// 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/sha1"
	"crypto/tls"
	"database/sql/driver"
	"encoding/binary"
	"errors"
	"fmt"
	"io"
	"net"
	"net/url"
	"strings"
	"time"
)

var (
	tlsConfigRegister map[string]*tls.Config // Register for custom tls.Configs

	errInvalidDSNUnescaped       = errors.New("Invalid DSN: Did you forget to escape a param value?")
	errInvalidDSNAddr            = errors.New("Invalid DSN: Network Address not terminated (missing closing brace)")
	errInvalidDSNNoSlash         = errors.New("Invalid DSN: Missing the slash separating the database name")
	errInvalidDSNUnsafeCollation = errors.New("Invalid DSN: interpolateParams can be used with ascii, latin1, utf8 and utf8mb4 charset")
)

func init() {
	tlsConfigRegister = make(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.
//
//  rootCertPool := x509.NewCertPool()
//  pem, err := ioutil.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" {
		return fmt.Errorf("Key '%s' is reserved", key)
	}

	tlsConfigRegister[key] = config
	return nil
}

// DeregisterTLSConfig removes the tls.Config associated with key.
func DeregisterTLSConfig(key string) {
	delete(tlsConfigRegister, key)
}

// parseDSN parses the DSN string to a config
func parseDSN(dsn string) (cfg *config, err error) {
	// New config with some default values
	cfg = &config{
		loc:       time.UTC,
		collation: defaultCollation,
	}

	// [user[:password]@][net[(addr)]]/dbname[?param1=value1&paramN=valueN]
	// Find the last '/' (since the password or the net addr might contain a '/')
	foundSlash := false
	for i := len(dsn) - 1; i >= 0; i-- {
		if dsn[i] == '/' {
			foundSlash = true
			var j, k int

			// left part is empty if i <= 0
			if i > 0 {
				// [username[:password]@][protocol[(address)]]
				// Find the last '@' in dsn[:i]
				for j = i; j >= 0; j-- {
					if dsn[j] == '@' {
						// username[:password]
						// Find the first ':' in dsn[:j]
						for k = 0; k < j; k++ {
							if dsn[k] == ':' {
								cfg.passwd = dsn[k+1 : j]
								break
							}
						}
						cfg.user = dsn[:k]

						break
					}
				}

				// [protocol[(address)]]
				// Find the first '(' in dsn[j+1:i]
				for k = j + 1; k < i; k++ {
					if dsn[k] == '(' {
						// dsn[i-1] must be == ')' if an address is specified
						if dsn[i-1] != ')' {
							if strings.ContainsRune(dsn[k+1:i], ')') {
								return nil, errInvalidDSNUnescaped
							}
							return nil, errInvalidDSNAddr
						}
						cfg.addr = dsn[k+1 : i-1]
						break
					}
				}
				cfg.net = dsn[j+1 : k]
			}

			// dbname[?param1=value1&...&paramN=valueN]
			// Find the first '?' in dsn[i+1:]
			for j = i + 1; j < len(dsn); j++ {
				if dsn[j] == '?' {
					if err = parseDSNParams(cfg, dsn[j+1:]); err != nil {
						return
					}
					break
				}
			}
			cfg.dbname = dsn[i+1 : j]

			break
		}
	}

	if !foundSlash && len(dsn) > 0 {
		return nil, errInvalidDSNNoSlash
	}

	if cfg.interpolateParams && unsafeCollations[cfg.collation] {
		return nil, errInvalidDSNUnsafeCollation
	}

	// Set default network if empty
	if cfg.net == "" {
		cfg.net = "tcp"
	}

	// Set default address if empty
	if cfg.addr == "" {
		switch cfg.net {
		case "tcp":
			cfg.addr = "127.0.0.1:3306"
		case "unix":
			cfg.addr = "/tmp/mysql.sock"
		default:
			return nil, errors.New("Default addr for network '" + cfg.net + "' unknown")
		}

	}

	return
}

// parseDSNParams parses the DSN "query string"
// Values must be url.QueryEscape'ed
func parseDSNParams(cfg *config, params string) (err error) {
	for _, v := range strings.Split(params, "&") {
		param := strings.SplitN(v, "=", 2)
		if len(param) != 2 {
			continue
		}

