Add a function to enable RACK in tests.

- Adds a function to enable RACK in tests.
- RACK update functions are guarded behind the flag tcpRecovery.

PiperOrigin-RevId: 355435973

pkg/tcpip/transport/tcp/snd.go

@@ -1320,7 +1320,9 @@ func (s *sender) handleRcvdSegment(rcvdSeg *segment) {
 		//   unacknowledged and also never retransmitted sequence below
 		//   RACK.fack, then the corresponding packet has been
 		//   reordered and RACK.reord is set to TRUE.
+		if s.ep.tcpRecovery&tcpip.TCPRACKLossDetection != 0 {
 			s.walkSACK(rcvdSeg)
+		}
 		s.SetPipe()
 	}
 
@@ -1339,7 +1341,9 @@ func (s *sender) handleRcvdSegment(rcvdSeg *segment) {
 	}
 
 	// See if TLP based recovery was successful.
+	if s.ep.tcpRecovery&tcpip.TCPRACKLossDetection != 0 {
 		s.detectTLPRecovery(ack, rcvdSeg)
+	}
 
 	// Stash away the current window size.
 	s.sndWnd = rcvdSeg.window
@@ -1421,7 +1425,7 @@ func (s *sender) handleRcvdSegment(rcvdSeg *segment) {
 			}
 
 			// Update the RACK fields if SACK is enabled.
-			if s.ep.sackPermitted && !seg.acked {
+			if s.ep.sackPermitted && !seg.acked && s.ep.tcpRecovery&tcpip.TCPRACKLossDetection != 0 {
 				s.rc.update(seg, rcvdSeg)
 				s.rc.detectReorder(seg)
 			}
@@ -1455,9 +1459,11 @@ func (s *sender) handleRcvdSegment(rcvdSeg *segment) {
 				// Update RACK when we are exiting fast or RTO
 				// recovery as described in the RFC
 				// draft-ietf-tcpm-rack-08 Section-7.2 Step 4.
+				if s.ep.tcpRecovery&tcpip.TCPRACKLossDetection != 0 {
 					s.rc.exitRecovery()
 				}
 			}
+		}
 
 		// It is possible for s.outstanding to drop below zero if we get
 		// a retransmit timeout, reset outstanding to zero but later
@@ -1483,7 +1489,9 @@ func (s *sender) handleRcvdSegment(rcvdSeg *segment) {
 	// See: https://tools.ietf.org/html/draft-ietf-tcpm-rack-08#section-7.2
 	// * Upon receiving an ACK:
 	// * Step 4: Update RACK reordering window
+	if s.ep.tcpRecovery&tcpip.TCPRACKLossDetection != 0 {
 		s.rc.updateRACKReorderWindow(rcvdSeg)
+	}
 
 	// Now that we've popped all acknowledged data from the retransmit
 	// queue, retransmit if needed.

pkg/tcpip/transport/tcp/tcp_rack_test.go

@@ -34,6 +34,14 @@ const (
 	mtu              = header.TCPMinimumSize + header.IPv4MinimumSize + maxTCPOptionSize + maxPayload
 )
 
+func setStackRACKPermitted(t *testing.T, c *context.Context) {
+	t.Helper()
+	opt := tcpip.TCPRecovery(tcpip.TCPRACKLossDetection)
+	if err := c.Stack().SetTransportProtocolOption(header.TCPProtocolNumber, &opt); err != nil {
+		t.Fatalf("c.s.SetTransportProtocolOption(%d, &%v(%v)): %s", header.TCPProtocolNumber, opt, opt, err)
+	}
+}
+
 // TestRACKUpdate tests the RACK related fields are updated when an ACK is
 // received on a SACK enabled connection.
 func TestRACKUpdate(t *testing.T) {
@@ -60,6 +68,7 @@ func TestRACKUpdate(t *testing.T) {
 		close(probeDone)
 	})
 	setStackSACKPermitted(t, c, true)
+	setStackRACKPermitted(t, c)
 	createConnectedWithSACKAndTS(c)
 
 	data := make([]byte, maxPayload)
@@ -116,6 +125,7 @@ func TestRACKDetectReorder(t *testing.T) {
 		close(probeDone)
 	})
 	setStackSACKPermitted(t, c, true)
+	setStackRACKPermitted(t, c)
 	createConnectedWithSACKAndTS(c)
 	data := make([]byte, ackNumToVerify*maxPayload)
 	for i := range data {
@@ -148,6 +158,7 @@ func TestRACKDetectReorder(t *testing.T) {
 
 func sendAndReceive(t *testing.T, c *context.Context, numPackets int) []byte {
 	setStackSACKPermitted(t, c, true)
+	setStackRACKPermitted(t, c)
 	createConnectedWithSACKAndTS(c)
 
 	data := make([]byte, numPackets*maxPayload)