I'm currently trying to implement udp hole punching on Android for my udp server. Things should work like this:
- The client (behind a nat; maybe 3G,..) sends a DatagramPacket to the server (the server has a public ip; port is also known to be 45555). The client repeats to send a Datagram with a given delay
- Once the server received a Datagram, it sends Datagrams ("signals") back every 500ms.
- If hole punching worked, the client should receive those signals
Here is my current Client implementation (Android):
//in onCreate()
DatagramSocket socket = new DatagramSocket(46222);
socket.setSoTimeout(2000);
final Thread t = new Thread(new Runnable(){
@Override
public void run() {
int delay = Integer.parseInt(e2.getText().toString());//e1 and e2 are EditTexts
String ip = e1.getText().toString();
try {
DatagramPacket packet = new DatagramPacket(new byte[1],1, InetAddress.getByName(ip), 45555);
while(!cleanUp){//cleanUp is set to true in onPause()
lock.lock(); //Lock lock = new ReentrantLock();
socket.send(packet);
lock.unlock();
Thread.sleep(delay);
}
} catch (Exception e) {
e.printStackTrace();
}finally{
if(socket!=null)
socket.close();
}
}
});
final Thread t2 = new Thread(new Runnable(){
@Override
public void run() {
try {
Thread.sleep(1000);
DatagramPacket packet = new DatagramPacket(new byte[1],1);
while(!cleanUp){
lock.lock();
try{
socket.receive(packet);
}catch(SocketTimeoutException e){
lock.unlock();
Thread.sleep(15);
continue;
}
lock.unlock();
final String s = tv.getText().toString()+"signal\n";
MainActivity.this.runOnUiThread(new Runnable(){
@Override
public void run() {
tv.setText(s);//tv is a TextView
}
});
Thread.sleep(10);
}
} catch (Exception e) {
e.printStackTrace();
}
finally{
if(socket!=null)
socket.close();
}
}
});
//start both threads
Here is the server-side implementation (Java):
//int static void main(String[] args):
final Thread t = new Thread(new Runnable(){
@Override
public void run() {
try {
DatagramPacket packet = new DatagramPacket(new byte[1],1, addr, port);
DatagramSocket socket = new DatagramSocket();
System.out.println("send");
while(true){
socket.send(packet);
Thread.sleep(500);
}
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
});
final Thread t2 = new Thread(new Runnable(){
@Override
public void run() {
try {
DatagramPacket packet = new DatagramPacket(new byte[1],1);
DatagramSocket socket = new DatagramSocket(45555);
socket.receive(packet);
addr = packet.getAddress(); //private static field InetAddress addr
port = packet.getPort();
System.out.println(addr+":"+ packet.getPort()); //field int port
t.start();
while(true){
socket.receive(packet);
System.out.println("idle");
}
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
});
t2.start();
Everything works when client and server are in the same private network. To imitate the public server I run the server-side code on my computer and set up a port on my router (which has a public ip)*. The clients will send its packets to the public ip of the router. But in both cases ( my smartphone is connected to internet via my wlan network / 3G or E) no signals are received (the server receives the datagrams of the client)
So why does the hole punching process not work?
regards
*: The router will forward any udp packets sent to its port 45555 to my computer
