Scanner should return one of int64,float64,bool,[]byte,string,time.Time,nil , but I got uint64 about mysql

[methane]

Yes, it violates database/sql convention.
But this violation is necessary to support uint64. So we can not fix it until database/sql supports uint64 natively.

[bronze1man]

@methane Is there any document or examples about how to implement sql.Scanner to work with https://github.com/go-sql-driver/mysql?
I do not like try and fail again and again.

[methane]

There is perfect document.

https://cs.opensource.google/go/go/+/master:src/database/sql/convert.go;l=219-480

mysql/packets.go

Lines 769 to 856 in d7ddb8b

	func (rows *textRows) readRow(dest []driver.Value) error {
	mc := rows.mc
	if rows.rs.done {
	return io.EOF
	}
	data, err := mc.readPacket()
	if err != nil {
	return err
	}
	// EOF Packet
	if data[0] == iEOF && len(data) == 5 {
	// server_status [2 bytes]
	rows.mc.status = readStatus(data[3:])
	rows.rs.done = true
	if !rows.HasNextResultSet() {
	rows.mc = nil
	}
	return io.EOF
	}
	if data[0] == iERR {
	rows.mc = nil
	return mc.handleErrorPacket(data)
	}
	// RowSet Packet
	var (
	n int
	isNull bool
	pos int = 0
	)
	for i := range dest {
	// Read bytes and convert to string
	var buf []byte
	buf, isNull, n, err = readLengthEncodedString(data[pos:])
	pos += n
	if err != nil {
	return err
	}
	if isNull {
	dest[i] = nil
	continue
	}
	switch rows.rs.columns[i].fieldType {
	case fieldTypeTimestamp,
	fieldTypeDateTime,
	fieldTypeDate,
	fieldTypeNewDate:
	if mc.parseTime {
	dest[i], err = parseDateTime(buf, mc.cfg.Loc)
	} else {
	dest[i] = buf
	}
	case fieldTypeTiny, fieldTypeShort, fieldTypeInt24, fieldTypeYear, fieldTypeLong:
	dest[i], err = strconv.ParseInt(string(buf), 10, 64)
	case fieldTypeLongLong:
	if rows.rs.columns[i].flags&flagUnsigned != 0 {
	dest[i], err = strconv.ParseUint(string(buf), 10, 64)
	} else {
	dest[i], err = strconv.ParseInt(string(buf), 10, 64)
	}
	case fieldTypeFloat:
	var d float64
	d, err = strconv.ParseFloat(string(buf), 32)
	dest[i] = float32(d)
	case fieldTypeDouble:
	dest[i], err = strconv.ParseFloat(string(buf), 64)
	default:
	dest[i] = buf
	}
	if err != nil {
	return err
	}
	}
	return nil
	}

