merge.go

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

package cidrman

import (
	"errors"
	"net"
)

type ipNets []*net.IPNet

func (nets ipNets) toCIDRs() []string {
	var cidrs []string
	for _, net := range nets {
		cidrs = append(cidrs, net.String())
	}

	return cidrs
}

// MergeIPNets accepts a list of IP networks and merges them into the smallest possible list of IPNets.
// It merges adjacent subnets where possible, those contained within others and removes any duplicates.
func MergeIPNets(nets []*net.IPNet) ([]*net.IPNet, error) {
	if nets == nil {
		return nil, nil
	}
	if len(nets) == 0 {
		return make([]*net.IPNet, 0), nil
	}

	// Split into IPv4 and IPv6 lists.
	// Merge the list separately and then combine.
	var block4s cidrBlock4s
	for _, net := range nets {
		ip4 := net.IP.To4()
		if ip4 != nil {
			block4s = append(block4s, newBlock4(ip4, net.Mask))
		} else {
			return nil, errors.New("Not implemented")
		}
	}

	merged, err := merge4(block4s)
	if err != nil {
		return nil, err
	}

	return merged, nil
}

// MergeCIDRs accepts a list of CIDR blocks and merges them into the smallest possible list of CIDRs.
func MergeCIDRs(cidrs []string) ([]string, error) {
	if cidrs == nil {
		return nil, nil
	}
	if len(cidrs) == 0 {
		return make([]string, 0), nil
	}

	var networks []*net.IPNet
	for _, cidr := range cidrs {
		_, network, err := net.ParseCIDR(cidr)
		if err != nil {
			return nil, err
		}
		networks = append(networks, network)
	}
	mergedNets, err := MergeIPNets(networks)
	if err != nil {
		return nil, err
	}

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