chore: update cron package

internal/cron/README.md

+Fork from https://github.com/robfig/cron

internal/cron/chain.go

+package cron
+
+import (
+	"fmt"
+	"runtime"
+	"sync"
+	"time"
+)
+
+// JobWrapper decorates the given Job with some behavior.
+type JobWrapper func(Job) Job
+
+// Chain is a sequence of JobWrappers that decorates submitted jobs with
+// cross-cutting behaviors like logging or synchronization.
+type Chain struct {
+	wrappers []JobWrapper
+}
+
+// NewChain returns a Chain consisting of the given JobWrappers.
+func NewChain(c ...JobWrapper) Chain {
+	return Chain{c}
+}
+
+// Then decorates the given job with all JobWrappers in the chain.
+//
+// This:
+//
+//	NewChain(m1, m2, m3).Then(job)
+//
+// is equivalent to:
+//
+//	m1(m2(m3(job)))
+func (c Chain) Then(j Job) Job {
+	for i := range c.wrappers {
+		j = c.wrappers[len(c.wrappers)-i-1](j)
+	}
+	return j
+}
+
+// Recover panics in wrapped jobs and log them with the provided logger.
+func Recover(logger Logger) JobWrapper {
+	return func(j Job) Job {
+		return FuncJob(func() {
+			defer func() {
+				if r := recover(); r != nil {
+					const size = 64 << 10
+					buf := make([]byte, size)
+					buf = buf[:runtime.Stack(buf, false)]
+					err, ok := r.(error)
+					if !ok {
+						err = fmt.Errorf("%v", r)
+					}
+					logger.Error(err, "panic", "stack", "...\n"+string(buf))
+				}
+			}()
+			j.Run()
+		})
+	}
+}
+
+// DelayIfStillRunning serializes jobs, delaying subsequent runs until the
+// previous one is complete. Jobs running after a delay of more than a minute
+// have the delay logged at Info.
+func DelayIfStillRunning(logger Logger) JobWrapper {
+	return func(j Job) Job {
+		var mu sync.Mutex
+		return FuncJob(func() {
+			start := time.Now()
+			mu.Lock()
+			defer mu.Unlock()
+			if dur := time.Since(start); dur > time.Minute {
+				logger.Info("delay", "duration", dur)
+			}
+			j.Run()
+		})
+	}
+}
+
+// SkipIfStillRunning skips an invocation of the Job if a previous invocation is
+// still running. It logs skips to the given logger at Info level.
+func SkipIfStillRunning(logger Logger) JobWrapper {
+	return func(j Job) Job {
+		var ch = make(chan struct{}, 1)
+		ch <- struct{}{}
+		return FuncJob(func() {
+			select {
+			case v := <-ch:
+				defer func() { ch <- v }()
+				j.Run()
+			default:
+				logger.Info("skip")
+			}
+		})
+	}
+}

