client: implemented messaging signing.

added support for the main RPC implementation of message signing.

lightning_client.go

@@ -271,6 +271,13 @@ type LightningClient interface {
 	// relevant to the wallet are sent over.
 	SubscribeTransactions(ctx context.Context) (<-chan Transaction,
 		<-chan error, error)
+
+	// SignMessage signs a message with this node's private key.
+	// The returned signature string is zbase32 encoded and pubkey
+	// recoverable, meaning that only the message digest and signature
+	// are needed for verification.
+	SignMessage(ctx context.Context, data []byte) (string,
+		error)
 }
 
 // Info contains info about the connected lnd node.
@@ -4132,6 +4139,23 @@ func (s *lightningClient) SendCustomMessage(ctx context.Context,
 	return err
 }
 
+// SignMessage signs a message with this node's private key.
+// The returned signature string is zbase32 encoded and pubkey
+// recoverable, meaning that only the message digest and signature
+// are needed for verification.
+func (s *lightningClient) SignMessage(ctx context.Context,
+	data []byte) (string, error) {
+
+	rpcCtx := s.adminMac.WithMacaroonAuth(ctx)
+	rpcReq := &lnrpc.SignMessageRequest{Msg: data}
+	rpcRes, err := s.client.SignMessage(rpcCtx, rpcReq)
+	if err != nil {
+		return "", err
+	}
+
+	return rpcRes.Signature, nil
+}
+
 // SubscribeCustomMessages subscribes to a stream of custom messages, optionally
 // filtering by peer and message type. The channels returned will be closed
 // when the subscription exits.

macaroon_recipes_test.go

@@ -12,7 +12,7 @@ import (
 
 var (
 	expectedPermissions = map[string]int{
-		"lnrpc":       11,
+		"lnrpc":       12,
 		"chainrpc":    1,
 		"invoicesrpc": 2,
 		"routerrpc":   2,