loop: add support for the probe API

loopdb/protocol_version.go

@@ -43,13 +43,17 @@ const (
 	// canceling loop out swaps.
 	ProtocolVersionLoopOutCancel = 7
 
+	// ProtocolVerionProbe indicates that the client is able to request
+	// the server to perform a probe to test inbound liquidty.
+	ProtocolVersionProbe ProtocolVersion = 8
+
 	// ProtocolVersionUnrecorded is set for swaps were created before we
 	// started saving protocol version with swaps.
 	ProtocolVersionUnrecorded ProtocolVersion = math.MaxUint32
 
 	// CurrentRPCProtocolVersion defines the version of the RPC protocol
 	// that is currently supported by the loop client.
-	CurrentRPCProtocolVersion = looprpc.ProtocolVersion_LOOP_OUT_CANCEL
+	CurrentRPCProtocolVersion = looprpc.ProtocolVersion_PROBE
 
 	// CurrentInternalProtocolVersion defines the RPC current protocol in
 	// the internal representation.
@@ -88,6 +92,9 @@ func (p ProtocolVersion) String() string {
 	case ProtocolVersionLoopOutCancel:
 		return "Loop Out Cancel"
 
+	case ProtocolVersionProbe:
+		return "Probe"
+
 	default:
 		return "Unknown"
 	}

loopdb/protocol_version_test.go

@@ -22,6 +22,7 @@ func TestProtocolVersionSanity(t *testing.T) {
 		ProtocolVersionHtlcV2,
 		ProtocolVersionMultiLoopIn,
 		ProtocolVersionLoopOutCancel,
+		ProtocolVersionProbe,
 	}
 
 	rpcVersions := [...]looprpc.ProtocolVersion{
@@ -33,6 +34,7 @@ func TestProtocolVersionSanity(t *testing.T) {
 		looprpc.ProtocolVersion_HTLC_V2,
 		looprpc.ProtocolVersion_MULTI_LOOP_IN,
 		looprpc.ProtocolVersion_LOOP_OUT_CANCEL,
+		looprpc.ProtocolVersion_PROBE,
 	}
 
 	require.Equal(t, len(versions), len(rpcVersions))