add a module for doing multicast work..

Makefile

@@ -168,8 +168,8 @@ runbuild: $(SRCS)
 	for i in $(.MAKEFILE_LIST) $(.ALLSRC) $$(cat $(DEPENDS) | gsed ':x; /\\$$/ { N; s/\\\n//; tx }' | sed -e 's/^[^:]*://'); do if [ "$$i" != ".." ]; then echo $$i; fi; done | entr -d sh -c 'echo starting...; cd $(.CURDIR) && $(MAKE) $(.MAKEFLAGS) depend && $(MAKE) $(.MAKEFLAGS) all'
 
 .PHONY: runtests
-runtests: Makefile lora_comms.py lora.py $(LIBLORA_TEST) $(LIBLORA_TEST_SRCS)
-	ls $(.ALLSRC) | entr sh -c '(cd $(.CURDIR) && $(MAKE) $(.MAKEFLAGS) $(LIBLORA_TEST)) && ((PYTHONPATH="$(.CURDIR)" python -m coverage run -m unittest lora && coverage report --omit=$(.CURDIR)/p/\* -m -i) 2>&1 | head -n 30)'
+runtests: Makefile lora_comms.py lora.py multicast.py $(LIBLORA_TEST) $(LIBLORA_TEST_SRCS)
+	ls $(.ALLSRC) | entr sh -c '(cd $(.CURDIR) && $(MAKE) $(.MAKEFLAGS) $(LIBLORA_TEST)) && ((PYTHONPATH="$(.CURDIR)" python -m coverage run -m unittest lora multicast && coverage report --omit=$(.CURDIR)/p/\* -m -i) 2>&1 | head -n 30)'
 
 # native objects
 .SUFFIXES: .no

multicast.py

@@ -0,0 +1,91 @@
+import asyncio
+import random
+import socket
+import struct
+import unittest
+
+from lora import timeout
+
+# This function based upon code from:
+# https://gist.github.com/petrdvor/e802bec72e78ace061ab9d4469418fae#file-async-multicast-receiver-server-py-L54-L72
+def make_multisock(maddr):
+	# family, type, proto, ??, addr)
+	addrinfo = socket.getaddrinfo(*maddr, type=socket.SOCK_DGRAM)[0]
+
+	sock = socket.socket(*addrinfo[:2])
+	sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEPORT, 1)
+
+	sock.bind(maddr)
+
+	group_bin = socket.inet_pton(addrinfo[0], addrinfo[4][0])
+	mreq = group_bin + struct.pack('=I', socket.INADDR_ANY)
+	sock.setsockopt(socket.IPPROTO_IP, socket.IP_ADD_MEMBERSHIP, mreq)
+
+	return sock
+
+class StupidProtocol(object):
+	def __init__(self):
+		self.transport = None
+
+	def connection_made(self, transport):
+		# Note: the connection_made call seems to be sync.  This
+		# isn't documented, and I don't know how to force a test
+		# if it isn't.
+		self.transport = transport
+
+class ReceiverProtocol(StupidProtocol):
+	def __init__(self):
+		super().__init__()
+
+		self._q = asyncio.Queue()
+
+	def datagram_received(self, data, addr):
+		self._q.put_nowait((data, addr))
+
+	async def recv(self):
+		return await self._q.get()
+
+async def create_multicast_receiver(maddr):
+	sock = make_multisock(maddr)
+
+	loop = asyncio.get_running_loop()
+	transport, protocol = await loop.create_datagram_endpoint(
+	    lambda: ReceiverProtocol(),
+	    sock=sock)
+
+	return protocol
+
+class TransmitterProtocol(StupidProtocol):
+	async def send(self, msg):
+		self.transport.sendto(msg)
+
+async def create_multicast_transmitter(maddr):
+	loop = asyncio.get_running_loop()
+	transport, protocol = await loop.create_datagram_endpoint(
+	    lambda: TransmitterProtocol(),
+	    remote_addr=maddr)
+
+	return protocol
+
+class TestMulticast(unittest.IsolatedAsyncioTestCase):
+	@timeout(2)
+	async def test_multicast(self):
+		# see: https://www.iana.org/assignments/multicast-addresses/multicast-addresses.xhtml#multicast-addresses-1
+		maddr = ('224.0.0.%d' % random.randint(151, 250), 3485)
+
+		l1 = await create_multicast_receiver(maddr)
+		l2 = await create_multicast_receiver(maddr)
+
+		t1 = await create_multicast_transmitter(maddr)
+		print('tm:', repr(t1))
+
+		msg = b'test message'
+
+		await t1.send(msg)
+		await t1.send(msg)
+
+		self.assertEqual((await l1.recv())[0], msg)
+		self.assertEqual((await l2.recv())[0], msg)
+
+		self.assertEqual((await l1.recv())[0], msg)
+		self.assertEqual((await l2.recv())[0], msg)