parser.go
将字符串解析为SpecSchedule的类。
package cron
import (
"fmt"
"math"
"strconv"
"strings"
"time"
)
// Configuration options for creating a parser. Most options specify which
// fields should be included, while others enable features. If a field is not
// included the parser will assume a default value. These options do not change
// the order fields are parse in.
type ParseOption int
const (
Second ParseOption = 1 << iota // Seconds field, default 0
Minute // Minutes field, default 0
Hour // Hours field, default 0
Dom // Day of month field, default *
Month // Month field, default *
Dow // Day of week field, default *
DowOptional // Optional day of week field, default *
Descriptor // Allow descriptors such as @monthly, @weekly, etc.
)
var places = []ParseOption{
Second,
Minute,
Hour,
Dom,
Month,
Dow,
}
var defaults = []string{
"0",
"0",
"0",
"*",
"*",
"*",
}
// A custom Parser that can be configured.
type Parser struct {
options ParseOption
optionals int
}
// Creates a custom Parser with custom options.
//
// // Standard parser without descriptors
// specParser := NewParser(Minute | Hour | Dom | Month | Dow)
// sched, err := specParser.Parse("0 0 15 */3 *")
//
// // Same as above, just excludes time fields
// subsParser := NewParser(Dom | Month | Dow)
// sched, err := specParser.Parse("15 */3 *")
//
// // Same as above, just makes Dow optional
// subsParser := NewParser(Dom | Month | DowOptional)
// sched, err := specParser.Parse("15 */3")
//
func NewParser(options ParseOption) Parser {
optionals := 0
if options&DowOptional > 0 {
options |= Dow
optionals++
}
return Parser{options, optionals}
}
// Parse returns a new crontab schedule representing the given spec.
// It returns a descriptive error if the spec is not valid.
// It accepts crontab specs and features configured by NewParser.
// 将字符串解析成为SpecSchedule 。 SpecSchedule符合Schedule接口
func (p Parser) Parse(spec string) (Schedule, error) {
// 直接处理特殊的特殊的字符串
if spec[0] == '@' && p.options&Descriptor > 0 {
return parseDescriptor(spec)
}
// Figure out how many fields we need
max := 0
for _, place := range places {
if p.options&place > 0 {
max++
}
}
min := max - p.optionals
// cron利用空白拆解出独立的items。
fields := strings.Fields(spec)
// 验证表达式取值范围
if count := len(fields); count < min || count > max {
if min == max {
return nil, fmt.Errorf("Expected exactly %d fields, found %d: %s", min, count, spec)
}
return nil, fmt.Errorf("Expected %d to %d fields, found %d: %s", min, max, count, spec)
}
// Fill in missing fields
fields = expandFields(fields, p.options)
var err error
field := func(field string, r bounds) uint64 {
if err != nil {
return 0
}
var bits uint64
bits, err = getField(field, r)
return bits
}
var (
second = field(fields[0], seconds)
minute = field(fields[1], minutes)
hour = field(fields[2], hours)
dayofmonth = field(fields[3], dom)
month = field(fields[4], months)
dayofweek = field(fields[5], dow)
)
if err != nil {
return nil, err
}
// 返回所需要的SpecSchedule
return &SpecSchedule{
Second: second,
Minute: minute,
Hour: hour,
Dom: dayofmonth,
Month: month,
Dow: dayofweek,
}, nil
}
func expandFields(fields []string, options ParseOption) []string {
n := 0
count := len(fields)
expFields := make([]string, len(places))
copy(expFields, defaults)
for i, place := range places {
if options&place > 0 {
expFields[i] = fields[n]
n++
}
if n == count {
break
}
}
return expFields
}
var standardParser = NewParser(
Minute | Hour | Dom | Month | Dow | Descriptor,
)
// ParseStandard returns a new crontab schedule representing the given standardSpec
// (https://en.wikipedia.org/wiki/Cron). It differs from Parse requiring to always
// pass 5 entries representing: minute, hour, day of month, month and day of week,
// in that order. It returns a descriptive error if the spec is not valid.
//
// It accepts
// - Standard crontab specs, e.g. "* * * * ?"
// - Descriptors, e.g. "@midnight", "@every 1h30m"
// 这里表示不仅可以使用cron表达式，也可以使用@midnight @every等方法
func ParseStandard(standardSpec string) (Schedule, error) {
return standardParser.Parse(standardSpec)
}
var defaultParser = NewParser(
Second | Minute | Hour | Dom | Month | DowOptional | Descriptor,
)
// Parse returns a new crontab schedule representing the given spec.
// It returns a descriptive error if the spec is not valid.
//
// It accepts
// - Full crontab specs, e.g. "* * * * * ?"
