Test TCP behavior when receiving unacceptable segment in CLOSE_WAIT

TCP, in CLOSE-WAIT state, MUST return ACK with proper SEQ and ACK numbers after
recv a seg with OTW SEQ or unacc ACK number, and remain in same state. If the
connection is in a synchronized state, any unacceptable segment (out of window
sequence number or unacceptable acknowledgment number) must elicit only an empty
acknowledgment segment containing the current send-sequence number and an
acknowledgment indicating the next sequence number expected to be received, and
the connection remains in the same state.

PiperOrigin-RevId: 306897984

1 files changed, 11 insertions, 3 deletions

diff --git a/test/packetimpact/testbench/connections.go b/test/packetimpact/testbench/connections.go
index be62d051d..c1b3c4380 100644
--- a/test/packetimpact/testbench/connections.go
+++ b/test/packetimpact/testbench/connections.go
@@ -189,6 +189,7 @@ type tcpState struct {
 	localSeqNum, remoteSeqNum *seqnum.Value
 	synAck                    *TCP
 	portPickerFD              int
+	finSent                   bool
 }
 
 var _ layerState = (*tcpState)(nil)
@@ -210,6 +211,7 @@ func newTCPState(out, in TCP) (*tcpState, error) {
 		in:           TCP{DstPort: &localPort},
 		localSeqNum:  SeqNumValue(seqnum.Value(rand.Uint32())),
 		portPickerFD: portPickerFD,
+		finSent:      false,
 	}
 	if err := s.out.merge(&out); err != nil {
 		return nil, err
@@ -254,12 +256,18 @@ func (s *tcpState) sent(sent Layer) error {
 	if !ok {
 		return fmt.Errorf("can't update tcpState with %T Layer", sent)
 	}
-	for current := tcp.next(); current != nil; current = current.next() {
-		s.localSeqNum.UpdateForward(seqnum.Size(current.length()))
+	if !s.finSent {
+		// update localSeqNum by the payload only when FIN is not yet sent by us
+		for current := tcp.next(); current != nil; current = current.next() {
+			s.localSeqNum.UpdateForward(seqnum.Size(current.length()))
+		}
 	}
 	if tcp.Flags != nil && *tcp.Flags&(header.TCPFlagSyn|header.TCPFlagFin) != 0 {
 		s.localSeqNum.UpdateForward(1)
 	}
+	if *tcp.Flags&(header.TCPFlagFin) != 0 {
+		s.finSent = true
+	}
 	return nil
 }
 
@@ -590,7 +598,7 @@ func (conn *TCPIPv4) RemoteSeqNum() *seqnum.Value {
 	return conn.state().remoteSeqNum
 }
 
-// LocalSeqNum returns the next expected sequence number from the DUT.
+// LocalSeqNum returns the next sequence number to send from the testbench.
 func (conn *TCPIPv4) LocalSeqNum() *seqnum.Value {
 	return conn.state().localSeqNum
 }