internal/cron/chain_test.go

+package cron
+
+import (
+	"io"
+	"log"
+	"reflect"
+	"sync"
+	"testing"
+	"time"
+)
+
+func appendingJob(slice *[]int, value int) Job {
+	var m sync.Mutex
+	return FuncJob(func() {
+		m.Lock()
+		*slice = append(*slice, value)
+		m.Unlock()
+	})
+}
+
+func appendingWrapper(slice *[]int, value int) JobWrapper {
+	return func(j Job) Job {
+		return FuncJob(func() {
+			appendingJob(slice, value).Run()
+			j.Run()
+		})
+	}
+}
+
+func TestChain(t *testing.T) {
+	var nums []int
+	var (
+		append1 = appendingWrapper(&nums, 1)
+		append2 = appendingWrapper(&nums, 2)
+		append3 = appendingWrapper(&nums, 3)
+		append4 = appendingJob(&nums, 4)
+	)
+	NewChain(append1, append2, append3).Then(append4).Run()
+	if !reflect.DeepEqual(nums, []int{1, 2, 3, 4}) {
+		t.Error("unexpected order of calls:", nums)
+	}
+}
+
+func TestChainRecover(t *testing.T) {
+	panickingJob := FuncJob(func() {
+		panic("panickingJob panics")
+	})
+
+	t.Run("panic exits job by default", func(t *testing.T) {
+		defer func() {
+			if err := recover(); err == nil {
+				t.Errorf("panic expected, but none received")
+			}
+		}()
+		NewChain().Then(panickingJob).
+			Run()
+	})
+
+	t.Run("Recovering JobWrapper recovers", func(t *testing.T) {
+		NewChain(Recover(PrintfLogger(log.New(io.Discard, "", 0)))).
+			Then(panickingJob).
+			Run()
+	})
+
+	t.Run("composed with the *IfStillRunning wrappers", func(t *testing.T) {
+		NewChain(Recover(PrintfLogger(log.New(io.Discard, "", 0)))).
+			Then(panickingJob).
+			Run()
+	})
+}
+
+type countJob struct {
+	m       sync.Mutex
+	started int
+	done    int
+	delay   time.Duration
+}
+
+func (j *countJob) Run() {
+	j.m.Lock()
+	j.started++
+	j.m.Unlock()
+	time.Sleep(j.delay)
+	j.m.Lock()
+	j.done++
+	j.m.Unlock()
+}
+
+func (j *countJob) Started() int {
+	defer j.m.Unlock()
+	j.m.Lock()
+	return j.started
+}
+
+func (j *countJob) Done() int {
+	defer j.m.Unlock()
+	j.m.Lock()
+	return j.done
+}
+
+func TestChainDelayIfStillRunning(t *testing.T) {
+
+	t.Run("runs immediately", func(t *testing.T) {
+		var j countJob
+		wrappedJob := NewChain(DelayIfStillRunning(DiscardLogger)).Then(&j)
+		go wrappedJob.Run()
+		time.Sleep(2 * time.Millisecond) // Give the job 2ms to complete.
+		if c := j.Done(); c != 1 {
+			t.Errorf("expected job run once, immediately, got %d", c)
+		}
+	})
+
+	t.Run("second run immediate if first done", func(t *testing.T) {
+		var j countJob
+		wrappedJob := NewChain(DelayIfStillRunning(DiscardLogger)).Then(&j)
+		go func() {
+			go wrappedJob.Run()
+			time.Sleep(time.Millisecond)
+			go wrappedJob.Run()
+		}()
+		time.Sleep(3 * time.Millisecond) // Give both jobs 3ms to complete.
+		if c := j.Done(); c != 2 {
+			t.Errorf("expected job run twice, immediately, got %d", c)
+		}
+	})
+
+	t.Run("second run delayed if first not done", func(t *testing.T) {
+		var j countJob
+		j.delay = 10 * time.Millisecond
+		wrappedJob := NewChain(DelayIfStillRunning(DiscardLogger)).Then(&j)
+		go func() {
+			go wrappedJob.Run()
+			time.Sleep(time.Millisecond)
+			go wrappedJob.Run()
+		}()
+
+		// After 5ms, the first job is still in progress, and the second job was
