netifmon

#!/usr/bin/python3
#	jbin - Joe's miscellaneous scripts, tools and configs
#	netifmon: Monitor a network interface for IP address changes
#	Copyright (C) 2024-2024 Johannes Bauer
#
#	This file is part of jbin.
#
#	jbin is free software; you can redistribute it and/or modify
#	it under the terms of the GNU General Public License as published by
#	the Free Software Foundation; this program is ONLY licensed under
#	version 3 of the License, later versions are explicitly excluded.
#
#	jbin is distributed in the hope that it will be useful,
#	but WITHOUT ANY WARRANTY; without even the implied warranty of
#	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#	GNU General Public License for more details.
#
#	You should have received a copy of the GNU General Public License
#	along with jbin. If not, see <http://www.gnu.org/licenses/>.
#
#	Johannes Bauer <JohannesBauer@gmx.de>

import sys
import time
import datetime
import re
import subprocess
from FriendlyArgumentParser import FriendlyArgumentParser

class NetIfMonitor():
	_ADDRESS_RE = re.compile(r"^\s+(inet|inet6) (?P<addr>[^\s]+)", flags = re.MULTILINE)
	_IFNAME_RE = re.compile(r"^\d+:\s+(?P<ifname>[^:]+):", flags = re.MULTILINE)

	def __init__(self, args):
		self._args = args
		self._last_addresses = { }
		self._interfaces = self._args.ifname
		if len(self._interfaces) == 0:
			self._interfaces = self._list_all_interfaces()

	def _list_all_interfaces(self):
		interfaces = [ ]
		output = subprocess.check_output([ "ip", "a" ]).decode("ascii")
		for rematch in self._IFNAME_RE.finditer(output):
			group = rematch.groupdict()
			interfaces.append(group["ifname"])
		interfaces.sort()
		return interfaces

	def _get_addresses(self, ifname):
		addresses = [ ]
		try:
			output = subprocess.check_output([ "ip", "a", "s", ifname ], stderr = subprocess.DEVNULL).decode("ascii")
		except subprocess.CalledProcessError:
			# Possibly interface has vanished, simply return no addresses.
			return addresses

		for rematch in self._ADDRESS_RE.finditer(output):
			group = rematch.groupdict()
			addresses.append(group["addr"])
		addresses.sort()
		return addresses

	def _get_all_addresses(self):
		addresses = { }
		for ifname in self._interfaces:
			addresses[ifname] = self._get_addresses(ifname)
		return addresses

	def _log_addresses(self, ifname, addresses):
		log_str = f"{datetime.datetime.now().strftime('%Y-%m-%d %H:%M:%S')}: {ifname} {' '.join(addresses)}"
		with open(self._args.output_logfile, "a") as f:
			print(log_str, file = f)
		if self._args.verbose >= 1:
			print(log_str)

	def _check_interface(self):
		all_addresses = self._get_all_addresses()
		for (ifname, addresses) in sorted(all_addresses.items()):
			if addresses != self._last_addresses.get(ifname):
				self._log_addresses(ifname, addresses)
		self._last_addresses = all_addresses

	def run(self):
		while True:
			self._check_interface()
			time.sleep(3)

parser = FriendlyArgumentParser(description = "Monitor a network interface for address changes.")
parser.add_argument("-o", "--output-logfile", metavar = "filename", default = "netifmon.log", help = "Filename to log to. Defaults to %(default)s.")
parser.add_argument("-v", "--verbose", action = "count", default = 0, help = "Increases verbosity. Can be specified multiple times to increase.")
parser.add_argument("ifname", nargs = "*", help = "Network interface(s) to monitor. If none specified, monitor all of them.")
args = parser.parse_args(sys.argv[1:])

nim = NetIfMonitor(args)
nim.run()