System.IO.BACnet.BacnetIpUdpProtocolTransport.OnReceiveData C# (CSharp) Méthode

        private void OnReceiveData(IAsyncResult asyncResult)
        {
            System.Net.Sockets.UdpClient conn = (System.Net.Sockets.UdpClient)asyncResult.AsyncState;
            try
            {
                System.Net.IPEndPoint ep = new Net.IPEndPoint(System.Net.IPAddress.Any, 0);
                byte[] local_buffer;
                int rx = 0;

                try
                {
                    local_buffer = conn.EndReceive(asyncResult, ref ep);
                    rx = local_buffer.Length;
                }
                catch (Exception) // ICMP port unreachable
                {
                    //restart data receive
                    conn.BeginReceive(OnReceiveData, conn);
                    return;
                }

                if (rx == 0)    // Empty frame : port scanner maybe
                {
                    //restart data receive
                    conn.BeginReceive(OnReceiveData, conn);
                    return;
                }

                try
                {
                    //verify message
                    BacnetAddress remote_address;
                    Convert((System.Net.IPEndPoint)ep, out remote_address);
                    BacnetBvlcFunctions function;
                    int msg_length;
                    if (rx < BVLC.BVLC_HEADER_LENGTH)
                    {
                        Trace.TraceWarning("Some garbage data got in");
                    }
                    else
                    {
                        // Basic Header lenght
                        int HEADER_LENGTH = bvlc.Decode(local_buffer, 0, out function, out msg_length, ep);

                        if (HEADER_LENGTH == -1)
                        {
                            Trace.WriteLine("Unknow BVLC Header");
                            return;
                        }

                        // response to BVLC_REGISTER_FOREIGN_DEVICE (could be BVLC_DISTRIBUTE_BROADCAST_TO_NETWORK ... but we are not a BBMD, don't care)
                        if (function == BacnetBvlcFunctions.BVLC_RESULT)
                        {
                            Trace.WriteLine("Receive Register as Foreign Device Response");
                        }

                        // a BVLC_FORWARDED_NPDU frame by a BBMD, change the remote_address to the original one (stored in the BVLC header)
                        // we don't care about the BBMD address
                        if (function == BacnetBvlcFunctions.BVLC_FORWARDED_NPDU)
                        {
                            long ip = ((long)local_buffer[7] << 24) + ((long)local_buffer[6] << 16) + ((long)local_buffer[5] << 8) + (long)local_buffer[4];
                            int port = (local_buffer[8] << 8) + local_buffer[9];    // 0xbac0 maybe
                            ep = new Net.IPEndPoint(ip, port);

                            Convert((System.Net.IPEndPoint)ep, out remote_address);

                        }

                        if ((function == BacnetBvlcFunctions.BVLC_ORIGINAL_UNICAST_NPDU) || (function == BacnetBvlcFunctions.BVLC_ORIGINAL_BROADCAST_NPDU) || (function == BacnetBvlcFunctions.BVLC_FORWARDED_NPDU))
                            //send to upper layers
                            if ((MessageRecieved != null)  &&(rx>HEADER_LENGTH)) MessageRecieved(this, local_buffer, HEADER_LENGTH, rx - HEADER_LENGTH, remote_address);
                    }
                }
                catch (Exception ex)
                {
                    Trace.TraceError("Exception in udp recieve: " + ex.Message);
                }
                finally
                {
                    //restart data receive
                    conn.BeginReceive(OnReceiveData, conn);
                }
            }
            catch (Exception ex)
            {
                //restart data receive
                if (conn.Client != null)
                {
                    Trace.TraceError("Exception in Ip OnRecieveData: " + ex.Message);
                    conn.BeginReceive(OnReceiveData, conn);
                }
            }
        }