+		// run but should be waiting for it to finish.
+		time.Sleep(5 * time.Millisecond)
+		started, done := j.Started(), j.Done()
+		if started != 1 || done != 0 {
+			t.Error("expected first job started, but not finished, got", started, done)
+		}
+
+		// Verify that the second job completes.
+		time.Sleep(25 * time.Millisecond)
+		started, done = j.Started(), j.Done()
+		if started != 2 || done != 2 {
+			t.Error("expected both jobs done, got", started, done)
+		}
+	})
+
+}
+
+func TestChainSkipIfStillRunning(t *testing.T) {
+
+	t.Run("runs immediately", func(t *testing.T) {
+		var j countJob
+		wrappedJob := NewChain(SkipIfStillRunning(DiscardLogger)).Then(&j)
+		go wrappedJob.Run()
+		time.Sleep(2 * time.Millisecond) // Give the job 2ms to complete.
+		if c := j.Done(); c != 1 {
+			t.Errorf("expected job run once, immediately, got %d", c)
+		}
+	})
+
+	t.Run("second run immediate if first done", func(t *testing.T) {
+		var j countJob
+		wrappedJob := NewChain(SkipIfStillRunning(DiscardLogger)).Then(&j)
+		go func() {
+			go wrappedJob.Run()
+			time.Sleep(time.Millisecond)
+			go wrappedJob.Run()
+		}()
+		time.Sleep(3 * time.Millisecond) // Give both jobs 3ms to complete.
+		if c := j.Done(); c != 2 {
+			t.Errorf("expected job run twice, immediately, got %d", c)
+		}
+	})
+
+	t.Run("second run skipped if first not done", func(t *testing.T) {
+		var j countJob
+		j.delay = 10 * time.Millisecond
+		wrappedJob := NewChain(SkipIfStillRunning(DiscardLogger)).Then(&j)
+		go func() {
+			go wrappedJob.Run()
+			time.Sleep(time.Millisecond)
+			go wrappedJob.Run()
+		}()
+
+		// After 5ms, the first job is still in progress, and the second job was
+		// aleady skipped.
+		time.Sleep(5 * time.Millisecond)
+		started, done := j.Started(), j.Done()
+		if started != 1 || done != 0 {
+			t.Error("expected first job started, but not finished, got", started, done)
+		}
+
+		// Verify that the first job completes and second does not run.
+		time.Sleep(25 * time.Millisecond)
+		started, done = j.Started(), j.Done()
+		if started != 1 || done != 1 {
+			t.Error("expected second job skipped, got", started, done)
+		}
+	})
+
+	t.Run("skip 10 jobs on rapid fire", func(t *testing.T) {
+		var j countJob
+		j.delay = 10 * time.Millisecond
+		wrappedJob := NewChain(SkipIfStillRunning(DiscardLogger)).Then(&j)
+		for i := 0; i < 11; i++ {
+			go wrappedJob.Run()
+		}
+		time.Sleep(200 * time.Millisecond)
+		done := j.Done()
+		if done != 1 {
+			t.Error("expected 1 jobs executed, 10 jobs dropped, got", done)
+		}
+	})
+
+	t.Run("different jobs independent", func(t *testing.T) {
+		var j1, j2 countJob
+		j1.delay = 10 * time.Millisecond
+		j2.delay = 10 * time.Millisecond
+		chain := NewChain(SkipIfStillRunning(DiscardLogger))
+		wrappedJob1 := chain.Then(&j1)
+		wrappedJob2 := chain.Then(&j2)
+		for i := 0; i < 11; i++ {
+			go wrappedJob1.Run()
+			go wrappedJob2.Run()
+		}
+		time.Sleep(100 * time.Millisecond)
+		var (
+			done1 = j1.Done()
+			done2 = j2.Done()
+		)
+		if done1 != 1 || done2 != 1 {
+			t.Error("expected both jobs executed once, got", done1, "and", done2)
+		}
+	})
+
+}

