command/flag: add timezone flag to common task flags

- Add Timezone type
- Resolve timezone name from /etc/localtime

pkg/command/flag/flag.go

@@ -131,6 +131,10 @@ func (w Wrapper) window(p *[]string) {
 	w.fs.StringSliceVar(p, "window", nil, usage["window"])
 }
 
+func (w Wrapper) timezone(p *Timezone) {
+	w.fs.Var(p, "timezone", usage["timezone"])
+}
+
 func (w Wrapper) interval(p *Duration) {
 	w.fs.VarP(p, "interval", "i", usage["interval"])
 	w.MustMarkDeprecated("interval", "use cron instead")

pkg/command/flag/task.go

@@ -6,6 +6,7 @@ import (
 	"time"
 
 	"github.com/scylladb/scylla-manager/pkg/managerclient"
+	"github.com/scylladb/scylla-manager/pkg/util/timeutc"
 	"github.com/spf13/cobra"
 )
 
@@ -18,6 +19,7 @@ type TaskBase struct {
 	name       string
 	cron       Cron
 	window     []string
+	timezone   Timezone
 	interval   Duration
 	startDate  Time
 	numRetries int
@@ -26,6 +28,7 @@ type TaskBase struct {
 
 func MakeTaskBase() TaskBase {
 	return TaskBase{
+		timezone:  Timezone{timeutc.LocalName},
 		retryWait: DurationWithDefault(10 * time.Minute),
 	}
 }
@@ -43,6 +46,7 @@ func (cmd *TaskBase) Init() {
 	w.name(&cmd.name)
 	w.cron(&cmd.cron)
 	w.window(&cmd.window)
+	w.timezone(&cmd.timezone)
 	w.interval(&cmd.interval)
 	w.startDate(&cmd.startDate)
 	w.numRetries(&cmd.numRetries, cmd.numRetries)
@@ -63,6 +67,7 @@ func (cmd *TaskBase) CreateTask(taskType string) *managerclient.Task {
 		Schedule: &managerclient.Schedule{
 			Cron:       cmd.cron.Value(),
 			Window:     cmd.window,
+			Timezone:   cmd.timezone.Value(),
 			Interval:   cmd.interval.String(),
 			StartDate:  cmd.startDate.DateTimePtr(),
 			NumRetries: int64(cmd.numRetries),
@@ -91,6 +96,10 @@ func (cmd *TaskBase) UpdateTask(task *managerclient.Task) bool {
 		task.Schedule.Window = cmd.window
 		ok = true
 	}
+	if cmd.Flag("timezone").Changed {
+		task.Schedule.Timezone = cmd.timezone.Value()
+		ok = true
+	}
 	if cmd.Flag("interval").Changed {
 		task.Schedule.Interval = cmd.interval.String()
 		ok = true

pkg/command/flag/task.yaml

@@ -16,6 +16,10 @@ window: |
   * '23:00,06:00' - can be executed every night from 11PM to 6AM
   * '23:00,06:00,SAT-00:00,SUN-23:59' - can be executed every night from 11PM to 6AM and all day during the weekend
 
+timezone: |
+  Timezone of --cron and --window flag values.
+  The default value is taken from this system, namely 'TZ' envvar or '/etc/localtime' file.
+
 interval: |
   Time after which a successfully completed task would be run again, supported units are:
 

pkg/command/flag/type.go

@@ -47,6 +47,36 @@ func (c *Cron) Type() string {
 	return "string"
 }
 
+// Timezone wraps string for early validation.
+type Timezone struct {
+	v string
+}
+
+var _ flag.Value = (*Timezone)(nil)
+
+func (c *Timezone) String() string {
+	return c.v
+}
+
+// Set implements pflag.Value.
+func (c *Timezone) Set(s string) error {
+	if _, err := time.LoadLocation(s); err != nil {
+		return err
+	}
+
+	c.v = s
+	return nil
+}
+
+func (c *Timezone) Value() string {
+	return c.v
+}
+
+// Type implements pflag.Value.
+func (c *Timezone) Type() string {
+	return "string"
+}
+
 // Time wraps time.Time and add support for now+duration syntax.
 type Time struct {
 	v time.Time

pkg/util/timeutc/zoneinfo.go

@@ -0,0 +1,34 @@
+// Copyright (C) 2021 ScyllaDB
+
+package timeutc
+
+import (
+	"os"
+	"strings"
+	"time"
+)
+
+// LocalName is name of the local time zone conforming to the IANA Time Zone database, such as "America/New_York".
+// Using time.Local if timezone is read from /etc/localtime its name is overwritten by "Local".
+// LocalName provides the name as read from /etc/localtime static link.
+var LocalName string
+
+func init() {
+	tz := time.Local.String()
+	if tz == "Local" {
+		p, err := os.Readlink("/etc/localtime")
+		if err != nil {
+			return
+		}
+		i := strings.LastIndex(p, "/zoneinfo/")
+		if i < 0 {
+			return
+		}
+		tz = p[i+len("/zoneinfo/"):]
+		if _, err := time.LoadLocation(tz); err != nil {
+			return
+		}
+	}
+
+	LocalName = tz
+}