time: implement the encoding.(Binary|Text)Appender for Time

"Time.Marshal(Binary|Text)" could also gain some performance
improvements. Here is the benchmark highlight:

                │     old      │                 new                 │
                │    sec/op    │   sec/op     vs base                │
MarshalText-8     104.00n ± 3%   67.27n ± 2%  -35.32% (p=0.000 n=10)
MarshalBinary-8    31.77n ± 2%   12.13n ± 1%  -61.82% (p=0.000 n=10)
geomean            57.48n        28.57n       -50.30%

                │    old     │                  new                   │
                │    B/op    │   B/op     vs base                     │
MarshalText-8     48.00 ± 0%   0.00 ± 0%  -100.00% (p=0.000 n=10)
MarshalBinary-8   16.00 ± 0%   0.00 ± 0%  -100.00% (p=0.000 n=10)

                │    old     │                   new                   │
                │ allocs/op  │ allocs/op   vs base                     │
MarshalText-8     1.000 ± 0%   0.000 ± 0%  -100.00% (p=0.000 n=10)
MarshalBinary-8   1.000 ± 0%   0.000 ± 0%  -100.00% (p=0.000 n=10)

For #62384

Author: apocelipes

api/next/62384.txt

@@ -9,3 +9,5 @@ pkg math/big, method (*Float) AppendText([]uint8) ([]uint8, error) #62384
 pkg math/big, method (*Int) AppendText([]uint8) ([]uint8, error) #62384
 pkg math/big, method (*Rat) AppendText([]uint8) ([]uint8, error) #62384
 pkg regexp, method (*Regexp) AppendText([]uint8) ([]uint8, error) #62384
+pkg time, method (Time) AppendBinary([]uint8) ([]uint8, error) #62384
+pkg time, method (Time) AppendText([]uint8) ([]uint8, error) #62384

doc/next/6-stdlib/99-minor/time/62384.md

@@ -0,0 +1 @@
+[Time] now implements the [encoding.BinaryAppender] and [encoding.TextAppender] interfaces.

src/time/time.go

@@ -119,9 +119,9 @@ import (
 // these methods does not change the actual instant it represents, only the time
 // zone in which to interpret it.
 //
-// Representations of a Time value saved by the [Time.GobEncode], [Time.MarshalBinary],
-// [Time.MarshalJSON], and [Time.MarshalText] methods store the [Time.Location]'s offset, but not
-// the location name. They therefore lose information about Daylight Saving Time.
+// Representations of a Time value saved by the [Time.GobEncode], [Time.MarshalBinary], [Time.AppendBinary],
+// [Time.MarshalJSON], [Time.MarshalText] and [Time.AppendText] methods store the [Time.Location]'s offset,
+// but not the location name. They therefore lose information about Daylight Saving Time.
 //
 // In addition to the required “wall clock” reading, a Time may contain an optional
 // reading of the current process's monotonic clock, to provide additional precision
@@ -1435,8 +1435,8 @@ const (
 	timeBinaryVersionV2                 // For LMT only
 )
 
-// MarshalBinary implements the encoding.BinaryMarshaler interface.
-func (t Time) MarshalBinary() ([]byte, error) {
+// AppendBinary implements the [encoding.BinaryAppender] interface.
+func (t Time) AppendBinary(b []byte) ([]byte, error) {
 	var offsetMin int16 // minutes east of UTC. -1 is UTC.
 	var offsetSec int8
 	version := timeBinaryVersionV1
@@ -1452,38 +1452,42 @@ func (t Time) MarshalBinary() ([]byte, error) {
 
 		offset /= 60
 		if offset < -32768 || offset == -1 || offset > 32767 {
-			return nil, errors.New("Time.MarshalBinary: unexpected zone offset")
+			return b, errors.New("Time.MarshalBinary: unexpected zone offset")
 		}
 		offsetMin = int16(offset)
 	}
 
 	sec := t.sec()
 	nsec := t.nsec()
-	enc := []byte{
-		version,         // byte 0 : version
-		byte(sec >> 56), // bytes 1-8: seconds
-		byte(sec >> 48),
-		byte(sec >> 40),
-		byte(sec >> 32),
-		byte(sec >> 24),
-		byte(sec >> 16),
-		byte(sec >> 8),
+	b = append(b,
+		version,       // byte 0 : version
+		byte(sec>>56), // bytes 1-8: seconds
+		byte(sec>>48),
+		byte(sec>>40),
+		byte(sec>>32),
+		byte(sec>>24),
+		byte(sec>>16),
+		byte(sec>>8),
 		byte(sec),
-		byte(nsec >> 24), // bytes 9-12: nanoseconds
-		byte(nsec >> 16),
-		byte(nsec >> 8),
+		byte(nsec>>24), // bytes 9-12: nanoseconds
+		byte(nsec>>16),
+		byte(nsec>>8),
 		byte(nsec),
-		byte(offsetMin >> 8), // bytes 13-14: zone offset in minutes
+		byte(offsetMin>>8), // bytes 13-14: zone offset in minutes
 		byte(offsetMin),
-	}
+	)
 	if version == timeBinaryVersionV2 {
-		enc = append(enc, byte(offsetSec))
+		b = append(b, byte(offsetSec))
 	}
+	return b, nil
+}
 
