refactor the code related to xtcp (#3449)

cmd/frpc/sub/root.go

@@ -53,6 +53,7 @@ var (
 	logFile         string
 	logMaxDays      int
 	disableLogColor bool
+	dnsServer       string
 
 	proxyName          string
 	localIP            string
@@ -94,6 +95,7 @@ func RegisterCommonFlags(cmd *cobra.Command) {
 	cmd.PersistentFlags().IntVarP(&logMaxDays, "log_max_days", "", 3, "log file reversed days")
 	cmd.PersistentFlags().BoolVarP(&disableLogColor, "disable_log_color", "", false, "disable log color in console")
 	cmd.PersistentFlags().BoolVarP(&tlsEnable, "tls_enable", "", false, "enable frpc tls")
+	cmd.PersistentFlags().StringVarP(&dnsServer, "dns_server", "", "", "specify dns server instead of using system default one")
 }
 
 var rootCmd = &cobra.Command{
@@ -108,26 +110,7 @@ var rootCmd = &cobra.Command{
 		// If cfgDir is not empty, run multiple frpc service for each config file in cfgDir.
 		// Note that it's only designed for testing. It's not guaranteed to be stable.
 		if cfgDir != "" {
-			var wg sync.WaitGroup
-			_ = filepath.WalkDir(cfgDir, func(path string, d fs.DirEntry, err error) error {
-				if err != nil {
-					return nil
-				}
-				if d.IsDir() {
-					return nil
-				}
-				wg.Add(1)
-				time.Sleep(time.Millisecond)
-				go func() {
-					defer wg.Done()
-					err := runClient(path)
-					if err != nil {
-						fmt.Printf("frpc service error for config file [%s]\n", path)
-					}
-				}()
-				return nil
-			})
-			wg.Wait()
+			_ = runMultipleClients(cfgDir)
 			return nil
 		}
 
@@ -141,6 +124,27 @@ var rootCmd = &cobra.Command{
 	},
 }
 
+func runMultipleClients(cfgDir string) error {
+	var wg sync.WaitGroup
+	err := filepath.WalkDir(cfgDir, func(path string, d fs.DirEntry, err error) error {
+		if err != nil || d.IsDir() {
+			return nil
+		}
+		wg.Add(1)
+		time.Sleep(time.Millisecond)
+		go func() {
+			defer wg.Done()
+			err := runClient(path)
+			if err != nil {
+				fmt.Printf("frpc service error for config file [%s]\n", path)
+			}
+		}()
+		return nil
+	})
+	wg.Wait()
+	return err
+}
+
 func Execute() {
 	if err := rootCmd.Execute(); err != nil {
 		os.Exit(1)
@@ -177,6 +181,7 @@ func parseClientCommonCfgFromCmd() (cfg config.ClientCommonConf, err error) {
 	cfg.LogFile = logFile
 	cfg.LogMaxDays = int64(logMaxDays)
 	cfg.DisableLogColor = disableLogColor
+	cfg.DNSServer = dnsServer
 
 	// Only token authentication is supported in cmd mode
 	cfg.ClientConfig = auth.GetDefaultClientConf()