Golang get the last/first n line of a bytes

main.go

// Get first 10th line
// x := trimByteLine(b, 10, false)
//
// Get last 20th line
// y := trimByteLine(b, 20, true)

func trimByteLine(b []byte, maxL int, reverse bool) []byte {
	line := 0
	byteLen := len(b) - 1
	if reverse {
		for byteLen > 0 && line < maxL {
			byteLen--
			if b[byteLen] == byte(10) {
				line++
			}
		}
		return b[byteLen+1:]
	}
	i := 0
	for i <= byteLen && line < maxL {
		if b[i] == byte(10) {
			line++
		}
		i++
	}
	if i == byteLen {
		return b
	}
	return b[:i-1]
}