Derive Broadcast Address from CIDR

iface-bcast.go

package main

import (
	"encoding/binary"
	"fmt"
	"net"
)

// Derive the broadcast address from an address in CIDR notation
func broadcastAddress(s string) (net.IP, error) {

	// Parse the CIDR
	_, ipnet, err := net.ParseCIDR(s)
	if err != nil {
		return nil, err
	}

	// Convert the IP address and mask to 32-bit integers
	// Note that byte order is actually irrelevant here
	ip := binary.LittleEndian.Uint32(ipnet.IP)
	mask := binary.LittleEndian.Uint32(ipnet.Mask)

	// Calculate the broadcast address
	addr := make([]byte, 4)
	binary.LittleEndian.PutUint32(addr, ip&mask|^mask)

	return addr, nil
}

func main() {

	cidr := "192.168.1.1/24"
	bcast, err := broadcastAddress(cidr)

	if err != nil {
		panic(err)
	}

	fmt.Println("CIDR:", cidr)
	fmt.Println("Broadcast:", bcast)
}