// - Descriptors, e.g. "@midnight", "@every 1h30m"
func Parse(spec string) (Schedule, error) {
return defaultParser.Parse(spec)
}
// getField returns an Int with the bits set representing all of the times that
// the field represents or error parsing field value. A "field" is a comma-separated
// list of "ranges".
func getField(field string, r bounds) (uint64, error) {
var bits uint64
ranges := strings.FieldsFunc(field, func(r rune) bool { return r == ',' })
for _, expr := range ranges {
bit, err := getRange(expr, r)
if err != nil {
return bits, err
}
bits |= bit
}
return bits, nil
}
// getRange returns the bits indicated by the given expression:
// number | number "-" number [ "/" number ]
// or error parsing range.
func getRange(expr string, r bounds) (uint64, error) {
var (
start, end, step uint
rangeAndStep = strings.Split(expr, "/")
lowAndHigh = strings.Split(rangeAndStep[0], "-")
singleDigit = len(lowAndHigh) == 1
err error
)
var extra uint64
if lowAndHigh[0] == "*" || lowAndHigh[0] == "?" {
start = r.min
end = r.max
extra = starBit
} else {
start, err = parseIntOrName(lowAndHigh[0], r.names)
if err != nil {
return 0, err
}
switch len(lowAndHigh) {
case 1:
end = start
case 2:
end, err = parseIntOrName(lowAndHigh[1], r.names)
if err != nil {
return 0, err
}
default:
return 0, fmt.Errorf("Too many hyphens: %s", expr)
}
}
switch len(rangeAndStep) {
case 1:
step = 1
case 2:
step, err = mustParseInt(rangeAndStep[1])
if err != nil {
return 0, err
}
// Special handling: "N/step" means "N-max/step".
if singleDigit {
end = r.max
}
default:
return 0, fmt.Errorf("Too many slashes: %s", expr)
}
if start < r.min {
return 0, fmt.Errorf("Beginning of range (%d) below minimum (%d): %s", start, r.min, expr)
}
if end > r.max {
return 0, fmt.Errorf("End of range (%d) above maximum (%d): %s", end, r.max, expr)
}
if start > end {
return 0, fmt.Errorf("Beginning of range (%d) beyond end of range (%d): %s", start, end, expr)
}
if step == 0 {
return 0, fmt.Errorf("Step of range should be a positive number: %s", expr)
}
return getBits(start, end, step) | extra, nil
}
// parseIntOrName returns the (possibly-named) integer contained in expr.
func parseIntOrName(expr string, names map[string]uint) (uint, error) {
if names != nil {
if namedInt, ok := names[strings.ToLower(expr)]; ok {
return namedInt, nil
}
}
return mustParseInt(expr)
}
// mustParseInt parses the given expression as an int or returns an error.
func mustParseInt(expr string) (uint, error) {
num, err := strconv.Atoi(expr)
if err != nil {
return 0, fmt.Errorf("Failed to parse int from %s: %s", expr, err)
}
if num < 0 {
return 0, fmt.Errorf("Negative number (%d) not allowed: %s", num, expr)
}
return uint(num), nil
}
// getBits sets all bits in the range [min, max], modulo the given step size.
func getBits(min, max, step uint) uint64 {
var bits uint64
// If step is 1, use shifts.
if step == 1 {
return ^(math.MaxUint64 << (max + 1)) & (math.MaxUint64 << min)
}
// Else, use a simple loop.
for i := min; i <= max; i += step {
bits |= 1 << i
}
return bits
}
// all returns all bits within the given bounds. (plus the star bit)
func all(r bounds) uint64 {
return getBits(r.min, r.max, 1) | starBit
}
// parseDescriptor returns a predefined schedule for the expression, or error if none matches.
func parseDescriptor(descriptor string) (Schedule, error) {
switch descriptor {
case "@yearly", "@annually":
return &SpecSchedule{
Second: 1 << seconds.min,
Minute: 1 << minutes.min,
Hour: 1 << hours.min,
Dom: 1 << dom.min,
Month: 1 << months.min,
Dow: all(dow),
}, nil
case "@monthly":
return &SpecSchedule{
Second: 1 << seconds.min,
Minute: 1 << minutes.min,
Hour: 1 << hours.min,
Dom: 1 << dom.min,
Month: all(months),
Dow: all(dow),
}, nil
case "@weekly":
return &SpecSchedule{
Second: 1 << seconds.min,
Minute: 1 << minutes.min,
Hour: 1 << hours.min,
Dom: all(dom),
Month: all(months),
Dow: 1 << dow.min,
}, nil
case "@daily", "@midnight":
return &SpecSchedule{
Second: 1 << seconds.min,
Minute: 1 << minutes.min,
Hour: 1 << hours.min,
Dom: all(dom),
Month: all(months),
Dow: all(dow),
}, nil
case "@hourly":
return &SpecSchedule{
Second: 1 << seconds.min,
Minute: 1 << minutes.min,
Hour: all(hours),
Dom: all(dom),
Month: all(months),
Dow: all(dow),
}, nil
}
const every = "@every "
if strings.HasPrefix(descriptor, every) {
duration, err := time.ParseDuration(descriptor[len(every):])
if err != nil {
return nil, fmt.Errorf("Failed to parse duration %s: %s", descriptor, err)
}
return Every(duration), nil
}
return nil, fmt.Errorf("Unrecognized descriptor: %s", descriptor)
}
