cmd/syncthing: Add --skip-port-probing (fixes #8090) (#8099)

* cmd/syncthing: Remove unnecessary function arguments.

The openGUI() function does not need a device ID to work, and there is
only one caller anyway which uses EmptyDeviceID.

The loadOrDefaultConfig() function is always called with the same
dummy values.

* cmd/syncthing: Avoid misleading info messages from monitor process.

In order to check whether panic reporting is enabled, the monitor
process utilizes the loadOrDefaultConfig() function.  In case there is
no config file yet, info messages may be logged during creation if the
config Wrapper, which is discarded immediately after.

Stop using the DefaultConfig() utility function from lib/syncthing and
directly generate a minimal config instead to avoid these.

Add comments to loadOrDefaultConfig() explaining its limited purpose.

* cmd/syncthing/generate: Always write updated config file.

Previously, an existing config file was left untouched unless either
of the --gui-user or --gui-password options was given.  Remove that
condition and simplify the checking code.

* lib/config: Factor out ProbeFreePorts().

* cmd/syncthing: Add option --skip-port-probing.

Applies to both the "generate" and "serve" subcommands, as well as the
deprecated --generate option, just as the --no-default-folder flag.

cmd/syncthing/cmdutil/options_common.go

@@ -12,4 +12,5 @@ type CommonOptions struct {
 	ConfDir         string `name:"config" placeholder:"PATH" help:"Set configuration directory (config and keys)"`
 	HomeDir         string `name:"home" placeholder:"PATH" help:"Set configuration and data directory"`
 	NoDefaultFolder bool   `env:"STNODEFAULTFOLDER" help:"Don't create the \"default\" folder on first startup"`
+	SkipPortProbing bool   `help:"Don't try to find free ports for GUI and listen addresses on first startup"`
 }

cmd/syncthing/generate/generate.go

@@ -58,13 +58,13 @@ func (c *CLI) Run() error {
 		c.GUIPassword = string(password)
 	}
 
-	if err := Generate(c.ConfDir, c.GUIUser, c.GUIPassword, c.NoDefaultFolder); err != nil {
+	if err := Generate(c.ConfDir, c.GUIUser, c.GUIPassword, c.NoDefaultFolder, c.SkipPortProbing); err != nil {
 		return fmt.Errorf("Failed to generate config and keys: %w", err)
 	}
 	return nil
 }
 
-func Generate(confDir, guiUser, guiPassword string, noDefaultFolder bool) error {
+func Generate(confDir, guiUser, guiPassword string, noDefaultFolder, skipPortProbing bool) error {
 	dir, err := fs.ExpandTilde(confDir)
 	if err != nil {
 		return err
@@ -92,7 +92,7 @@ func Generate(confDir, guiUser, guiPassword string, noDefaultFolder bool) error
 	cfgFile := locations.Get(locations.ConfigFile)
 	cfg, _, err := config.Load(cfgFile, myID, events.NoopLogger)
 	if fs.IsNotExist(err) {
-		if cfg, err = syncthing.DefaultConfig(cfgFile, myID, events.NoopLogger, noDefaultFolder); err != nil {
+		if cfg, err = syncthing.DefaultConfig(cfgFile, myID, events.NoopLogger, noDefaultFolder, skipPortProbing); err != nil {
 			return fmt.Errorf("create config: %w", err)
 		}
 	} else if err != nil {

cmd/syncthing/main.go

@@ -337,7 +337,7 @@ func (options serveOptions) Run() error {
 	}
 
 	if options.GenerateDir != "" {
-		if err := generate.Generate(options.GenerateDir, "", "", options.NoDefaultFolder); err != nil {
+		if err := generate.Generate(options.GenerateDir, "", "", options.NoDefaultFolder, options.SkipPortProbing); err != nil {
 			l.Warnln("Failed to generate config and keys:", err)
 			os.Exit(svcutil.ExitError.AsInt())
 		}
@@ -551,7 +551,7 @@ func syncthingMain(options serveOptions) {
 	evLogger := events.NewLogger()
 	earlyService.Add(evLogger)
 
