SocketChannel Client-Server

Question

The client connects to the server and then enters the following loop. It takes one line of input from the console, sends it to the server. If the input line is a single ‘x’ character, the client exits.

The server

At first, it prints out its own socket address to the screen. When it receives a connection, it prints the peer’s socket address to the screen (so you can check who connected to the server), then enters the following loop. It receives a line of message from the client, prints the received message to the screen.

Non-blocking mode

The client should use buffers and a non-blocking socket channel.

Blocking mode

The server should use buffers and a blocking socket channel.

The issue

The issue that I am having is that the buffer, in the server side, is not flushing and is printing the old input with the new input. Example:

Message received: hello

Message received: helloworld

Message received: helloworldthis

Message received: helloworldthisis

Message received: helloworldthisis Edwin

And it should be printing: hello

world

this

is

Edwin.

This is the server soure code:

public class EchoServer_1 
{
    //  private static CharBuffer buffer = CharBuffer.allocate(1024);
    private static ByteBuffer buffer = ByteBuffer.allocate(1024);
    private static StringBuffer reqString = new StringBuffer();
    public static void main(String[] args) throws IOException
    {

        ServerSocketChannel serverSocketChannel = null;
        int serverPort = 10007;

        try{
            serverSocketChannel = ServerSocketChannel.open();
            serverSocketChannel.socket().bind(new InetSocketAddress (serverPort));
            //Blocking mode
            serverSocketChannel.configureBlocking(true);

            System.out.println("Port number: " + serverPort);
            System.out.println("Waiting for connection ..");

            SocketChannel sc = serverSocketChannel.accept();

            System.out.println ("Incoming connection from: " 
                    + sc.socket().getRemoteSocketAddress( ));

            // Read message from client
            while (true)
            {   
                buffer.clear();
                sc.read(buffer);
                buffer.flip();
                while(buffer.hasRemaining()) {
                    char c = (char) buffer.get();
                    if (c == '\r' || c == '\n') break;
                    reqString.append(c);             
                }

                log("Message received: " + reqString);

            }
        }catch (IOException ex)
        {
            if (serverSocketChannel != null)
                serverSocketChannel.close();
            System.err.println("Client has disconneted");
        }
    }
    private static void log(String str) {
        System.out.println(str);
    }
}

This is the client source code:

public class EchoClient_1 
{

    private static Scanner stdIn = new Scanner(System.in);
    //  private static CharBuffer buffer = CharBuffer.allocate(1024);
    private static ByteBuffer buffer = ByteBuffer.allocate(256);

    public static void main(String[] args) throws IOException
    {
        String hostname = new String ("127.0.0.1");
        int port = 10007;

        try{
            InetSocketAddress address = new InetSocketAddress(hostname, port);
            SocketChannel sC = SocketChannel.open(address);
            sC.configureBlocking(false);

            log("Local address: " + hostname + " connecting to Server on port " + port
                    + "...");
            String userInput;

            System.out.println("Enter lines of characters: " );

            while ((userInput = stdIn.nextLine()) != null)
            {
                //Checks if user wants to exit
                if (userInput.equalsIgnoreCase("x")) 
                {

                    buffer.put (userInput.getBytes());
                    buffer.flip();
                    sC.write(buffer);
                    buffer.clear();
                    System.out.println("Closing ..");
                    sC.close();
                    break;
                }

                buffer.put (userInput.getBytes());
                buffer.flip();  
                sC.write(buffer);
                buffer.clear();                             
            }

            sC.close();

        }catch (IOException ex)
        {
        }
    }

    private static void log(String str) {
        System.out.println(str);
    }
}

Answer 1

You are never clearing reqString. You should do that after you log it.