Merge pull request robfig#74 from soltysh/issue33

Refactor parsing to return error instead of using panic/recover

Author: robfig

parser.go

@@ -2,7 +2,6 @@ package cron
 
 import (
 	"fmt"
-	"log"
 	"math"
 	"strconv"
 	"strings"
@@ -17,36 +16,46 @@ import (
 // It accepts
 //   - Standard crontab specs, e.g. "* * * * ?"
 //   - Descriptors, e.g. "@midnight", "@every 1h30m"
-func ParseStandard(standardSpec string) (_ Schedule, err error) {
-	// Convert panics into errors
-	defer func() {
-		if recovered := recover(); recovered != nil {
-			err = fmt.Errorf("%v", recovered)
-		}
-	}()
-
+func ParseStandard(standardSpec string) (Schedule, error) {
 	if standardSpec[0] == '@' {
-		return parseDescriptor(standardSpec), nil
+		return parseDescriptor(standardSpec)
 	}
 
 	// Split on whitespace.  We require exactly 5 fields.
 	// (minute) (hour) (day of month) (month) (day of week)
 	fields := strings.Fields(standardSpec)
 	if len(fields) != 5 {
-		log.Panicf("Expected exactly 5, found %d: %s", len(fields), standardSpec)
+		return nil, fmt.Errorf("Expected exactly 5 fields, found %d: %s", len(fields), standardSpec)
 	}
 
-	schedule := &SpecSchedule{
-		Second: 1 << seconds.min,
-		Minute: getField(fields[0], minutes),
-		Hour:   getField(fields[1], hours),
-		Dom:    getField(fields[2], dom),
-		Month:  getField(fields[3], months),
-		Dow:    getField(fields[4], dow),
+	var err error
+	field := func(field string, r bounds) uint64 {
+		if err != nil {
+			return uint64(0)
+		}
+		var bits uint64
+		bits, err = getField(field, r)
+		return bits
+	}
+	var (
+		minute     = field(fields[0], minutes)
+		hour       = field(fields[1], hours)
+		dayofmonth = field(fields[2], dom)
+		month      = field(fields[3], months)
+		dayofweek  = field(fields[4], dow)
+	)
+	if err != nil {
+		return nil, err
 	}
 
-	return schedule, nil
-
+	return &SpecSchedule{
+		Second: 1 << seconds.min,
+		Minute: minute,
+		Hour:   hour,
+		Dom:    dayofmonth,
+		Month:  month,
+		Dow:    dayofweek,
+	}, nil
 }
 
 // Parse returns a new crontab schedule representing the given spec.
@@ -55,63 +64,81 @@ func ParseStandard(standardSpec string) (_ Schedule, err error) {
 // It accepts
 //   - Full crontab specs, e.g. "* * * * * ?"
 //   - Descriptors, e.g. "@midnight", "@every 1h30m"
-func Parse(spec string) (_ Schedule, err error) {
-	// Convert panics into errors
-	defer func() {
-		if recovered := recover(); recovered != nil {
-			err = fmt.Errorf("%v", recovered)
-		}
-	}()
-
+func Parse(spec string) (Schedule, error) {
 	if spec[0] == '@' {
-		return parseDescriptor(spec), nil
+		return parseDescriptor(spec)
 	}
 
 	// Split on whitespace.  We require 5 or 6 fields.
 	// (second) (minute) (hour) (day of month) (month) (day of week, optional)
 	fields := strings.Fields(spec)
 	if len(fields) != 5 && len(fields) != 6 {
-		log.Panicf("Expected 5 or 6 fields, found %d: %s", len(fields), spec)
+		return nil, fmt.Errorf("Expected 5 or 6 fields, found %d: %s", len(fields), spec)
 	}
 
 	// If a sixth field is not provided (DayOfWeek), then it is equivalent to star.
 	if len(fields) == 5 {
 		fields = append(fields, "*")
 	}
 
-	schedule := &SpecSchedule{
-		Second: getField(fields[0], seconds),
-		Minute: getField(fields[1], minutes),
-		Hour:   getField(fields[2], hours),
-		Dom:    getField(fields[3], dom),
-		Month:  getField(fields[4], months),
-		Dow:    getField(fields[5], dow),
+	var err error
+	field := func(field string, r bounds) uint64 {
+		if err != nil {
+			return uint64(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
 	}
 
-	return schedule, nil
+	return &SpecSchedule{
+		Second: second,
+		Minute: minute,
+		Hour:   hour,
+		Dom:    dayofmonth,
+		Month:  month,
+		Dow:    dayofweek,
+	}, nil
 }
 
 // getField returns an Int with the bits set representing all of the times that
-// the field represents.  A "field" is a comma-separated list of "ranges".
-func getField(field string, r bounds) uint64 {
-	// list = range {"," range}
+// 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 {
-		bits |= getRange(expr, r)
+		bit, err := getRange(expr, r)
+		if err != nil {
+			return bits, err
+		}
+		bits |= bit
 	}
-	return bits
+	return bits, nil
 }
 
