time: improve ParseDuration performance for invalid input

src/time/format.go

@@ -1602,6 +1602,16 @@ func leadingFraction(s string) (x uint64, scale float64, rem string) {
 	return x, scale, s[i:]
 }
 
+// parseDurationError describes a problem parsing a duration string.
+type parseDurationError struct {
+	message string
+	value   string
+}
+
+func (e *parseDurationError) Error() string {
+	return "time: " + e.message + " " + quote(e.value)
+}
+
 var unitMap = map[string]uint64{
 	"ns": uint64(Nanosecond),
 	"us": uint64(Microsecond),
@@ -1637,7 +1647,7 @@ func ParseDuration(s string) (Duration, error) {
 		return 0, nil
 	}
 	if s == "" {
-		return 0, errors.New("time: invalid duration " + quote(orig))
+		return 0, &parseDurationError{"invalid duration", orig}
 	}
 	for s != "" {
 		var (
@@ -1649,13 +1659,13 @@ func ParseDuration(s string) (Duration, error) {
 
 		// The next character must be [0-9.]
 		if !(s[0] == '.' || '0' <= s[0] && s[0] <= '9') {
-			return 0, errors.New("time: invalid duration " + quote(orig))
+			return 0, &parseDurationError{"invalid duration", orig}
 		}
 		// Consume [0-9]*
 		pl := len(s)
 		v, s, err = leadingInt(s)
 		if err != nil {
-			return 0, errors.New("time: invalid duration " + quote(orig))
+			return 0, &parseDurationError{"invalid duration", orig}
 		}
 		pre := pl != len(s) // whether we consumed anything before a period
 
@@ -1669,7 +1679,7 @@ func ParseDuration(s string) (Duration, error) {
 		}
 		if !pre && !post {
 			// no digits (e.g. ".s" or "-.s")
-			return 0, errors.New("time: invalid duration " + quote(orig))
+			return 0, &parseDurationError{"invalid duration", orig}
 		}
 
 		// Consume unit.
@@ -1681,17 +1691,17 @@ func ParseDuration(s string) (Duration, error) {
 			}
 		}
 		if i == 0 {
-			return 0, errors.New("time: missing unit in duration " + quote(orig))
+			return 0, &parseDurationError{"missing unit in duration", orig}
 		}
 		u := s[:i]
 		s = s[i:]
 		unit, ok := unitMap[u]
 		if !ok {
-			return 0, errors.New("time: unknown unit " + quote(u) + " in duration " + quote(orig))
+			return 0, &parseDurationError{"unknown unit " + quote(u) + " in duration", orig}
 		}
 		if v > 1<<63/unit {
 			// overflow
-			return 0, errors.New("time: invalid duration " + quote(orig))
+			return 0, &parseDurationError{"invalid duration", orig}
 		}
 		v *= unit
 		if f > 0 {
@@ -1700,19 +1710,19 @@ func ParseDuration(s string) (Duration, error) {
 			v += uint64(float64(f) * (float64(unit) / scale))
 			if v > 1<<63 {
 				// overflow
-				return 0, errors.New("time: invalid duration " + quote(orig))
+				return 0, &parseDurationError{"invalid duration", orig}
 			}
 		}
 		d += v
 		if d > 1<<63 {
-			return 0, errors.New("time: invalid duration " + quote(orig))
+			return 0, &parseDurationError{"invalid duration", orig}
 		}
 	}
 	if neg {
 		return -Duration(d), nil
 	}
 	if d > 1<<63-1 {
-		return 0, errors.New("time: invalid duration " + quote(orig))
+		return 0, &parseDurationError{"invalid duration", orig}
 	}
 	return Duration(d), nil
 }

src/time/time_test.go

@@ -1620,6 +1620,13 @@ func BenchmarkParseDuration(b *testing.B) {
 	}
 }
 
+func BenchmarkParseDurationError(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		ParseDuration("9223372036854775810ns") // overflow
+		ParseDuration("9007199254.740993")     // missing unit
+	}
+}
+
 func BenchmarkHour(b *testing.B) {
 	t := Now()
 	for i := 0; i < b.N; i++ {