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21 results

utils.go

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  • utils.go 20.67 KiB
    // Go MySQL Driver - A MySQL-Driver for Go's database/sql package
    //
    // Copyright 2012 The Go-MySQL-Driver Authors. All rights reserved.
    //
    // This Source Code Form is subject to the terms of the Mozilla Public
    // License, v. 2.0. If a copy of the MPL was not distributed with this file,
    // You can obtain one at http://mozilla.org/MPL/2.0/.
    
    package mysql
    
    import (
    	"crypto/tls"
    	"database/sql"
    	"database/sql/driver"
    	"encoding/binary"
    	"errors"
    	"fmt"
    	"io"
    	"strconv"
    	"strings"
    	"sync"
    	"sync/atomic"
    	"time"
    )
    
    // Registry for custom tls.Configs
    var (
    	tlsConfigLock     sync.RWMutex
    	tlsConfigRegistry map[string]*tls.Config
    )
    
    // RegisterTLSConfig registers a custom tls.Config to be used with sql.Open.
    // Use the key as a value in the DSN where tls=value.
    //
    // Note: The provided tls.Config is exclusively owned by the driver after
    // registering it.
    //
    //	rootCertPool := x509.NewCertPool()
    //	pem, err := os.ReadFile("/path/ca-cert.pem")
    //	if err != nil {
    //	    log.Fatal(err)
    //	}
    //	if ok := rootCertPool.AppendCertsFromPEM(pem); !ok {
    //	    log.Fatal("Failed to append PEM.")
    //	}
    //	clientCert := make([]tls.Certificate, 0, 1)
    //	certs, err := tls.LoadX509KeyPair("/path/client-cert.pem", "/path/client-key.pem")
    //	if err != nil {
    //	    log.Fatal(err)
    //	}
    //	clientCert = append(clientCert, certs)
    //	mysql.RegisterTLSConfig("custom", &tls.Config{
    //	    RootCAs: rootCertPool,
    //	    Certificates: clientCert,
    //	})
    //	db, err := sql.Open("mysql", "user@tcp(localhost:3306)/test?tls=custom")
    func RegisterTLSConfig(key string, config *tls.Config) error {
    	if _, isBool := readBool(key); isBool || strings.ToLower(key) == "skip-verify" || strings.ToLower(key) == "preferred" {
    		return fmt.Errorf("key '%s' is reserved", key)
    	}
    
    	tlsConfigLock.Lock()
    	if tlsConfigRegistry == nil {
    		tlsConfigRegistry = make(map[string]*tls.Config)
    	}
    
    	tlsConfigRegistry[key] = config
    	tlsConfigLock.Unlock()
    	return nil
    }
    
    // DeregisterTLSConfig removes the tls.Config associated with key.
    func DeregisterTLSConfig(key string) {
    	tlsConfigLock.Lock()
    	if tlsConfigRegistry != nil {
    		delete(tlsConfigRegistry, key)
    	}
    	tlsConfigLock.Unlock()
    }
    
    func getTLSConfigClone(key string) (config *tls.Config) {
    	tlsConfigLock.RLock()
    	if v, ok := tlsConfigRegistry[key]; ok {
    		config = v.Clone()
    	}
    	tlsConfigLock.RUnlock()
    	return
    }
    
    // Returns the bool value of the input.
    // The 2nd return value indicates if the input was a valid bool value
    func readBool(input string) (value bool, valid bool) {
    	switch input {
    	case "1", "true", "TRUE", "True":
    		return true, true
    	case "0", "false", "FALSE", "False":
    		return false, true
    	}
    
