golang CIDR IPMask

// 如 255.255.255.0 对应的网络位长度为 24
func SubNetMaskToLen(netmask string) (int, error) {
    ipSplitArr := strings.Split(netmask, ".")
    if len(ipSplitArr) != 4 {
        return 0, fmt.Errorf("netmask:%v is not valid, pattern should like: 255.255.255.0", netmask)
    }
    ipv4MaskArr := make([]byte, 4)
    for i, value := range ipSplitArr {
        intValue, err := strconv.Atoi(value)
        if err != nil {
            return 0, fmt.Errorf("ipMaskToInt call strconv.Atoi error:[%v] string value is: [%s]", err, value)
        }
        if intValue > 255 {
            return 0, fmt.Errorf("netmask cannot greater than 255, current value is: [%s]", value)
        }
        ipv4MaskArr[i] = byte(intValue)
    }

    ones, _ := net.IPv4Mask(ipv4MaskArr[0], ipv4MaskArr[1], ipv4MaskArr[2], ipv4MaskArr[3]).Size()
    return ones, nil
}

// 如 24 对应的子网掩码地址为 255.255.255.0
func LenToSubNetMask(subnet int) string {
    var buff bytes.Buffer
    for i := 0; i < subnet; i++ {
        buff.WriteString("1")
    }
    for i := subnet; i < 32; i++ {
        buff.WriteString("0")
    }
    masker := buff.String()
    a, _ := strconv.ParseUint(masker[:8], 2, 64)
    b, _ := strconv.ParseUint(masker[8:16], 2, 64)
    c, _ := strconv.ParseUint(masker[16:24], 2, 64)
    d, _ := strconv.ParseUint(masker[24:32], 2, 64)
    resultMask := fmt.Sprintf("%v.%v.%v.%v", a, b, c, d)
    return resultMask
}