Multicast udp socket

[leon1995]

Hi, I am trying to create an udp socket wich joins a multicast group to receive udp packets from a multicast group.

Basically, I am trying to replace the following code with anyio

async def create_multicast_udp(multicast_addr: str, addr: str, port: int, ttl: int = 15)
    sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP)
    sock.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_TTL, ttl)
    sock.setblocking(False)
    sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
    sock.setsockopt(
        socket.IPPROTO_IP,
        socket.IP_ADD_MEMBERSHIP,
        struct.pack(
            "4s4s",
            socket.inet_aton(multicast_addr),
            socket.inet_aton(addr),
        ),
    )
    sock.bind((self.addr, self.port))
    ... = await loop.create_datagram_endpoint(..., sock=sock)
    ...

but when I create the udp socket with await anyio.create_udp_socket(family=socket.AF_INET, local_host=self.addr, local_port=self.port) then I receive a

  File "<redacted>\anyio\_core\_sockets.py", line 424, in create_udp_socket
    sock = await get_async_backend().create_udp_socket(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "<redacted>\anyio\_backends\_asyncio.py", line 2624, in create_udp_socket
    transport, protocol = await get_running_loop().create_datagram_endpoint(
                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "<redacted>\asyncio\base_events.py", line 1422, in create_datagram_endpoint
    raise exceptions[0]
  File "<redacted>\asyncio\base_events.py", line 1406, in create_datagram_endpoint
    sock.bind(local_address)
PermissionError: [WinError 10013] Der Zugriff auf einen Socket war aufgrund der Zugriffsrechte des Sockets unzulässig

(socket.error: [Errno 10013] An attempt was made to access a socket in a way forbidden by its access permissions)
when I call this function with '127.0.0.1' and port 3702

netstat -na|findstr 3702
  UDP    0.0.0.0:3702           *:*                    
  UDP    0.0.0.0:3702           *:*                    
  UDP    0.0.0.0:3702           *:*                    
  UDP    0.0.0.0:3702           *:*                    
  UDP    [::]:3702              *:*                    
  UDP    [::]:3702              *:*                    
  UDP    [::]:3702              *:*                    
  UDP    [::]:3702              *:*    

How can I set additional socket options before the socket is bound to?

[leon1995]

I think I found a way

udp_socket = await anyio.create_udp_socket(family=socket.AF_INET)
raw_socket = typing.cast(socket.socket, udp_socket.extra_attributes[SocketAttribute.raw_socket]())

and then set the options with raw_socket.setsockopt(...). Is this the intended way?

[agronholm]

Are there any legit use cases for passing socket options at this stage other than multicast?

[agronholm]

Right - broadcasting: sock.setsockopt(socket.SOL_SOCKET, socket.SO_BROADCAST, 1)

[agronholm]

I would really prefer a higher-level interface here. For really strange use cases, #845 would be the escape hatch.

[leon1995]

something like async def create_multicast_socket(multicast_grp: str, local_host: str, local_port: int, ttl: int | None) -> UDPSocket?

[agronholm]

I had a look at the socket options list and it made me think that a low-level socket_opts argument would indeed be warranted, as there are even more socket options that need to be set before bind(). For multicast there could be a high-level convenience wrapper.