begin adding test for #19

Author: soypat

control_user.go

@@ -87,6 +87,8 @@ func (tcb *ControlBlock) Close() (err error) {
 		tcb.pending[0] = (tcb.pending[0] & FlagACK) | FlagFIN
 	case StateFinWait2, StateTimeWait:
 		err = errConnectionClosing
+	default:
+		err = errInvalidState
 	}
 	if err == nil {
 		tcb.trace("tcb:close", slog.String("state", tcb.state.String()))
@@ -134,7 +136,8 @@ func (tcb *ControlBlock) Send(seg Segment) error {
 	// Advance pending flags queue.
 	tcb.pending[0] &^= seg.Flags
 	if tcb.pending[0] == 0 {
-		tcb.pending = [2]Flags{tcb.pending[1], 0}
+		// Ensure we don't queue a FINACK if we have already sent a FIN.
+		tcb.pending = [2]Flags{tcb.pending[1] &^ (seg.Flags & (FlagFIN)), 0}
 	}
 	tcb.pending[0] |= newPending
 
@@ -183,6 +186,11 @@ func (tcb *ControlBlock) Recv(seg Segment) (err error) {
 		if seg.Flags.HasAny(FlagACK) {
 			tcb.close()
 		}
+	// case StateClosing:
+	// 	if seg.Flags.HasAny(FlagACK) {
+	// 		tcb.state = StateTimeWait
+	// 		pending = FlagACK
+	// 	}
 	default:
 		panic("unexpected state" + tcb.state.String())
 	}

seqs_test.go

@@ -667,3 +667,37 @@ var exchangeHelloWorld = [][]byte{
 	// server ACK
 	11: []byte("\xd8\x5e\xd3\x43\x03\xeb\x28\xcd\xc1\x05\x4d\xbb\x08\x00\x45\x00\x00\x28\x00\x00\x40\x00\x40\x06\xb6\x5b\xc0\xa8\x01\x91\xc0\xa8\x01\x93\x04\xd2\x84\x96\xbe\x6e\x4c\x28\x5e\x72\x2b\x97\x50\x10\x10\x00\xfd\x56\x00\x00\x00\x00\x00\x00\x00\x00"),
 }
+
+func TestUnexpectedStateClosing(t *testing.T) {
+	// TCB is a server which returns an HTTP response and receives a FINACK.
+	var tcb seqs.ControlBlock
+	const httpLen = 1192
+	const issA, issB, windowA, windowB = 1, 127, 2000, 2000
+	tcb.HelperInitState(seqs.StateEstablished, issA, issA, windowA)
+	tcb.HelperInitRcv(issB, issB, windowB)
+
+	ex := []seqs.Exchange{
+		0: { // Server sends HTTP response.
+			Outgoing:  &seqs.Segment{SEQ: issA, ACK: issB, Flags: PSHACK, WND: windowA, DATALEN: httpLen},
+			WantState: seqs.StateEstablished,
+		},
+		1: { // Client sends an ACK to server.
+			Incoming:  &seqs.Segment{SEQ: issB, ACK: issA + httpLen, Flags: seqs.FlagACK, WND: windowB},
+			WantState: seqs.StateEstablished,
+		},
+		2: { //  Client sends FIN|ACK to server.
+			Incoming:    &seqs.Segment{SEQ: issB, ACK: issA + httpLen, Flags: FINACK, WND: windowB},
+			WantPending: &seqs.Segment{SEQ: issA + httpLen, ACK: issB + 1, Flags: seqs.FlagACK, WND: windowA},
+			WantState:   seqs.StateCloseWait,
+		},
+		3: { // Server sends out FINACK.
+			Outgoing:  &seqs.Segment{SEQ: issA + httpLen, ACK: issB + 1, Flags: FINACK, WND: windowA},
+			WantState: seqs.StateLastAck,
+		},
+		4: { // Client sends back ACK.
+			Incoming:  &seqs.Segment{SEQ: issB + 1, ACK: issA + httpLen + 1, Flags: seqs.FlagACK, WND: windowB},
+			WantState: seqs.StateClosed,
+		},
+	}
+	tcb.HelperExchange(t, ex[:])
+}

seqsinternal_test.go

@@ -193,15 +193,15 @@ func (ex *Exchange) appendVisualization(buf []byte, A, B State) []byte {
 	}
 	var seg *Segment
 	sentByA := ex.Outgoing != nil
-	if ex.Outgoing != nil {
+	if sentByA {
 		seg = ex.Outgoing
 	} else if ex.Incoming != nil {
 		seg = ex.Incoming
 	} else {
 		return buf
 	}
 	dirSep := []byte(" <-- ")
-	if !sentByA {
+	if sentByA {
 		dirSep = []byte(" --> ")
 	}
 	astr := A.String()