How to relay NAT dynamic port numbers if the server receives 0 as port no?

I'm trying to implement udp punch holing through a Java servlet. However when I use req.getRemotePort() I always get 0 (i.e. dynamic). That's doesn't help. Any way around that? Alternative solutions?

http://sss.mysimpatico.com/server?authentication=unregistered

The code that prints the first 0 and the one attached to the ip:

final int port = req.getRemotePort();
pw.println(port);
final String ip = req.getRemoteAddr() + ":" + port;

Th开发者_如何学Cere is a GAE issue (please star it if you are interested): http://code.google.com/p/googleappengine/issues/detail?id=4210

Your question is tagged as google-app-engine; Google App Engine uses HTTP (see the sandbox section), HTTP uses TCP not UDP.