    	// Not a valid bool value
    	return
    }
    
    /******************************************************************************
    *                           Time related utils                                *
    ******************************************************************************/
    
    func parseDateTime(b []byte, loc *time.Location) (time.Time, error) {
    	const base = "0000-00-00 00:00:00.000000"
    	switch len(b) {
    	case 10, 19, 21, 22, 23, 24, 25, 26: // up to "YYYY-MM-DD HH:MM:SS.MMMMMM"
    		if string(b) == base[:len(b)] {
    			return time.Time{}, nil
    		}
    
    		year, err := parseByteYear(b)
    		if err != nil {
    			return time.Time{}, err
    		}
    		if b[4] != '-' {
    			return time.Time{}, fmt.Errorf("bad value for field: `%c`", b[4])
    		}
    
    		m, err := parseByte2Digits(b[5], b[6])
    		if err != nil {
    			return time.Time{}, err
    		}
    		month := time.Month(m)
    
    		if b[7] != '-' {
    			return time.Time{}, fmt.Errorf("bad value for field: `%c`", b[7])
    		}
    
    		day, err := parseByte2Digits(b[8], b[9])
    		if err != nil {
    			return time.Time{}, err
    		}
    		if len(b) == 10 {
    			return time.Date(year, month, day, 0, 0, 0, 0, loc), nil
    		}
    
    		if b[10] != ' ' {
    			return time.Time{}, fmt.Errorf("bad value for field: `%c`", b[10])
    		}
    
    		hour, err := parseByte2Digits(b[11], b[12])
    		if err != nil {
    			return time.Time{}, err
    		}
    		if b[13] != ':' {
    			return time.Time{}, fmt.Errorf("bad value for field: `%c`", b[13])
    		}
    
    		min, err := parseByte2Digits(b[14], b[15])
    		if err != nil {
    			return time.Time{}, err
    		}
    		if b[16] != ':' {
    			return time.Time{}, fmt.Errorf("bad value for field: `%c`", b[16])
    		}
    
    		sec, err := parseByte2Digits(b[17], b[18])
    		if err != nil {
    			return time.Time{}, err
    		}
    		if len(b) == 19 {
    			return time.Date(year, month, day, hour, min, sec, 0, loc), nil
    		}
    
    		if b[19] != '.' {
    			return time.Time{}, fmt.Errorf("bad value for field: `%c`", b[19])
    		}
    		nsec, err := parseByteNanoSec(b[20:])
    		if err != nil {
    			return time.Time{}, err
    		}
    		return time.Date(year, month, day, hour, min, sec, nsec, loc), nil
    	default:
    		return time.Time{}, fmt.Errorf("invalid time bytes: %s", b)
    	}
    }
    
    func parseByteYear(b []byte) (int, error) {
    	year, n := 0, 1000
    	for i := 0; i < 4; i++ {
    		v, err := bToi(b[i])
    		if err != nil {
    			return 0, err
    		}
    		year += v * n
    		n /= 10
    	}
    	return year, nil
    }
    
    func parseByte2Digits(b1, b2 byte) (int, error) {
    	d1, err := bToi(b1)
    	if err != nil {
    		return 0, err
    	}
    	d2, err := bToi(b2)
    	if err != nil {
    		return 0, err
    	}
    	return d1*10 + d2, nil
    }
    
    func parseByteNanoSec(b []byte) (int, error) {
    	ns, digit := 0, 100000 // max is 6-digits
    	for i := 0; i < len(b); i++ {
    		v, err := bToi(b[i])
    		if err != nil {
    			return 0, err
    		}
    		ns += v * digit
    		digit /= 10
    	}
    	// nanoseconds has 10-digits. (needs to scale digits)
    	// 10 - 6 = 4, so we have to multiple 1000.
    	return ns * 1000, nil
    }
    
    func bToi(b byte) (int, error) {
    	if b < '0' || b > '9' {
    		return 0, errors.New("not [0-9]")
    	}
    	return int(b - '0'), nil
    }
    
