keep working on xnet TCP

tcp/definitions.go

@@ -111,7 +111,8 @@ func StringExchange(seg Segment, A, B State, invertDir bool) string {
 //
 //	SynSent --> <SEQ=300><ACK=91>[SYN,ACK]  --> SynRcvd
 func appendStringExchange(buf []byte, seg Segment, A, B State, invertDir bool) []byte {
-	const emptySpaces = "             "
+	const emptySpaces = "                    "
+	const spacelen = len(emptySpaces)
 	const fill = len(emptySpaces) - 1
 	appendVal := func(buf []byte, name string, i Value) []byte {
 		buf = append(buf, '<')

tcp/handler.go

@@ -177,6 +177,12 @@ func (h *Handler) Recv(incomingPacket []byte) error {
 		}
 		return err
 	}
+	if h.scb.State() == StateClosed {
+		// TCB aborted, likely because it received an ACK in LastAck state.
+		// Clean up connection now.
+		h.reset(0, 0, 0)
+		return net.ErrClosed
+	}
 	if prevState != h.scb.State() {
 		h.info("tcp.Handler:rx-statechange", slog.Uint64("port", uint64(h.localPort)), slog.String("old", prevState.String()), slog.String("new", h.scb.State().String()), slog.String("rxflags", segIncoming.Flags.String()))
 	}
@@ -269,7 +275,12 @@ func (h *Handler) Send(b []byte) (int, error) {
 	tfrm.SetDestinationPort(h.remotePort)
 	tfrm.SetSegment(segment, offset)
 	tfrm.SetUrgentPtr(0)
-	return int(offset)*4 + int(segment.DATALEN), nil
+	datalen := int(offset)*4 + int(segment.DATALEN)
+	closedSuccess := prevState == StateTimeWait && segment.Flags.HasAny(FlagACK)
+	if closedSuccess {
+		h.reset(0, 0, 0)
+	}
+	return datalen, nil
 }
 
 // FreeTx returns the amount of space free in the transmit buffer. A call to [Handler.Write] with a larger buffer will fail.

tcp/tcp_test.go

@@ -792,6 +792,10 @@ func TestIssue19(t *testing.T) {
 		t.Fatal(err)
 	}
 	assertState(tcp.StateFinWait1)
+	pending, ok = tcb.PendingSegment(0)
+	if ok {
+		t.Fatal("expected no pending segment after finack")
+	}
 
 	// Receive FINACK response from client.
 	err = tcb.Recv(tcp.Segment{SEQ: issB, ACK: issA + httpLen, Flags: FINACK, WND: windowB})