		// cfg params
		switch value := param[1]; param[0] {

		// Enable client side placeholder substitution
		case "interpolateParams":
			var isBool bool
			cfg.interpolateParams, isBool = readBool(value)
			if !isBool {
				return fmt.Errorf("Invalid Bool value: %s", value)
			}

		// Disable INFILE whitelist / enable all files
		case "allowAllFiles":
			var isBool bool
			cfg.allowAllFiles, isBool = readBool(value)
			if !isBool {
				return fmt.Errorf("Invalid Bool value: %s", value)
			}

		// Use cleartext authentication mode (MySQL 5.5.10+)
		case "allowCleartextPasswords":
			var isBool bool
			cfg.allowCleartextPasswords, isBool = readBool(value)
			if !isBool {
				return fmt.Errorf("Invalid Bool value: %s", value)
			}

		// Use old authentication mode (pre MySQL 4.1)
		case "allowOldPasswords":
			var isBool bool
			cfg.allowOldPasswords, isBool = readBool(value)
			if !isBool {
				return fmt.Errorf("Invalid Bool value: %s", value)
			}

		// Switch "rowsAffected" mode
		case "clientFoundRows":
			var isBool bool
			cfg.clientFoundRows, isBool = readBool(value)
			if !isBool {
				return fmt.Errorf("Invalid Bool value: %s", value)
			}

		// Collation
		case "collation":
			collation, ok := collations[value]
			if !ok {
				// Note possibility for false negatives:
				// could be triggered  although the collation is valid if the
				// collations map does not contain entries the server supports.
				err = errors.New("unknown collation")
				return
			}
			cfg.collation = collation
			break

		case "columnsWithAlias":
			var isBool bool
			cfg.columnsWithAlias, isBool = readBool(value)
			if !isBool {
				return fmt.Errorf("Invalid Bool value: %s", value)
			}

		// Time Location
		case "loc":
			if value, err = url.QueryUnescape(value); err != nil {
				return
			}
			cfg.loc, err = time.LoadLocation(value)
			if err != nil {
				return
			}

		// Dial Timeout
		case "timeout":
			cfg.timeout, err = time.ParseDuration(value)
			if err != nil {
				return
			}

		// TLS-Encryption
		case "tls":
			boolValue, isBool := readBool(value)
			if isBool {
				if boolValue {
					cfg.tls = &tls.Config{}
				}
			} else if value, err := url.QueryUnescape(value); err != nil {
				return fmt.Errorf("Invalid value for tls config name: %v", err)
			} else {
				if strings.ToLower(value) == "skip-verify" {
					cfg.tls = &tls.Config{InsecureSkipVerify: true}
				} else if tlsConfig, ok := tlsConfigRegister[value]; ok {
					if len(tlsConfig.ServerName) == 0 && !tlsConfig.InsecureSkipVerify {
						host, _, err := net.SplitHostPort(cfg.addr)
						if err == nil {
							tlsConfig.ServerName = host
						}
					}

					cfg.tls = tlsConfig
				} else {
					return fmt.Errorf("Invalid value / unknown config name: %s", value)
				}
			}

		default:
			// lazy init
			if cfg.params == nil {
				cfg.params = make(map[string]string)
			}

			if cfg.params[param[0]], err = url.QueryUnescape(value); err != nil {
				return
			}
		}
	}

	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
}

/******************************************************************************
*                             Authentication                                  *
******************************************************************************/

// Encrypt password using 4.1+ method
func scramblePassword(scramble, password []byte) []byte {
	if len(password) == 0 {
		return nil
	}

	// stage1Hash = SHA1(password)
	crypt := sha1.New()
	crypt.Write(password)
	stage1 := crypt.Sum(nil)

	// scrambleHash = SHA1(scramble + SHA1(stage1Hash))
	// inner Hash
	crypt.Reset()
	crypt.Write(stage1)
	hash := crypt.Sum(nil)

	// outer Hash
	crypt.Reset()
	crypt.Write(scramble)
	crypt.Write(hash)
	scramble = crypt.Sum(nil)

