util.go

package binlog

import (
	"io"
)

// ReadNBytes read n bytes from io.Reader
func ReadNBytes(rd io.Reader, size int64) ([]byte, error) {
	data := make([]byte, size)
	n, err := rd.Read(data)
	total := n
	for int64(total) < size && err == nil {
		n, err = rd.Read(data[total:])
		total += n
	}

	if n == 0 && err != nil {
		return nil, err
	}

	return data, err
}

// FixedLengthInt will turn byte to uint64
// this function is from 'github.com/siddontang/go-mysql/replication/util.go'
func FixedLengthInt(buf []byte) uint64 {
	var num uint64
	for i, b := range buf {
		num |= uint64(b) << (uint(i) * 8)
	}
	return num
}

// LengthEncodedInt will decode byte to uint64
// this function is from 'github.com/siddontang/go-mysql/replication/util.go'
func LengthEncodedInt(b []byte) (num uint64, isNull bool, n int) {
	switch b[0] {
	case 0xfb:
		// 251: NULL
		n = 1
		isNull = true
		return
	case 0xfc:
		// 252: value of following 2
		num = uint64(b[1]) | uint64(b[2])<<8
		n = 3
		return
	case 0xfd:
		// 253: value of following 3
		num = uint64(b[1]) | uint64(b[2])<<8 | uint64(b[3])<<16
		n = 4
		return
	case 0xfe:
		// 254: value of following 8
		num = 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
		n = 9
		return
	}

	// 0-250: value of first byte
	num = uint64(b[0])
	n = 1
	return
}

// LengthEncodedString will decode bytes
func LengthEncodedString(b []byte) ([]byte, bool, int, error) {
	// Get length
	num, isNull, n := LengthEncodedInt(b)
	if num < 1 {
		return nil, 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
}