    func parseBinaryDateTime(num uint64, data []byte, loc *time.Location) (driver.Value, error) {
    	switch num {
    	case 0:
    		return time.Time{}, nil
    	case 4:
    		return time.Date(
    			int(binary.LittleEndian.Uint16(data[:2])), // year
    			time.Month(data[2]),                       // month
    			int(data[3]),                              // day
    			0, 0, 0, 0,
    			loc,
    		), nil
    	case 7:
    		return time.Date(
    			int(binary.LittleEndian.Uint16(data[:2])), // year
    			time.Month(data[2]),                       // month
    			int(data[3]),                              // day
    			int(data[4]),                              // hour
    			int(data[5]),                              // minutes
    			int(data[6]),                              // seconds
    			0,
    			loc,
    		), nil
    	case 11:
    		return time.Date(
    			int(binary.LittleEndian.Uint16(data[:2])), // year
    			time.Month(data[2]),                       // month
    			int(data[3]),                              // day
    			int(data[4]),                              // hour
    			int(data[5]),                              // minutes
    			int(data[6]),                              // seconds
    			int(binary.LittleEndian.Uint32(data[7:11]))*1000, // nanoseconds
    			loc,
    		), nil
    	}
    	return nil, fmt.Errorf("invalid DATETIME packet length %d", num)
    }
    
    func appendDateTime(buf []byte, t time.Time, timeTruncate time.Duration) ([]byte, error) {
    	if timeTruncate > 0 {
    		t = t.Truncate(timeTruncate)
    	}
    
    	year, month, day := t.Date()
    	hour, min, sec := t.Clock()
    	nsec := t.Nanosecond()
    
    	if year < 1 || year > 9999 {
    		return buf, errors.New("year is not in the range [1, 9999]: " + strconv.Itoa(year)) // use errors.New instead of fmt.Errorf to avoid year escape to heap
    	}
    	year100 := year / 100
    	year1 := year % 100
    
    	var localBuf [len("2006-01-02T15:04:05.999999999")]byte // does not escape
    	localBuf[0], localBuf[1], localBuf[2], localBuf[3] = digits10[year100], digits01[year100], digits10[year1], digits01[year1]
    	localBuf[4] = '-'
    	localBuf[5], localBuf[6] = digits10[month], digits01[month]
    	localBuf[7] = '-'
    	localBuf[8], localBuf[9] = digits10[day], digits01[day]
    
    	if hour == 0 && min == 0 && sec == 0 && nsec == 0 {
    		return append(buf, localBuf[:10]...), nil
    	}
    
    	localBuf[10] = ' '
    	localBuf[11], localBuf[12] = digits10[hour], digits01[hour]
    	localBuf[13] = ':'
    	localBuf[14], localBuf[15] = digits10[min], digits01[min]
    	localBuf[16] = ':'
    	localBuf[17], localBuf[18] = digits10[sec], digits01[sec]
    
    	if nsec == 0 {
    		return append(buf, localBuf[:19]...), nil
    	}
    	nsec100000000 := nsec / 100000000
    	nsec1000000 := (nsec / 1000000) % 100
    	nsec10000 := (nsec / 10000) % 100
    	nsec100 := (nsec / 100) % 100
    	nsec1 := nsec % 100
    	localBuf[19] = '.'
    
    	// milli second
    	localBuf[20], localBuf[21], localBuf[22] =
    		digits01[nsec100000000], digits10[nsec1000000], digits01[nsec1000000]
    	// micro second
    	localBuf[23], localBuf[24], localBuf[25] =
    		digits10[nsec10000], digits01[nsec10000], digits10[nsec100]
    	// nano second
    	localBuf[26], localBuf[27], localBuf[28] =
    		digits01[nsec100], digits10[nsec1], digits01[nsec1]
    
    	// trim trailing zeros
    	n := len(localBuf)
    	for n > 0 && localBuf[n-1] == '0' {
    		n--
    	}
    
    	return append(buf, localBuf[:n]...), nil
    }
    
    // zeroDateTime is used in formatBinaryDateTime to avoid an allocation
    // if the DATE or DATETIME has the zero value.
    // It must never be changed.
    // The current behavior depends on database/sql copying the result.
    var zeroDateTime = []byte("0000-00-00 00:00:00.000000")
    
    const digits01 = "0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789"
    const digits10 = "0000000000111111111122222222223333333333444444444455555555556666666666777777777788888888889999999999"
    
