htlcswitch: add an always on mode to interceptable switch

Co-authored-by: Juan Pablo Civile <elementohb@gmail.com>

htlcswitch/switch_test.go

@@ -3273,7 +3273,7 @@ func TestSwitchHoldForward(t *testing.T) {
 		t:               t,
 		interceptedChan: make(chan InterceptedPacket),
 	}
-	switchForwardInterceptor := NewInterceptableSwitch(s)
+	switchForwardInterceptor := NewInterceptableSwitch(s, false)
 	require.NoError(t, switchForwardInterceptor.Start())
 
 	switchForwardInterceptor.SetInterceptor(forwardInterceptor.InterceptForwardHtlc)
@@ -3281,9 +3281,9 @@ func TestSwitchHoldForward(t *testing.T) {
 
 	// Test resume a hold forward.
 	assertNumCircuits(t, s, 0, 0)
-	if err := switchForwardInterceptor.ForwardPackets(linkQuit, ogPacket); err != nil {
-		t.Fatalf("can't forward htlc packet: %v", err)
-	}
+	err = switchForwardInterceptor.ForwardPackets(linkQuit, false, ogPacket)
+	require.NoError(t, err)
+
 	assertNumCircuits(t, s, 0, 0)
 	assertOutgoingLinkReceive(t, bobChannelLink, false)
 
@@ -3303,15 +3303,16 @@ func TestSwitchHoldForward(t *testing.T) {
 			PaymentPreimage: preimage,
 		},
 	}
-	if err := switchForwardInterceptor.ForwardPackets(linkQuit, settle); err != nil {
-		t.Fatalf("can't forward htlc packet: %v", err)
-	}
+	err = switchForwardInterceptor.ForwardPackets(linkQuit, false, settle)
+	require.NoError(t, err)
+
 	assertOutgoingLinkReceive(t, aliceChannelLink, true)
 	assertNumCircuits(t, s, 0, 0)
 
 	// Test resume a hold forward after disconnection.
-	err = switchForwardInterceptor.ForwardPackets(nil, ogPacket)
-	require.NoError(t, err)
+	require.NoError(t, switchForwardInterceptor.ForwardPackets(
+		linkQuit, false, ogPacket,
+	))
 
 	// Wait until the packet is offered to the interceptor.
 	_ = forwardInterceptor.getIntercepted()
@@ -3328,7 +3329,9 @@ func TestSwitchHoldForward(t *testing.T) {
 
 	// Settle the htlc to close the circuit.
 	settle.outgoingHTLCID = 1
-	require.NoError(t, switchForwardInterceptor.ForwardPackets(nil, settle))
+	require.NoError(t, switchForwardInterceptor.ForwardPackets(
+		linkQuit, false, settle,
+	))
 
 	assertOutgoingLinkReceive(t, aliceChannelLink, true)
 	assertNumCircuits(t, s, 0, 0)
@@ -3338,9 +3341,9 @@ func TestSwitchHoldForward(t *testing.T) {
 		forwardInterceptor.InterceptForwardHtlc,
 	)
 
-	if err := switchForwardInterceptor.ForwardPackets(linkQuit, ogPacket); err != nil {
-		t.Fatalf("can't forward htlc packet: %v", err)
-	}
+	require.NoError(t, switchForwardInterceptor.ForwardPackets(
+		linkQuit, false, ogPacket,
+	))
 	assertNumCircuits(t, s, 0, 0)
 	assertOutgoingLinkReceive(t, bobChannelLink, false)
 
@@ -3355,7 +3358,7 @@ func TestSwitchHoldForward(t *testing.T) {
 
 	// Test failing a hold forward with a failure message.
 	require.NoError(t,
-		switchForwardInterceptor.ForwardPackets(linkQuit, ogPacket),
+		switchForwardInterceptor.ForwardPackets(linkQuit, false, ogPacket),
 	)
 	assertNumCircuits(t, s, 0, 0)
 	assertOutgoingLinkReceive(t, bobChannelLink, false)
@@ -3375,7 +3378,7 @@ func TestSwitchHoldForward(t *testing.T) {
 	assertNumCircuits(t, s, 0, 0)
 
