Socket does not send data in while loop

Question

I'm trying to do make simple network communication where a client sends a user input string to the server, which server then displays to the console. When I send only one string, it works fine, but as soon as I wrap my user input code and send code in a while loop, the server receives nothing.

SERVER :

        ServerSocket serverSocket = null;
        try {
            serverSocket = new ServerSocket(PORT);
            System.out.println("Server now hosted on port " + PORT);
            Socket s = serverSocket.accept();
            System.out.println("A client has connected !");

            BufferedInputStream bis = new BufferedInputStream(s.getInputStream());
            BufferedOutputStream bos = new BufferedOutputStream(s.getOutputStream());

            while(true){            
                //RECEIVE
                int data;
                String inString = "";
                while((data=bis.read()) != -1){
                    inString += (char)data;
                }
                System.out.println("SLAVE : " + inString);              
            }
        } catch (IOException e) {
            // TODO Auto-generated catch block
            System.out.println("Port déjà utilisé");
        }finally {
            try {
                serverSocket.close();
                System.out.println("Server closed");
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
                System.out.println("Could not close port " + PORT);
            }
        }

CLIENT :

Scanner sc = new Scanner(System.in);
        Socket s = null;

        try {
            s = new Socket("127.0.0.1", PORT);

            BufferedInputStream bis = new BufferedInputStream(s.getInputStream());
            BufferedOutputStream bos = new BufferedOutputStream(s.getOutputStream());

            System.out.println("Connexion established !");
            while(true){ // without this while loop, it works fine
                String send = "";
                System.out.print(">> ");
                send = sc.nextLine();
                bos.write(send.getBytes());
                bos.flush();
            }

        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            System.out.println("Could not connect");;
        }
        finally {
            try {
                s.close();
                System.out.println("Closing socket");
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
                System.out.println("Could not close connection");;
            }
        }
        System.out.println("End of client");
    }

I expected the server to write any data it's reading from the socket as it's comming. But it just does nothing. I'm not quiet sure is the problem is comming from the server or the client.

Get rid of the outer while (true) loop. It serves no purpose. Once you've read -1 from the input stream, that's it, there will never be any more input. — user207421
– user207421, Commented Apr 24, 2019 at 6:42

Scary Wombat · Accepted Answer · 2019-04-24 06:46:41Z

3

The problem is with your while((data=bis.read()) != -1){ code.

It is looping until the EOS is received -1

When you don't have a client loop your Stream is closed, allowing the -1 to be sent, but not when you have a loop. Try printing with the server loop as below

while((data=bis.read()) != -1){
   inString += (char)data;

   if (((char)data) == '\n') {
       System.out.println("SLAVE : " + inString);   
       inString = "";
   }
}

edited Apr 24, 2019 at 6:46

answered Apr 24, 2019 at 6:36

Scary Wombat

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3 Comments

user207421 Over a year ago

I can't make any sense of your first or second paragraphs.

Alexandre Ringot Over a year ago

Yep, that works. (Well, now I have to add the '\n' when building the input string for some reasons. I thought sc.nextLine() already did that.) But I understand why my initial attempt didn't work. I should look into file input/output. I've never taken the time to do that. Thank you very much.

Scary Wombat Over a year ago

nextLine will strip off the CRLF

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