    func appendMicrosecs(dst, src []byte, decimals int) []byte {
    	if decimals <= 0 {
    		return dst
    	}
    	if len(src) == 0 {
    		return append(dst, ".000000"[:decimals+1]...)
    	}
    
    	microsecs := binary.LittleEndian.Uint32(src[:4])
    	p1 := byte(microsecs / 10000)
    	microsecs -= 10000 * uint32(p1)
    	p2 := byte(microsecs / 100)
    	microsecs -= 100 * uint32(p2)
    	p3 := byte(microsecs)
    
    	switch decimals {
    	default:
    		return append(dst, '.',
    			digits10[p1], digits01[p1],
    			digits10[p2], digits01[p2],
    			digits10[p3], digits01[p3],
    		)
    	case 1:
    		return append(dst, '.',
    			digits10[p1],
    		)
    	case 2:
    		return append(dst, '.',
    			digits10[p1], digits01[p1],
    		)
    	case 3:
    		return append(dst, '.',
    			digits10[p1], digits01[p1],
    			digits10[p2],
    		)
    	case 4:
    		return append(dst, '.',
    			digits10[p1], digits01[p1],
    			digits10[p2], digits01[p2],
    		)
    	case 5:
    		return append(dst, '.',
    			digits10[p1], digits01[p1],
    			digits10[p2], digits01[p2],
    			digits10[p3],
    		)
    	}
    }
    
    func formatBinaryDateTime(src []byte, length uint8) (driver.Value, error) {
    	// length expects the deterministic length of the zero value,
    	// negative time and 100+ hours are automatically added if needed
    	if len(src) == 0 {
    		return zeroDateTime[:length], nil
    	}
    	var dst []byte      // return value
    	var p1, p2, p3 byte // current digit pair
    
    	switch length {
    	case 10, 19, 21, 22, 23, 24, 25, 26:
    	default:
    		t := "DATE"
    		if length > 10 {
    			t += "TIME"
    		}
    		return nil, fmt.Errorf("illegal %s length %d", t, length)
    	}
    	switch len(src) {
    	case 4, 7, 11:
    	default:
    		t := "DATE"
    		if length > 10 {
    			t += "TIME"
    		}
    		return nil, fmt.Errorf("illegal %s packet length %d", t, len(src))
    	}
    	dst = make([]byte, 0, length)
    	// start with the date
    	year := binary.LittleEndian.Uint16(src[:2])
    	pt := year / 100
    	p1 = byte(year - 100*uint16(pt))
    	p2, p3 = src[2], src[3]
    	dst = append(dst,
    		digits10[pt], digits01[pt],
    		digits10[p1], digits01[p1], '-',
    		digits10[p2], digits01[p2], '-',
    		digits10[p3], digits01[p3],
    	)
    	if length == 10 {
    		return dst, nil
    	}
    	if len(src) == 4 {
    		return append(dst, zeroDateTime[10:length]...), nil
    	}
    	dst = append(dst, ' ')
    	p1 = src[4] // hour
    	src = src[5:]
    
    	// p1 is 2-digit hour, src is after hour
    	p2, p3 = src[0], src[1]
    	dst = append(dst,
    		digits10[p1], digits01[p1], ':',
    		digits10[p2], digits01[p2], ':',
    		digits10[p3], digits01[p3],
    	)
    	return appendMicrosecs(dst, src[2:], int(length)-20), nil
    }
    
    func formatBinaryTime(src []byte, length uint8) (driver.Value, error) {
    	// length expects the deterministic length of the zero value,
    	// negative time and 100+ hours are automatically added if needed
    	if len(src) == 0 {
    		return zeroDateTime[11 : 11+length], nil
    	}
    	var dst []byte // return value
    
