cmd/cli: change "ctrld start" behavior

Without reading the documentation, users may think that "ctrld start"
will just start ctrld service. However, this is not the case, and may
lead to unexpected result from user's point of view.

This commit changes "ctrld start" to just start already installed ctrld
service, so users won't lost what they did installed before. If there
are any arguments specified, performing the current behavior.

README.md

@@ -105,9 +105,11 @@ Available Commands:
   start       Quick start service and configure DNS on interface
   stop        Quick stop service and remove DNS from interface
   restart     Restart the ctrld service
+  reload      Reload the ctrld service
   status      Show status of the ctrld service
   uninstall   Stop and uninstall the ctrld service
   clients     Manage clients
+  upgrade     Upgrading ctrld to latest version
 
 Flags:
   -h, --help            help for ctrld

cmd/cli/cli.go

@@ -115,7 +115,7 @@ func initCLI() {
 		&verbose,
 		"verbose",
 		"v",
-		`verbose log output, "-v" basic logging, "-vv" debug level logging`,
+		`verbose log output, "-v" basic logging, "-vv" debug logging`,
 	)
 	rootCmd.PersistentFlags().BoolVarP(
 		&silent,
@@ -163,7 +163,10 @@ func initCLI() {
 		},
 		Use:   "start",
 		Short: "Install and start the ctrld service",
-		Args:  cobra.NoArgs,
+		Long: `Install and start the ctrld service
+
+NOTE: running "ctrld start" without any arguments will start already installed ctrld service.`,
+		Args: cobra.NoArgs,
 		Run: func(cmd *cobra.Command, args []string) {
 			checkStrFlagEmpty(cmd, cdUidFlagName)
 			checkStrFlagEmpty(cmd, cdOrgFlagName)
@@ -187,8 +190,9 @@ func initCLI() {
 				return
 			}
 
-			status, _ := s.Status()
+			status, err := s.Status()
 			isCtrldRunning := status == service.StatusRunning
+			isCtrldInstalled := !errors.Is(err, service.ErrNotInstalled)
 
 			// If pin code was set, do not allow running start command.
 			if isCtrldRunning {
@@ -197,6 +201,54 @@ func initCLI() {
 				}
 			}
 
+			if !startOnly {
+				startOnly = len(osArgs) == 0
+			}
+			// If user run "ctrld start" and ctrld is already installed, starting existing service.
+			if startOnly && isCtrldInstalled {
+				tryReadingConfigWithNotice(false, true)
+				if err := v.Unmarshal(&cfg); err != nil {
+					mainLog.Load().Fatal().Msgf("failed to unmarshal config: %v", err)
+				}
+
+				initLogging()
+				tasks := []task{
+					resetDnsTask(p, s),
+					{s.Stop, false},
+					{func() error {
+						// Save current DNS so we can restore later.
+						withEachPhysicalInterfaces("", "save DNS settings", func(i *net.Interface) error {
+							return saveCurrentStaticDNS(i)
+						})
+						return nil
+					}, false},
+					{s.Start, true},
+					{noticeWritingControlDConfig, false},
+				}
+				mainLog.Load().Notice().Msg("Starting existing ctrld service")
+				if doTasks(tasks) {
+					mainLog.Load().Notice().Msg("Service started")
+					sockDir, err := socketDir()
+					if err != nil {
+						mainLog.Load().Warn().Err(err).Msg("Failed to get socket directory")
+						os.Exit(1)
+					}
+					if cc := newSocketControlClient(s, sockDir); cc != nil {
+						if resp, _ := cc.post(ifacePath, nil); resp != nil && resp.StatusCode == http.StatusOK {
+							if iface == "auto" {
+								iface = defaultIfaceName()
+							}
+							logger := mainLog.Load().With().Str("iface", iface).Logger()
+							logger.Debug().Msg("setting DNS successfully")
+						}
+					}
+				} else {
+					mainLog.Load().Error().Err(err).Msg("Failed to start existing ctrld service")
+					os.Exit(1)
+				}
+				return
+			}
+
 			if cdUID != "" {
 				doValidateCdRemoteConfig(cdUID)
 			} else if uid := cdUIDFromProvToken(); uid != "" {
@@ -373,6 +425,8 @@ func initCLI() {
 	startCmd.Flags().StringVarP(&nextdns, nextdnsFlagName, "", "", "NextDNS resolver id")
 	startCmd.Flags().StringVarP(&cdUpstreamProto, "proto", "", ctrld.ResolverTypeDOH, `Control D upstream type, either "doh" or "doh3"`)
 	startCmd.Flags().BoolVarP(&skipSelfChecks, "skip_self_checks", "", false, `Skip self checks after installing ctrld service`)
+	startCmd.Flags().BoolVarP(&startOnly, "start_only", "", false, "Do not install new service")
+	_ = startCmd.Flags().MarkHidden("start_only")
 
 	routerCmd := &cobra.Command{
 		Use: "setup",
@@ -739,7 +793,13 @@ NOTE: Uninstalling will set DNS to values provided by DHCP.`,
 		},
 		Use:   "start",
 		Short: "Quick start service and configure DNS on interface",
+		Long: `Quick start service and configure DNS on interface
+
+NOTE: running "ctrld start" without any arguments will start already installed ctrld service.`,
 		Run: func(cmd *cobra.Command, args []string) {
+			if len(os.Args) == 2 {
+				startOnly = true
+			}
 			if !cmd.Flags().Changed("iface") {
 				os.Args = append(os.Args, "--iface="+ifaceStartStop)
 			}

cmd/cli/main.go

@@ -37,6 +37,7 @@ var (
 	deactivationPin   int64
 	skipSelfChecks    bool
 	cleanup           bool
+	startOnly         bool
 
 	mainLog       atomic.Pointer[zerolog.Logger]
 	consoleWriter zerolog.ConsoleWriter