	// token = scrambleHash XOR stage1Hash
	for i := range scramble {
		scramble[i] ^= stage1[i]
	}
	return scramble
}

// Encrypt password using pre 4.1 (old password) method
// https://github.com/atcurtis/mariadb/blob/master/mysys/my_rnd.c
type myRnd struct {
	seed1, seed2 uint32
}

const myRndMaxVal = 0x3FFFFFFF

// Pseudo random number generator
func newMyRnd(seed1, seed2 uint32) *myRnd {
	return &myRnd{
		seed1: seed1 % myRndMaxVal,
		seed2: seed2 % myRndMaxVal,
	}
}

// Tested to be equivalent to MariaDB's floating point variant
// http://play.golang.org/p/QHvhd4qved
// http://play.golang.org/p/RG0q4ElWDx
func (r *myRnd) NextByte() byte {
	r.seed1 = (r.seed1*3 + r.seed2) % myRndMaxVal
	r.seed2 = (r.seed1 + r.seed2 + 33) % myRndMaxVal

	return byte(uint64(r.seed1) * 31 / myRndMaxVal)
}

// Generate binary hash from byte string using insecure pre 4.1 method
func pwHash(password []byte) (result [2]uint32) {
	var add uint32 = 7
	var tmp uint32

	result[0] = 1345345333
	result[1] = 0x12345671

	for _, c := range password {
		// skip spaces and tabs in password
		if c == ' ' || c == '\t' {
			continue
		}

		tmp = uint32(c)
		result[0] ^= (((result[0] & 63) + add) * tmp) + (result[0] << 8)
		result[1] += (result[1] << 8) ^ result[0]
		add += tmp
	}

	// Remove sign bit (1<<31)-1)
	result[0] &= 0x7FFFFFFF
	result[1] &= 0x7FFFFFFF

	return
}

// Encrypt password using insecure pre 4.1 method
func scrambleOldPassword(scramble, password []byte) []byte {
	if len(password) == 0 {
		return nil
	}

	scramble = scramble[:8]

	hashPw := pwHash(password)
	hashSc := pwHash(scramble)

	r := newMyRnd(hashPw[0]^hashSc[0], hashPw[1]^hashSc[1])

	var out [8]byte
	for i := range out {
		out[i] = r.NextByte() + 64
	}

	mask := r.NextByte()
	for i := range out {
		out[i] ^= mask
	}

	return out[:]
}

/******************************************************************************
*                           Time related utils                                *
******************************************************************************/

// NullTime represents a time.Time that may be NULL.
// NullTime implements the Scanner interface so
// it can be used as a scan destination:
//
//  var nt NullTime
//  err := db.QueryRow("SELECT time FROM foo WHERE id=?", id).Scan(&nt)
//  ...
//  if nt.Valid {
//     // use nt.Time
//  } else {
//     // NULL value
//  }
//
// This NullTime implementation is not driver-specific
type NullTime struct {
	Time  time.Time
	Valid bool // Valid is true if Time is not NULL
}

// Scan implements the Scanner interface.
// The value type must be time.Time or string / []byte (formatted time-string),
// otherwise Scan fails.
func (nt *NullTime) Scan(value interface{}) (err error) {
	if value == nil {
		nt.Time, nt.Valid = time.Time{}, false
		return
	}

	switch v := value.(type) {
	case time.Time:
		nt.Time, nt.Valid = v, true
		return
	case []byte:
		nt.Time, err = parseDateTime(string(v), time.UTC)
		nt.Valid = (err == nil)
		return
	case string:
		nt.Time, err = parseDateTime(v, time.UTC)
		nt.Valid = (err == nil)
		return
	}

	nt.Valid = false
	return fmt.Errorf("Can't convert %T to time.Time", value)
}

// Value implements the driver Valuer interface.
func (nt NullTime) Value() (driver.Value, error) {
	if !nt.Valid {
		return nil, nil
	}
	return nt.Time, nil
}

func parseDateTime(str string, loc *time.Location) (t time.Time, err error) {
	base := "0000-00-00 00:00:00.0000000"
	switch len(str) {
	case 10, 19, 21, 22, 23, 24, 25, 26: // up to "YYYY-MM-DD HH:MM:SS.MMMMMM"
		if str == base[:len(str)] {
			return
		}
		t, err = time.Parse(timeFormat[:len(str)], str)
	default:
		err = fmt.Errorf("Invalid Time-String: %s", str)
		return
	}

