File Transfer (Missing start of file)

Question

Hi there, I'm undertaking part of a software project at University and struggling to fix a piece of code myself and a friend have wrote after exhausing most of the good java programmers in our department.
We're simply trying to send files over a network via TCP, the main problem we're encountering is that if we send say a text file, a varying number of characters will appear missing. Normally we'll recieve between 300-400 of the 500 bytes we send for example, and these characters are always missing from the start of the file. Obviously this is the bit we need to fix, at the end we're aiming to be able to send media files (jpg, gif, txt, wav, avi) and hopefully objects aswell.
The way its intended to work at present is that the server sends file information to the client (filename and filesize), and then the client listens, and writes the same number of bytes as the filesize to the new file it creates (though I'm sure you'll work that out in seconds). The file has been read in, and wrote back on the server side just to ensure the reading/sending section was working which it was.
Server Side:
FileServer.java: import java.io.*;
import java.net.*;
public class FileServer
   private ServerSocket serverSocket = null;
   private Socket socket = null;     
   public String fileDir = "H:/JAVA/";
   public String fileName = "text.txt";
   public String filePath = fileDir + fileName;
   public PrintWriter log;
   public BufferedReader in;
   public PrintStream out;
   public FileServer() throws IOException
      try {
              serverSocket = new ServerSocket(1138);
              System.out.println("Server initialised and listening on port : 1138.");
      catch (IOException e){
         System.out.println("Could not listen on port : 1138");
      try {
         socket = serverSocket.accept();
         System.out.println("Client" + serverSocket.getInetAddress() + "connected.");
         in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
         out = new PrintStream(socket.getOutputStream(), true);
      catch (IOException e){
         System.out.println("Could not accept client.");
         System.exit(1);
     boolean done = false;
     while (!done)
        try{
           String line = in.readLine();               
           if (line == null)
              done = true;
          else
               if (!line.trim().equals("CLOSE"))               
                   if (line.trim().equals("SEND FILE"))
                       sendFile(filePath, socket);
               else
                   done = true;                         
            catch (IOException e) {
               System.out.println("Cannot read data from client");
               System.exit(1);
      socket.close();
public void sendFile( String filename, Socket socket )
   File file;     
   try{
         file= new File(filePath);
         int c =0;
         FileInputStream fis = new FileInputStream(file);
         out.println(fileName+":"+file.length());
         OutputStream os = socket.getOutputStream();
         int i = 0;
         while((c = fis.read()) != -1)
             i++;
            System.out.println(i +"  "+ c);
            os.write(c);
         System.out.println("File "+filePath+" sent:"+file.length());
         fis.close();
   catch( Exception e ) {
        System.out.println("sending file error");
        e.printStackTrace();
        System.exit(1);
public static void main (String [] args) throws IOException
   FileServer myFileServer = new FileServer();
Client Side:
Client.java: import java.net.*;
import java.io.*;
import java.lang.*;
import java.util.*;
public class Client
  private Socket clientSocket = null;
  public String filePath = "H:/java/Temp";
  PrintWriter out = null;
  BufferedReader in = null;
  String host = "144.32.152.154";
  int port = 1138;
  Integer fileSize;
  String filename;
  public Client() throws IOException {
    InputStream inputStream;
    try {
      clientSocket = new Socket(host, port);
    catch (IOException e) {
      System.out.println("Could not create connection");
      System.exit(1);
    out = new PrintWriter(clientSocket.getOutputStream(), true);
    inputStream = clientSocket.getInputStream();
    in = new BufferedReader(new InputStreamReader(inputStream));
    out.println("SEND FILE");
   String details;
   while((details = in.readLine()) != null)     
      System.out.println(details);
      StringTokenizer sToken = new StringTokenizer(details, ":");
      filename = sToken.nextToken();
      fileSize = Integer.valueOf((sToken.nextToken()));
      System.out.println(filename);
      System.out.println(fileSize);
      FileOutputStream file = new FileOutputStream(new File(filePath,filename));
         for (long i=0; i<fileSize.longValue(); i++)
            int c = inputStream.read();
            file.write(c);
            System.out.println(i);
            System.out.println(fileSize);
        System.out.println("Exited Loop");
        file.flush();
        file.close();
        clientSocket.close();
        System.out.println("The End");
        System.exit(-1);
  public static void main(String[] args) throws IOException
    Client myClient = new Client();
} I'd appreciate any help you can offer to fix the problem! Thanks
Ian Wright

