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

class TCPServer {

    public static void main(String argv[]) throws Exception
    {
	// TCP socket variables
	ServerSocket welcomeSocket;
	Socket connectionSocket;
	
	// client variables
	String clientSentence, serverSentence;

	// command-line arguments
	int port;

	// process command-line arguments
	if (argv.length < 1) {
	    System.out.println ("Usage: java TCPServer port\n");
	    System.exit (-1);
	}
	port = Integer.parseInt(argv[0]);

	// Create welcoming socket using the given port
	welcomeSocket = new ServerSocket(port);

	System.out.println("Listening on port " + port + "...");

	// While loop to handle arbitrary sequence of clients making requests
	while(true) {

	    // Waits for some client to connect and creates new socket 
	    // for connection
	    connectionSocket = welcomeSocket.accept();
	    System.out.println("Client Made Connection");                

	    // Create (buffered) input stream attached to connection socket
	    BufferedReader inFromClient = new BufferedReader(
				      new InputStreamReader(
				    connectionSocket.getInputStream()));

	    // Create output stream attached to connection socket
	    DataOutputStream outToClient = new DataOutputStream(
					   connectionSocket.getOutputStream());

	    // Read input line from socket
	    clientSentence = inFromClient.readLine();
	    System.out.println("FROM CLIENT: " + clientSentence);

	    // Capitalize the sentence 
	    serverSentence = clientSentence.toUpperCase();

	    // Write output line to socket (add a newline)
	    outToClient.writeBytes(serverSentence + '\n');
	    System.out.println ("TO CLIENT: " + serverSentence);

	    // Close the connection socket
	    connectionSocket.close();

	} //  end while; loop back to accept a new client connection

    } // end main

} // end class