lightningclient: add send custom message api

Author: carlaKC

lightning_client.go

@@ -198,6 +198,9 @@ type LightningClient interface {
 	RegisterRPCMiddleware(ctx context.Context, middlewareName,
 		customCaveatName string, readOnly bool, timeout time.Duration,
 		intercept InterceptFunction) (chan error, error)
+
+	// SendCustomMessage sends a custom message to a peer.
+	SendCustomMessage(ctx context.Context, msg CustomMessage) error
 }
 
 // Info contains info about the connected lnd node.
@@ -1076,6 +1079,18 @@ type QueryRoutesResponse struct {
 	TotalAmtMsat lnwire.MilliSatoshi
 }
 
+// CustomMessage describes custom messages exchanged with peers.
+type CustomMessage struct {
+	// Peer is the peer that the message was exchanged with.
+	Peer route.Vertex
+
+	// MsgType is the protocol message type number for the custom message.
+	MsgType uint32
+
+	// Data is the data exchanged.
+	Data []byte
+}
+
 var (
 	// ErrNoRouteFound is returned if we can't find a path with the passed
 	// parameters.
@@ -3723,3 +3738,22 @@ func (s *lightningClient) RegisterRPCMiddleware(ctx context.Context,
 
 	return errChan, nil
 }
+
+// SendCustomMessage sends a custom message to one of our existing peers. Note
+// that lnd must already be connected to a peer to send it messages.
+func (s *lightningClient) SendCustomMessage(ctx context.Context,
+	msg CustomMessage) error {
+
+	rpcCtx, cancel := context.WithTimeout(ctx, s.timeout)
+	defer cancel()
+
+	rpcCtx = s.adminMac.WithMacaroonAuth(rpcCtx)
+	rpcReq := &lnrpc.SendCustomMessageRequest{
+		Peer: msg.Peer[:],
+		Type: msg.MsgType,
+		Data: msg.Data,
+	}
+
+	_, err := s.client.SendCustomMessage(rpcCtx, rpcReq)
+	return err
+}

testdata/permissions.json

@@ -476,6 +476,14 @@
                 }
             ]
         },
+	"/lnrpc.Lightning/SendCustomMessage": {
+            "permissions": [
+                {
+                    "entity": "peers",
+                    "action": "write"
+                }
+            ]
+        },
         "/lnrpc.Lightning/SendPayment": {
             "permissions": [
                 {