Fix handling of unacceptable ACKs during close.

On receiving an ACK with unacceptable ACK number, in a closing state,
TCP, needs to reply back with an ACK with correct seq and ack numbers and
remain in same state. This change is as per RFC793 page 37, but with a
difference that it does not apply to ESTABLISHED state, just as in Linux.
Also add more tests to check for OTW sequence number and unacceptable
ack numbers in these states.

Fixes #3785

PiperOrigin-RevId: 329616283

2 files changed, 27 insertions, 1 deletions

diff --git a/test/packetimpact/testbench/connections.go b/test/packetimpact/testbench/connections.go
index 3af5f83fd..a90046f69 100644
--- a/test/packetimpact/testbench/connections.go
+++ b/test/packetimpact/testbench/connections.go
@@ -615,7 +615,7 @@ func (conn *Connection) ExpectFrame(t *testing.T, layers Layers, timeout time.Du
 			if errs == nil {
 				return nil, fmt.Errorf("got no frames matching %v during %s", layers, timeout)
 			}
-			return nil, fmt.Errorf("got no frames matching %v during %s: got %w", layers, timeout, errs)
+			return nil, fmt.Errorf("got frames %w want %v during %s", errs, layers, timeout)
 		}
 		if conn.match(layers, gotLayers) {
 			for i, s := range conn.layerStates {
diff --git a/test/packetimpact/testbench/dut.go b/test/packetimpact/testbench/dut.go
index 73c532e75..ff269d949 100644
--- a/test/packetimpact/testbench/dut.go
+++ b/test/packetimpact/testbench/dut.go
@@ -700,3 +700,29 @@ func (dut *DUT) RecvWithErrno(ctx context.Context, t *testing.T, sockfd, len, fl
 	}
 	return resp.GetRet(), resp.GetBuf(), syscall.Errno(resp.GetErrno_())
 }
+
+// Shutdown calls shutdown on the DUT and causes a fatal test failure if it doesn't
+// succeed. If more control over the timeout or error handling is needed, use
+// ShutdownWithErrno.
+func (dut *DUT) Shutdown(t *testing.T, fd, how int32) error {
+	t.Helper()
+
+	ctx, cancel := context.WithTimeout(context.Background(), RPCTimeout)
+	defer cancel()
+	return dut.ShutdownWithErrno(ctx, t, fd, how)
+}
+
+// ShutdownWithErrno calls shutdown on the DUT.
+func (dut *DUT) ShutdownWithErrno(ctx context.Context, t *testing.T, fd, how int32) error {
+	t.Helper()
+
+	req := pb.ShutdownRequest{
+		Fd:  fd,
+		How: how,
+	}
+	resp, err := dut.posixServer.Shutdown(ctx, &req)
+	if err != nil {
+		t.Fatalf("failed to call Shutdown: %s", err)
+	}
+	return syscall.Errno(resp.GetErrno_())
+}