c＃ - 使用recieveFrom获取组播数据包的源IP

Question

Good day all

Problem:

I am trying to get the source IP of multicast packets, however all that I get is 0.0.0.0:80

What I have tried:

I tried methods shown in these sites, not sure if I correctly implemented it, but all return the same IP which is 0.0.0.0, this post and this one

Both links refer to using socket.recieveFrom() or socket.BeginRecieveMessageFrom() instead of socket.recieve()

        private void recieveText()
        {
            //initialise multicast group and bind to interface
            Socket _listener_socket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
            IPEndPoint ipep = new IPEndPoint(IPAddress.Any, _PORT);
            _listener_socket.Bind(ipep);
            IPAddress localip = IPAddress.Parse("224.5.6.7");
            _listener_socket.SetSocketOption(SocketOptionLevel.IP, SocketOptionName.AddMembership, new MulticastOption(localip, IPAddress.Any));

            //recieve data to multicast group
            while (_listener_socket.IsBound)
            {
                updateLabel("listening...");
                byte[] b = new byte[1024];
                updateLabel("message recieved");
                updateRedBox("\n---------------------------------\n New Message :\n");
                EndPoint IPEPoint = (EndPoint)ipep;
                _listener_socket.BeginReceiveMessageFrom(b, 0, b.Length, 0, ref IPEPoint, null, null);
                updateRedBox(IPEPoint.ToString());
                char[] chars = new char[b.Length / sizeof(char)];
                System.Buffer.BlockCopy(b, 0, chars, 0, b.Length);

                string t = new string(chars).Trim();
                updateRedBox(t);
                updateRedBox("\n----------------------------------\n");
            }
        }

Answer 1

You should use the synchronous ReceiveMessageFrom call or call EndReceiveMessageFrom after calling the asynchronous BeginReceiveMessageFrom

private void recieveText()
{
    //initialise multicast group and bind to interface
    Socket _listener_socket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
    IPEndPoint ipep = new IPEndPoint(IPAddress.Any, _PORT);
    _listener_socket.Bind(ipep);
    IPAddress localip = IPAddress.Parse("224.5.6.7");
    _listener_socket.SetSocketOption(SocketOptionLevel.IP, SocketOptionName.AddMembership, new MulticastOption(localip, IPAddress.Any));

    //recieve data to multicast group
    while (_listener_socket.IsBound)
    {
        updateLabel("listening...");
        byte[] b = new byte[1024];
        updateLabel("message recieved");
        updateRedBox("\n---------------------------------\n New Message :\n");
        EndPoint IPEPoint = (EndPoint)ipep;
        var res = _listener_socket.BeginReceiveMessageFrom(b, 0, b.Length, 0, ref IPEPoint, null, null);
        SocketFlags flags = SocketFlags.None;
        IPPacketInformation packetInfo;
        _listener_socket.EndReceiveMessageFrom(res, ref flags, ref IPEPoint, out packetInfo);
        updateRedBox(IPEPoint.ToString());
        char[] chars = new char[b.Length / sizeof(char)];
        System.Buffer.BlockCopy(b, 0, chars, 0, b.Length);

        string t = new string(chars).Trim();
        updateRedBox(t);
        updateRedBox("\n----------------------------------\n");
    }
}

Look at the 3 lines following BeginReceiveMessageFrom that I have added. In addition to the Remote IP Address, you can use the flags to find out whether this message was received as a Multicast message and the multicast group IP Address can be obtained from packetInfo