Question

The PC Windows is sending the confirmation. But that is not arriving to Linux.
What am i missing? (But when i do not use Windows 7 and do the same code under Linux to Linux it works.)

Any ideas!!!

Windows 7 PC: Sender/Replyer

System.out.println("[UDP]: " 
          + "RemoteIP: " + IPAddress.toString() + " "
          + "Port: " + port + " " 
          + "Length: " + send.length() + " "
          + "Sending confirmation!"); // it shows it has correct ip, port and lenght                   
sockOutput = new DatagramPacket(send.getBytes(), send.length(), IPAddress, port);
serverSock.send(sockOutput);// is it failing???

Linux PC: Receiver/Commander

String receive = sendUDPBytes("request", ip).toString();

if (receive.length()<=0) // Waiting forever, and nothing happens LINUX.
{
    System.out.println("FAILED");
    System.exit(0);
} else {
      try {                                          
            /* JOB todo */
      } catch (Exception ex) {

      }                    
}
sockOutput.write(receive.getBytes());

public static String sendUDPBytes(String bytes, String[] ip) throws IOException
{            
    String downloaded = null;      
    DatagramSocket socket = new DatagramSocket();
    InetAddress IPAddress = InetAddress.getByName(ip[2]);

    byte[] sendData = new byte[14024];
    byte[] receiveData = new byte[14024];

    sendData = bytes.getBytes();
    DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length);
    socket.connect(IPAddress, 58889);
    if (socket.isConnected())
    {
        System.out.println("[UDP]: sending....., waiting......... until receive....");
        socket.send(sendPacket);
    }

    DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);
    socket.receive(receivePacket);      
    downloaded = new String(receivePacket.getData());

    System.out.println("[UDP]: closing.....");
    socket.close();              
    return downloaded;
}

Follow up:

0) Do not get confuse with “ARE U IN A SAME SUBSET???”, so if you have /28 network all in can exchange the packet. In that case it works but that is not the case most of the time.

1) The code is perfect, when i test LAN to LAN no matter what operating system it is, it works (no firewall ofcource)

2) When i test Windows to Windows in the same PC it works too

3) When i test Linux to Linux it works too

4) When i test Linux to Windows or Windows to Linux it works too

5) The same code i put in one central server and same code i ran in local Windows PC, and other ISP seems to allow it.

6) Sp-ended 10 hours to find it

Guess:

What exactly was then the cause? Well, ISP is losing the packet that was sent to my public IP or they maybe disabling those even i have Public IP.

Answer 1

You are doing String bytes and getBytes() depends on the platform encoding. getBytes("UTF-8") would be explicit.

Another thing are the differing newlines: Linux \n, Windows \r\n.

The toString() might throw an exception if the bytes stem from Windows Latin-1 (Cp1252), and it tries to interprete them as UTF-8.

---

private void test(OutputStream sockOutput, String[] ip) throws IOException {
    String receive = sendUDPBytes("request", ip);

    if (receive.length() <= 0) // Waiting forever, and nothing happens LINUX.
    {
        System.out.println("FAILED");
        System.exit(0);
    } else {
        try {
            /*
             * JOB todo
             */
        } catch (Exception ex) {
        }
    }
    sockOutput.write(receive.getBytes("UTF-8"));
}

public static String sendUDPBytes(String bytes, String[] ip) throws IOException {
    return new String(sendUDPBytesRaw(bytes.getBytes("UTF-8"), ip), "UTF-8");
}

public static byte[] sendUDPBytesRaw(byte[] sendData, String[] ip) throws IOException {
    DatagramSocket socket = new DatagramSocket();
    InetAddress IPAddress = InetAddress.getByName(ip[2]);

    byte[] receiveData = new byte[14024];

    DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length);
    socket.connect(IPAddress, 58889);
    if (socket.isConnected()) {
        System.out.println("[UDP]: sending....., waiting......... until receive....");
        socket.send(sendPacket);
    }

    DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);
    socket.receive(receivePacket);
    byte[] downloaded = receivePacket.getData();

    System.out.println("[UDP]: closing.....");
    socket.close();
    return downloaded;
}