net.IpMask互转int（ip格式的掩码与掩码前缀的互转）

方法1:：string转int转byte再转ipmask最后转回int

     func ipMaskToInt(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
     }

ipmask转byte转Int转string

     func IntToipMask(netmask int) string {
        Mask := net.CIDRMask(netmask, 32)
        val := make([]byte, len(Mask))
        copy(val, Mask)
        var s []string
        for _, i := range val[:] {
            s = append(s, strconv.Itoa(int(i)))
        }
        return strings.Join(s, ".")
     }

方法2：sscanf获取byte转int

       var a, b, c, d byte
       _, _ = fmt.Sscanf("255.255.255.0", "%d.%d.%d.%d", &a, &b, &c, &d)
       one, _ := net.IPv4Mask(a, b, c, d).Size()

sprintf获取byte转string

Mask := net.CIDRMask(21, 32)
     s := fmt.Sprintf("%d.%d.%d.%d", Mask[0], Mask[1], Mask[2], Mask[3])