Read MAC addresses from your dhcp.leases file and send them Magic Packets to Wake On LAN

wol_via_dhcp.go

package main

// Core code borrowed from the cmd/ files in http://github.com/sabhiram/go-wol

import (
	"bufio"
	"errors"
	"flag"
	"fmt"
	"os"
	"regexp"
	"time"

	wol "github.com/sabhiram/go-wol"
)

const defaultInterval time.Duration = 10 * time.Millisecond

var (
	dhcpPath           = flag.String("leases-path", "/var/db/isc/dhcpd/dhcpd.leases", "Path to dhcp leases file")
	broadcastInterface = flag.String("interface", "", "Broadcast interface")
	broadcastIP        = flag.String("bcast", "255.255.255.255", "Broadcast IP")
	udpPort            = flag.String("port", "9", "UDP Port")
	delay              = flag.Duration("interval", defaultInterval, "Time to wait between waking")
)

func main() {
	flag.Parse()
	exitCode := run()
	os.Exit(exitCode)
}

func parseMACAddresses(path string) ([]string, error) {
	f, err := os.Open(path)
	defer f.Close()
	if err != nil {
		return nil, err
	}
	var macAdresses []string
	re := regexp.MustCompile(`hardware ethernet ([0-9A-Fa-f:]+);`)
	buf := bufio.NewScanner(f)

	for {
		if buf.Scan() {
			matches := re.FindStringSubmatch(buf.Text())
			if len(matches) > 1 {
				macAdresses = append(macAdresses, matches[1])
			}
		} else {
			break
		}
	}
	return macAdresses, nil
}

func run() int {
	exitCode := 0
	macAddresses, err := parseMACAddresses(*dhcpPath)
	if err != nil {
		fmt.Printf("%s\n", err.Error())
		exitCode = 1
	}
	for _, address := range macAddresses {
		_ = runWakeCommand(address)
		time.Sleep(*delay)
	}
	return exitCode
}

func runWakeCommand(macAddr string) error {
	var err error
	// bcastInterface can be "eth0", "eth1", etc.. An empty string implies
	// that we use the default interface when sending the UDP packet (nil)
	bcastInterface := ""

	// Always use the interface specified in the command line, if it exists
	if *broadcastInterface != "" {
		bcastInterface = *broadcastInterface
	}

	err = wol.SendMagicPacket(macAddr, *broadcastIP+":"+*udpPort, bcastInterface)
	if err != nil {
		fmt.Printf("ERROR: %s\n", err.Error())
		return errors.New("Unable to send magic packet")
	}

	fmt.Printf("Magic packet sent successfully to %s\n", macAddr)
	return nil
}