Is it possible to decode bytes on a server which were sent from a client as a byte array?

Question

I'm just trying to test sending bytes over a TCP socket connection, I know it wasn't really meant for that but I'm just trying to figure out whether this is possible or not

what i'm trying to do:

• get bytes from a string on client

• sent it as bytes to the server

• get the bytes on the server and decode it back to the original string

Client:

package ByteClientServer;

import java.io.DataOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.*;

public class Client {


    String hostAddress = "localhost";
    int port = 1010;


    public Client()
    {
        try {

            Socket socket = new Socket(hostAddress, port);

            String test = "hello"; //dycrypt bytes from this string on server side

            byte[] byteArray = test.getBytes();

            OutputStream out = socket.getOutputStream(); 
            DataOutputStream dos = new DataOutputStream(out);

            dos.write(byteArray);

        } 
        catch (UnknownHostException e) 
        {
            e.printStackTrace();
        } 
        catch (IOException e) 
        {
            e.printStackTrace();
        }
    }


    public static void main(String[] args)
    {
        new Client();
    }




}

Server:

package ByteClientServer;

import java.io.*;
import java.net.*;


public class Server {

    public static void main(String[] args) 
    {
        try
        {                       
            ServerSocket server = new ServerSocket(1010);
            server.setSoTimeout(0);

            Socket connectionToClient = server.accept();
            InputStream is = connectionToClient.getInputStream();
            DataInputStream dis = new DataInputStream(is);


            byte[] data = dis.readUTF().getBytes();

            //dis.readFully(data, 0, data.length);

            String s = new String(data);

            System.out.println(s);


        }
        catch(IOException e)
        {
            e.printStackTrace();
            //System.err.println("Server was terminated.");
        }
    }
}

it doesn't like this line on server:

byte[] data = dis.readUTF().getBytes();

and throws the exception:

java.net.SocketException: Connection reset at java.net.SocketInputStream.read(Unknown Source) at java.net.SocketInputStream.read(Unknown Source) at java.io.DataInputStream.readFully(Unknown Source) at java.io.DataInputStream.readUTF(Unknown Source) at java.io.DataInputStream.readUTF(Unknown Source) at ByteClientServer.Server.main(Server.java:21)

Answer 1

I came up with a simple workaround

Client:

import java.io.*;
import java.net.*;

public class Client {


    public static void main(String[] args)
    {

        String hostAddress = "localhost";
        int port = 8080;

        Socket socket = null;


        String test = "hello"; //decode bytes from this string on the server

        byte[] byteArray = test.getBytes();


        try 
        {
            socket = new Socket(hostAddress, port);
            OutputStream out = socket.getOutputStream();
            DataOutputStream dos = new DataOutputStream(out);

            dos.write(byteArray, 0, byteArray.length);
        } 
        catch (IOException e) 
        {
            e.printStackTrace();
        } 
    }
}

Server:

import java.io.*;
import java.net.*;


public class Server {

    public static void main(String[] args) throws SocketException 
    {
        try
        {                       
            ServerSocket server = new ServerSocket(8080);
            server.setSoTimeout(0);

            Socket connectionToClient = server.accept();
            InputStream is = connectionToClient.getInputStream();
            DataInputStream dis = new DataInputStream(is);

            int buffersize = connectionToClient.getReceiveBufferSize();

            byte[] bytes = new byte[buffersize];


            if(dis.read(bytes) > 0)
            {
                String s = new String(bytes);
                System.out.print(s);
            }   


            dis.close();
            server.close();
        }
        catch(IOException e)
        {       
            e.printStackTrace();
            System.err.println("Server was terminated.");
        }
    }
}

Answer 2

If you want to use readUTF then you need to use writeUTF. if you want to just write bytes, then you need to read just bytes.

Answer 3

You are writing bytes with default encoding then reading it as UTF-8 encoding. Thats the issue. Here is John Skeets blog explaining how to debug these errors and some pitfalls