	// Adjust location
	if err == nil && loc != time.UTC {
		y, mo, d := t.Date()
		h, mi, s := t.Clock()
		t, err = time.Date(y, mo, d, h, mi, s, t.Nanosecond(), loc), nil
	}

	return
}

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)
}

// 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 formatBinaryDateTime(src []byte, length uint8, justTime bool) (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 {
		if justTime {
			return zeroDateTime[11 : 11+length], nil
		}
		return zeroDateTime[:length], nil
	}
	var dst []byte          // return value
	var pt, p1, p2, p3 byte // current digit pair
	var zOffs byte          // offset of value in zeroDateTime
	if justTime {
		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, '-')
		}
		if src[1] != 0 {
			hour := uint16(src[1])*24 + uint16(src[5])
			pt = byte(hour / 100)
			p1 = byte(hour - 100*uint16(pt))
			dst = append(dst, digits01[pt])
		} else {
			p1 = src[5]
		}
		zOffs = 11
		src = src[6:]
	} else {
		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 = byte(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],
	)
	if length <= byte(len(dst)) {
		return dst, nil
	}
	src = src[2:]
	if len(src) == 0 {
		return append(dst, zeroDateTime[19:zOffs+length]...), nil
	}
	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 := zOffs + length - 20; decimals {
	default:
		return append(dst, '.',
			digits10[p1], digits01[p1],
			digits10[p2], digits01[p2],
			digits10[p3], digits01[p3],
		), nil
	case 1:
		return append(dst, '.',
			digits10[p1],
		), nil
	case 2:
		return append(dst, '.',
			digits10[p1], digits01[p1],
		), nil
	case 3:
		return append(dst, '.',
			digits10[p1], digits01[p1],
			digits10[p2],
		), nil
	case 4:
		return append(dst, '.',
			digits10[p1], digits01[p1],
			digits10[p2], digits01[p2],
		), nil
	case 5:
		return append(dst, '.',
			digits10[p1], digits01[p1],
			digits10[p2], digits01[p2],
			digits10[p3],
		), 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, wheter 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], 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))
}

// 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] = '\\'
			buf[pos+1] = '0'
			pos += 2
		case '\n':
			buf[pos] = '\\'
			buf[pos+1] = 'n'
			pos += 2
		case '\r':
			buf[pos] = '\\'
			buf[pos+1] = 'r'
			pos += 2
		case '\x1a':
			buf[pos] = '\\'
			buf[pos+1] = 'Z'
			pos += 2
		case '\'':
			buf[pos] = '\\'
			buf[pos+1] = '\''
			pos += 2
		case '"':
			buf[pos] = '\\'
			buf[pos+1] = '"'
			pos += 2
		case '\\':
			buf[pos] = '\\'
			buf[pos+1] = '\\'
			pos += 2
		default:
			buf[pos] = c
			pos += 1
		}
	}

	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] = '\\'
			buf[pos+1] = '0'
			pos += 2
		case '\n':
			buf[pos] = '\\'
			buf[pos+1] = 'n'
			pos += 2
		case '\r':
			buf[pos] = '\\'
			buf[pos+1] = 'r'
			pos += 2
		case '\x1a':
			buf[pos] = '\\'
			buf[pos+1] = 'Z'
			pos += 2
		case '\'':
			buf[pos] = '\\'
			buf[pos+1] = '\''
			pos += 2
		case '"':
			buf[pos] = '\\'
			buf[pos+1] = '"'
			pos += 2
		case '\\':
			buf[pos] = '\\'
			buf[pos+1] = '\\'
			pos += 2
		default:
			buf[pos] = c
			pos += 1
		}
	}

	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] = '\''
			buf[pos+1] = '\''
			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] = '\''
			buf[pos+1] = '\''
			pos += 2
		} else {
			buf[pos] = c
			pos++
		}
	}

	return buf[:pos]
}