time: add ParseDuration.

R=rsc, r, r
CC=golang-dev
https://golang.org/cl/5489111

src/pkg/time/format.go

@@ -283,25 +283,16 @@ var atoiError = errors.New("time: invalid number")
 
 // Duplicates functionality in strconv, but avoids dependency.
 func atoi(s string) (x int, err error) {
-	i := 0
-	if len(s) > 0 && s[0] == '-' {
-		i++
+	neg := false
+	if s != "" && s[0] == '-' {
+		neg = true
+		s = s[1:]
 	}
-	if i >= len(s) {
+	x, rem, err := leadingInt(s)
+	if err != nil || rem != "" {
 		return 0, atoiError
 	}
-	for ; i < len(s); i++ {
-		c := s[i]
-		if c < '0' || c > '9' {
-			return 0, atoiError
-		}
-		if x >= (1<<31-10)/10 {
-			// will overflow
-			return 0, atoiError
-		}
-		x = x*10 + int(c) - '0'
-	}
-	if s[0] == '-' {
+	if neg {
 		x = -x
 	}
 	return x, nil
@@ -893,3 +884,126 @@ func parseNanoseconds(value string, nbytes int) (ns int, rangeErrString string,
 	}
 	return
 }
+
+var errLeadingInt = errors.New("time: bad [0-9]*") // never printed
+
+// leadingInt consumes the leading [0-9]* from s.
+func leadingInt(s string) (x int, rem string, err error) {
+	i := 0
+	for ; i < len(s); i++ {
+		c := s[i]
+		if c < '0' || c > '9' {
+			break
+		}
+		if x >= (1<<31-10)/10 {
+			// overflow
+			return 0, "", errLeadingInt
+		}
+		x = x*10 + int(c) - '0'
+	}
+	return x, s[i:], nil
+}
+
+var unitMap = map[string]float64{
+	"ns": float64(Nanosecond),
+	"us": float64(Microsecond),
+	"µs": float64(Microsecond), // U+00B5 = micro symbol
+	"μs": float64(Microsecond), // U+03BC = Greek letter mu
+	"ms": float64(Millisecond),
+	"s":  float64(Second),
+	"m":  float64(Minute),
+	"h":  float64(Hour),
+}
+
+// ParseDuration parses a duration string.
+// A duration string is a possibly signed sequence of
+// decimal numbers, each with optional fraction and a unit suffix,
+// such as "300ms", "-1.5h" or "2h45m".
+// Valid time units are "ns", "us" (or "µs"), "ms", "s", "m", "h".
+func ParseDuration(s string) (Duration, error) {
+	// [-+]?([0-9]*(\.[0-9]*)?[a-z]+)+
+	orig := s
+	f := float64(0)
+	neg := false
+
+	// Consume [-+]?
+	if s != "" {
+		c := s[0]
+		if c == '-' || c == '+' {
+			neg = c == '-'
+			s = s[1:]
+		}
+	}
+	// Special case: if all that is left is "0", this is zero.
+	if s == "0" {
+		return 0, nil
+	}
+	if s == "" {
+		return 0, errors.New("time: invalid duration " + orig)
+	}
+	for s != "" {
+		g := float64(0) // this element of the sequence
+
+		var x int
+		var err error
+
+		// The next character must be [0-9.]
+		if !(s[0] == '.' || ('0' <= s[0] && s[0] <= '9')) {
+			return 0, errors.New("time: invalid duration " + orig)
+		}
+		// Consume [0-9]*
+		pl := len(s)
+		x, s, err = leadingInt(s)
+		if err != nil {
+			return 0, errors.New("time: invalid duration " + orig)
+		}
+		g = float64(x)
+		pre := pl != len(s) // whether we consumed anything before a period
+
+		// Consume (\.[0-9]*)?
+		post := false
+		if s != "" && s[0] == '.' {
+			s = s[1:]
+			pl := len(s)
+			x, s, err = leadingInt(s)
+			if err != nil {
+				return 0, errors.New("time: invalid duration " + orig)
+			}
+			scale := 1
+			for n := pl - len(s); n > 0; n-- {
+				scale *= 10
+			}
+			g += float64(x) / float64(scale)
+			post = pl != len(s)
+		}
+		if !pre && !post {
+			// no digits (e.g. ".s" or "-.s")
+			return 0, errors.New("time: invalid duration " + orig)
+		}
+
+		// Consume unit.
+		i := 0
+		for ; i < len(s); i++ {
+			c := s[i]
+			if c == '.' || ('0' <= c && c <= '9') {
+				break
+			}
+		}
+		if i == 0 {
+			return 0, errors.New("time: missing unit in duration " + orig)
+		}
+		u := s[:i]
+		s = s[i:]
+		unit, ok := unitMap[u]
+		if !ok {
+			return 0, errors.New("time: unknown unit " + u + " in duration " + orig)
+		}
+
+		f += g * unit
+	}
+
+	if neg {
+		f = -f
+	}
+	return Duration(f), nil
+}