 	// Test failing a hold forward with a malformed htlc failure.
-	err = switchForwardInterceptor.ForwardPackets(linkQuit, ogPacket)
+	err = switchForwardInterceptor.ForwardPackets(linkQuit, false, ogPacket)
 	require.NoError(t, err)
 
 	assertNumCircuits(t, s, 0, 0)
@@ -3404,9 +3407,9 @@ func TestSwitchHoldForward(t *testing.T) {
 	assertNumCircuits(t, s, 0, 0)
 
 	// Test settling a hold forward
-	if err := switchForwardInterceptor.ForwardPackets(linkQuit, ogPacket); err != nil {
-		t.Fatalf("can't forward htlc packet: %v", err)
-	}
+	require.NoError(t, switchForwardInterceptor.ForwardPackets(
+		linkQuit, false, ogPacket,
+	))
 	assertNumCircuits(t, s, 0, 0)
 	assertOutgoingLinkReceive(t, bobChannelLink, false)
 
@@ -3420,6 +3423,73 @@ func TestSwitchHoldForward(t *testing.T) {
 	assertNumCircuits(t, s, 0, 0)
 
 	require.NoError(t, switchForwardInterceptor.Stop())
+
+	// Test always-on interception.
+	switchForwardInterceptor = NewInterceptableSwitch(s, true)
+	require.NoError(t, switchForwardInterceptor.Start())
+
+	// Forward a fresh packet. It is expected to be failed immediately,
+	// because there is no interceptor registered.
+	require.NoError(t, switchForwardInterceptor.ForwardPackets(
+		linkQuit, false, ogPacket,
+	))
+
+	assertOutgoingLinkReceive(t, bobChannelLink, false)
+	assertOutgoingLinkReceive(t, aliceChannelLink, true)
+	assertNumCircuits(t, s, 0, 0)
+
+	// Forward a replayed packet. It is expected to be held until the
+	// interceptor connects. To continue the test, it needs to be ran in a
+	// goroutine.
+	errChan := make(chan error)
+	go func() {
+		errChan <- switchForwardInterceptor.ForwardPackets(
+			linkQuit, true, ogPacket,
+		)
+	}()
+
+	// Assert that nothing is forward to the switch.
+	assertOutgoingLinkReceive(t, bobChannelLink, false)
+	assertNumCircuits(t, s, 0, 0)
+
+	// Register an interceptor.
+	switchForwardInterceptor.SetInterceptor(
+		forwardInterceptor.InterceptForwardHtlc,
+	)
+
+	// Expect the ForwardPackets call to unblock.
+	require.NoError(t, <-errChan)
+
+	// Now expect the queued packet to come through.
+	forwardInterceptor.getIntercepted()
+
+	// Disconnect and reconnect interceptor.
+	switchForwardInterceptor.SetInterceptor(nil)
+	switchForwardInterceptor.SetInterceptor(
+		forwardInterceptor.InterceptForwardHtlc,
+	)
+
+	// A replay of the held packet is expected.
+	intercepted := forwardInterceptor.getIntercepted()
+
+	// Settle the packet.
+	require.NoError(t, switchForwardInterceptor.resolve(&FwdResolution{
+		Key:      intercepted.IncomingCircuit,
+		Action:   FwdActionSettle,
+		Preimage: preimage,
+	}))
+	assertOutgoingLinkReceive(t, bobChannelLink, false)
+	assertOutgoingLinkReceive(t, aliceChannelLink, true)
+	assertNumCircuits(t, s, 0, 0)
+
+	require.NoError(t, switchForwardInterceptor.Stop())
+
+	select {
+	case <-forwardInterceptor.interceptedChan:
+		require.Fail(t, "unexpected interception")
+
+	default:
+	}
 }
 
 // TestSwitchDustForwarding tests that the switch properly fails HTLC's which