fix: ensure daemon start successfully after update damon offline

cli/update_daemon.go

@@ -117,8 +117,9 @@ func (udc *DaemonUpdateCommand) updateDaemonConfigFile() error {
 	}
 
 	daemonConfig := &config.Config{}
-	if err = json.NewDecoder(bytes.NewReader(contents)).Decode(daemonConfig); err != nil {
-		return errors.Wrap(err, "failed to decode json: %s")
+	// do not return error if config file is empty
+	if err := json.NewDecoder(bytes.NewReader(contents)).Decode(daemonConfig); err != nil && err != io.EOF {
+		return errors.Wrapf(err, "failed to decode json: %s", udc.configFile)
 	}
 
 	flagSet := udc.cmd.Flags()

daemon/config/config.go

@@ -114,8 +114,9 @@ type Config struct {
 	// add a resolution later if it needed.
 	Runtimes map[string]types.Runtime `json:"add-runtime,omitempty"`
 
-	// Namespace is passed to containerd
-	Namespace string
+	// Namespace is passed to containerd, Namespace is not a daemon flag,
+	// do not marshal this field to config file.
+	Namespace string `json:"-"`
 }
 
 // Validate validates the user input config.

test/z_cli_daemon_test.go

@@ -470,6 +470,7 @@ func (suite *PouchDaemonSuite) TestDaemonWithMultiRuntimes(c *check.C) {
 	dcfg2.KillDaemon()
 }
 
+// TestUpdateDaemonWithLabels tests update daemon online with labels updated
 func (suite *PouchDaemonSuite) TestUpdateDaemonWithLabels(c *check.C) {
 	cfg := daemon.NewConfig()
 	err := cfg.StartDaemon()
@@ -485,3 +486,23 @@ func (suite *PouchDaemonSuite) TestUpdateDaemonWithLabels(c *check.C) {
 	updated := strings.Contains(ret.Stdout(), "aaa=bbb")
 	c.Assert(updated, check.Equals, true)
 }
+
+// TestUpdateDaemonWithLabels tests update daemon offline
+func (suite *PouchDaemonSuite) TestUpdateDaemonOffline(c *check.C) {
+	path := "/tmp/pouchconfig.json"
+	fd, err := os.Create(path)
+	c.Assert(err, check.IsNil)
+	fd.Close()
+	defer os.Remove(path)
+
+	cfg := daemon.NewConfig()
+	err = cfg.StartDaemon()
+	c.Assert(err, check.IsNil)
+
+	defer cfg.KillDaemon()
+
+	RunWithSpecifiedDaemon(&cfg, "updatedaemon", "--config-file", path, "--offline=true").Assert(c, icmd.Success)
+
+	ret := RunWithSpecifiedDaemon(&cfg, "info")
+	ret.Assert(c, icmd.Success)
+}