Question

I’m beginning client-server programming. what I’m trying to do is basically a Echo server but instead of return the same thing as the client inserted, I want the server to return 2*(The number I insert).

I have the following server:

public class Server {

public static void main(String args[]) throws Exception {
    ServerSocket server = new ServerSocket(6789);
    while(true) {
        try {
            Socket aux = server.accept();

            DataInputStream dis = new DataInputStream(aux.getInputStream());
            DataOutputStream dos = new DataOutputStream(aux.getOutputStream());
            int total = 0;
            while(dis != null) {
                int res = dis.read();
                total = 2*(res);
                dos.writeInt(total);
            }

        }
        catch (EOFException e) {
            out.println("The client exit!");
            continue;
        }
    }
}

}

And the following client:

public class Client {


public static void main(String args[]) throws Exception {


    Socket client = new Socket("localhost", 6789);
    DataInputStream dis = new DataInputStream(client.getInputStream());
    DataOutputStream dos = new DataOutputStream(client.getOutputStream());
    BufferedReader input = new BufferedReader(new InputStreamReader(in));       

    while(true) {
            int fromClient = input.read();
            dos.writeInt(fromClient);
            client.shutdownOutput(); //to show to the server the end of file
            int fromServer = dis.readInt();
            out.println(fromServer);
    }       
}       

}

Can somebody help please?

I got the following error on the server side:

Exception in thread "main" java.net.SocketException: Broken pipe
    at java.net.SocketOutputStream.socketWrite0(Native Method)
    at java.net.SocketOutputStream.socketWrite(SocketOutputStream.java:109)
    at java.net.SocketOutputStream.write(SocketOutputStream.java:132)
    at java.io.DataOutputStream.writeInt(DataOutputStream.java:197)
    at Server.main(Exercicio3.java:21)

And on the client side when I insert a value (in this case ‘1’):

1
0
Exception in thread "main" java.net.SocketException: Broken pipe
    at java.net.SocketOutputStream.socketWrite0(Native Method)
    at java.net.SocketOutputStream.socketWrite(SocketOutputStream.java:109)
    at java.net.SocketOutputStream.write(SocketOutputStream.java:132)
    at java.io.DataOutputStream.writeInt(DataOutputStream.java:197)
    at Client.main(Exercicio4.java:25)

Thanks

Answer 1

• There is an infinite loop before you send the result back to the
  client.

         while(dis != null) {
             int res = dis.read();
             total = 2*(res);
         }
         dos.writeInt(total);
  

  Move that last line inside the brackets and it should work.

         while(dis != null) {
             int res = dis.read();
             total = 2*(res);
             dos.writeInt(total);
         }
  

• Additionally, calling client.shutdownOutput() is not necessary. You
  will just get exceptions when you try to write to it the next time:

  Disables the output stream for this socket. For a TCP socket, any previously written data will be sent followed by TCP's normal
  

  connection termination sequence. If you write to a socket output
  stream after invoking shutdownOutput() on the socket, the stream will
  throw an IOException. `

• And then there is also the issue mentioned previously:

  int res = dis.read();
  

  should be

  int res = dis.readInt();
  

• You have a similar issue reading the user’s input in the client.
  Use this instead:

  int fromClient = Integer.parseInt(input.readLine());