lnrpc: receive custom message

lnwire/lnwire_test.go

@@ -240,7 +240,7 @@ func TestMaxOutPointIndex(t *testing.T) {
 func TestEmptyMessageUnknownType(t *testing.T) {
 	t.Parallel()
 
-	fakeType := MessageType(math.MaxUint16)
+	fakeType := CustomTypeStart - 1
 	if _, err := makeEmptyMessage(fakeType); err == nil {
 		t.Fatalf("should not be able to make an empty message of an " +
 			"unknown type")

lnwire/message.go

@@ -233,7 +233,12 @@ func makeEmptyMessage(msgType MessageType) (Message, error) {
 	case MsgGossipTimestampRange:
 		msg = &GossipTimestampRange{}
 	default:
-		return nil, &UnknownMessage{msgType}
+		if msgType < CustomTypeStart {
+			return nil, &UnknownMessage{msgType}
+		}
+		msg = &Custom{
+			Type: msgType,
+		}
 	}
 
 	return msg, nil