Answer 1

OK. There were some mistakes in the code. Some made by me, some by you.
First of all: The byte array which acts as a buffer for reading the file content from the socket cannot have the size of the whole file. Normally it is suggested to set to 8-32kB.
Second thing: I was too fast in giving you the idea of reading the details only once to an array. Sometimes the Client program is faster than the FileServer and although the array has space for "nameLength" bytes it reads a lot less. That way the details aren't recieved properly. To solve this I've added a loop that waits for the inputStream to retrieve enought data.
Last but not least: I've been told that it is not wise to close the socket at the server side. If you close the socket the OutputStream is cut off without a warning. Close the OutputStream instead.
I remember that you asked me to reply via e-mail but I think that posting the solution here will be more usfull to others. Here's the code:
Client3.java
import java.net.*;
import java.io.*;
import java.util.*;
public class Client3
  private Socket clientSocket = null;
  OutputStream out;
  public String filePath = "E:/";
  String host = "127.0.0.1";
  int port = 1138;
  Integer fileSize;
  String filename;
  static final byte SEND = 1;
  static final byte DONE = 2;
  static final byte ERROR = 0;
  public Client3()throws IOException{
    DataInputStream inputStream;
    System.out.println("Hello");
    try {
      clientSocket = new Socket(host, port);
    catch (IOException e) {
      System.out.println("Could not create connection");
      System.exit(1);
    out = clientSocket.getOutputStream();
    inputStream = new DataInputStream(clientSocket.getInputStream());
    out.write(SEND);
     byte nameLength = (byte)inputStream.read();
     byte[] nameArray = new byte[nameLength];
     while (inputStream.available()<nameLength) // we have to wait for the details to arrive :]
          try {
               Thread.sleep(10);
          } catch (InterruptedException e) {
               System.out.println("Client impatient ... couldn't wait");
          inputStream.read(nameArray);
     String details = new String(nameArray);
     StringTokenizer sToken = new StringTokenizer(details, ":");
    filename = sToken.nextToken();
    fileSize = Integer.valueOf((sToken.nextToken()));
     System.out.println(filename+":"+fileSize);
      FileOutputStream file = new FileOutputStream(new File(filePath,filename));
               while (true) { // now read the file one piece after a nother :P
                    byte[] fileBuffer = new byte[8*1024];
                    int cnt = 0;
                    cnt = inputStream.read(fileBuffer);
                    if (cnt==-1) break;
                    file.write(fileBuffer,0,cnt);
      file.flush();
      file.close();
      out.close(); // T100 would say: Hasta la vista ... baby!
      System.out.println("The End");
      System.exit(-1);
  public static void main(String[] args) throws IOException{
       Client3 client = new Client3();
FileServer3.java
import java.io.*;
import java.net.*;
public class FileServer3 {
   private ServerSocket serverSocket = null;
   private Socket socket = null;     
   public String fileDir = "";
   public String fileName = "image.bmp";
   public String filePath = fileDir + fileName;
   public PrintWriter log;
   public InputStream in;
   public DataOutputStream out;
   static final byte SEND = 1;
   static final byte DONE = 2;
   static final byte ERROR = 0;
   public FileServer3() throws IOException
      try {
              serverSocket = new ServerSocket(1138);
              System.out.println("Server initialised and listening on port : 1138.");
      catch (IOException e){
         System.out.println("Could not listen on port : 1138");
    while(true){
      try {
         socket = serverSocket.accept();
         System.out.println("Client" + serverSocket.getInetAddress() + "connected.");
         in = socket.getInputStream();
         out = new DataOutputStream(socket.getOutputStream());
      catch (IOException e){
         System.out.println("Could not accept client.");
         System.exit(1);
      try{
           byte b =(byte)in.read();
          if (b == SEND)               
                       sendFile(filePath, out);
       catch (IOException e) {
               System.out.println("Cannot read data from client");
               System.exit(1);
public void sendFile( String filePath, DataOutputStream out ) {
     File file;
   try{
     file = new File(filePath);
         FileInputStream fis = new FileInputStream(file);
     String details = fileName+":"+Long.toString(file.length());
     System.out.println((byte)details.length()+": "+details);
     out.write((byte)details.length());
     out.writeBytes(details);
     System.out.println("File details sent");
     while (true) { // Momma always said to bite before swallowing :D
          byte[] byteArray = new byte[8*1024];
          int cnt = fis.read(byteArray);
          if (cnt == -1) break;
          out.write(byteArray,0,cnt);
         System.out.println("File "+filePath+" sent:"+file.length());
         out.close(); // Say goodbye and the door will close by it self %)
   catch( Exception e ) {
        System.out.println("sending file error");
        e.printStackTrace();
        System.exit(1);
  public static void main (String [] args) throws IOException {
     FileServer3 myFileServer = new FileServer3();
}I hope this will help you out. If there are any other errors that I've missed than point them out to me and I'll se what can be done later. I have a cake in the oven and don't have enough time right now :].
...:: byElwiZ ::...