Java-Client PHP-Server UDP Hole Punching example code

Question

I'm working on a project that will require ea p2p server, but I haven't found any java-client php-server example code. I understand the concept of how udp hole punching works but I can't get anything to work in code.

What I've tried:

TheSocket.java

public class TheSocket {

public static String response = "hello";
public static String request;
public static String webServerAddress;

public static ServerSocket s;

protected static ServerSocket getServerSocket(int port)throws Exception{
    return new ServerSocket(port);
}

public static void handleRequest(Socket s){
    BufferedReader is;
    PrintWriter os;

    try{
        webServerAddress = s.getInetAddress().toString();
        is = new BufferedReader(new InputStreamReader(s.getInputStream()));

        request = is.readLine();

        System.out.println(request);

        os = new PrintWriter(s.getOutputStream(), true);
        os.println("HTTP/1.0 200");
        os.println("Content-type: text/html");
        os.println("Server-name: TheSocket");
        os.println("Content-length: " + response.length());
        os.println("");
        os.println(response);
        os.flush();
        os.close();
        s.close();

    }catch(Exception e){
        System.out.println("Failed to send response to client: " + e.getMessage());
    }finally{
        if(s != null){
            try{
                s.close();
            }catch(Exception e){
                e.printStackTrace();
            }
        }
    }
    return;
}
}

Main.java

public class Main {

public static void main(String[] args)throws Exception{
    TheSocket.s = TheSocket.getServerSocket(6789);
    while(true){
        Socket serverSocket = TheSocket.s.accept();
        TheSocket.handleRequest(serverSocket);
    }
}

PHP-CONNECT.php - to get the other users port, I manually connect and use the port shown on webpage.

<?php
    echo $_SERVER['REMOTE_ADDR'].':'.$_SERVER['REMOTE_PORT'];
?>

The issue with the code above, is that it cant make it to the socket unless I port forward.

Comment if you have any questions!

Answer 1

I was facing a similar problem. And was trying to solve it in a similar way.

Some parts of your code look wrong to me. Sockets in Java are made for TCP but the title says UDP. Therefore u should use DatagramSockets. But then we come to the point where i stuck too. HTTP-Requests use tcp as well, so opening the port with HTTP might lead to a corrupt port, after tcp session was closed. (Just a guess)

---

public class Main {

    public static void main(String[] args) {

        try
        {

            String httpRequest = "GET /index.php HTTP/1.1\n" +
                    "Host: <PHP SERVER NAME HERE>";

            InetAddress IPAddress = InetAddress.getByName(<PHP SERVER IP HERE>);

            DatagramSocket clientSocket = new DatagramSocket();
            byte[] sendData = new byte[1024];
            byte[] receiveData = new byte[1024];
            String sentence = httpRequest;
            sendData = sentence.getBytes();

            DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, IPAddress, 80);
            clientSocket.send(sendPacket);
            DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);
            clientSocket.receive(receivePacket);

            String modifiedSentence = new String(receivePacket.getData());
            System.out.println("FROM SERVER:" + modifiedSentence);

            clientSocket.close();

        }catch(Exception e){e.printStackTrace();}

    }


}

The Code above theoretically sents a HTTP over UDP request. So that the displayed Port will be the UDP one. In my case i didnt get any response from the PHP Server and stuck at clientSocket.recieve(..) . I guess because the firewall of my webserver is blocking udp packets. If the code works by anyone i would proceed like this:

1. save all accessing ips and ports to a DB and list them to the other client.
2. Write ur Data in DatagramPackets like above to the other client.

I hope this may help. If anyone can get it completly working i would also be interested in it :)