Go: Convert IP to CIDR

Golang-IP-to-CIDR

/ Convert IPv4 range into CIDR
func iPv4RangeToCIDRRange(ipStart string, ipEnd string) (cidrs []string, err error) {

	cidr2mask := []uint32{
		0x00000000, 0x80000000, 0xC0000000,
		0xE0000000, 0xF0000000, 0xF8000000,
		0xFC000000, 0xFE000000, 0xFF000000,
		0xFF800000, 0xFFC00000, 0xFFE00000,
		0xFFF00000, 0xFFF80000, 0xFFFC0000,
		0xFFFE0000, 0xFFFF0000, 0xFFFF8000,
		0xFFFFC000, 0xFFFFE000, 0xFFFFF000,
		0xFFFFF800, 0xFFFFFC00, 0xFFFFFE00,
		0xFFFFFF00, 0xFFFFFF80, 0xFFFFFFC0,
		0xFFFFFFE0, 0xFFFFFFF0, 0xFFFFFFF8,
		0xFFFFFFFC, 0xFFFFFFFE, 0xFFFFFFFF,
	}

	ipStartUint32 := iPv4ToUint32(ipStart)
	ipEndUint32 := iPv4ToUint32(ipEnd)

	if ipStartUint32 > ipEndUint32 {
		log.Fatalf("start IP:%s must be less than end IP:%s", ipStart, ipEnd)
	}

	for ipEndUint32 >= ipStartUint32 {
		maxSize := 32
		for maxSize > 0 {

			maskedBase := ipStartUint32 & cidr2mask[maxSize - 1]

			if maskedBase != ipStartUint32 {
				break
			}
			maxSize--

		}

		x := math.Log(float64(ipEndUint32 - ipStartUint32 + 1)) / math.Log(2)
		maxDiff := 32 - int(math.Floor(x))
		if maxSize < maxDiff {
			maxSize = maxDiff
		}

		cidrs = append(cidrs,  uInt32ToIPv4(ipStartUint32) + "/" +  strconv.Itoa(maxSize))

		ipStartUint32 += uint32(math.Exp2(float64(32 - maxSize)))
	}

	return cidrs, err
}

//Convert IPv4 to uint32
func iPv4ToUint32(iPv4 string ) uint32 {

	ipOctets := [4]uint64{}

	for i, v := range strings.SplitN(iPv4,".", 4) {
		ipOctets[i], _  = strconv.ParseUint(v, 10, 32)
	}

	result := (ipOctets[0] << 24) | (ipOctets[1] << 16) | (ipOctets[2] << 8) | ipOctets[3]

	return uint32(result)
}

//Convert uint32 to IP
func uInt32ToIPv4(iPuInt32 uint32) (iP string) {
	iP =  fmt.Sprintf ("%d.%d.%d.%d",
		iPuInt32 >> 24,
		(iPuInt32 & 0x00FFFFFF)>> 16,
		(iPuInt32 & 0x0000FFFF) >> 8,
		iPuInt32 & 0x000000FF)
	return iP
}

It works perfectly. Thank you. What about doing the same with IPv6? Specially the first function: iPv4RangeToCIDRRange(ipStart string, ipEnd string)

Could be possible? Thanks!

Thank you for the comment. It's actually a really good idea. I need some time to complete some articles and will update the following repo to support IPv6: https://github.com/P-A-R-U-S/Go-Network-Scanner

And I will appreciate "star" for this repo :))

I'll be waiting. Thank you!

Thank you very much, very useful

Thank you very much, very useful

You're welcome. Looks like time to add IPv6.

Thank you very much, very useful

You're welcome. Looks like time to add IPv6.

To meet the needs, I have done this first, it should be able to be used for testing

and I found the same implementation in other languages ​​here

https://blog.ip2location.com/knowledge-base/how-to-convert-ip-address-range-into-cidr/

func IpRangeToCIDRRange(ipFrom, ipTo string) ([]string, error) {
	url := "https://www.ipaddressguide.com/cidr"
	if strings.IndexByte(ipFrom, '.') < 0 {
		url = "https://www.ipaddressguide.com/ipv6-cidr"
	}
	resp, err := http.Post(url, "application/x-www-form-urlencoded",
		strings.NewReader("mode=range&ipFrom="+ipFrom+"&ipTo="+ipTo))
	if err != nil {
		return nil, err
	}

	data, err := io.ReadAll(resp.Body)
	_ = resp.Body.Close()
	if err != nil {
		return nil, err
	}

	if e := bytes.Index(data, []byte("</code></pre></div>")); e > 0 {
		if s := bytes.LastIndexByte(data[:e], '>'); s > 0 {
			return strings.Split(string(data[s+1:e]), "\n"), nil
		}
	}
	return nil, errors.New("not find")
}

@P-A-R-U-S @xinternetx

I found a method that works for both ipv4 and ipv6

package main

import (
	"errors"
	"fmt"
	"math/big"
	"net/netip"
	"strings"
)

func main() {
	ss, err := IpRangeToCIDR("172.17.0.0", "172.17.5.0")
	if err != nil {
		panic(err)
	}
	fmt.Println(strings.Join(ss, "\n"))

	ss, err = IpRangeToCIDR("2001:4860:4860:ffff:ffff:ffff:ffff:ffff", "2001:4860:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF")
	if err != nil {
		panic(err)
	}
	fmt.Println(strings.Join(ss, "\n"))
}

func IpRangeToCIDR(start, end string) ([]string, error) {
	ips, err := netip.ParseAddr(start)
	if err != nil {
		return nil, err
	}
	ipe, err := netip.ParseAddr(end)
	if err != nil {
		return nil, err
	}

	isV4 := ips.Is4()
	if isV4 != ipe.Is4() {
		return nil, errors.New("start and end types are different")
	}
	if ips.Compare(ipe) > 0 {
		return nil, errors.New("start > end")
	}

	var (
		ipsInt = new(big.Int).SetBytes(ips.AsSlice())
		ipeInt = new(big.Int).SetBytes(ipe.AsSlice())
		nextIp = new(big.Int)
		maxBit = new(big.Int)
		cmpSh  = new(big.Int)
		bits   = new(big.Int)
		mask   = new(big.Int)
		one    = big.NewInt(1)
		buf    []byte
		cidr   []string
		bitSh  uint
	)
	if isV4 {
		maxBit.SetUint64(32)
		buf = make([]byte, 4)
	} else {
		maxBit.SetUint64(128)
		buf = make([]byte, 16)
	}

	for {
		bits.SetUint64(1)
		mask.SetUint64(1)
		for bits.Cmp(maxBit) < 0 {
			nextIp.Or(ipsInt, mask)

			bitSh = uint(bits.Uint64())
			cmpSh.Lsh(cmpSh.Rsh(ipsInt, bitSh), bitSh)
			if (nextIp.Cmp(ipeInt) > 0) || (cmpSh.Cmp(ipsInt) != 0) {
				bits.Sub(bits, one)
				mask.Rsh(mask, 1)
				break
			}
			bits.Add(bits, one)
			mask.Add(mask.Lsh(mask, 1), one)
		}

		addr, _ := netip.AddrFromSlice(ipsInt.FillBytes(buf))
		cidr = append(cidr, addr.String()+"/"+bits.Sub(maxBit, bits).String())

		if nextIp.Or(ipsInt, mask); nextIp.Cmp(ipeInt) >= 0 {
			break
		}
		ipsInt.Add(nextIp, one)
	}
	return cidr, nil
}