internal/cron/constantdelay.go

+package cron
+
+import "time"
+
+// ConstantDelaySchedule represents a simple recurring duty cycle, e.g. "Every 5 minutes".
+// It does not support jobs more frequent than once a second.
+type ConstantDelaySchedule struct {
+	Delay time.Duration
+}
+
+// Every returns a crontab Schedule that activates once every duration.
+// Delays of less than a second are not supported (will round up to 1 second).
+// Any fields less than a Second are truncated.
+func Every(duration time.Duration) ConstantDelaySchedule {
+	if duration < time.Second {
+		duration = time.Second
+	}
+	return ConstantDelaySchedule{
+		Delay: duration - time.Duration(duration.Nanoseconds())%time.Second,
+	}
+}
+
+// Next returns the next time this should be run.
+// This rounds so that the next activation time will be on the second.
+func (schedule ConstantDelaySchedule) Next(t time.Time) time.Time {
+	return t.Add(schedule.Delay - time.Duration(t.Nanosecond())*time.Nanosecond)
+}

internal/cron/constantdelay_test.go

+package cron
+
+import (
+	"testing"
+	"time"
+)
+
+func TestConstantDelayNext(t *testing.T) {
+	tests := []struct {
+		time     string
+		delay    time.Duration
+		expected string
+	}{
+		// Simple cases
+		{"Mon Jul 9 14:45 2012", 15*time.Minute + 50*time.Nanosecond, "Mon Jul 9 15:00 2012"},
+		{"Mon Jul 9 14:59 2012", 15 * time.Minute, "Mon Jul 9 15:14 2012"},
+		{"Mon Jul 9 14:59:59 2012", 15 * time.Minute, "Mon Jul 9 15:14:59 2012"},
+
+		// Wrap around hours
+		{"Mon Jul 9 15:45 2012", 35 * time.Minute, "Mon Jul 9 16:20 2012"},
+
+		// Wrap around days
+		{"Mon Jul 9 23:46 2012", 14 * time.Minute, "Tue Jul 10 00:00 2012"},
+		{"Mon Jul 9 23:45 2012", 35 * time.Minute, "Tue Jul 10 00:20 2012"},
+		{"Mon Jul 9 23:35:51 2012", 44*time.Minute + 24*time.Second, "Tue Jul 10 00:20:15 2012"},
+		{"Mon Jul 9 23:35:51 2012", 25*time.Hour + 44*time.Minute + 24*time.Second, "Thu Jul 11 01:20:15 2012"},
+
+		// Wrap around months
+		{"Mon Jul 9 23:35 2012", 91*24*time.Hour + 25*time.Minute, "Thu Oct 9 00:00 2012"},
+
+		// Wrap around minute, hour, day, month, and year
+		{"Mon Dec 31 23:59:45 2012", 15 * time.Second, "Tue Jan 1 00:00:00 2013"},
+
+		// Round to nearest second on the delay
+		{"Mon Jul 9 14:45 2012", 15*time.Minute + 50*time.Nanosecond, "Mon Jul 9 15:00 2012"},
+
+		// Round up to 1 second if the duration is less.
+		{"Mon Jul 9 14:45:00 2012", 15 * time.Millisecond, "Mon Jul 9 14:45:01 2012"},
+
+		// Round to nearest second when calculating the next time.
+		{"Mon Jul 9 14:45:00.005 2012", 15 * time.Minute, "Mon Jul 9 15:00 2012"},
+
+		// Round to nearest second for both.
+		{"Mon Jul 9 14:45:00.005 2012", 15*time.Minute + 50*time.Nanosecond, "Mon Jul 9 15:00 2012"},
+	}
+
+	for _, c := range tests {
+		actual := Every(c.delay).Next(getTime(c.time))
+		expected := getTime(c.expected)
+		if actual != expected {
+			t.Errorf("%s, \"%s\": (expected) %v != %v (actual)", c.time, c.delay, expected, actual)
+		}
+	}
+}

