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.

[Prajanya Shrestha]

Can I get the working code please.

[Matthew Bendford]

Prajanya Shrestha wrote:Can I get the working code please.

Aside from this forum doesn't work in this way I highly recommend against what was used back then. If you need to transfer data use proper protocols like http or ftp.

[Tim Moores]

Prajanya Shrestha wrote:Can I get the working code please.

That discussion happened 11 years ago; the participants are likely to have moved on long ago. But the code Rob Spoor posted should work; are you looking for something else?

Matthew Bendford wrote:If you need to transfer data use proper protocols like http or ftp.

There's a place in this world for socket communications where trying to fit it into HTTP doesn't necessarily make sense. And FTP should be taken out and shot :-)

[Prajanya Shrestha]

I need to send 3 different text files from server to client using socket. I tried the code but not working.
//Server Code

import java.io.*;  
import java.net.ServerSocket;
import java.net.Socket;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.security.*;  
public class GenerateDigitalSignature  
{  
    public static String sendFile = "C:\\Users\\Prajanya\\Documents\\NetBeansProjects\\Project\\src\\tpoint\\send.txt";
    public static String signFile = "C:\\Users\\Prajanya\\Documents\\NetBeansProjects\\Project\\src\\tpoint\\signature.txt";
    public static String pubkeyFile = "C:\\Users\\Prajanya\\Documents\\NetBeansProjects\\Project\\src\\tpoint\\publickey.txt";
    
    public static void main(String args[]) throws IOException, InterruptedException {
        generateDigitalSingature();
        ServerSocket servsock = new ServerSocket(55555);
        while (true) {
            System.out.println("Waiting...");
            Socket socket = servsock.accept();
            System.out.println("Accepted connection : " + socket);
            DataOutputStream dos = new DataOutputStream(socket.getOutputStream());
            
            File myFile = new File(sendFile);
            byte[] contents = new byte[(int) myFile.length()];
            FileInputStream fis1 = new FileInputStream(myFile);
            BufferedInputStream bis1 = new BufferedInputStream(fis1);
            bis1.read(contents,0,contents.length);
            byte[] nameInBytes = sendFile.getBytes("UTF-8");
            dos.writeInt(nameInBytes.length);
            dos.write(nameInBytes);
            dos.writeInt(contents.length);
            dos.write(contents);
            System.out.println(dos);
            dos.flush();         
            
            myFile = new File(signFile);
            contents = new byte[(int) myFile.length()];
            fis1 = new FileInputStream(myFile);
            bis1 = new BufferedInputStream(fis1);
            bis1.read(contents,0,contents.length);
            nameInBytes = sendFile.getBytes("UTF-8");
            dos.writeInt(nameInBytes.length);
            dos.write(nameInBytes);
            dos.writeInt(contents.length);
            dos.write(contents);
            dos.flush();  
            
            myFile = new File(pubkeyFile);
            contents = new byte[(int) myFile.length()];
            fis1 = new FileInputStream(myFile);
            bis1 = new BufferedInputStream(fis1);
            bis1.read(contents,0,contents.length);
            nameInBytes = sendFile.getBytes("UTF-8");
            dos.writeInt(nameInBytes.length);
            dos.write(nameInBytes);
            dos.writeInt(contents.length);
            dos.write(contents);
            dos.flush();  
        }
    }

    
    public static void generateDigitalSingature()
    {
        try  
        {  
            /* Generate a key pair */  
            KeyPairGenerator keyGen = KeyPairGenerator.getInstance("DSA", "SUN");  
            SecureRandom random = SecureRandom.getInstance("SHA1PRNG", "SUN");  
            keyGen.initialize(1024, random);  
            KeyPair pair = keyGen.generateKeyPair();  
            PrivateKey priv = pair.getPrivate();  
            PublicKey pub = pair.getPublic();  
        
            /* Create a Signature object and initialize it with the private key */  
            Signature dsa = Signature.getInstance("SHA1withDSA", "SUN");   
            dsa.initSign(priv);  
            /* Update and sign the data */  
            FileInputStream fis = new FileInputStream(sendFile);  
            BufferedInputStream bufin = new BufferedInputStream(fis);  
            byte[] buffer = new byte[1024];  
            int len;  
            while (bufin.available() != 0)   
            {  
            len = bufin.read(buffer);  
            dsa.update(buffer, 0, len);  
            }  
            bufin.close();  
            /* Now that all the data to be signed has been read in, generate a signature for it */  
            byte[] realSig = dsa.sign();  
            /* Save the signature in a file */  
            FileOutputStream sigfos = new FileOutputStream(signFile);  
            sigfos.write(realSig);  
            sigfos.close();  
            /* Save the public key in a file */  
            byte[] key = pub.getEncoded();  
            FileOutputStream keyfos = new FileOutputStream(pubkeyFile);  
            keyfos.write(key);  
            keyfos.close();                         
        }   
        catch (Exception e)   
        {  
            System.err.println("Caught exception " + e.toString());  
        }  
    }
}  

[Matthew Bendford]

Tim Moores wrote:

Matthew Bendford wrote:If you need to transfer data use proper protocols like http or ftp.

There's a place in this world for socket communications where trying to fit it into HTTP doesn't necessarily make sense. And FTP should be taken out and shot :-)

Well, implementing a whole http stack may be too much for some situations, I agree on that, and ftp has it's flaws (although it still can be set up in a rather secure way) but they are decades old protocols and both server and client implementation are available in many languages. Reinventing the wheel instead of using existing ones also requires some justification.

@OP
As I mentioned: Don't use that code this way - it has quite some flaws and many resource leaks. Also: Doing the same three times? Use a method.

[Prajanya Shrestha]

I just need to send 3 .txt files in same network using java.  I am able to send one file. But How to send 3 different files? I'm not able to understand code shown in this forum & is not working. Can some expert help me.