Sending files with Mulicast sockets

Question

Hi,
I'm trying to write a multicast sender/receiver applications for windows.
The problem I'm having is that the receiver create bigger file than the source (double or bigger).
Chcking with debugger the sender does not send the file more than one time & file length is measured correctly.
What am I doing wrong? Is Java multicast reliable on windows?
Please see below my code and comment.
Thanks,
Alonex
/* Multicast sender */
import java.io.*;
import java.net.*;
public class Outcoming extends Thread
     int port;     //4446     
     String multicastServer="230.0.0.1";     
     MulticastSocket out;
     byte[] outBuffer;
     String username;
     String msg;
     DatagramPacket dp;
     InetAddress multicastserverIP;
     static boolean done = false;
     public Outcoming() throws IOException, UnknownHostException
          port=4446;
          username="kostas";
          out=new MulticastSocket(4446);
          out.setTimeToLive(10);
//          out.joinGroup(InetAddress.getByName(multicastServer));          
     }/////////////////////Outcoming     
     public void run()
          while (!done)
          try {
               multicastserverIP=InetAddress.getByName("230.0.0.1");
          catch (UnknownHostException e)     
               System.out.println("Cannot resolve ip address");
          try {
               System.out.println("ttl"+out.getTimeToLive());
               out.joinGroup(multicastserverIP);
          catch (IOException e)
               System.out.println("Failed to join group");
          boolean readMore=true;
          String line="";     
          createAndSendPacket(line);
          while (readMore)
               System.out.print(">"); 
               BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
               try     {
                    line=br.readLine().trim();
               catch (IOException e)     {
                    e.printStackTrace();
               if (line.equalsIgnoreCase("quit"))     
                    readMore=false;
               createAndSendPacket(line);
//     }/////////////////////run
//     Returns the contents of the file in a byte array.
      public static byte[] getBytesFromFile(File file) throws IOException {
           InputStream is = new FileInputStream(file);
           // Get the size of the file
           long length = file.length();
           // You cannot create an array using a long type.
           // It needs to be an int type.
           // Before converting to an int type, check
           // to ensure that file is not larger than Integer.MAX_VALUE.
           if (length > Integer.MAX_VALUE) {
                // File is too large
           // Create the byte array to hold the data
           byte[] bytes = new byte[(int)length];
           // Read in the bytes
           int offset = 0;
           int numRead = 0;
           while (offset < bytes.length
                    && (numRead=is.read(bytes, offset, bytes.length-offset)) >= 0) {
                offset += numRead;
           // Ensure all the bytes have been read in
           if (offset < bytes.length) {
                throw new IOException("Could not completely read file "+file.getName());
           // Close the input stream and return bytes
           is.close();
           return bytes;
     private void createAndSendPacket(String msg)
          int i,j=0,s=1;
         byte[] buf1=new byte[64000];
          try     {
               msg=username+"#!#"+msg;
//               byte[] buf=msg.getBytes();
               File fileTest = new File("c:\\test.exe");
               byte[] buf=getBytesFromFile(fileTest);
               int size = 64000;
               while (j<buf.length)
                    if ((s*64000)>buf.length)
                         size = buf.length-((s-1)*64000);
                         buf1 = new byte[size];
                         done=true;
               for (i=0;i<size;i++,j++) //buf.length;i++)
                    if (j==1822845)
                         System.out.println("here");
                    buf1=buf[j];
               if (i==size)
                    dp=new DatagramPacket(buf1, buf1.length,multicastserverIP , port);
                    out.send(dp);
                    try
                    Thread.sleep(3000);
                    catch (InterruptedException ie){}
                    System.err.println("Packet sent");
                    s++;
          catch (UnknownHostException e)
               System.out.println("createAndSendPacket: UnknownHostException");
          catch (IOException e)
               System.out.println("createAndSendPacket: IOException "+e.toString());
     }/////////////////////createAndSendPacket
     public static void main(String[] args) throws IOException, UnknownHostException
          new Outcoming().run();
/* Multicast Receiver */
import java.io.*;
import java.net.*;
public class Incoming extends Thread
     int port;     //4446     
     String multicastServer="230.0.0.1";
     MulticastSocket in;
     byte[] inBuffer;
     String username;
     String msg;
     InetAddress multicastserverIP;
     public Incoming()
          port=4446;
          msg="";
          try {
               in=new MulticastSocket(port);
               in.setTimeToLive(10);
          catch (IOException e)
               System.out.println("Failed to create multicast socket");
     public void run()
          try {
               multicastserverIP=InetAddress.getByName(multicastServer);
          catch (UnknownHostException e)     
          try {
               in.joinGroup(multicastserverIP);
          catch (IOException e)
               System.out.println("Failed to join group");
          while (!msg.trim().equalsIgnoreCase("quit"))
               readSocket();
               writeFromBuffer();
     private void readSocket()
          inBuffer=new byte[64000];
          DatagramPacket rcv=new DatagramPacket(inBuffer, inBuffer.length, multicastserverIP , port);
          try     {
               in.receive(rcv);
          catch(IOException e)
               System.err.println("Failed to receive incoming message");
     private void writeFromBuffer()
          try
          FileOutputStream fos = new FileOutputStream(new File("c:\\temp.exe"),true);
          fos.write(inBuffer);
          fos.close();
          catch(IOException ie){};
     public static void main(String[] args) throws IOException, UnknownHostException
          new Incoming().run();

Answer 1

(a) Multicast isn't reliable on any platform. Datagrams may be lost, duplicated, or delivered out of order, and datagrams greater than 534 bytes are unlikely to get though routers at all even if multicasts do.
(b) Why are you joining the multicast group every time around the loop?
(c) You are ignoring the actual length of the received datagram, just assuming it is 64000.
(d) In fact you are also ignoring exceptions when reading and still writing out 64000 bytes even if nothing was read at all.
All in all you need to rethink this.