public TRTrackerServerUDP(String _name, int _port, boolean _start_up_ready) {
    super(_name, _start_up_ready);

    port = _port;

    thread_pool = new ThreadPool("TrackerServer:UDP:" + port, THREAD_POOL_SIZE);

    try {
      InetAddress bind_ip = NetworkAdmin.getSingleton().getSingleHomedServiceBindAddress();

      InetSocketAddress address;

      DatagramSocket socket;

      if (bind_ip == null) {

        address = new InetSocketAddress(InetAddress.getByName("127.0.0.1"), port);

        socket = new DatagramSocket(port);

      } else {

        current_bind_ip = bind_ip;

        address = new InetSocketAddress(bind_ip, port);

        socket = new DatagramSocket(address);
      }

      socket.setReuseAddress(true);

      dg_socket = socket;

      final InetSocketAddress f_address = address;

      Thread recv_thread =
          new AEThread("TRTrackerServerUDP:recv.loop") {
            public void runSupport() {
              recvLoop(dg_socket, f_address);
            }
          };

      recv_thread.setDaemon(true);

      recv_thread.start();

      Logger.log(new LogEvent(LOGID, "TRTrackerServerUDP: recv established on port " + port));

    } catch (Throwable e) {

      Logger.log(
          new LogEvent(
              LOGID, "TRTrackerServerUDP: " + "DatagramSocket bind failed on port " + port, e));
    }
  }
  protected void recvLoop(DatagramSocket socket, InetSocketAddress address) {
    long successful_accepts = 0;
    long failed_accepts = 0;

    while (!closed) {

      try {
        byte[] buf = new byte[PRUDPPacket.MAX_PACKET_SIZE];

        DatagramPacket packet = new DatagramPacket(buf, buf.length, address);

        socket.receive(packet);

        successful_accepts++;

        failed_accepts = 0;

        String ip = packet.getAddress().getHostAddress();

        if (!ip_filter.isInRange(ip, "Tracker", null)) {

          thread_pool.run(new TRTrackerServerProcessorUDP(this, socket, packet));
        }

      } catch (Throwable e) {

        if (!closed) {

          failed_accepts++;

          Logger.log(new LogEvent(LOGID, "TRTrackerServer: receive failed on port " + port, e));

          if ((failed_accepts > 100 && successful_accepts == 0) || failed_accepts > 1000) {

            // looks like its not going to work...
            // some kind of socket problem

            Logger.logTextResource(
                new LogAlert(LogAlert.UNREPEATABLE, LogAlert.AT_ERROR, "Network.alert.acceptfail"),
                new String[] {"" + port, "UDP"});

            break;
          }
        }
      }
    }
  }
  public void runSupport() {
    byte[] input_buffer = new byte[request_dg.getLength()];

    System.arraycopy(request_dg.getData(), 0, input_buffer, 0, input_buffer.length);

    int packet_data_length = input_buffer.length;

    String auth_user = null;
    byte[] auth_user_bytes = null;
    byte[] auth_hash = null;

    if (server.isTrackerPasswordEnabled()) {

      // auth detail should be attached to the packet. Auth details are 16
      // bytes

      if (input_buffer.length < 17) {

        Logger.log(
            new LogEvent(
                LOGID,
                LogEvent.LT_WARNING,
                "TRTrackerServerProcessorUDP: " + "packet received but authorisation missing"));

        return;
      }

      packet_data_length -= 16;

      auth_user_bytes = new byte[8];

      auth_hash = new byte[8];

      System.arraycopy(input_buffer, packet_data_length, auth_user_bytes, 0, 8);

      int user_len = 0;

      while (user_len < 8 && auth_user_bytes[user_len] != 0) {

        user_len++;
      }

      auth_user = new String(auth_user_bytes, 0, user_len);

      System.arraycopy(input_buffer, packet_data_length + 8, auth_hash, 0, 8);
    }

    DataInputStream is =
        new DataInputStream(new ByteArrayInputStream(input_buffer, 0, packet_data_length));

    try {
      String client_ip_address = request_dg.getAddress().getHostAddress();

      PRUDPPacketRequest request = PRUDPPacketRequest.deserialiseRequest(null, is);

      Logger.log(
          new LogEvent(
              LOGID, "TRTrackerServerProcessorUDP: packet received: " + request.getString()));

