Fix cron for schedules that do not match any time

Author: yiminc

common/backoff/cron.go

@@ -36,13 +36,22 @@ import (
 // NoBackoff is used to represent backoff when no cron backoff is needed
 const NoBackoff = time.Duration(-1)
 
+// InfiniteBackoff is used to represent a long backoff that in practice won't fire
+const InfiniteBackoff = 1<<63 - 1
+
 // ValidateSchedule validates a cron schedule spec
 func ValidateSchedule(cronSchedule string) error {
 	if cronSchedule == "" {
 		return nil
 	}
-	if _, err := cron.ParseStandard(cronSchedule); err != nil {
-		return serviceerror.NewInvalidArgument("Invalid CronSchedule.")
+	schedule, err := cron.ParseStandard(cronSchedule)
+	if err != nil {
+		return serviceerror.NewInvalidArgument("invalid CronSchedule.")
+	}
+	nextTime := schedule.Next(time.Now().UTC())
+	if nextTime.IsZero() {
+		// no time can be found to satisfy the schedule
+		return serviceerror.NewInvalidArgument("invalid CronSchedule, no time can be found to satisfy the schedule")
 	}
 	return nil
 }
@@ -68,9 +77,13 @@ func GetBackoffForNextSchedule(cronSchedule string, scheduledTime time.Time, now
 	} else {
 		nextScheduleTime = schedule.Next(scheduledUTCTime)
 		// Calculate the next schedule start time which is nearest to now (right after now).
-		for nextScheduleTime.Before(nowUTC) {
+		for !nextScheduleTime.IsZero() && nextScheduleTime.Before(nowUTC) {
 			nextScheduleTime = schedule.Next(nextScheduleTime)
 		}
+		if nextScheduleTime.IsZero() {
+			// no time can be found to satisfy the schedule
+			return InfiniteBackoff
+		}
 	}
 
 	backoffInterval := nextScheduleTime.Sub(nowUTC)

