Exerscise 5: Network and Programming Frameworks

1. Investigate a simple chat client/server system. Look at some program code and describe how it works with multiple users.


1: A simple server that will accept a single client connection and display everything the client says on the screen. If the client user types ".bye", the client and the server will both quit.
2: A server as before, but this time it will remain 'open' for additional connection once a client has quit. The server can handle at most one connection at a time.
3: A server as before, but this time it can handle multiple clients simultaneously. The output from all connected clients will appear on the server's screen.
4: A server as before, but this time it sends all text received from any of the connected clients to all clients. This means that the server has to receive and send, and the client has to send as well as receive
5: Wrapping the client from step 4 into a very simple GUI interface but not changing the functionality of either server or client. The client is implemented as an Applet, but a Frame would have worked just as well (for a stand-alone program).

Step 1: Simple, one-time Server

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

public class ChatServer
{ private Socket socket = null;
private ServerSocket server = null;
private DataInputStream streamIn = null;

public ChatServer(int port)
{ try
{ System.out.println("Binding to port " + port + ", please wait ...");
server = new ServerSocket(port);
System.out.println("Server started: " + server);
System.out.println("Waiting for a client ...");
socket = server.accept();
System.out.println("Client accepted: " + socket);
open();
boolean done = false;
while (!done)
{ try
{ String line = streamIn.readUTF();
System.out.println(line);
done = line.equals(".bye");
}
catch(IOException ioe)
{ done = true;
}
}
close();
}
catch(IOException ioe)
{ System.out.println(ioe);
}
}
public void open() throws IOException
{ streamIn = new DataInputStream(new BufferedInputStream(socket.getInputStream()));
}
public void close() throws IOException
{ if (socket != null) socket.close();
if (streamIn != null) streamIn.close();
}
public static void main(String args[])
{ ChatServer server = null;
if (args.length != 1)
System.out.println("Usage: java ChatServer port");
else
server = new ChatServer(Integer.parseInt(args[0]));
}
}

The Simple Client corresponding to the previous server (and to step 2 and step 3 servers as well):

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

public class ChatClient
{ private Socket socket = null;
private DataInputStream console = null;
private DataOutputStream streamOut = null;

public ChatClient(String serverName, int serverPort)
{ System.out.println("Establishing connection. Please wait ...");
try
{ socket = new Socket(serverName, serverPort);
System.out.println("Connected: " + socket);
start();
}
catch(UnknownHostException uhe)
{ System.out.println("Host unknown: " + uhe.getMessage());
}
catch(IOException ioe)
{ System.out.println("Unexpected exception: " + ioe.getMessage());
}
String line = "";
while (!line.equals(".bye"))
{ try
{ line = console.readLine();
streamOut.writeUTF(line);
streamOut.flush();
}
catch(IOException ioe)
{ System.out.println("Sending error: " + ioe.getMessage());
}
}
}
public void start() throws IOException
{ console = new DataInputStream(System.in);
streamOut = new DataOutputStream(socket.getOutputStream());
}
public void stop()
{ try
{ if (console != null) console.close();
if (streamOut != null) streamOut.close();
if (socket != null) socket.close();
}
catch(IOException ioe)
{ System.out.println("Error closing ...");
}
}
public static void main(String args[])
{ ChatClient client = null;
if (args.length != 2)
System.out.println("Usage: java ChatClient host port");
else
client = new ChatClient(args[0], Integer.parseInt(args[1]));
}
}


Step 2: Many Time Server, One Client (Client is as before)

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

public class ChatServer implements Runnable
{ private Socket socket = null;
private ServerSocket server = null;
private Thread thread = null;
private DataInputStream streamIn = null;

public ChatServer(int port)
{ try
{ System.out.println("Binding to port " + port + ", please wait ...");
server = new ServerSocket(port);
System.out.println("Server started: " + server);
start();
}
catch(IOException ioe)
{ System.out.println(ioe);
}
}
public void run()
{ while (thread != null)
{ try
{ System.out.println("Waiting for a client ...");
socket = server.accept();
System.out.println("Client accepted: " + socket);
open();
boolean done = false;
while (!done)
{ try
{ String line = streamIn.readUTF();
System.out.println(line);
done = line.equals(".bye");
}
catch(IOException ioe)
{ done = true; }
}
close();
}
catch(IOException ie)
{ System.out.println("Acceptance Error: " + ie); }
}
}
public void start()
{ if (thread == null)
{ thread = new Thread(this);
thread.start();
}
}
public void stop()
{ if (thread != null)
{ thread.stop();
thread = null;
}
}
public void open() throws IOException
{ streamIn = new DataInputStream(new
BufferedInputStream(socket.getInputStream()));
}
public void close() throws IOException
{ if (socket != null) socket.close();
if (streamIn != null) streamIn.close();
}
public static void main(String args[])
{ ChatServer server = null;
if (args.length != 1)
System.out.println("Usage: java ChatServer port");
else
server = new ChatServer(Integer.parseInt(args[0]));
}
}

Step 3: Multi-Server handling Multi-Client (Client as before)

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

public class ChatServer implements Runnable
{ private ServerSocket server = null;
private Thread thread = null;
private ChatServerThread client = null;

public ChatServer(int port)
{ try
{ System.out.println("Binding to port " + port + ", please wait ...");
server = new ServerSocket(port);
System.out.println("Server started: " + server);
start();
}
catch(IOException ioe)
{ System.out.println(ioe); }
}
public void run()
{ while (thread != null)
{ try
{ System.out.println("Waiting for a client ...");
addThread(server.accept());
}
catch(IOException ie)
{ System.out.println("Acceptance Error: " + ie); }
}
}
public void addThread(Socket socket)
{ System.out.println("Client accepted: " + socket);
client = new ChatServerThread(this, socket);
try
{ client.open();
client.start();
}
catch(IOException ioe)
{ System.out.println("Error opening thread: " + ioe); }
}
public void start() { /* no change */ }
public void stop() { /* no change */ }
public static void main(String args[]){ /* no change */ }
}