      PRUDPPacket reply = null;
      TRTrackerServerTorrentImpl torrent = null;

      if (auth_user_bytes != null) {

        // user name is irrelevant as we only have one at the moment

        // <parg_home> so <new_packet> = <old_packet> + <user_padded_to_8_bytes> + <hash>
        // <parg_home> where <hash> = first 8 bytes of sha1(<old_packet> + <user_padded_to_8> +
        // sha1(pass))
        // <XTF> Yes

        byte[] sha1_pw = null;

        if (server.hasExternalAuthorisation()) {

          try {
            URL resource = new URL("udp://" + server.getHost() + ":" + server.getPort() + "/");

            sha1_pw = server.performExternalAuthorisation(resource, auth_user);

          } catch (MalformedURLException e) {

            Debug.printStackTrace(e);
          }

          if (sha1_pw == null) {

            Logger.log(
                new LogEvent(
                    LOGID,
                    LogEvent.LT_ERROR,
                    "TRTrackerServerProcessorUDP: auth fails for user '" + auth_user + "'"));

            reply = new PRUDPPacketReplyError(request.getTransactionId(), "Access Denied");
          }
        } else {

          sha1_pw = server.getPassword();
        }

        // if we haven't already failed then check the PW

        if (reply == null) {

          SHA1Hasher hasher = new SHA1Hasher();

          hasher.update(input_buffer, 0, packet_data_length);
          hasher.update(auth_user_bytes);
          hasher.update(sha1_pw);

          byte[] digest = hasher.getDigest();

          for (int i = 0; i < auth_hash.length; i++) {

            if (auth_hash[i] != digest[i]) {

              Logger.log(
                  new LogEvent(
                      LOGID,
                      LogEvent.LT_ERROR,
                      "TRTrackerServerProcessorUDP: auth fails for user '" + auth_user + "'"));

              reply = new PRUDPPacketReplyError(request.getTransactionId(), "Access Denied");

              break;
            }
          }
        }
      }

      int request_type = TRTrackerServerRequest.RT_UNKNOWN;

      if (reply == null) {

        if (server.isEnabled()) {

          try {
            int type = request.getAction();

            if (type == PRUDPPacketTracker.ACT_REQUEST_CONNECT) {

              reply = handleConnect(client_ip_address, request);

            } else if (type == PRUDPPacketTracker.ACT_REQUEST_ANNOUNCE) {

              Object[] x =
                  handleAnnounceAndScrape(
                      client_ip_address, request, TRTrackerServerRequest.RT_ANNOUNCE);

              if (x == null) {

                throw (new Exception("Connection ID mismatch"));
              }

              reply = (PRUDPPacket) x[0];
              torrent = (TRTrackerServerTorrentImpl) x[1];

              request_type = TRTrackerServerRequest.RT_ANNOUNCE;

            } else if (type == PRUDPPacketTracker.ACT_REQUEST_SCRAPE) {

              Object[] x =
                  handleAnnounceAndScrape(
                      client_ip_address, request, TRTrackerServerRequest.RT_SCRAPE);

              if (x == null) {

                throw (new Exception("Connection ID mismatch"));
              }

              reply = (PRUDPPacket) x[0];
              torrent = (TRTrackerServerTorrentImpl) x[1];

              request_type = TRTrackerServerRequest.RT_SCRAPE;

            } else {

              reply = new PRUDPPacketReplyError(request.getTransactionId(), "unsupported action");
            }
          } catch (Throwable e) {

            // e.printStackTrace();

            String error = e.getMessage();

            if (error == null) {

              error = e.toString();
            }

            reply = new PRUDPPacketReplyError(request.getTransactionId(), error);
          }
        } else {

          System.out.println("UDP Tracker: replying 'disabled' to " + client_ip_address);

          reply = new PRUDPPacketReplyError(request.getTransactionId(), "UDP Tracker disabled");
        }
      }

      if (reply != null) {

        InetAddress address = request_dg.getAddress();

        ByteArrayOutputStream baos = new ByteArrayOutputStream();

        DataOutputStream os = new DataOutputStream(baos);

        reply.serialise(os);

        byte[] output_buffer = baos.toByteArray();

        DatagramPacket reply_packet =
            new DatagramPacket(output_buffer, output_buffer.length, address, request_dg.getPort());

        socket.send(reply_packet);

        server.updateStats(request_type, torrent, input_buffer.length, output_buffer.length);
      }

    } catch (Throwable e) {

      Logger.log(new LogEvent(LOGID, "TRTrackerServerProcessorUDP: processing fails", e));
    } finally {

      try {
        is.close();

      } catch (Throwable e) {

      }
    }
  }