common/backoff/cron_test.go

@@ -37,27 +37,30 @@ var crontests = []struct {
 	scheduledTime string
 	now           string
 	result        time.Duration
+	err           string
 }{
-	{"0 10 * * *", "2018-12-17T08:00:00-08:00", "", time.Hour * 18},
-	{"0 10 * * *", "2018-12-18T02:00:00-08:00", "", time.Hour * 24},
-	{"0 * * * *", "2018-12-17T08:08:00+00:00", "", time.Minute * 52},
-	{"0 * * * *", "2018-12-17T09:00:00+00:00", "", time.Hour},
-	{"* * * * *", "2018-12-17T08:08:18+00:00", "", time.Second * 42},
-	{"0 * * * *", "2018-12-17T09:00:00+00:00", "", time.Minute * 60},
-	{"0 10 * * *", "2018-12-17T08:00:00+00:00", "2018-12-20T00:00:00+00:00", time.Hour * 10},
-	{"0 10 * * *", "2018-12-17T08:00:00+00:00", "2018-12-17T09:00:00+00:00", time.Hour},
-	{"*/10 * * * *", "2018-12-17T00:04:00+00:00", "2018-12-17T01:02:00+00:00", time.Minute * 8},
-	{"invalid-cron-spec", "2018-12-17T00:04:00+00:00", "2018-12-17T01:02:00+00:00", NoBackoff},
-	{"@every 5h", "2018-12-17T08:00:00+00:00", "2018-12-17T09:00:00+00:00", time.Hour * 4},
-	{"@every 5h", "2018-12-17T08:00:00+00:00", "2018-12-18T00:00:00+00:00", time.Hour * 4},
-	{"0 3 * * 0-6", "2018-12-17T08:00:00-08:00", "", time.Hour * 11},
-	{"@every 30s", "2020-07-17T09:00:02-01:00", "2020-07-17T09:00:02-01:00", time.Second * 30},
-	{"@every 30s", "2020-07-17T09:00:02-01:00", "2020-09-17T03:00:53-01:00", time.Second * 9},
-	{"@every 30m", "2020-07-17T09:00:00-01:00", "2020-07-17T08:45:00-01:00", time.Minute * 15},
+	{"0 0 31 2 *", "2018-12-17T08:00:00-08:00", "", 0, "invalid CronSchedule, no time can be found to satisfy the schedule"},
+	{"invalid-cron-spec", "2018-12-17T00:04:00+00:00", "2018-12-17T01:02:00+00:00", NoBackoff, "invalid CronSchedule"},
+
+	{"0 10 * * *", "2018-12-17T08:00:00-08:00", "", time.Hour * 18, ""},
+	{"0 10 * * *", "2018-12-18T02:00:00-08:00", "", time.Hour * 24, ""},
+	{"0 * * * *", "2018-12-17T08:08:00+00:00", "", time.Minute * 52, ""},
+	{"0 * * * *", "2018-12-17T09:00:00+00:00", "", time.Hour, ""},
+	{"* * * * *", "2018-12-17T08:08:18+00:00", "", time.Second * 42, ""},
+	{"0 * * * *", "2018-12-17T09:00:00+00:00", "", time.Minute * 60, ""},
+	{"0 10 * * *", "2018-12-17T08:00:00+00:00", "2018-12-20T00:00:00+00:00", time.Hour * 10, ""},
+	{"0 10 * * *", "2018-12-17T08:00:00+00:00", "2018-12-17T09:00:00+00:00", time.Hour, ""},
+	{"*/10 * * * *", "2018-12-17T00:04:00+00:00", "2018-12-17T01:02:00+00:00", time.Minute * 8, ""},
+	{"@every 5h", "2018-12-17T08:00:00+00:00", "2018-12-17T09:00:00+00:00", time.Hour * 4, ""},
+	{"@every 5h", "2018-12-17T08:00:00+00:00", "2018-12-18T00:00:00+00:00", time.Hour * 4, ""},
+	{"0 3 * * 0-6", "2018-12-17T08:00:00-08:00", "", time.Hour * 11, ""},
+	{"@every 30s", "2020-07-17T09:00:02-01:00", "2020-07-17T09:00:02-01:00", time.Second * 30, ""},
+	{"@every 30s", "2020-07-17T09:00:02-01:00", "2020-09-17T03:00:53-01:00", time.Second * 9, ""},
+	{"@every 30m", "2020-07-17T09:00:00-01:00", "2020-07-17T08:45:00-01:00", time.Minute * 15, ""},
 	// At 16:05 East Coast (Day light saving on)
-	{"CRON_TZ=America/New_York 5 16 * * *", "2021-03-14T00:00:00-04:00", "2021-03-14T15:05:00-04:00", time.Hour * 1},
+	{"CRON_TZ=America/New_York 5 16 * * *", "2021-03-14T00:00:00-04:00", "2021-03-14T15:05:00-04:00", time.Hour * 1, ""},
 	// At 04:05 East Coast (Day light saving off)
-	{"CRON_TZ=America/New_York 5 4 * * *", "2021-11-25T00:00:00-05:00", "2021-11-25T03:05:00-05:00", time.Hour * 1},
+	{"CRON_TZ=America/New_York 5 4 * * *", "2021-11-25T00:00:00-05:00", "2021-11-25T03:05:00-05:00", time.Hour * 1, ""},
 }
 
 func TestCron(t *testing.T) {
@@ -71,11 +74,15 @@ func TestCron(t *testing.T) {
 				assert.NoError(t, err, "Parse end time: %v", tt.now)
 			}
 			err = ValidateSchedule(tt.cron)
-			if tt.result != NoBackoff {
-				assert.NoError(t, err)
+			if len(tt.err) > 0 {
+				assert.Error(t, err)
+				assert.Contains(t, err.Error(), tt.err)
+			} else {
+				assert.NoError(t, err, "Failed on cron schedule: %v", tt.cron)
+
+				backoff := GetBackoffForNextSchedule(tt.cron, start, end)
+				assert.Equal(t, tt.result, backoff, "The cron spec is %s and the expected result is %s", tt.cron, tt.result)
 			}
-			backoff := GetBackoffForNextSchedule(tt.cron, start, end)
-			assert.Equal(t, tt.result, backoff, "The cron spec is %s and the expected result is %s", tt.cron, tt.result)
 		})
 	}
 }