Add --dry option to run command

cmd/pebble/cmd_run.go

@@ -15,6 +15,7 @@
 package main
 
 import (
+	"errors"
 	"fmt"
 	"os"
 	"os/signal"
@@ -40,6 +41,7 @@ type cmdRun struct {
 	clientMixin
 
 	CreateDirs bool   `long:"create-dirs"`
+	Dry        bool   `long:"dry"`
 	Hold       bool   `long:"hold"`
 	HTTP       string `long:"http"`
 	Verbose    bool   `short:"v" long:"verbose"`
@@ -49,6 +51,7 @@ func init() {
 	addCommand("run", shortRunHelp, longRunHelp, func() flags.Commander { return &cmdRun{} },
 		map[string]string{
 			"create-dirs": "Create pebble directory on startup if it doesn't exist",
+			"dry":         "Don't start the pebble daemon. This option is incompatible with --create-dirs",
 			"hold":        "Do not start default services automatically",
 			"http":        `Start HTTP API listening on this address (e.g., ":4000")`,
 			"verbose":     "Log all output from services to stdout",
@@ -60,6 +63,10 @@ func (rcmd *cmdRun) Execute(args []string) error {
 		return ErrExtraArgs
 	}
 
+	if rcmd.CreateDirs && rcmd.Dry {
+		return errors.New("cannot run pebble: --create-dirs and --dry are mutually exclusive")
+	}
+
 	sigs := make(chan os.Signal, 2)
 	signal.Notify(sigs, syscall.SIGINT, syscall.SIGTERM, syscall.SIGQUIT)
 
@@ -126,6 +133,7 @@ func runDaemon(rcmd *cmdRun, ch chan os.Signal) error {
 	dopts := daemon.Options{
 		Dir:        pebbleDir,
 		SocketPath: socketPath,
+		Dry:        rcmd.Dry,
 	}
 	if rcmd.Verbose {
 		dopts.ServiceOutput = os.Stdout
@@ -152,10 +160,13 @@ func runDaemon(rcmd *cmdRun, ch chan os.Signal) error {
 		tic = time.NewTicker(checkRunningConditionsRetryDelay)
 		checkTicker = tic.C
 	}
-
 	d.Version = cmd.Version
 	d.Start()
 
+	if rcmd.Dry {
+		return nil
+	}
+
 	watchdog, err := runWatchdog(d)
 	if err != nil {
 		return fmt.Errorf("cannot run software watchdog: %v", err)

internal/daemon/daemon.go

@@ -72,6 +72,8 @@ type Options struct {
 	// ServiceOuput is an optional io.Writer for the service log output, if set, all services
 	// log output will be written to the writer.
 	ServiceOutput io.Writer
+
+	Dry bool
 }
 
 // A Daemon listens for requests and routes them to the right command
@@ -92,6 +94,7 @@ type Daemon struct {
 	tomb                tomb.Tomb
 	router              *mux.Router
 	standbyOpinions     *standby.StandbyOpinions
+	dry                 bool
 
 	// set to remember we need to restart the system
 	restartSystem bool
@@ -354,6 +357,13 @@ func logit(handler http.Handler) http.Handler {
 // Init sets up the Daemon's internal workings.
 // Don't call more than once.
 func (d *Daemon) Init() error {
+	if _, err := d.overlord.ServiceManager().Plan(); err != nil {
+		return err
+	}
+	if d.dry {
+		return nil
+	}
+
 	listenerMap := make(map[string]net.Listener)
 
 	if listener, err := getListener(d.normalSocketPath, listenerMap); err == nil {
@@ -453,6 +463,9 @@ func (d *Daemon) initStandbyHandling() {
 }
 
 func (d *Daemon) Start() {
+	if d.dry {
+		return
+	}
 	if d.rebootIsMissing {
 		// we need to schedule and wait for a system restart
 		d.tomb.Kill(nil)
@@ -786,6 +799,7 @@ func New(opts *Options) (*Daemon, error) {
 		normalSocketPath:    opts.SocketPath,
 		untrustedSocketPath: opts.SocketPath + ".untrusted",
 		httpAddress:         opts.HTTPAddress,
+		dry:                 opts.Dry,
 	}
 
 	ovld, err := overlord.New(opts.Dir, d, opts.ServiceOutput)