    	switch length {
    	case
    		8,                      // time (can be up to 10 when negative and 100+ hours)
    		10, 11, 12, 13, 14, 15: // time with fractional seconds
    	default:
    		return nil, fmt.Errorf("illegal TIME length %d", length)
    	}
    	switch len(src) {
    	case 8, 12:
    	default:
    		return nil, fmt.Errorf("invalid TIME packet length %d", len(src))
    	}
    	// +2 to enable negative time and 100+ hours
    	dst = make([]byte, 0, length+2)
    	if src[0] == 1 {
    		dst = append(dst, '-')
    	}
    	days := binary.LittleEndian.Uint32(src[1:5])
    	hours := int64(days)*24 + int64(src[5])
    
    	if hours >= 100 {
    		dst = strconv.AppendInt(dst, hours, 10)
    	} else {
    		dst = append(dst, digits10[hours], digits01[hours])
    	}
    
    	min, sec := src[6], src[7]
    	dst = append(dst, ':',
    		digits10[min], digits01[min], ':',
    		digits10[sec], digits01[sec],
    	)
    	return appendMicrosecs(dst, src[8:], int(length)-9), nil
    }
    
    /******************************************************************************
    *                       Convert from and to bytes                             *
    ******************************************************************************/
    
    func uint64ToBytes(n uint64) []byte {
    	return []byte{
    		byte(n),
    		byte(n >> 8),
    		byte(n >> 16),
    		byte(n >> 24),
    		byte(n >> 32),
    		byte(n >> 40),
    		byte(n >> 48),
    		byte(n >> 56),
    	}
    }
    
    func uint64ToString(n uint64) []byte {
    	var a [20]byte
    	i := 20
    
    	// U+0030 = 0
    	// ...
    	// U+0039 = 9
    
    	var q uint64
    	for n >= 10 {
    		i--
    		q = n / 10
    		a[i] = uint8(n-q*10) + 0x30
    		n = q
    	}
    
    	i--
    	a[i] = uint8(n) + 0x30
    
    	return a[i:]
    }
    
    // treats string value as unsigned integer representation
    func stringToInt(b []byte) int {
    	val := 0
    	for i := range b {
    		val *= 10
    		val += int(b[i] - 0x30)
    	}
    	return val
    }
    
    // returns the string read as a bytes slice, whether the value is NULL,
    // the number of bytes read and an error, in case the string is longer than
    // the input slice
    func readLengthEncodedString(b []byte) ([]byte, bool, int, error) {
    	// Get length
    	num, isNull, n := readLengthEncodedInteger(b)
    	if num < 1 {
    		return b[n:n], isNull, n, nil
    	}
    
    	n += int(num)
    
    	// Check data length
    	if len(b) >= n {
    		return b[n-int(num) : n : n], false, n, nil
    	}
    	return nil, false, n, io.EOF
    }
    
    // returns the number of bytes skipped and an error, in case the string is
    // longer than the input slice
    func skipLengthEncodedString(b []byte) (int, error) {
    	// Get length
    	num, _, n := readLengthEncodedInteger(b)
    	if num < 1 {
    		return n, nil
    	}
    
    	n += int(num)
    
    	// Check data length
    	if len(b) >= n {
    		return n, nil
    	}
    	return n, io.EOF
    }
    
    // returns the number read, whether the value is NULL and the number of bytes read
    func readLengthEncodedInteger(b []byte) (uint64, bool, int) {
    	// See issue #349
    	if len(b) == 0 {
    		return 0, true, 1
    	}
    
    	switch b[0] {
    	// 251: NULL
    	case 0xfb:
    		return 0, true, 1
    
    	// 252: value of following 2
    	case 0xfc:
    		return uint64(b[1]) | uint64(b[2])<<8, false, 3
    
    	// 253: value of following 3
    	case 0xfd:
    		return uint64(b[1]) | uint64(b[2])<<8 | uint64(b[3])<<16, false, 4
    
    	// 254: value of following 8
    	case 0xfe:
    		return uint64(b[1]) | uint64(b[2])<<8 | uint64(b[3])<<16 |
    				uint64(b[4])<<24 | uint64(b[5])<<32 | uint64(b[6])<<40 |
    				uint64(b[7])<<48 | uint64(b[8])<<56,
    			false, 9
    	}
    
