Load assets for dashboard/admin panel on demand

The client and server services now only attempt to load assets if the
dashboard or admin panel are enabled. This change makes it possible to
use FRP as a library without having to manage assets. If a library user
wants to start a server with the dashboard enabled, they will need to
set the DashboardPort and AssetsDir fields of ServerCommonConf.

client/service.go

@@ -52,13 +52,6 @@ type Service struct {
 }
 
 func NewService(pxyCfgs map[string]config.ProxyConf, visitorCfgs map[string]config.VisitorConf) (svr *Service, err error) {
-	// Init assets
-	err = assets.Load("")
-	if err != nil {
-		err = fmt.Errorf("Load assets error: %v", err)
-		return
-	}
-
 	svr = &Service{
 		pxyCfgs:     pxyCfgs,
 		visitorCfgs: visitorCfgs,
@@ -102,7 +95,13 @@ func (svr *Service) Run() error {
 	go svr.keepControllerWorking()
 
 	if g.GlbClientCfg.AdminPort != 0 {
-		err := svr.RunAdminServer(g.GlbClientCfg.AdminAddr, g.GlbClientCfg.AdminPort)
+		// Init admin server assets
+		err := assets.Load("")
+		if err != nil {
+			return fmt.Errorf("Load assets error: %v", err)
+		}
+
+		err = svr.RunAdminServer(g.GlbClientCfg.AdminAddr, g.GlbClientCfg.AdminPort)
 		if err != nil {
 			log.Warn("run admin server error: %v", err)
 		}

server/service.go

@@ -108,13 +108,6 @@ func NewService() (svr *Service, err error) {
 	// Init HTTP group controller
 	svr.rc.HTTPGroupCtl = group.NewHTTPGroupController(svr.httpVhostRouter)
 
-	// Init assets
-	err = assets.Load(cfg.AssetsDir)
-	if err != nil {
-		err = fmt.Errorf("Load assets error: %v", err)
-		return
-	}
-
 	// Init 404 not found page
 	vhost.NotFoundPagePath = cfg.Custom404Page
 
@@ -231,6 +224,13 @@ func NewService() (svr *Service, err error) {
 	var statsEnable bool
 	// Create dashboard web server.
 	if cfg.DashboardPort > 0 {
+		// Init dashboard assets
+		err = assets.Load(cfg.AssetsDir)
+		if err != nil {
+			err = fmt.Errorf("Load assets error: %v", err)
+			return
+		}
+
 		err = svr.RunDashboardServer(cfg.DashboardAddr, cfg.DashboardPort)
 		if err != nil {
 			err = fmt.Errorf("Create dashboard web server error, %v", err)