Transfer multiple files from Server to Client using Sockets

[Nathan Heimdall]

Hello all,

A project that I'm working on needs to pass 3 text files from the Server to the Client.
This what I'm doing
Server side :Wait for client, once connected to client pick up the files and transmit it to the client one after another.
Client side :Connect to server and accept the files one after an other.

I'm only able to receive the first txt file after which I'm getting an ArrayIndexOutOfBoundsException.
In debug mode I noticed that no data is being read on the second read segment on the client side.

Here is a segment of the server side code:

   // create socket
		  ServerSocket servsock = new ServerSocket(13267);
		  while (true) 
		  {
		  System.out.println("Waiting...");
		  Socket sock = servsock.accept();
		  System.out.println("Accepted connection : " + sock);
          // sendfile 1
		  File myFile = new File (file);
		  byte [] mybytearray  = new byte [(int)myFile.length()];
		  FileInputStream fis1 = new FileInputStream(myFile);
		  BufferedInputStream bis1 = new BufferedInputStream(fis1);
		  bis1.read(mybytearray,0,mybytearray.length);
		  OutputStream os = sock.getOutputStream();
		  
		  System.out.println("Sending...");
		  os.write(mybytearray,0,mybytearray.length);
		  
		  os.flush();
		  Thread.sleep(1000);
		  
		// sendfile 2
		  myFile = new File (sign);
		  mybytearray  = new byte [(int)myFile.length()];
		  fis1 = new FileInputStream(myFile);
		  bis1 = new BufferedInputStream(fis1);
		  bis1.read(mybytearray,0,mybytearray.length);
		  os = sock.getOutputStream();
		  System.out.println("Sending...");
		  os.write(mybytearray,0,mybytearray.length);
		  os.flush();
		  Thread.sleep(1000);
		  
		// sendfile 3
		  myFile = new File (key);
		  mybytearray  = new byte [(int)myFile.length()];
		  fis1 = new FileInputStream(myFile);
		  bis1 = new BufferedInputStream(fis1);
		  bis1.read(mybytearray,0,mybytearray.length);
		  os = sock.getOutputStream();
		  System.out.println("Sending...");
		  os.write(mybytearray,0,mybytearray.length);
		  os.flush();
		  sock.close();

This is the client side code :

    
Socket sock = new Socket("127.0.0.1",13267);
    System.out.println("Connecting...");

    // receive file
    byte [] mybytearray  = new byte [filesize];
    InputStream is = sock.getInputStream();
    FileOutputStream fos = new FileOutputStream("file2.txt");
    BufferedOutputStream bos = new BufferedOutputStream(fos);
    bytesRead = is.read(mybytearray,0,mybytearray.length);
    current = bytesRead;

  
    do {
       bytesRead =
          is.read(mybytearray, current, (mybytearray.length-current));
       if(bytesRead >= 0) current += bytesRead;
    } while(bytesRead > -1);

    bos.write(mybytearray, 0 , current);
    bos.flush();
    long end = System.currentTimeMillis();
    System.out.println(end-start);
    bos.close();
    
    //file 2
    mybytearray  = new byte [filesize];
    is = sock.getInputStream();
    fos = new FileOutputStream("sign2.txt");
    bos = new BufferedOutputStream(fos);
    bytesRead = is.read(mybytearray,0,mybytearray.length);
    current = bytesRead;

    do {
       bytesRead =
          is.read(mybytearray, current, (mybytearray.length-current));
       if(bytesRead >= 0) current += bytesRead;
    } while(bytesRead > -1);

    bos.write(mybytearray, 0 , current);
    bos.flush();
    end = System.currentTimeMillis();
    System.out.println(end-start);
    bos.close();
    
  //file 3
    mybytearray  = new byte [filesize];
    is = sock.getInputStream();
    fos = new FileOutputStream("key2.txt");
    bos = new BufferedOutputStream(fos);
    bytesRead = is.read(mybytearray,0,mybytearray.length);
    current = bytesRead;

    do {
       bytesRead =
          is.read(mybytearray, current, (mybytearray.length-current));
       if(bytesRead >= 0) current += bytesRead;
    } while(bytesRead > -1);

    bos.write(mybytearray, 0 , current);
    bos.flush();
    end = System.currentTimeMillis();
    System.out.println(end-start);
    bos.close();
    
    sock.close();
 

Any help on how to synchronize the file sending so the client reads all three files is much appreciated

[Paul Clapham]

I don't see in your code how the receiver is supposed to tell where one file ends and the next one starts. It has this mysterious "filesize" variable which I don't see where that comes from or what it's set to. Do you only ever plan to send files of that size and no other size?

[Nathan Heimdall]

Mr.Clapman,

That is the problem I'm having, I don't know how to inform the receiver that the first file has ended and the second has started.
How can put such a system of notification into place?
Also I don't plan to fix the size of the files as all three files are of different sizes

[Rob Spoor]

Your protocol needs to be redesigned so it knows when a new portion is read. An example of what could be sent:
- an int indicating the name's length when converted to byte[] using a fixed charset (e.g. UTF-8)
- the file name as a byte[] using that charset
- an int indicating the file size
- the file in bytes.

In short, the sending code:

// String name and byte[] contents are already available
DataOutputStream dos = new DataOutputStream(socket.getOutputStream());
byte[] nameInBytes = name.getBytes("UTF-8");
dos.writeInt(nameInBytes.length);
dos.write(nameInBytes);
dos.writeInt(contents.length);
dos.write(contents);
dos.flush();

The receiving code:

DataInputStream dis = new DataInputStream(socket.getInputStream());
int size = dis.readInt();
byte[] nameInBytes = new byte[size];
dis.readFully(nameInBytes);
String name = new String(nameInBytes, "UTF-8");
size = dis.readInt();
byte[] contents = new byte[size];
dis.readFully(contents);

[Nathan Heimdall]

Thanks Mr.Prime,
I changed it and it worked perfectly

[Rob Spoor]

You're welcome.