invoicesrpc: create sub server

Sub server implementation is still empty. This is a preparatory
step for adding invoice functionality.

lnrpc/invoicesrpc/invoices_server.go

@@ -0,0 +1,89 @@
+// +build invoicesrpc
+
+package invoicesrpc
+
+import (
+	"github.com/lightningnetwork/lnd/lnrpc"
+	"google.golang.org/grpc"
+	"gopkg.in/macaroon-bakery.v2/bakery"
+)
+
+const (
+	// subServerName is the name of the sub rpc server. We'll use this name
+	// to register ourselves, and we also require that the main
+	// SubServerConfigDispatcher instance recognize it as the name of our
+	// RPC service.
+	subServerName = "InvoicesRPC"
+)
+
+var (
+	// macPermissions maps RPC calls to the permissions they require.
+	macPermissions = map[string][]bakery.Op{}
+)
+
+// Server is a sub-server of the main RPC server: the invoices RPC. This sub
+// RPC server allows external callers to access the status of the invoices
+// currently active within lnd, as well as configuring it at runtime.
+type Server struct {
+	started  int32 // To be used atomically.
+	shutdown int32 // To be used atomically.
+
+	cfg *Config
+}
+
+// A compile time check to ensure that Server fully implements the
+// InvoicesServer gRPC service.
+var _ InvoicesServer = (*Server)(nil)
+
+// New returns a new instance of the invoicesrpc Invoices sub-server. We also
+// return the set of permissions for the macaroons that we may create within
+// this method. If the macaroons we need aren't found in the filepath, then
+// we'll create them on start up. If we're unable to locate, or create the
+// macaroons we need, then we'll return with an error.
+func New(cfg *Config) (*Server, lnrpc.MacaroonPerms, error) {
+	// We don't create any new macaroons for this subserver, instead reuse
+	// existing onchain/offchain permissions.
+	server := &Server{
+		cfg: cfg,
+	}
+
+	return server, macPermissions, nil
+}
+
+// Start launches any helper goroutines required for the Server to function.
+//
+// NOTE: This is part of the lnrpc.SubServer interface.
+func (s *Server) Start() error {
+	return nil
+}
+
+// Stop signals any active goroutines for a graceful closure.
+//
+// NOTE: This is part of the lnrpc.SubServer interface.
+func (s *Server) Stop() error {
+	return nil
+}
+
+// Name returns a unique string representation of the sub-server. This can be
+// used to identify the sub-server and also de-duplicate them.
+//
+// NOTE: This is part of the lnrpc.SubServer interface.
+func (s *Server) Name() string {
+	return subServerName
+}
+
+// RegisterWithRootServer will be called by the root gRPC server to direct a sub
+// 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 (s *Server) 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.
+	RegisterInvoicesServer(grpcServer, s)
+
+	log.Debugf("Invoices RPC server successfully register with root " +
+		"gRPC server")
+
+	return nil
+}