range.go

// Inspired by the Python netaddr iprange_to_cidrs function:
// https://netaddr.readthedocs.io/en/latest/api.html#netaddr.iprange_to_cidrs.

package cidrman

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

// IPRangeToIPNets accepts an arbitrary start and end IP address and returns a list of
// CIDR subnets that fit exactly between the boundaries of the two with no overlap.
func IPRangeToIPNets(start, end net.IP) ([]*net.IPNet, error) {
	start4 := start.To4()
	end4 := end.To4()

	if ((start4 == nil) && (end4 != nil)) || ((start4 != nil) && (end4 == nil)) {
		return nil, errors.New("Mismatched IP address types")
	}

	var cidrs []*net.IPNet

	if start4 != nil {
		lo := ipv4ToUInt32(start4)
		hi := ipv4ToUInt32(end4)
		if hi < lo {
			return nil, errors.New("End < Start")
		}

		if err := splitRange4(0, 0, lo, hi, &cidrs); err != nil {
			return nil, err
		}
	} else {
		start6 := start.To16()
		if start6 == nil {
			return nil, fmt.Errorf("Invalid IP address: %v", start)
		}
		end6 := end.To16()
		if end6 == nil {
			return nil, fmt.Errorf("Invalid IP address: %v", end)
		}

		lo := ipv6ToUInt128(start6)
		hi := ipv6ToUInt128(end6)
		if hi.Cmp(lo) < 0 {
			return nil, errors.New("End < Start")
		}
		if err := splitRange6(big.NewInt(0), 0, lo, hi, &cidrs); err != nil {
			return nil, err
		}
	}

	return cidrs, nil
}

// IPRangeToCIDRs accepts an arbitrary start and end IP address and returns a list of
// CIDR subnets that fit exactly between the boundaries of the two with no overlap.
func IPRangeToCIDRs(start, end string) ([]string, error) {
	ipStart := net.ParseIP(start)
	if ipStart == nil {
		return nil, fmt.Errorf("Invalid IP address: %s", start)
	}
	ipEnd := net.ParseIP(end)
	if ipEnd == nil {
		return nil, fmt.Errorf("Invalid IP address: %s", end)
	}

	nets, err := IPRangeToIPNets(ipStart, ipEnd)
	if err != nil {
		return nil, err
	}

	return ipNets(nets).toCIDRs(), nil
}