Add coroutine for handling mDNS query responses.

We can now discover our device. Maybe. I'm really not sure if I'm doing
the protocol correctly, but it looks pretty good. *shrug*.

pnpdevice/discovery.py

@@ -0,0 +1,37 @@
+import logging
+import socket
+
+from zeroconf import IPVersion
+from zeroconf.asyncio import AsyncServiceInfo, AsyncZeroconf
+
+LOGGER = logging.getLogger(__name__)
+
+# From https://stackoverflow.com/questions/166506/finding-local-ip-addresses-using-pythons-stdlib/
+def get_ip() -> str:
+	"Get the primary IP"
+	LOGGER.info("Determining IP address")
+	s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+	s.settimeout(0)
+	try:
+		# doesn't even have to be reachable
+		s.connect(('10.254.254.254', 1))
+		ip = s.getsockname()[0]
+	except Exception:
+		ip = '127.0.0.1'
+	finally:
+		s.close()
+	LOGGER.info("IP address seems to be %s", ip)
+	return ip
+
+async def handle():
+	"Handle requests for discovery"
+	ip = get_ip()
+	info = AsyncServiceInfo(
+		"_http._tcp.local.",
+		"pnpdevice._http._tcp.local.",
+		addresses=[socket.inet_aton("127.0.0.1")],
+		port=13344,
+		server=ip,
+	)
+	aiozc = AsyncZeroconf(ip_version=IPVersion.V4Only)
+	await aiozc.async_register_service(info)

pnpdevice/main.py

@@ -2,10 +2,12 @@ import argparse
 import asyncio
 import logging
 
+import pnpdevice.discovery
 
 LOGGER = logging.getLogger(__name__)
 
 async def run():
+	asyncio.ensure_future(pnpdevice.discovery.handle())
 	while True:
 		await asyncio.sleep(1)
 		LOGGER.info("Tick.")