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| 1 | +#!/usr/bin/env python |
| 2 | + |
| 3 | +"""Re-announce services when the host's network interfaces change. |
| 4 | +
|
| 5 | +``AsyncZeroconf.async_update_interfaces()`` reconciles the sockets in use to the |
| 6 | +live interface set: it binds responders for interfaces that appeared, tears down |
| 7 | +the ones that went away, and re-announces existing registrations on the new |
| 8 | +senders. A call where nothing changed is a no-op. |
| 9 | +
|
| 10 | +zeroconf does not poll for interface changes itself; detection is |
| 11 | +platform-specific and is best driven from whatever signal a host already has (a |
| 12 | +netlink subscription on Linux, a framework's adapter-change event, etc.). When |
| 13 | +no such signal is available, a small periodic poller like the one below is |
| 14 | +enough: snapshot the addresses and reconcile only when they change. The piece |
| 15 | +worth copying carefully is the lifecycle, cancel the monitor task before |
| 16 | +closing the AsyncZeroconf so it does not outlive the instance. |
| 17 | +""" |
| 18 | + |
| 19 | +from __future__ import annotations |
| 20 | + |
| 21 | +import argparse |
| 22 | +import asyncio |
| 23 | +import contextlib |
| 24 | +import logging |
| 25 | + |
| 26 | +import ifaddr |
| 27 | + |
| 28 | +from zeroconf.asyncio import AsyncServiceInfo, AsyncZeroconf |
| 29 | + |
| 30 | +_LOGGER = logging.getLogger("interface_monitor") |
| 31 | + |
| 32 | + |
| 33 | +def address_snapshot() -> set[tuple[str, int]]: |
| 34 | + """A snapshot of the host's current addresses; a change triggers a reconcile.""" |
| 35 | + return {(str(ip.ip), ip.network_prefix) for adapter in ifaddr.get_adapters() for ip in adapter.ips} |
| 36 | + |
| 37 | + |
| 38 | +async def monitor_interfaces(aiozc: AsyncZeroconf, interval: float) -> None: |
| 39 | + """Reconcile sockets whenever the host's addresses change, until cancelled.""" |
| 40 | + previous = address_snapshot() |
| 41 | + while True: |
| 42 | + await asyncio.sleep(interval) |
| 43 | + current = address_snapshot() |
| 44 | + if current == previous: |
| 45 | + continue |
| 46 | + try: |
| 47 | + print("Interfaces changed, reconciling sockets...") |
| 48 | + await aiozc.async_update_interfaces() |
| 49 | + except Exception: |
| 50 | + # Log and retry on the next tick rather than letting the monitor |
| 51 | + # die; leave ``previous`` unchanged so the change is re-attempted. |
| 52 | + _LOGGER.exception("Interface reconcile failed; will retry") |
| 53 | + else: |
| 54 | + previous = current |
| 55 | + |
| 56 | + |
| 57 | +class AsyncRunner: |
| 58 | + def __init__(self) -> None: |
| 59 | + self.aiozc: AsyncZeroconf | None = None |
| 60 | + self.monitor: asyncio.Task | None = None |
| 61 | + |
| 62 | + async def run(self, info: AsyncServiceInfo, interval: float) -> None: |
| 63 | + self.aiozc = AsyncZeroconf() |
| 64 | + await self.aiozc.async_register_service(info) |
| 65 | + self.monitor = asyncio.create_task(monitor_interfaces(self.aiozc, interval)) |
| 66 | + print("Registered; monitoring interfaces. Press Ctrl-C to exit...") |
| 67 | + await asyncio.Event().wait() |
| 68 | + |
| 69 | + async def close(self, info: AsyncServiceInfo) -> None: |
| 70 | + assert self.aiozc is not None |
| 71 | + # Stop the monitor before closing so it can't reconcile a closed instance. |
| 72 | + if self.monitor is not None: |
| 73 | + self.monitor.cancel() |
| 74 | + with contextlib.suppress(asyncio.CancelledError): |
| 75 | + await self.monitor |
| 76 | + # Await the goodbye broadcast so the TTL-0 records are actually sent. |
| 77 | + await (await self.aiozc.async_unregister_service(info)) |
| 78 | + await self.aiozc.async_close() |
| 79 | + |
| 80 | + |
| 81 | +if __name__ == "__main__": |
| 82 | + logging.basicConfig(level=logging.INFO) |
| 83 | + |
| 84 | + parser = argparse.ArgumentParser() |
| 85 | + parser.add_argument("--debug", action="store_true") |
| 86 | + parser.add_argument("--interval", type=float, default=30.0, help="poll seconds") |
| 87 | + args = parser.parse_args() |
| 88 | + if args.debug: |
| 89 | + logging.getLogger("zeroconf").setLevel(logging.DEBUG) |
| 90 | + |
| 91 | + info = AsyncServiceInfo( |
| 92 | + "_http._tcp.local.", |
| 93 | + "Interface Monitor Demo._http._tcp.local.", |
| 94 | + port=80, |
| 95 | + properties={"path": "/"}, |
| 96 | + server="interface-monitor-demo.local.", |
| 97 | + ) |
| 98 | + |
| 99 | + loop = asyncio.get_event_loop() |
| 100 | + runner = AsyncRunner() |
| 101 | + try: |
| 102 | + loop.run_until_complete(runner.run(info, args.interval)) |
| 103 | + except KeyboardInterrupt: |
| 104 | + loop.run_until_complete(runner.close(info)) |
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