-	return enc, nil
+// MarshalBinary implements the [encoding.BinaryMarshaler] interface.
+func (t Time) MarshalBinary() ([]byte, error) {
+	return t.AppendBinary(make([]byte, 0, 16))
 }
 
-// UnmarshalBinary implements the encoding.BinaryUnmarshaler interface.
+// UnmarshalBinary implements the [encoding.BinaryUnmarshaler] interface.
 func (t *Time) UnmarshalBinary(data []byte) error {
 	buf := data
 	if len(buf) == 0 {
@@ -1576,15 +1580,27 @@ func (t *Time) UnmarshalJSON(data []byte) error {
 	return err
 }
 
-// MarshalText implements the [encoding.TextMarshaler] interface.
+// AppendText implements the [encoding.TextAppender] interface.
 // The time is formatted in RFC 3339 format with sub-second precision.
 // If the timestamp cannot be represented as valid RFC 3339
 // (e.g., the year is out of range), then an error is reported.
-func (t Time) MarshalText() ([]byte, error) {
-	b := make([]byte, 0, len(RFC3339Nano))
+func (t Time) AppendText(b []byte) ([]byte, error) {
 	b, err := t.appendStrictRFC3339(b)
 	if err != nil {
-		return nil, errors.New("Time.MarshalText: " + err.Error())
+		return b, errors.New("Time.MarshalText: " + err.Error())
+	}
+	return b, nil
+}
+
+// MarshalText implements the [encoding.TextMarshaler] interface. The output
+// matches that of calling the [Time.AppendText] method.
+//
+// See [Time.AppendText] for more information.
+func (t Time) MarshalText() ([]byte, error) {
+	// This is semantically similar to t.AppendText(nil), and has better performance.
+	b, err := t.AppendText(make([]byte, 0, len(RFC3339Nano)))
+	if err != nil {
+		return nil, err
 	}
 	return b, nil
 }

src/time/time_test.go

@@ -1403,6 +1403,13 @@ var defaultLocTests = []struct {
 	{"UnixMilli", func(t1, t2 Time) bool { return t1.UnixMilli() == t2.UnixMilli() }},
 	{"UnixMicro", func(t1, t2 Time) bool { return t1.UnixMicro() == t2.UnixMicro() }},
 
+	{"AppendBinary", func(t1, t2 Time) bool {
+		buf1 := make([]byte, 4, 32)
+		buf2 := make([]byte, 4, 32)
+		a1, b1 := t1.AppendBinary(buf1)
+		a2, b2 := t2.AppendBinary(buf2)
+		return bytes.Equal(a1[4:], a2[4:]) && b1 == b2
+	}},
 	{"MarshalBinary", func(t1, t2 Time) bool {
 		a1, b1 := t1.MarshalBinary()
 		a2, b2 := t2.MarshalBinary()
@@ -1418,6 +1425,14 @@ var defaultLocTests = []struct {
 		a2, b2 := t2.MarshalJSON()
 		return bytes.Equal(a1, a2) && b1 == b2
 	}},
+	{"AppendText", func(t1, t2 Time) bool {
+		maxCap := len(RFC3339Nano) + 4
+		buf1 := make([]byte, 4, maxCap)
+		buf2 := make([]byte, 4, maxCap)
+		a1, b1 := t1.AppendText(buf1)
+		a2, b2 := t2.AppendText(buf2)
+		return bytes.Equal(a1[4:], a2[4:]) && b1 == b2
+	}},
 	{"MarshalText", func(t1, t2 Time) bool {
 		a1, b1 := t1.MarshalText()
 		a2, b2 := t2.MarshalText()
@@ -1510,6 +1525,13 @@ func BenchmarkMarshalText(b *testing.B) {
 	}
 }
 
+func BenchmarkMarshalBinary(b *testing.B) {
+	t := Now()
+	for i := 0; i < b.N; i++ {
+		t.MarshalBinary()
+	}
+}
+
 func BenchmarkParse(b *testing.B) {
 	for i := 0; i < b.N; i++ {
 		Parse(ANSIC, "Mon Jan  2 15:04:05 2006")