internal/cron/logger.go

+package cron
+
+import (
+	"io"
+	"log"
+	"os"
+	"strings"
+	"time"
+)
+
+// DefaultLogger is used by Cron if none is specified.
+var DefaultLogger Logger = PrintfLogger(log.New(os.Stdout, "cron: ", log.LstdFlags))
+
+// DiscardLogger can be used by callers to discard all log messages.
+var DiscardLogger Logger = PrintfLogger(log.New(io.Discard, "", 0))
+
+// Logger is the interface used in this package for logging, so that any backend
+// can be plugged in. It is a subset of the github.com/go-logr/logr interface.
+type Logger interface {
+	// Info logs routine messages about cron's operation.
+	Info(msg string, keysAndValues ...interface{})
+	// Error logs an error condition.
+	Error(err error, msg string, keysAndValues ...interface{})
+}
+
+// PrintfLogger wraps a Printf-based logger (such as the standard library "log")
+// into an implementation of the Logger interface which logs errors only.
+func PrintfLogger(l interface{ Printf(string, ...interface{}) }) Logger {
+	return printfLogger{l, false}
+}
+
+// VerbosePrintfLogger wraps a Printf-based logger (such as the standard library
+// "log") into an implementation of the Logger interface which logs everything.
+func VerbosePrintfLogger(l interface{ Printf(string, ...interface{}) }) Logger {
+	return printfLogger{l, true}
+}
+
+type printfLogger struct {
+	logger  interface{ Printf(string, ...interface{}) }
+	logInfo bool
+}
+
+func (pl printfLogger) Info(msg string, keysAndValues ...interface{}) {
+	if pl.logInfo {
+		keysAndValues = formatTimes(keysAndValues)
+		pl.logger.Printf(
+			formatString(len(keysAndValues)),
+			append([]interface{}{msg}, keysAndValues...)...)
+	}
+}
+
+func (pl printfLogger) Error(err error, msg string, keysAndValues ...interface{}) {
+	keysAndValues = formatTimes(keysAndValues)
+	pl.logger.Printf(
+		formatString(len(keysAndValues)+2),
+		append([]interface{}{msg, "error", err}, keysAndValues...)...)
+}
+
+// formatString returns a logfmt-like format string for the number of
+// key/values.
+func formatString(numKeysAndValues int) string {
+	var sb strings.Builder
+	sb.WriteString("%s")
+	if numKeysAndValues > 0 {
+		sb.WriteString(", ")
+	}
+	for i := 0; i < numKeysAndValues/2; i++ {
+		if i > 0 {
+			sb.WriteString(", ")
+		}
+		sb.WriteString("%v=%v")
+	}
+	return sb.String()
+}
+
+// formatTimes formats any time.Time values as RFC3339.
+func formatTimes(keysAndValues []interface{}) []interface{} {
+	var formattedArgs []interface{}
+	for _, arg := range keysAndValues {
+		if t, ok := arg.(time.Time); ok {
+			arg = t.Format(time.RFC3339)
+		}
+		formattedArgs = append(formattedArgs, arg)
+	}
+	return formattedArgs
+}

internal/cron/option.go

+package cron
+
+import (
+	"time"
+)
+
+// Option represents a modification to the default behavior of a Cron.
+type Option func(*Cron)
+
+// WithLocation overrides the timezone of the cron instance.
+func WithLocation(loc *time.Location) Option {
+	return func(c *Cron) {
+		c.location = loc
+	}
+}
+
+// WithSeconds overrides the parser used for interpreting job schedules to
+// include a seconds field as the first one.
+func WithSeconds() Option {
+	return WithParser(NewParser(
+		Second | Minute | Hour | Dom | Month | Dow | Descriptor,
+	))
+}
+
+// WithParser overrides the parser used for interpreting job schedules.
+func WithParser(p ScheduleParser) Option {
+	return func(c *Cron) {
+		c.parser = p
+	}
+}
+
+// WithChain specifies Job wrappers to apply to all jobs added to this cron.
+// Refer to the Chain* functions in this package for provided wrappers.
+func WithChain(wrappers ...JobWrapper) Option {
+	return func(c *Cron) {
+		c.chain = NewChain(wrappers...)
+	}
+}
+
+// WithLogger uses the provided logger.
+func WithLogger(logger Logger) Option {
+	return func(c *Cron) {
+		c.logger = logger
+	}
+}

internal/cron/option_test.go

+package cron
+
+import (
+	"log"
+	"strings"
+	"testing"
+	"time"
+)
+
+func TestWithLocation(t *testing.T) {
+	c := New(WithLocation(time.UTC))
+	if c.location != time.UTC {
+		t.Errorf("expected UTC, got %v", c.location)
+	}
+}
+
+func TestWithParser(t *testing.T) {
+	var parser = NewParser(Dow)
+	c := New(WithParser(parser))
+	if c.parser != parser {
+		t.Error("expected provided parser")
+	}
+}
+
+func TestWithVerboseLogger(t *testing.T) {
+	var buf syncWriter
+	var logger = log.New(&buf, "", log.LstdFlags)
+	c := New(WithLogger(VerbosePrintfLogger(logger)))
+	if c.logger.(printfLogger).logger != logger {
+		t.Error("expected provided logger")
+	}
+
+	c.AddFunc("@every 1s", func() {})
+	c.Start()
+	time.Sleep(OneSecond)
+	c.Stop()
+	out := buf.String()
+	if !strings.Contains(out, "schedule,") ||
+		!strings.Contains(out, "run,") {
+		t.Error("expected to see some actions, got:", out)
+	}
+}