-	cfgWrapper, err := syncthing.LoadConfigAtStartup(locations.Get(locations.ConfigFile), cert, evLogger, options.AllowNewerConfig, options.NoDefaultFolder)
+	cfgWrapper, err := syncthing.LoadConfigAtStartup(locations.Get(locations.ConfigFile), cert, evLogger, options.AllowNewerConfig, options.NoDefaultFolder, options.SkipPortProbing)
 	if err != nil {
 		l.Warnln("Failed to initialize config:", err)
 		os.Exit(svcutil.ExitError.AsInt())

lib/config/config.go

@@ -113,18 +113,16 @@ func New(myID protocol.DeviceID) Configuration {
 	return cfg
 }
 
-func NewWithFreePorts(myID protocol.DeviceID) (Configuration, error) {
-	cfg := New(myID)
-
+func (cfg *Configuration) ProbeFreePorts() error {
 	port, err := getFreePort("127.0.0.1", DefaultGUIPort)
 	if err != nil {
-		return Configuration{}, errors.Wrap(err, "get free port (GUI)")
+		return errors.Wrap(err, "get free port (GUI)")
 	}
 	cfg.GUI.RawAddress = fmt.Sprintf("127.0.0.1:%d", port)
 
 	port, err = getFreePort("0.0.0.0", DefaultTCPPort)
 	if err != nil {
-		return Configuration{}, errors.Wrap(err, "get free port (BEP)")
+		return errors.Wrap(err, "get free port (BEP)")
 	}
 	if port == DefaultTCPPort {
 		cfg.Options.RawListenAddresses = []string{"default"}
@@ -136,7 +134,7 @@ func NewWithFreePorts(myID protocol.DeviceID) (Configuration, error) {
 		}
 	}
 
-	return cfg, nil
+	return nil
 }
 
 type xmlConfiguration struct {

lib/syncthing/utils.go

@@ -59,9 +59,12 @@ func GenerateCertificate(certFile, keyFile string) (tls.Certificate, error) {
 	return tlsutil.NewCertificate(certFile, keyFile, tlsDefaultCommonName, deviceCertLifetimeDays)
 }
 
-func DefaultConfig(path string, myID protocol.DeviceID, evLogger events.Logger, noDefaultFolder bool) (config.Wrapper, error) {
-	newCfg, err := config.NewWithFreePorts(myID)
-	if err != nil {
+func DefaultConfig(path string, myID protocol.DeviceID, evLogger events.Logger, noDefaultFolder, skipPortProbing bool) (config.Wrapper, error) {
+	newCfg := config.New(myID)
+
+	if skipPortProbing {
+		l.Infoln("Using default network port numbers instead of probing for free ports")
+	} else if err := newCfg.ProbeFreePorts(); err != nil {
 		return nil, err
 	}
 
@@ -84,11 +87,11 @@ func DefaultConfig(path string, myID protocol.DeviceID, evLogger events.Logger,
 // creates a default one, without the default folder if noDefaultFolder is ture.
 // Otherwise it checks the version, and archives and upgrades the config if
 // necessary or returns an error, if the version isn't compatible.
-func LoadConfigAtStartup(path string, cert tls.Certificate, evLogger events.Logger, allowNewerConfig, noDefaultFolder bool) (config.Wrapper, error) {
+func LoadConfigAtStartup(path string, cert tls.Certificate, evLogger events.Logger, allowNewerConfig, noDefaultFolder, skipPortProbing bool) (config.Wrapper, error) {
 	myID := protocol.NewDeviceID(cert.Certificate[0])
 	cfg, originalVersion, err := config.Load(path, myID, evLogger)
 	if fs.IsNotExist(err) {
-		cfg, err = DefaultConfig(path, myID, evLogger, noDefaultFolder)
+		cfg, err = DefaultConfig(path, myID, evLogger, noDefaultFolder, skipPortProbing)
 		if err != nil {
 			return nil, errors.Wrap(err, "failed to generate default config")
 		}