How does this relate to what the OP is asking? Your code still relies to the client knowing the servers IP address and won't help him solve his problem. Which (if you read the thread) he did anyway, almost 12 hours before you posted your node, so what's the point? Also:

UDP requires root privileges, IIRC

Err, no. Stick to port numbers <1024 >1024 and you can send/receive UDP just fine as an unprivileged user.