internal/cron/schedule.go

-package cron
-
-import (
-	"strconv"
-	"strings"
-	"time"
-
-	"github.com/pkg/errors"
-)
-
-// Moment represents a parsed single time moment.
-type Moment struct {
-	Minute    int `json:"minute"`
-	Hour      int `json:"hour"`
-	Day       int `json:"day"`
-	Month     int `json:"month"`
-	DayOfWeek int `json:"dayOfWeek"`
-}
-
-// NewMoment creates a new Moment from the specified time.
-func NewMoment(t time.Time) *Moment {
-	return &Moment{
-		Minute:    t.Minute(),
-		Hour:      t.Hour(),
-		Day:       t.Day(),
-		Month:     int(t.Month()),
-		DayOfWeek: int(t.Weekday()),
-	}
-}
-
-// Schedule stores parsed information for each time component when a cron job should run.
-type Schedule struct {
-	Minutes    map[int]struct{} `json:"minutes"`
-	Hours      map[int]struct{} `json:"hours"`
-	Days       map[int]struct{} `json:"days"`
-	Months     map[int]struct{} `json:"months"`
-	DaysOfWeek map[int]struct{} `json:"daysOfWeek"`
-}
-
-// IsDue checks whether the provided Moment satisfies the current Schedule.
-func (s *Schedule) IsDue(m *Moment) bool {
-	if _, ok := s.Minutes[m.Minute]; !ok {
-		return false
-	}
-
-	if _, ok := s.Hours[m.Hour]; !ok {
-		return false
-	}
-
-	if _, ok := s.Days[m.Day]; !ok {
-		return false
-	}
-
-	if _, ok := s.DaysOfWeek[m.DayOfWeek]; !ok {
-		return false
-	}
-
-	if _, ok := s.Months[m.Month]; !ok {
-		return false
-	}
-
-	return true
-}
-
-// NewSchedule creates a new Schedule from a cron expression.
-//
-// A cron expression is consisted of 5 segments separated by space,
-// representing: minute, hour, day of the month, month and day of the week.
-//
-// Each segment could be in the following formats:
-//   - wildcard: *
-//   - range:    1-30
-//   - step:     */n or 1-30/n
-//   - list:     1,2,3,10-20/n
-func NewSchedule(cronExpr string) (*Schedule, error) {
-	segments := strings.Split(cronExpr, " ")
-	if len(segments) != 5 {
-		return nil, errors.New("invalid cron expression - must have exactly 5 space separated segments")
-	}
-
-	minutes, err := parseCronSegment(segments[0], 0, 59)
-	if err != nil {
-		return nil, err
-	}
-
-	hours, err := parseCronSegment(segments[1], 0, 23)
-	if err != nil {
-		return nil, err
-	}
-
-	days, err := parseCronSegment(segments[2], 1, 31)
-	if err != nil {
-		return nil, err
-	}
-
-	months, err := parseCronSegment(segments[3], 1, 12)
-	if err != nil {
-		return nil, err
-	}
-
-	daysOfWeek, err := parseCronSegment(segments[4], 0, 6)
-	if err != nil {
-		return nil, err
-	}
-
-	return &Schedule{
-		Minutes:    minutes,
-		Hours:      hours,
-		Days:       days,
-		Months:     months,
-		DaysOfWeek: daysOfWeek,
-	}, nil
-}
-
-// parseCronSegment parses a single cron expression segment and
-// returns its time schedule slots.
-func parseCronSegment(segment string, min int, max int) (map[int]struct{}, error) {
-	slots := map[int]struct{}{}
-
-	list := strings.Split(segment, ",")
-	for _, p := range list {
-		stepParts := strings.Split(p, "/")
-
-		// step (*/n, 1-30/n)
-		var step int
-		switch len(stepParts) {
-		case 1:
-			step = 1
-		case 2:
-			parsedStep, err := strconv.Atoi(stepParts[1])
-			if err != nil {
-				return nil, err
-			}
-			if parsedStep < 1 || parsedStep > max {
-				return nil, errors.Errorf("invalid segment step boundary - the step must be between 1 and the %d", max)
-			}
-			step = parsedStep
-		default:
-			return nil, errors.New("invalid segment step format - must be in the format */n or 1-30/n")
-		}
-
-		// find the min and max range of the segment part
-		var rangeMin, rangeMax int
-		if stepParts[0] == "*" {
-			rangeMin = min
-			rangeMax = max
-		} else {
-			// single digit (1) or range (1-30)
-			rangeParts := strings.Split(stepParts[0], "-")
-			switch len(rangeParts) {
-			case 1:
-				if step != 1 {
-					return nil, errors.New("invalid segment step - step > 1 could be used only with the wildcard or range format")
-				}
-				parsed, err := strconv.Atoi(rangeParts[0])
-				if err != nil {
-					return nil, err
-				}
-				if parsed < min || parsed > max {
-					return nil, errors.New("invalid segment value - must be between the min and max of the segment")
-				}
-				rangeMin = parsed
-				rangeMax = rangeMin
-			case 2:
-				parsedMin, err := strconv.Atoi(rangeParts[0])
-				if err != nil {
-					return nil, err
-				}
-				if parsedMin < min || parsedMin > max {
-					return nil, errors.Errorf("invalid segment range minimum - must be between %d and %d", min, max)
-				}
-				rangeMin = parsedMin
-
-				parsedMax, err := strconv.Atoi(rangeParts[1])
-				if err != nil {
-					return nil, err
-				}
-				if parsedMax < parsedMin || parsedMax > max {
-					return nil, errors.Errorf("invalid segment range maximum - must be between %d and %d", rangeMin, max)
-				}
-				rangeMax = parsedMax
-			default:
-				return nil, errors.New("invalid segment range format - the range must have 1 or 2 parts")
-			}
-		}
-
-		// fill the slots
-		for i := rangeMin; i <= rangeMax; i += step {
-			slots[i] = struct{}{}
-		}
-	}
-
-	return slots, nil
-}