 // getRange returns the bits indicated by the given expression:
 //   number | number "-" number [ "/" number ]
-func getRange(expr string, r bounds) uint64 {
-
+// 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
+		zero             = uint64(0)
 	)
 
 	var extra_star uint64
@@ -120,68 +147,77 @@ func getRange(expr string, r bounds) uint64 {
 		end = r.max
 		extra_star = starBit
 	} else {
-		start = parseIntOrName(lowAndHigh[0], r.names)
+		start, err = parseIntOrName(lowAndHigh[0], r.names)
+		if err != nil {
+			return zero, err
+		}
 		switch len(lowAndHigh) {
 		case 1:
 			end = start
 		case 2:
-			end = parseIntOrName(lowAndHigh[1], r.names)
+			end, err = parseIntOrName(lowAndHigh[1], r.names)
+			if err != nil {
+				return zero, err
+			}
 		default:
-			log.Panicf("Too many hyphens: %s", expr)
+			return zero, fmt.Errorf("Too many hyphens: %s", expr)
 		}
 	}
 
 	switch len(rangeAndStep) {
 	case 1:
 		step = 1
 	case 2:
-		step = mustParseInt(rangeAndStep[1])
+		step, err = mustParseInt(rangeAndStep[1])
+		if err != nil {
+			return zero, err
+		}
 
 		// Special handling: "N/step" means "N-max/step".
 		if singleDigit {
 			end = r.max
 		}
 	default:
-		log.Panicf("Too many slashes: %s", expr)
+		return zero, fmt.Errorf("Too many slashes: %s", expr)
 	}
 
 	if start < r.min {
-		log.Panicf("Beginning of range (%d) below minimum (%d): %s", start, r.min, expr)
+		return zero, fmt.Errorf("Beginning of range (%d) below minimum (%d): %s", start, r.min, expr)
 	}
 	if end > r.max {
-		log.Panicf("End of range (%d) above maximum (%d): %s", end, r.max, expr)
+		return zero, fmt.Errorf("End of range (%d) above maximum (%d): %s", end, r.max, expr)
 	}
 	if start > end {
-		log.Panicf("Beginning of range (%d) beyond end of range (%d): %s", start, end, expr)
+		return zero, fmt.Errorf("Beginning of range (%d) beyond end of range (%d): %s", start, end, expr)
 	}
 	if step == 0 {
-		log.Panicf("Step of range should be a positive number: %s", expr)
+		return zero, fmt.Errorf("Step of range should be a positive number: %s", expr)
 	}
 
-	return getBits(start, end, step) | extra_star
+	return getBits(start, end, step) | extra_star, nil
 }
 
 // parseIntOrName returns the (possibly-named) integer contained in expr.
-func parseIntOrName(expr string, names map[string]uint) uint {
+func parseIntOrName(expr string, names map[string]uint) (uint, error) {
 	if names != nil {
 		if namedInt, ok := names[strings.ToLower(expr)]; ok {
-			return namedInt
+			return namedInt, nil
 		}
 	}
 	return mustParseInt(expr)
 }
 
-// mustParseInt parses the given expression as an int or panics.
-func mustParseInt(expr string) uint {
+// 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 {
-		log.Panicf("Failed to parse int from %s: %s", expr, err)
+		return 0, fmt.Errorf("Failed to parse int from %s: %s", expr, err)
 	}
 	if num < 0 {
-		log.Panicf("Negative number (%d) not allowed: %s", num, expr)
+		return 0, fmt.Errorf("Negative number (%d) not allowed: %s", num, expr)
 	}
 
-	return uint(num)
+	return uint(num), nil
 }
 
 // getBits sets all bits in the range [min, max], modulo the given step size.
@@ -205,10 +241,9 @@ func all(r bounds) uint64 {
 	return getBits(r.min, r.max, 1) | starBit
 }
 
-// parseDescriptor returns a pre-defined schedule for the expression, or panics
-// if none matches.
-func parseDescriptor(spec string) Schedule {
-	switch spec {
+// 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,
@@ -217,7 +252,7 @@ func parseDescriptor(spec string) Schedule {
 			Dom:    1 << dom.min,
 			Month:  1 << months.min,
 			Dow:    all(dow),
-		}
+		}, nil
 
 	case "@monthly":
 		return &SpecSchedule{
@@ -227,7 +262,7 @@ func parseDescriptor(spec string) Schedule {
 			Dom:    1 << dom.min,
 			Month:  all(months),
 			Dow:    all(dow),
-		}
+		}, nil
 
 	case "@weekly":
 		return &SpecSchedule{
@@ -237,7 +272,7 @@ func parseDescriptor(spec string) Schedule {
 			Dom:    all(dom),
 			Month:  all(months),
 			Dow:    1 << dow.min,
-		}
+		}, nil
 
 	case "@daily", "@midnight":
 		return &SpecSchedule{
@@ -247,7 +282,7 @@ func parseDescriptor(spec string) Schedule {
 			Dom:    all(dom),
 			Month:  all(months),
 			Dow:    all(dow),
-		}
+		}, nil
 
 	case "@hourly":
 		return &SpecSchedule{
@@ -257,18 +292,17 @@ func parseDescriptor(spec string) Schedule {
 			Dom:    all(dom),
 			Month:  all(months),
 			Dow:    all(dow),
-		}
+		}, nil
 	}
 
 	const every = "@every "
-	if strings.HasPrefix(spec, every) {
-		duration, err := time.ParseDuration(spec[len(every):])
+	if strings.HasPrefix(descriptor, every) {
+		duration, err := time.ParseDuration(descriptor[len(every):])
 		if err != nil {
-			log.Panicf("Failed to parse duration %s: %s", spec, err)
+			return nil, fmt.Errorf("Failed to parse duration %s: %s", descriptor, err)
 		}
-		return Every(duration)
+		return Every(duration), nil
 	}
 
-	log.Panicf("Unrecognized descriptor: %s", spec)
-	return nil
+	return nil, fmt.Errorf("Unrecognized descriptor: %s", descriptor)
 }