//-------------------------------------------------------------------
// CSE 461 - Winter 1998
//
//    EchoServer.java:  implementation of an echo server and
//                      a simple client
//
//  USAGE: java EchoServer [host]
//    If [host] is specified, then connect to that host as a client,
//    otherwise run as a server.
//
// Andy Collins - acollins@cs.washington.edu
//-------------------------------------------------------------------

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

class EchoServer
{
   // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
   // The well-known port for the server.  Client and server need
   // to be compiled together so they get the same constant.
   // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
   private static int PORT = 4321;     // arbitrary, >1024

   public static void main (String[] args)
   {
      if (args.length == 0)
         RunServer ();
      else
         RunClient (args[0]);
   }

    
   // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
   // RunServer: a typical server loop.  Creates a socket on the
   //            well-known address and accepts each connection.
   //            processes that connection until it runs out of 
   //            data, then closes and accepts another connection.
   //            This implementation does not attempt to use 
   //            multithreading to handle multiple connections 
   //            simulataneously.  
   //
   // EXERCISES:
   //            1) What happens if multiple clients connect at the
   //               same time (you can determine this by reading or
   //               by experimentation)
   //
   //            2) (Optional) Extend this code so that multiple 
   //               clients can be handled in parallel.
   // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

   private static void RunServer ()
   {
      System.out.println ("Echo Server: starting");

      try
         {
         // NOTE: no inet address, always local host
         ServerSocket serve = new ServerSocket (PORT);

         for (;;)
            {
            Socket sock = serve.accept ();
            System.out.println ("Opened connection...");

            PrintStream output = new PrintStream (sock.getOutputStream ());
            DataInputStream input = 
                              new DataInputStream (sock.getInputStream ());

            // Read and reply until failure
            String msg = input.readLine ();
            while (msg != null)
               {
               output.println (msg);
               System.out.println ("   echoed '" + msg + "'");
               msg = input.readLine ();
               }

            sock.close ();
            System.out.println ("  closed connection");
            }
         }
      catch (IOException e)
         {
         System.out.println ("Server IO error, exiting");
         }
   }


   // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
   // RunClient: a typical one-shot client.  Opens a socket to the
   //            server, then prints 10 messages and checks the
   //            result.  The client closes the connection in this
   //            setup.
   // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
   private static void RunClient (String hostname)
   {
      System.out.println ("Echo Client: starting");
      try
         {
         // HINT: try InetAddress.getLocalHost () for testing
         InetAddress hostAddr = InetAddress.getByName (hostname);

         Socket sock = new Socket (hostAddr, PORT);
         PrintStream output = new PrintStream (sock.getOutputStream ());
         DataInputStream input = 
                           new DataInputStream (sock.getInputStream ());
 
         System.out.println ("connected");

         Random rand = new Random ();
         for (int i=0; i<10; ++i)
            {
            String msg = "Test message " + rand.nextLong ();
            System.out.print ("   sending message '" + msg + "'... ");
            output.println (msg);
            String back = input.readLine ();
            if (!back.equals (msg))
                System.out.println (" != '" + back + "'");
            else
                System.out.println (" ok");
            }

         sock.close ();
         System.out.println ("  closing connection");
         }
      catch (UnknownHostException e)
         {
         System.out.println ("Hostname '" + hostname + "' unknown.");
         }
      catch (IOException e)
         {
         System.out.println ("IO error connecting, sending or receiving");
         }         
   }
}