lnrpc: wrap subservers in GrpcHandler

In order to be able to register the subservers with the root grpc server
before we have all dependencies available, we wrap them in an
GrpcHandler struct. This struct will initially hold an empty reference
to the subservers, which allows us to register with the GRPC server, and
later populate and create the subserver instance.

lnrpc/wtclientrpc/driver.go

@@ -12,7 +12,7 @@ import (
 // that is meant for us in the config dispatcher, then we'll exit with an
 // error.
 func createNewSubServer(configRegistry lnrpc.SubServerConfigDispatcher) (
-	lnrpc.SubServer, lnrpc.MacaroonPerms, error) {
+	*WatchtowerClient, lnrpc.MacaroonPerms, error) {
 
 	// We'll attempt to look up the config that we expect, according to our
 	// subServerName name. If we can't find this, then we'll exit with an
@@ -46,9 +46,8 @@ func createNewSubServer(configRegistry lnrpc.SubServerConfigDispatcher) (
 func init() {
 	subServer := &lnrpc.SubServerDriver{
 		SubServerName: subServerName,
-		New: func(c lnrpc.SubServerConfigDispatcher) (lnrpc.SubServer,
-			lnrpc.MacaroonPerms, error) {
-			return createNewSubServer(c)
+		NewGrpcHandler: func() lnrpc.GrpcHandler {
+			return &ServerShell{}
 		},
 	}
 

lnrpc/wtclientrpc/wtclient.go

@@ -64,6 +64,13 @@ var (
 	ErrWtclientNotActive = errors.New("watchtower client not active")
 )
 
+// ServerShell is a shell struct holding a reference to the actual sub-server.
+// It is used to register the gRPC sub-server with the root server before we
+// have the necessary dependencies to populate the actual sub-server.
+type ServerShell struct {
+	WatchtowerClientServer
+}
+
 // WatchtowerClient is the RPC server we'll use to interact with the backing
 // active watchtower client.
 //
@@ -112,14 +119,11 @@ func (c *WatchtowerClient) Name() string {
 // RPC server to register itself with the main gRPC root server. Until this is
 // called, each sub-server won't be able to have requests routed towards it.
 //
-// NOTE: This is part of the lnrpc.SubServer interface.
-func (c *WatchtowerClient) RegisterWithRootServer(grpcServer *grpc.Server) error {
+// NOTE: This is part of the lnrpc.GrpcHandler interface.
+func (r *ServerShell) RegisterWithRootServer(grpcServer *grpc.Server) error {
 	// We make sure that we register it with the main gRPC server to ensure
 	// all our methods are routed properly.
-	RegisterWatchtowerClientServer(grpcServer, c)
-
-	c.cfg.Log.Debugf("WatchtowerClient RPC server successfully registered " +
-		"with  root gRPC server")
+	RegisterWatchtowerClientServer(grpcServer, r)
 
 	return nil
 }
@@ -128,8 +132,8 @@ func (c *WatchtowerClient) RegisterWithRootServer(grpcServer *grpc.Server) error
 // RPC server to register itself with the main REST mux server. Until this is
 // called, each sub-server won't be able to have requests routed towards it.
 //
-// NOTE: This is part of the lnrpc.SubServer interface.
-func (c *WatchtowerClient) RegisterWithRestServer(ctx context.Context,
+// NOTE: This is part of the lnrpc.GrpcHandler interface.
+func (r *ServerShell) RegisterWithRestServer(ctx context.Context,
 	mux *runtime.ServeMux, dest string, opts []grpc.DialOption) error {
 
 	// We make sure that we register it with the main REST server to ensure
@@ -142,6 +146,25 @@ func (c *WatchtowerClient) RegisterWithRestServer(ctx context.Context,
 	return nil
 }
 
+// CreateSubServer populates the subserver's dependencies using the passed
+// SubServerConfigDispatcher. This method should fully initialize the
+// sub-server instance, making it ready for action. It returns the macaroon
+// permissions that the sub-server wishes to pass on to the root server for all
+// methods routed towards it.
+//
+// NOTE: This is part of the lnrpc.GrpcHandler interface.
+func (r *ServerShell) CreateSubServer(configRegistry lnrpc.SubServerConfigDispatcher) (
+	lnrpc.SubServer, lnrpc.MacaroonPerms, error) {
+
+	subServer, macPermissions, err := createNewSubServer(configRegistry)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	r.WatchtowerClientServer = subServer
+	return subServer, macPermissions, nil
+}
+
 // isActive returns nil if the watchtower client is initialized so that we can
 // process RPC requests.
 func (c *WatchtowerClient) isActive() error {