Fix AssocCongestionControl test

Author: philipch07

association.go

@@ -299,7 +299,7 @@ type Config struct {
 	// Step of congestion window increase at Congestion Avoidance
 	CwndCAStep uint32
 
-	// RACK loss detection: DISABLED by default (although it should probably be enabled by default..?)
+	// Whether RACK loss detection is disabled (default: false, which means RACK is enabled)
 	DisableRACK bool
 	// Optional: cap the minimum reordering window: 0 = use quarter-RTT
 	RACKReoWndFloor time.Duration
@@ -3111,7 +3111,7 @@ func (a *Association) onRackAfterSACK(
 	} else {
 		base := max(a.rackMinRTT/4, a.rackReoWndFloor)
 		// if we have never seen reordering for this connection, set to zero *during loss recovery* (RACK for SCTP section 2B)
-		// we approximate “during loss recovery” with inFastRecovery or T3-Rtx pending. Outside recovery keep base.
+		// we approximate "during loss recovery" with inFastRecovery or T3-Rtx pending. outside recovery we can keep base.
 		if !a.rackReorderingSeen && (a.inFastRecovery || a.t3RTX.isRunning()) {
 			a.rackReoWnd = 0
 		} else if a.rackReoWnd == 0 {
@@ -3160,7 +3160,7 @@ func (a *Association) onRackAfterSACK(
 					a.name, chunk.tsn, chunk.since, a.rackDeliveredTime, a.rackReoWnd)
 			}
 		}
-		// if we marked anything, kick the writer
+		// if we marked anything then wake the writer
 		a.awakeWriteLoop()
 	}
 

association_test.go

@@ -1835,8 +1835,7 @@ func TestAssocCongestionControl(t *testing.T) { //nolint:cyclop,maintidx
 			assert.Equal(t, n, len(sbuf), "unexpected length of received data")
 		}
 
-		// process packets for 500 msec, assuming that the fast retrans/recover
-		// should complete within 500 msec.
+		// process packets for 500 msec; recovery should complete without RTO
 		for i := 0; i < 50; i++ {
 			br.Tick()
 			time.Sleep(10 * time.Millisecond)
@@ -1860,7 +1859,7 @@ func TestAssocCongestionControl(t *testing.T) { //nolint:cyclop,maintidx
 				return
 			}
 			assert.Equal(t, len(sbuf), n, "unexpected length of received data")
-			assert.Equal(t, i, int(binary.BigEndian.Uint32(rbuf)), "unexpected length of received data")
+			assert.Equal(t, i, int(binary.BigEndian.Uint32(rbuf)), "unexpected payload sequence")
 			assert.Equal(t, ppi, PayloadTypeWebRTCBinary, "unexpected ppi")
 		}
 
@@ -1873,8 +1872,13 @@ func TestAssocCongestionControl(t *testing.T) { //nolint:cyclop,maintidx
 		t.Logf("nSACKs      : %d\n", a0.stats.getNumSACKsReceived())
 		t.Logf("nAckTimeouts: %d\n", a1.stats.getNumAckTimeouts())
 		t.Logf("nFastRetrans: %d\n", a0.stats.getNumFastRetrans())
+		t.Logf("nT3Timeouts : %d\n", a0.stats.getNumT3Timeouts())
 
-		assert.Equal(t, uint64(1), a0.stats.getNumFastRetrans(), "should be 1")
+		// With RACK enabled, recovery may happen without classic fast retransmit.
+		// Require recovery before RTO; allow FR count to be 0 or 1.
+		assert.Equal(t, uint64(0), a0.stats.getNumT3Timeouts(), "recovery should complete before any RTO")
+		fr := a0.stats.getNumFastRetrans()
+		assert.Truef(t, fr == 0 || fr == 1, "expected fast retrans 0 or 1 (RACK may bypass FR), got %d", fr)
 
 		closeAssociationPair(br, a0, a1)
 	})