#!/usr/bin/env python3

myip_url	= "https://YOUR_IP_FETCH_URL"
dyndns_url	= "https://YOUR_DYNDNS_UPDATE_URL"
dyndns_domain	= "EXAMPLE.COM"
dyndns_user	= "USER"
dyndns_pw	= "PASSWORD"
v6netlen	= 64

import subprocess
import ipaddress

def wget(url, v4=None):
	args = ["wget", ]
	if v4 is not None:
		args.append("-4" if v4 else "-6")
	args.extend(["--quiet", "-O", "-", url])
	print(" ".join(args))
	p = subprocess.Popen(args, stdout=subprocess.PIPE)
	out, err = p.communicate()
	if p.returncode != 0 or not out:
		raise Exception("wget failed.")
	return out.decode("UTF-8")

def getfield(raw, name):
	for line in raw.splitlines():
		if line.startswith(name + "="):
			return line[len(name) + 1 : ]
	return ""

raw_v4 = wget(myip_url, v4=True)
raw_v6 = wget(myip_url, v4=False)

ipv4 = getfield(raw_v4, "REMOTE_ADDR")
ipv6 = getfield(raw_v6, "REMOTE_ADDR")
if not ipv4 and not ipv6:
	raise Exception("Got neither v4 nor v6 address.")

dualstack = "1" if ipv4 and ipv6 else "0"
if ipv6:
	adr = int(ipaddress.ip_address(ipv6))
	msk = ((1 << v6netlen) - 1) << (128 - v6netlen)
	ipv6pfx = f"{ipaddress.ip_address(adr & msk)}/{v6netlen}"
else:
	ipv6pfx = ""

r = wget(f"{dyndns_url}?"
	 f"domain={dyndns_domain}&"
	 f"user={dyndns_user}&"
	 f"pw={dyndns_pw}&"
	 f"ip4={ipv4}&"
	 f"ip6={ipv6}&"
	 f"ip6pfx={ipv6pfx}&"
	 f"dualstack={dualstack}")
print(f"result: {r.strip()}")