mysql/packets.go

Lines 1230 to 1403 in d7ddb8b

	func (rows *binaryRows) readRow(dest []driver.Value) error {
	data, err := rows.mc.readPacket()
	if err != nil {
	return err
	}
	// packet indicator [1 byte]
	if data[0] != iOK {
	// EOF Packet
	if data[0] == iEOF && len(data) == 5 {
	rows.mc.status = readStatus(data[3:])
	rows.rs.done = true
	if !rows.HasNextResultSet() {
	rows.mc = nil
	}
	return io.EOF
	}
	mc := rows.mc
	rows.mc = nil
	// Error otherwise
	return mc.handleErrorPacket(data)
	}
	// NULL-bitmap, [(column-count + 7 + 2) / 8 bytes]
	pos := 1 + (len(dest)+7+2)>>3
	nullMask := data[1:pos]
	for i := range dest {
	// Field is NULL
	// (byte >> bit-pos) % 2 == 1
	if ((nullMask[(i+2)>>3] >> uint((i+2)&7)) & 1) == 1 {
	dest[i] = nil
	continue
	}
	// Convert to byte-coded string
	switch rows.rs.columns[i].fieldType {
	case fieldTypeNULL:
	dest[i] = nil
	continue
	// Numeric Types
	case fieldTypeTiny:
	if rows.rs.columns[i].flags&flagUnsigned != 0 {
	dest[i] = int64(data[pos])
	} else {
	dest[i] = int64(int8(data[pos]))
	}
	pos++
	continue
	case fieldTypeShort, fieldTypeYear:
	if rows.rs.columns[i].flags&flagUnsigned != 0 {
	dest[i] = int64(binary.LittleEndian.Uint16(data[pos : pos+2]))
	} else {
	dest[i] = int64(int16(binary.LittleEndian.Uint16(data[pos : pos+2])))
	}
	pos += 2
	continue
	case fieldTypeInt24, fieldTypeLong:
	if rows.rs.columns[i].flags&flagUnsigned != 0 {
	dest[i] = int64(binary.LittleEndian.Uint32(data[pos : pos+4]))
	} else {
	dest[i] = int64(int32(binary.LittleEndian.Uint32(data[pos : pos+4])))
	}
	pos += 4
	continue
	case fieldTypeLongLong:
	if rows.rs.columns[i].flags&flagUnsigned != 0 {
	val := binary.LittleEndian.Uint64(data[pos : pos+8])
	if val > math.MaxInt64 {
	dest[i] = uint64ToString(val)
	} else {
	dest[i] = int64(val)
	}
	} else {
	dest[i] = int64(binary.LittleEndian.Uint64(data[pos : pos+8]))
	}
	pos += 8
	continue
	case fieldTypeFloat:
	dest[i] = math.Float32frombits(binary.LittleEndian.Uint32(data[pos : pos+4]))
	pos += 4
	continue
	case fieldTypeDouble:
	dest[i] = math.Float64frombits(binary.LittleEndian.Uint64(data[pos : pos+8]))
	pos += 8
	continue
	// Length coded Binary Strings
	case fieldTypeDecimal, fieldTypeNewDecimal, fieldTypeVarChar,
	fieldTypeBit, fieldTypeEnum, fieldTypeSet, fieldTypeTinyBLOB,
	fieldTypeMediumBLOB, fieldTypeLongBLOB, fieldTypeBLOB,
	fieldTypeVarString, fieldTypeString, fieldTypeGeometry, fieldTypeJSON:
	var isNull bool
	var n int
	dest[i], isNull, n, err = readLengthEncodedString(data[pos:])
	pos += n
	if err == nil {
	if !isNull {
	continue
	} else {
	dest[i] = nil
	continue
	}
	}
	return err
	case
	fieldTypeDate, fieldTypeNewDate, // Date YYYY-MM-DD
	fieldTypeTime, // Time [-][H]HH:MM:SS[.fractal]
	fieldTypeTimestamp, fieldTypeDateTime: // Timestamp YYYY-MM-DD HH:MM:SS[.fractal]
	num, isNull, n := readLengthEncodedInteger(data[pos:])
	pos += n
	switch {
	case isNull:
	dest[i] = nil
	continue
	case rows.rs.columns[i].fieldType == fieldTypeTime:
	// database/sql does not support an equivalent to TIME, return a string
	var dstlen uint8
	switch decimals := rows.rs.columns[i].decimals; decimals {
	case 0x00, 0x1f:
	dstlen = 8
	case 1, 2, 3, 4, 5, 6:
	dstlen = 8 + 1 + decimals
	default:
	return fmt.Errorf(
	"protocol error, illegal decimals value %d",
	rows.rs.columns[i].decimals,
	)
	}
	dest[i], err = formatBinaryTime(data[pos:pos+int(num)], dstlen)
	case rows.mc.parseTime:
	dest[i], err = parseBinaryDateTime(num, data[pos:], rows.mc.cfg.Loc)
	default:
	var dstlen uint8
	if rows.rs.columns[i].fieldType == fieldTypeDate {
	dstlen = 10
	} else {
	switch decimals := rows.rs.columns[i].decimals; decimals {
	case 0x00, 0x1f:
	dstlen = 19
	case 1, 2, 3, 4, 5, 6:
	dstlen = 19 + 1 + decimals
	default:
	return fmt.Errorf(
	"protocol error, illegal decimals value %d",
	rows.rs.columns[i].decimals,
	)
	}
	}
	dest[i], err = formatBinaryDateTime(data[pos:pos+int(num)], dstlen)
	}
	if err == nil {
	pos += int(num)
	continue
	} else {
	return err
	}
	// Please report if this happens!
	default:
	return fmt.Errorf("unknown field type %d", rows.rs.columns[i].fieldType)
	}
	}

It must be readable than my English.