title: Detect closed client UDP channel in Netty 4
body: <p>I'm using Netty as part of a UDP server which opens a number of persistent connections with various clients on a single server channel. I need to perform some cleanup when a client terminates the connection. Specifically, I need to know when the connection is terminated and from which IP address the terminating client is located at so that I can cleanup the data.</p>
  
  <p>Perhaps I'm misunderstanding the Netty model, but I'm unsure how to detect this. I normally distinguish between various clients by checking the sender's IP address from the <code>DatagramPacket</code> instances, perhaps that is wrong and I should be using multiple channels or something like that? Either way, I'm looking for some way to handle a closed connection.</p>