internal/cron/spec.go

+package cron
+
+import "time"
+
+// SpecSchedule specifies a duty cycle (to the second granularity), based on a
+// traditional crontab specification. It is computed initially and stored as bit sets.
+type SpecSchedule struct {
+	Second, Minute, Hour, Dom, Month, Dow uint64
+
+	// Override location for this schedule.
+	Location *time.Location
+}
+
+// bounds provides a range of acceptable values (plus a map of name to value).
+type bounds struct {
+	min, max uint
+	names    map[string]uint
+}
+
+// The bounds for each field.
+var (
+	seconds = bounds{0, 59, nil}
+	minutes = bounds{0, 59, nil}
+	hours   = bounds{0, 23, nil}
+	dom     = bounds{1, 31, nil}
+	months  = bounds{1, 12, map[string]uint{
+		"jan": 1,
+		"feb": 2,
+		"mar": 3,
+		"apr": 4,
+		"may": 5,
+		"jun": 6,
+		"jul": 7,
+		"aug": 8,
+		"sep": 9,
+		"oct": 10,
+		"nov": 11,
+		"dec": 12,
+	}}
+	dow = bounds{0, 6, map[string]uint{
+		"sun": 0,
+		"mon": 1,
+		"tue": 2,
+		"wed": 3,
+		"thu": 4,
+		"fri": 5,
+		"sat": 6,
+	}}
+)
+
+const (
+	// Set the top bit if a star was included in the expression.
+	starBit = 1 << 63
+)
+
+// Next returns the next time this schedule is activated, greater than the given
+// time.  If no time can be found to satisfy the schedule, return the zero time.
+func (s *SpecSchedule) Next(t time.Time) time.Time {
+	// General approach
+	//
+	// For Month, Day, Hour, Minute, Second:
+	// Check if the time value matches.  If yes, continue to the next field.
+	// If the field doesn't match the schedule, then increment the field until it matches.
+	// While incrementing the field, a wrap-around brings it back to the beginning
+	// of the field list (since it is necessary to re-verify previous field
+	// values)
+
+	// Convert the given time into the schedule's timezone, if one is specified.
+	// Save the original timezone so we can convert back after we find a time.
+	// Note that schedules without a time zone specified (time.Local) are treated
+	// as local to the time provided.
+	origLocation := t.Location()
+	loc := s.Location
+	if loc == time.Local {
+		loc = t.Location()
+	}
+	if s.Location != time.Local {
+		t = t.In(s.Location)
+	}
+
+	// Start at the earliest possible time (the upcoming second).
+	t = t.Add(1*time.Second - time.Duration(t.Nanosecond())*time.Nanosecond)
+
+	// This flag indicates whether a field has been incremented.
+	added := false
+
