BroadcastListenerRunnable.java

package com.door43.translationstudio.network;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetSocketAddress;
import java.net.SocketException;
import java.nio.channels.DatagramChannel;

/**
 * This class listens for broadcast messages from servers.
 */
public class BroadcastListenerRunnable implements Runnable {
    private final int mPort;
    private final OnBroadcastListenerEventListener mListener;
    private DatagramSocket mSocket;

    /**
     * Creates a new runnable that listens for UDB broadcasts
     * @param port the port on which the client will listen
     */
    public BroadcastListenerRunnable(int port, OnBroadcastListenerEventListener listener) {
        mPort = port;
        mListener = listener;
    }

    @Override
    public void run() {
        // set up the socket for listening
        DatagramChannel channel;
        try {
            channel = DatagramChannel.open();
        } catch (IOException e) {
            mListener.onError(e);
            return;
        }
        mSocket = channel.socket();
        // TRICKY: we set the address to reusable so we don't get port binding errors when turning the client on and off.
        try {
            mSocket.setReuseAddress(true);
        } catch (SocketException e) {
            mListener.onError(e);
            return;
        }
        InetSocketAddress socketAddress = new InetSocketAddress(mPort);
        try {
            mSocket.bind(socketAddress);
        } catch (SocketException e) {
            mListener.onError(e);
            return;
        }

        // begin listening
        try {
            while (!Thread.currentThread().isInterrupted()) {
                // TODO: it's not really safe to hard code the byte size.
                byte[] recvBuf = new byte[1024];
                if (mSocket == null || mSocket.isClosed()) {
                    mSocket = new DatagramSocket(mPort);
                }
                DatagramPacket packet = new DatagramPacket(recvBuf, recvBuf.length);

                // receive broadcast message
                mSocket.receive(packet);
                String senderIP = packet.getAddress().getHostAddress();
                String message = new String(packet.getData()).trim();

                // notify listener of broadcast message
                mListener.onMessageReceived(message, senderIP);
            }
        } catch (Exception e) {
            mListener.onError(e);
        } finally {
            mSocket.close();
        }
    }

    public void stop() {
        if(mSocket != null) {
            mSocket.close();
        }
    }

    /**
     * An interface to handle events from the broadcast listener
     */
    public interface OnBroadcastListenerEventListener {
        void onError(Exception e);
        void onMessageReceived(String message, String senderIP);
    }
}