAcks implements congestionControl.HandleNDupAcks.
-func (r *renoState) HandleNDupAcks() {
-	// A retransmit was triggered due to nDupAckThreshold
-	// being hit. Reduce our slow start threshold.
+// HandleLossDetected implements congestionControl.HandleLossDetected.
+func (r *renoState) HandleLossDetected() {
+	// A retransmit was triggered due to nDupAckThreshold or when RACK
+	// detected loss. Reduce our slow start threshold.
 	r.reduceSlowStartThreshold()
 }
 

pkg/tcpip/transport/tcp/snd.go

@@ -51,9 +51,10 @@ const (
 // congestionControl is an interface that must be implemented by any supported
 // congestion control algorithm.
 type congestionControl interface {
-	// HandleNDupAcks is invoked when sender.dupAckCount >= nDupAckThreshold
-	// just before entering fast retransmit.
-	HandleNDupAcks()
+	// HandleLossDetected is invoked when the loss is detected by RACK or
+	// sender.dupAckCount >= nDupAckThreshold just before entering fast
+	// retransmit.
+	HandleLossDetected()
 
 	// HandleRTOExpired is invoked when the retransmit timer expires.
 	HandleRTOExpired()
@@ -1152,7 +1153,7 @@ func (s *sender) detectLoss(seg *segment) (fastRetransmit bool) {
 		s.dupAckCount = 0
 		return false
 	}
-	s.cc.HandleNDupAcks()
+	s.cc.HandleLossDetected()
 	s.enterRecovery()
 	s.dupAckCount = 0
 	return true