checksum.go

/*
Copyright 2018 liipx(lipengxiang)

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package binlog

import (
	"bytes"
	"encoding/binary"
	"hash/crc32"
	"strconv"
	"strings"
	"unicode"
)

// https://dev.mysql.com/doc/refman/5.6/en/replication-options-binary-log.html#option_mysqld_binlog-checksum
// Beginning with MySQL 5.6.2, MySQL supports reading and writing of binary log checksums.
// ------------------------------------
// | Default Value (>= 5.6.6) | CRC32 |
// | Default Value (<= 5.6.5) | NONE  |
// ------------------------------------
// Enabling this option causes the master to write checksums for events written to the binary log.
// Set to NONE to disable, or the name of the algorithm to be used for generating checksums;
// currently, only CRC32 checksums are supported. As of MySQL 5.6.6, CRC32 is the default.
// This option was added in MySQL 5.6.2.
const binlogChecksumLength = 4

var mysqlChecksumVersion = 5<<10<<10 + 6<<10 + 2

func mysqlVersion(versionStr string) int {
	var version int
	split := strings.Split(versionStr, ".")
	f, _ := strconv.Atoi(split[0])
	s, _ := strconv.Atoi(split[1])
	version = f<<10<<10 + s<<10
	if len(split) < 3 {
		return version
	}

	index := 0
	for i, c := range split[2] {
		if !unicode.IsNumber(c) {
			index = i
			break
		}
	}

	t, _ := strconv.Atoi(split[2][:index])
	version += t
	return version
}

func hasChecksum(versionStr string) bool {
	return mysqlVersion(versionStr) >= mysqlChecksumVersion
}

// ChecksumValidate will validate binary log event checksum
// This information is from 'github.com/siddontang/go-mysql/replication/parser.go'
// mysql use zlib's CRC32 implementation, which uses polynomial 0xedb88320UL.
// reference: https://github.com/madler/zlib/blob/master/crc32.c
// https://github.com/madler/zlib/blob/master/doc/rfc1952.txt#L419
func ChecksumValidate(checksumType byte, expectedChecksum []byte, data []byte) bool {
	switch checksumType {
	case BinlogChecksumAlgCRC32:
		return crc32Validate(expectedChecksum, data)
	case BinlogChecksumAlgUndef, BinlogChecksumAlgOff:
		fallthrough
	default:
		return true
	}
}

func crc32Validate(expectedChecksum []byte, data []byte) bool {
	checksum := crc32.ChecksumIEEE(data)
	computed := make([]byte, binlogChecksumLength)
	binary.LittleEndian.PutUint32(computed, checksum)
	if !bytes.Equal(expectedChecksum, computed) {
		return false
	}
	return true
}