database/sql: convertAssign string and time.Time into RawBytes

A new switch case for converting the source string type into a
destination RawBytes type avoids the reflection based conversion.
Speed up from old ~61.7ns/op down to ~49ns/op.

A second new switch case allows to convert and assign a source time.Time
type into a destination sql.RawBytes type. This switch case appends
the time to the reset RawBytes slice. This allows the reuse of RawBytes
and avoids allocations.

Fixes #20746

Change-Id: Ib0563fd5c5c7cb6d9d0acaa1d9aa7b2927f1329c
Reviewed-on: https://go-review.googlesource.com/66830
Run-TryBot: Daniel Theophanes <kardianos@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Daniel Theophanes <kardianos@gmail.com>

src/database/sql/convert.go

@@ -234,6 +234,12 @@ func convertAssign(dest, src interface{}) error {
 			}
 			*d = []byte(s)
 			return nil
+		case *RawBytes:
+			if d == nil {
+				return errNilPtr
+			}
+			*d = append((*d)[:0], s...)
+			return nil
 		}
 	case []byte:
 		switch d := dest.(type) {
@@ -273,6 +279,12 @@ func convertAssign(dest, src interface{}) error {
 			}
 			*d = []byte(s.Format(time.RFC3339Nano))
 			return nil
+		case *RawBytes:
+			if d == nil {
+				return errNilPtr
+			}
+			*d = s.AppendFormat((*d)[:0], time.RFC3339Nano)
+			return nil
 		}
 	case nil:
 		switch d := dest.(type) {

src/database/sql/convert_test.go

@@ -106,6 +106,7 @@ var conversionTests = []conversionTest{
 	// To RawBytes
 	{s: nil, d: &scanraw, wantraw: nil},
 	{s: []byte("byteslice"), d: &scanraw, wantraw: RawBytes("byteslice")},
+	{s: "string", d: &scanraw, wantraw: RawBytes("string")},
 	{s: 123, d: &scanraw, wantraw: RawBytes("123")},
 	{s: int8(123), d: &scanraw, wantraw: RawBytes("123")},
 	{s: int64(123), d: &scanraw, wantraw: RawBytes("123")},
@@ -114,6 +115,9 @@ var conversionTests = []conversionTest{
 	{s: uint32(123), d: &scanraw, wantraw: RawBytes("123")},
 	{s: uint64(123), d: &scanraw, wantraw: RawBytes("123")},
 	{s: 1.5, d: &scanraw, wantraw: RawBytes("1.5")},
+	// time.Time has been placed here to check that the RawBytes slice gets
+	// correctly reset when calling time.Time.AppendFormat.
+	{s: time.Unix(2, 5).UTC(), d: &scanraw, wantraw: RawBytes("1970-01-01T00:00:02.000000005Z")},
 
 	// Strings to integers
 	{s: "255", d: &scanuint8, wantuint: 255},
@@ -347,6 +351,7 @@ func TestRawBytesAllocs(t *testing.T) {
 		{"float32", float32(1.5), "1.5"},
 		{"float64", float64(64), "64"},
 		{"bool", false, "false"},
+		{"time", time.Unix(2, 5).UTC(), "1970-01-01T00:00:02.000000005Z"},
 	}
 
 	buf := make(RawBytes, 10)