MulticastUdpChatKeyboardSender.java

package UdpExamples;

import static UdpExamples.MulticastUdpReceiver.BUFFER_LENGTH;
import edu.nps.moves.dis7.utilities.DisThreadedNetworkInterface;
import java.io.*;
import java.net.*;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * Get keyboard input to send string packets on a UDP multicast group.
 * The source looks a lot like MulticastUdpSender.  
 * TODO: Start this after launching MulticastUdpReceiver.
 * Multicast must be enabled for the (wired or wireless) LAN that the system is connected too.
 * Note that these paired programs can communicate within a remote LAN (such as a wireless 
 * home network) even if one or both machines are connected via a 
 * <a href="https://en.wikipedia.org/wiki/Virtual_private_network" target="_blank">Virtual Private Network (VPN)</a>.
 * 
 * Privacy note: this sender advertises your user name as part of the multicast packet message
 * 
 * @author mcgredo
 * @author brutzman@nps.edu
 */
public class MulticastUdpChatKeyboardSender
{
    /** Default constructor */
    public MulticastUdpChatKeyboardSender()
    {
        // default constructor
    }
    // reserved range for all IPv4 multicast: 224.0.0.0 through 239.255.255.255
    // https://www.iana.org/assignments/multicast-addresses/multicast-addresses.xhtml

    /** Default multicast group address for send and receive connections.
     * @see <a href="https://en.wikipedia.org/wiki/Multicast_address" target="_blank">https://en.wikipedia.org/wiki/Multicast_address</a> */
    public static final String MULTICAST_ADDRESS = "239.1.2.15"; // within reserved multicast address range
    /** Default socket port used, matches Wireshark DIS capture default
     * @see <a href="https://en.wikipedia.org/wiki/Port_(computer_networking)" target="_blank">https://en.wikipedia.org/wiki/Port_(computer_networking)</a> */
    public static final int     DESTINATION_PORT = 1718;
    
    /** Time to live: how many router-decrement levels can be crossed */
    public static final int TTL = 10;
	
    /** How many packets to send prior to termination */
    public static final int MAXLOOPSIZE = 100; // or maybe 20000
	
    /** How many packets to send prior to termination */
    public static final String LINE_TERMINATOR = "###;"; // do not begin with ;
    
    /** Receiving this message causes termination
     * @see <a href="https://en.wikipedia.org/wiki/Sentinel_value" target="_blank">https://en.wikipedia.org/wiki/Sentinel_value</a> */
    public static final String QUIT_SENTINEL = "QUIT QUIT QUIT!";
    private static NetworkInterface ni;
    
    /**
     * Program invocation, execution starts here.
     * TODO:  allow setting address/port group and provide help message.
     * @param args command-line arguments
     * @throws java.io.IOException execution error
     */
    @SuppressWarnings("SleepWhileInLoop")
    public static void main(String[] args) throws IOException 
    {
        MulticastSocket multicastSocket = null;
        InetSocketAddress group = null;
        
        // Put together a message with binary content. "ByteArrayOutputStream"
        // is a java.io utility that lets us put together an array of binary
        // data, which we put into the UDP packet.
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        DataOutputStream       dos = new DataOutputStream(baos);
        
        try
        {
            System.out.println("UdpExamples.MulticastUdpChatKeyboardSender started...");
            // https://stackoverflow.com/questions/18747134/getting-cant-assign-requested-address-java-net-socketexception-using-ehcache
            System.setProperty("java.net.preferIPv4Stack", "true");
            
            // multicast group we are sending to--not a single host
            multicastSocket = new MulticastSocket(/*DESTINATION_PORT*/);
            multicastSocket.setTimeToLive(TTL); // time to live reduces scope of transmission
            InetAddress multicastAddress = InetAddress.getByName(MULTICAST_ADDRESS);
            System.out.println("Multicast address/port: " + multicastAddress.getHostAddress() + "/" + DESTINATION_PORT);
            
            group = new InetSocketAddress(multicastAddress, DESTINATION_PORT);
            // Join group useful on receiving side
            multicastSocket.joinGroup(group, ni = DisThreadedNetworkInterface.findIpv4Interface());
            // You can join multiple groups here
            
            byte[] buffer = baos.toByteArray();
            DatagramPacket packet = new DatagramPacket(buffer, buffer.length, group/*, DESTINATION_PORT*/);
            
            String   userName = System.getProperty("user.name");
            String newMessage = new String(); // from user via keyboard
            
            for (int messageIndex = 1; messageIndex < MAXLOOPSIZE; messageIndex++)
            {
                String spacer = new String(); // align console outputs
                if (messageIndex < 10)
                    spacer = " ";
                
                // Put together an updated packet to send
                if (messageIndex < MAXLOOPSIZE)
                {
                    System.out.print ("type new message here:  ");
                    newMessage = System.console().readLine(); // this line blocks, awaiting keyboard input from user
//                  System.out.println ("[trace] console return: " + newMessage);

                    // avoid overrunning receive buffer
                    int maxStringLength = BUFFER_LENGTH - LINE_TERMINATOR.length() - userName.length() - 5;
                    if (newMessage.length() > maxStringLength)
                        newMessage = newMessage.substring(0, maxStringLength);
                      
                    // Put together an updated packet to send
                    dos.writeChars("[" + userName + " " + spacer + messageIndex + "] ");
                    dos.writeChars(newMessage + LINE_TERMINATOR); // string chars for readability, include ; semicolon as termination sentinel
                }
                else dos.writeChars(QUIT_SENTINEL + LINE_TERMINATOR); // note string must include ; semicolon as termination sentinel
                
                buffer = baos.toByteArray();
                packet.setData(buffer);
                multicastSocket.send(packet);
                System.out.print  ("Sent packet " + spacer + (messageIndex) + " of " + MAXLOOPSIZE + ": ");
                System.out.println("\"" + newMessage + "\"");
                baos.reset();

                // How fast does this go? Does UDP try to slow it down, or does
                // this cause network problems? (hint: yes for an unlimited send
                // rate, unlike TCP). How do you know on the receiving side
                // that you haven't received a duplicate UDP packet, out of
                // order packet, or dropped packet?  Necessary considerations.
                Thread.sleep(1000); // only send one per second
            }
            System.out.println("MulticastSender complete.");
        }
        catch(IOException | InterruptedException e)
        {
            System.err.println("Problem with MulticastSender, see exception trace:");
            System.err.println(e);
        } finally {
            
            if (multicastSocket != null && !multicastSocket.isClosed()) {
                try {
                    multicastSocket.leaveGroup(group, ni);
                } catch (IOException ex) {
                    Logger.getLogger(MulticastUdpChatKeyboardSender.class.getName()).log(Level.SEVERE, null, ex);
                }
                multicastSocket.close();
            }
            
            dos.close();
        }
    }
    
}