    	// 0-250: value of first byte
    	return uint64(b[0]), false, 1
    }
    
    // encodes a uint64 value and appends it to the given bytes slice
    func appendLengthEncodedInteger(b []byte, n uint64) []byte {
    	switch {
    	case n <= 250:
    		return append(b, byte(n))
    
    	case n <= 0xffff:
    		return append(b, 0xfc, byte(n), byte(n>>8))
    
    	case n <= 0xffffff:
    		return append(b, 0xfd, byte(n), byte(n>>8), byte(n>>16))
    	}
    	return append(b, 0xfe, byte(n), byte(n>>8), byte(n>>16), byte(n>>24),
    		byte(n>>32), byte(n>>40), byte(n>>48), byte(n>>56))
    }
    
    func appendLengthEncodedString(b []byte, s string) []byte {
    	b = appendLengthEncodedInteger(b, uint64(len(s)))
    	return append(b, s...)
    }
    
    // reserveBuffer checks cap(buf) and expand buffer to len(buf) + appendSize.
    // If cap(buf) is not enough, reallocate new buffer.
    func reserveBuffer(buf []byte, appendSize int) []byte {
    	newSize := len(buf) + appendSize
    	if cap(buf) < newSize {
    		// Grow buffer exponentially
    		newBuf := make([]byte, len(buf)*2+appendSize)
    		copy(newBuf, buf)
    		buf = newBuf
    	}
    	return buf[:newSize]
    }
    
    // escapeBytesBackslash escapes []byte with backslashes (\)
    // This escapes the contents of a string (provided as []byte) by adding backslashes before special
    // characters, and turning others into specific escape sequences, such as
    // turning newlines into \n and null bytes into \0.
    // https://github.com/mysql/mysql-server/blob/mysql-5.7.5/mysys/charset.c#L823-L932
    func escapeBytesBackslash(buf, v []byte) []byte {
    	pos := len(buf)
    	buf = reserveBuffer(buf, len(v)*2)
    
    	for _, c := range v {
    		switch c {
    		case '\x00':
    			buf[pos+1] = '0'
    			buf[pos] = '\\'
    			pos += 2
    		case '\n':
    			buf[pos+1] = 'n'
    			buf[pos] = '\\'
    			pos += 2
    		case '\r':
    			buf[pos+1] = 'r'
    			buf[pos] = '\\'
    			pos += 2
    		case '\x1a':
    			buf[pos+1] = 'Z'
    			buf[pos] = '\\'
    			pos += 2
    		case '\'':
    			buf[pos+1] = '\''
    			buf[pos] = '\\'
    			pos += 2
    		case '"':
    			buf[pos+1] = '"'
    			buf[pos] = '\\'
    			pos += 2
    		case '\\':
    			buf[pos+1] = '\\'
    			buf[pos] = '\\'
    			pos += 2
    		default:
    			buf[pos] = c
    			pos++
    		}
    	}
    
    	return buf[:pos]
    }
    
    // escapeStringBackslash is similar to escapeBytesBackslash but for string.
    func escapeStringBackslash(buf []byte, v string) []byte {
    	pos := len(buf)
    	buf = reserveBuffer(buf, len(v)*2)
    
    	for i := 0; i < len(v); i++ {
    		c := v[i]
    		switch c {
    		case '\x00':
    			buf[pos+1] = '0'
    			buf[pos] = '\\'
    			pos += 2
    		case '\n':
    			buf[pos+1] = 'n'
    			buf[pos] = '\\'
    			pos += 2
    		case '\r':
    			buf[pos+1] = 'r'
    			buf[pos] = '\\'
    			pos += 2
    		case '\x1a':
    			buf[pos+1] = 'Z'
    			buf[pos] = '\\'
    			pos += 2
    		case '\'':
    			buf[pos+1] = '\''
    			buf[pos] = '\\'
    			pos += 2
    		case '"':
    			buf[pos+1] = '"'
    			buf[pos] = '\\'
    			pos += 2
    		case '\\':
    			buf[pos+1] = '\\'
    			buf[pos] = '\\'
    			pos += 2
    		default:
    			buf[pos] = c
    			pos++
    		}
    	}
    
