socket_comms: fix multicast sockets on Windows without IP

Fix multicast sockets on Windows when there is no multicast capable
external interface. The writing socket is now unconditionally bound
to the localhost interface, and the receiving socket updated to be
properly bound to the multicast group on Windows.

Signed-off-by: Jordan Yates <jordan@embeint.com>

Author: JordanYates

src/infuse_iot/socket_comms.py

@@ -273,8 +273,7 @@ def __init__(self, multicast_address):
         # Multicast output socket
         self._output_sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP)
         self._output_sock.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_TTL, 2)
-        if sys.platform != "win32":
-            self._output_sock.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_IF, socket.inet_aton("127.0.0.1"))
+        self._output_sock.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_IF, socket.inet_aton("127.0.0.1"))
         self._output_addr = multicast_address
         # Single input socket
         unicast_address = ("localhost", multicast_address[1] + 1)
@@ -303,11 +302,10 @@ def __init__(self, multicast_address, rx_timeout=0.2):
         self._input_sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP)
         self._input_sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
         if sys.platform == "win32":
-            self._input_sock.bind(("", multicast_address[1]))
-            mreq = struct.pack("4sl", socket.inet_aton(multicast_address[0]), socket.INADDR_ANY)
+            self._input_sock.bind(("127.0.0.1", multicast_address[1]))
         else:
             self._input_sock.bind(multicast_address)
-            mreq = struct.pack("4s4s", socket.inet_aton(multicast_address[0]), socket.inet_aton("127.0.0.1"))
+        mreq = struct.pack("4s4s", socket.inet_aton(multicast_address[0]), socket.inet_aton("127.0.0.1"))
         self._input_sock.setsockopt(socket.IPPROTO_IP, socket.IP_ADD_MEMBERSHIP, mreq)
         self._input_sock.settimeout(rx_timeout)
         # Unicast output socket