+	// If no time is found within five years, return zero.
+	yearLimit := t.Year() + 5
+
+WRAP:
+	if t.Year() > yearLimit {
+		return time.Time{}
+	}
+
+	// Find the first applicable month.
+	// If it's this month, then do nothing.
+	for 1<<uint(t.Month())&s.Month == 0 {
+		// If we have to add a month, reset the other parts to 0.
+		if !added {
+			added = true
+			// Otherwise, set the date at the beginning (since the current time is irrelevant).
+			t = time.Date(t.Year(), t.Month(), 1, 0, 0, 0, 0, loc)
+		}
+		t = t.AddDate(0, 1, 0)
+
+		// Wrapped around.
+		if t.Month() == time.January {
+			goto WRAP
+		}
+	}
+
+	// Now get a day in that month.
+	//
+	// NOTE: This causes issues for daylight savings regimes where midnight does
+	// not exist.  For example: Sao Paulo has DST that transforms midnight on
+	// 11/3 into 1am. Handle that by noticing when the Hour ends up != 0.
+	for !dayMatches(s, t) {
+		if !added {
+			added = true
+			t = time.Date(t.Year(), t.Month(), t.Day(), 0, 0, 0, 0, loc)
+		}
+		t = t.AddDate(0, 0, 1)
+		// Notice if the hour is no longer midnight due to DST.
+		// Add an hour if it's 23, subtract an hour if it's 1.
+		if t.Hour() != 0 {
+			if t.Hour() > 12 {
+				t = t.Add(time.Duration(24-t.Hour()) * time.Hour)
+			} else {
+				t = t.Add(time.Duration(-t.Hour()) * time.Hour)
+			}
+		}
+
+		if t.Day() == 1 {
+			goto WRAP
+		}
+	}
+
+	for 1<<uint(t.Hour())&s.Hour == 0 {
+		if !added {
+			added = true
+			t = time.Date(t.Year(), t.Month(), t.Day(), t.Hour(), 0, 0, 0, loc)
+		}
+		t = t.Add(1 * time.Hour)
+
+		if t.Hour() == 0 {
+			goto WRAP
+		}
+	}
+
+	for 1<<uint(t.Minute())&s.Minute == 0 {
+		if !added {
+			added = true
+			t = t.Truncate(time.Minute)
+		}
+		t = t.Add(1 * time.Minute)
+
+		if t.Minute() == 0 {
+			goto WRAP
+		}
+	}
+
+	for 1<<uint(t.Second())&s.Second == 0 {
+		if !added {
+			added = true
+			t = t.Truncate(time.Second)
+		}
+		t = t.Add(1 * time.Second)
+
+		if t.Second() == 0 {
+			goto WRAP
+		}
+	}
+
+	return t.In(origLocation)
+}
+
+// dayMatches returns true if the schedule's day-of-week and day-of-month
+// restrictions are satisfied by the given time.
+func dayMatches(s *SpecSchedule, t time.Time) bool {
+	var (
+		domMatch bool = 1<<uint(t.Day())&s.Dom > 0
+		dowMatch bool = 1<<uint(t.Weekday())&s.Dow > 0
+	)
+	if s.Dom&starBit > 0 || s.Dow&starBit > 0 {
+		return domMatch && dowMatch
+	}
+	return domMatch || dowMatch
+}