convert arp packets to wake-on-lan packets

arp2wol.py

#!/usr/bin/env python3
# Send wake-on-lan packets to targets of ARP packets

MAX_AGE = 86400 * 7

from sys import argv, stderr
from time import time
import os
import subprocess as sp

if len(argv) != 2:
	print(f'usage: {argv[0]} <interface>', file=stderr)
	exit(1)

intf = argv[1]

td = sp.Popen(['tcpdump', '--immediate-mode', '-l', '-enti', intf,
	'arp or icmp6[icmp6type] = icmp6-neighborsolicit or icmp6[icmp6type] = icmp6-neighboradvert'],
	stdin=sp.DEVNULL, stdout=sp.PIPE, universal_newlines=True)

class R:
	def __init__(self, intf):
		self.macs = {}
		self.last_clean = 0
		self.intf = intf
		self.ethers = {}
		self.ethers_time = 0
		self.update_ethers()
	def update_ethers(self):
		st = None
		try:
			st = os.stat('/etc/ethers')
		except FileNotFoundError:
			self.ethers = {}
			self.ethers_time = 0
			return
		if st.st_mtime <= self.ethers_time:
			return
		self.ethers_time = st.st_mtime
		self.ethers = {}
		with open('/etc/ethers') as f:
			for l in f.readlines():
				l = l.split()
				mac = l[0]
				ip = l[1]
				self.ethers[ip] = mac
	def clean(self):
		now = time()
		if now - self.last_clean < 60:
			return
		d = []
		for m in self.macs:
			if now - self.macs[m]['time'] > MAX_AGE:
				d.append(m)
		for m in d:
			del self.macs[d]
		self.last_clean = now
	def learn(self, ip, mac):
		if ip in self.ethers:
			return
		print(f'learning {ip} is at {mac}')
		self.macs[ip] = {
				'mac': mac,
				'time': time()
				}
	def wake(self, ip):
		self.clean()
		if ip in self.ethers:
			print(f'waking {ip} at {self.ethers[ip]}')
			self.wakemac(self.ethers[ip])
		elif ip in self.macs:
			print(f'waking {ip} at {self.macs[ip]["mac"]}')
			self.wakemac(self.macs[ip]['mac'])
		else:
			print(f'waking {ip} failed unknown mac')
	def wakemac(self, mac):
		sp.run(['etherwake', '-bi', self.intf, mac], stdin=sp.DEVNULL)

r = R(intf)

while True:
	l = td.stdout.readline()
	if not l:
		break
	l = l.strip()
	src = l[0:17]
	dst = l[20:37]
	msg = l[40:].split(':', 1)[1].strip()

	if 'who-has' in msg:
		r.wake(msg.split()[2])
	elif 'who has' in msg:
		r.wake(msg.split()[8])
	elif 'is-at' in msg:
		m = msg.split()
		r.learn(m[1], m[3])
	elif 'neighbor advertisement' in msg:
		r.learn(msg.split()[8], src)