src/pkg/time/time_test.go

@@ -8,6 +8,7 @@ import (
 	"bytes"
 	"encoding/gob"
 	"encoding/json"
+	"math/rand"
 	"strconv"
 	"strings"
 	"testing"
@@ -816,6 +817,82 @@ func TestNotJSONEncodableTime(t *testing.T) {
 	}
 }
 
+var parseDurationTests = []struct {
+	in   string
+	ok   bool
+	want Duration
+}{
+	// simple
+	{"0", true, 0},
+	{"5s", true, 5 * Second},
+	{"30s", true, 30 * Second},
+	{"1478s", true, 1478 * Second},
+	// sign
+	{"-5s", true, -5 * Second},
+	{"+5s", true, 5 * Second},
+	{"-0", true, 0},
+	{"+0", true, 0},
+	// decimal
+	{"5.0s", true, 5 * Second},
+	{"5.6s", true, 5*Second + 600*Millisecond},
+	{"5.s", true, 5 * Second},
+	{".5s", true, 500 * Millisecond},
+	{"1.0s", true, 1 * Second},
+	{"1.00s", true, 1 * Second},
+	{"1.004s", true, 1*Second + 4*Millisecond},
+	{"1.0040s", true, 1*Second + 4*Millisecond},
+	{"100.00100s", true, 100*Second + 1*Millisecond},
+	// different units
+	{"10ns", true, 10 * Nanosecond},
+	{"11us", true, 11 * Microsecond},
+	{"12µs", true, 12 * Microsecond}, // U+00B5
+	{"12μs", true, 12 * Microsecond}, // U+03BC
+	{"13ms", true, 13 * Millisecond},
+	{"14s", true, 14 * Second},
+	{"15m", true, 15 * Minute},
+	{"16h", true, 16 * Hour},
+	// composite durations
+	{"3h30m", true, 3*Hour + 30*Minute},
+	{"10.5s4m", true, 4*Minute + 10*Second + 500*Millisecond},
+	{"-2m3.4s", true, -(2*Minute + 3*Second + 400*Millisecond)},
+	{"1h2m3s4ms5us6ns", true, 1*Hour + 2*Minute + 3*Second + 4*Millisecond + 5*Microsecond + 6*Nanosecond},
+	{"39h9m14.425s", true, 39*Hour + 9*Minute + 14*Second + 425*Millisecond},
+
+	// errors
+	{"", false, 0},
+	{"3", false, 0},
+	{"-", false, 0},
+	{"s", false, 0},
+	{".", false, 0},
+	{"-.", false, 0},
+	{".s", false, 0},
+	{"+.s", false, 0},
+}
+
+func TestParseDuration(t *testing.T) {
+	for _, tc := range parseDurationTests {
+		d, err := ParseDuration(tc.in)
+		if tc.ok && (err != nil || d != tc.want) {
+			t.Errorf("ParseDuration(%q) = %v, %v, want %v, nil", tc.in, d, err, tc.want)
+		} else if !tc.ok && err == nil {
+			t.Errorf("ParseDuration(%q) = _, nil, want _, non-nil", tc.in)
+		}
+	}
+}
+
+func TestParseDurationRoundTrip(t *testing.T) {
+	for i := 0; i < 100; i++ {
+		// Resolutions finer than milliseconds will result in
+		// imprecise round-trips.
+		d0 := Duration(rand.Int31()) * Millisecond
+		s := d0.String()
+		d1, err := ParseDuration(s)
+		if err != nil || d0 != d1 {
+			t.Errorf("round-trip failed: %d => %q => %d, %v", d0, s, d1, err)
+		}
+	}
+}
+
 func BenchmarkNow(b *testing.B) {
 	for i := 0; i < b.N; i++ {
 		Now()