database/sql: optimized []byte copy + []byte(nil) -> *interface fix

Make the copy directly in the convert switch instead of an extra loop.
Also stops converting nil-[]byte to zero-[]byte when assigning to *interface

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/7962044

src/pkg/database/sql/convert.go

@@ -112,15 +112,13 @@ func convertAssign(dest, src interface{}) error {
 			if d == nil {
 				return errNilPtr
 			}
-			bcopy := make([]byte, len(s))
+			*d = cloneBytes(s)
-			copy(bcopy, s)
-			*d = bcopy
 			return nil
 		case *[]byte:
 			if d == nil {
 				return errNilPtr
 			}
-			*d = s
+			*d = cloneBytes(s)
 			return nil
 		case *RawBytes:
 			if d == nil {
@@ -131,6 +129,12 @@ func convertAssign(dest, src interface{}) error {
 		}
 	case nil:
 		switch d := dest.(type) {
+		case *interface{}:
+			if d == nil {
+				return errNilPtr
+			}
+			*d = nil
+			return nil
 		case *[]byte:
 			if d == nil {
 				return errNilPtr
@@ -250,6 +254,16 @@ func convertAssign(dest, src interface{}) error {
 	return fmt.Errorf("unsupported driver -> Scan pair: %T -> %T", src, dest)
 }
 
+func cloneBytes(b []byte) []byte {
+	if b == nil {
+		return nil
+	} else {
+		c := make([]byte, len(b))
+		copy(c, b)
+		return c
+	}
+}
+
 func asString(src interface{}) string {
 	switch v := src.(type) {
 	case string:

src/pkg/database/sql/convert_test.go

@@ -143,6 +143,7 @@ var conversionTests = []conversionTest{
 	{s: []byte("byteslice"), d: &scaniface, wantiface: []byte("byteslice")},
 	{s: true, d: &scaniface, wantiface: true},
 	{s: nil, d: &scaniface},
+	{s: []byte(nil), d: &scaniface, wantiface: []byte(nil)},
 }
 
 func intPtrValue(intptr interface{}) interface{} {
@@ -221,7 +222,7 @@ func TestConversions(t *testing.T) {
 			}
 			if srcBytes, ok := ct.s.([]byte); ok {
 				dstBytes := (*ifptr).([]byte)
-				if &dstBytes[0] == &srcBytes[0] {
+				if len(srcBytes) > 0 && &dstBytes[0] == &srcBytes[0] {
 					errf("copy into interface{} didn't copy []byte data")
 				}
 			}

src/pkg/database/sql/sql.go

@@ -1301,24 +1301,6 @@ func (rs *Rows) Scan(dest ...interface{}) error {
 			return fmt.Errorf("sql: Scan error on column index %d: %v", i, err)
 		}
 	}
-	for _, dp := range dest {
-		b, ok := dp.(*[]byte)
-		if !ok {
-			continue
-		}
-		if *b == nil {
-			// If the []byte is now nil (for a NULL value),
-			// don't fall through to below which would
-			// turn it into a non-nil 0-length byte slice
-			continue
-		}
-		if _, ok = dp.(*RawBytes); ok {
-			continue
-		}
-		clone := make([]byte, len(*b))
-		copy(clone, *b)
-		*b = clone
-	}
 	return nil
 }