    	return buf[:pos]
    }
    
    // escapeBytesQuotes escapes apostrophes in []byte by doubling them up.
    // This escapes the contents of a string by doubling up any apostrophes that
    // it contains. This is used when the NO_BACKSLASH_ESCAPES SQL_MODE is in
    // effect on the server.
    // https://github.com/mysql/mysql-server/blob/mysql-5.7.5/mysys/charset.c#L963-L1038
    func escapeBytesQuotes(buf, v []byte) []byte {
    	pos := len(buf)
    	buf = reserveBuffer(buf, len(v)*2)
    
    	for _, c := range v {
    		if c == '\'' {
    			buf[pos+1] = '\''
    			buf[pos] = '\''
    			pos += 2
    		} else {
    			buf[pos] = c
    			pos++
    		}
    	}
    
    	return buf[:pos]
    }
    
    // escapeStringQuotes is similar to escapeBytesQuotes but for string.
    func escapeStringQuotes(buf []byte, v string) []byte {
    	pos := len(buf)
    	buf = reserveBuffer(buf, len(v)*2)
    
    	for i := 0; i < len(v); i++ {
    		c := v[i]
    		if c == '\'' {
    			buf[pos+1] = '\''
    			buf[pos] = '\''
    			pos += 2
    		} else {
    			buf[pos] = c
    			pos++
    		}
    	}
    
    	return buf[:pos]
    }
    
    /******************************************************************************
    *                               Sync utils                                    *
    ******************************************************************************/
    
    // noCopy may be embedded into structs which must not be copied
    // after the first use.
    //
    // See https://github.com/golang/go/issues/8005#issuecomment-190753527
    // for details.
    type noCopy struct{}
    
    // Lock is a no-op used by -copylocks checker from `go vet`.
    func (*noCopy) Lock() {}
    
    // Unlock is a no-op used by -copylocks checker from `go vet`.
    // noCopy should implement sync.Locker from Go 1.11
    // https://github.com/golang/go/commit/c2eba53e7f80df21d51285879d51ab81bcfbf6bc
    // https://github.com/golang/go/issues/26165
    func (*noCopy) Unlock() {}
    
    // atomicError is a wrapper for atomically accessed error values
    type atomicError struct {
    	_     noCopy
    	value atomic.Value
    }
    
    // Set sets the error value regardless of the previous value.
    // The value must not be nil
    func (ae *atomicError) Set(value error) {
    	ae.value.Store(value)
    }
    
    // Value returns the current error value
    func (ae *atomicError) Value() error {
    	if v := ae.value.Load(); v != nil {
    		// this will panic if the value doesn't implement the error interface
    		return v.(error)
    	}
    	return nil
    }
    
    func namedValueToValue(named []driver.NamedValue) ([]driver.Value, error) {
    	dargs := make([]driver.Value, len(named))
    	for n, param := range named {
    		if len(param.Name) > 0 {
    			// TODO: support the use of Named Parameters #561
    			return nil, errors.New("mysql: driver does not support the use of Named Parameters")
    		}
    		dargs[n] = param.Value
    	}
    	return dargs, nil
    }
    
    func mapIsolationLevel(level driver.IsolationLevel) (string, error) {
    	switch sql.IsolationLevel(level) {
    	case sql.LevelRepeatableRead:
    		return "REPEATABLE READ", nil
    	case sql.LevelReadCommitted:
    		return "READ COMMITTED", nil
    	case sql.LevelReadUncommitted:
    		return "READ UNCOMMITTED", nil
    	case sql.LevelSerializable:
    		return "SERIALIZABLE", nil
    	default:
    		return "", fmt.Errorf("mysql: unsupported isolation level: %v", level)
    	}
    }