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

public class ChatServerThread extends Thread
{ private Socket socket = null;
private ChatServer server = null;
private int ID = -1;
private DataInputStream streamIn = null;

public ChatServerThread(ChatServer _server, Socket _socket)
{ server = _server; socket = _socket; ID = socket.getPort();
}
public void run()
{ System.out.println("Server Thread " + ID + " running.");
while (true)
{ try
{ System.out.println(streamIn.readUTF());
}
catch(IOException ioe) { }
}
}
public void open() throws IOException
{ streamIn = new DataInputStream(new BufferedInputStream(socket.getInputStream()));
}
public void close() throws IOException
{ if (socket != null) socket.close();
if (streamIn != null) streamIn.close();
}
}


Step 4: A Simple but functional, text based chat server/client

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

public class ChatServer implements Runnable
{ private ChatServerThread clients[] = new ChatServerThread[50];
private ServerSocket server = null;
private Thread thread = null;
private int clientCount = 0;

public ChatServer(int port)
{ try
{ System.out.println("Binding to port " + port + ", please wait ...");
server = new ServerSocket(port);
System.out.println("Server started: " + server);
start(); }
catch(IOException ioe)
{ System.out.println("Can not bind to port " + port + ": " + ioe.getMessage()); }
}
public void run()
{ while (thread != null)
{ try
{ System.out.println("Waiting for a client ...");
addThread(server.accept()); }
catch(IOException ioe)
{ System.out.println("Server accept error: " + ioe); stop(); }
}
}
public void start() { /* as before */ }
public void stop() { /* as before */ }
private int findClient(int ID)
{ for (int i = 0; i < clientCount; i++)
if (clients[i].getID() == ID)
return i;
return -1;
}
public synchronized void handle(int ID, String input)
{ if (input.equals(".bye"))
{ clients[findClient(ID)].send(".bye");
remove(ID); }
else
for (int i = 0; i < clientCount; i++)
clients[i].send(ID + ": " + input);
}
public synchronized void remove(int ID)
{ int pos = findClient(ID);
if (pos >= 0)
{ ChatServerThread toTerminate = clients[pos];
System.out.println("Removing client thread " + ID + " at " + pos);
if (pos < clientCount-1)
for (int i = pos+1; i < clientCount; i++)
clients[i-1] = clients[i];
clientCount--;
try
{ toTerminate.close(); }
catch(IOException ioe)
{ System.out.println("Error closing thread: " + ioe); }
toTerminate.stop(); }
}
private void addThread(Socket socket)
{ if (clientCount < clients.length)
{ System.out.println("Client accepted: " + socket);
clients[clientCount] = new ChatServerThread(this, socket);
try
{ clients[clientCount].open();
clients[clientCount].start();
clientCount++; }
catch(IOException ioe)
{ System.out.println("Error opening thread: " + ioe); } }
else
System.out.println("Client refused: maximum " + clients.length + " reached.");
}
public static void main(String args[]) { /* as before */ }
}

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

public class ChatServerThread extends Thread
{ private ChatServer server = null;
private Socket socket = null;
private int ID = -1;
private DataInputStream streamIn = null;
private DataOutputStream streamOut = null;

public ChatServerThread(ChatServer _server, Socket _socket)
{ super();
server = _server;
socket = _socket;
ID = socket.getPort();
}
public void send(String msg)
{ try
{ streamOut.writeUTF(msg);
streamOut.flush();
}
catch(IOException ioe)
{ System.out.println(ID + " ERROR sending: " + ioe.getMessage());
server.remove(ID);
stop();
}
}
public int getID()
{ return ID;
}
public void run()
{ System.out.println("Server Thread " + ID + " running.");
while (true)
{ try
{ server.handle(ID, streamIn.readUTF());
}
catch(IOException ioe)
{ System.out.println(ID + " ERROR reading: " + ioe.getMessage());
server.remove(ID);
stop();
}
}
}
public void open() throws IOException
{ streamIn = new DataInputStream(new
BufferedInputStream(socket.getInputStream()));
streamOut = new DataOutputStream(new
BufferedOutputStream(socket.getOutputStream()));
}
public void close() throws IOException
{ if (socket != null) socket.close();
if (streamIn != null) streamIn.close();
if (streamOut != null) streamOut.close();
}
}

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

public class ChatClient implements Runnable
{ private Socket socket = null;
private Thread thread = null;
private DataInputStream console = null;
private DataOutputStream streamOut = null;
private ChatClientThread client = null;

public ChatClient(String serverName, int serverPort)
{ System.out.println("Establishing connection. Please wait ...");
try
{ socket = new Socket(serverName, serverPort);
System.out.println("Connected: " + socket);
start();
}
catch(UnknownHostException uhe)
{ System.out.println("Host unknown: " + uhe.getMessage()); }
catch(IOException ioe)
{ System.out.println("Unexpected exception: " + ioe.getMessage()); }
}
public void run()
{ while (thread != null)
{ try
{ streamOut.writeUTF(console.readLine());
streamOut.flush();
}
catch(IOException ioe)
{ System.out.println("Sending error: " + ioe.getMessage());
stop();
}
}
}
public void handle(String msg)
{ if (msg.equals(".bye"))
{ System.out.println("Good bye. Press RETURN to exit ...");
stop();
}
else
System.out.println(msg);
}
public void start() throws IOException
{ console = new DataInputStream(System.in);
streamOut = new DataOutputStream(socket.getOutputStream());
if (thread == null)
{ client = new ChatClientThread(this, socket);
thread = new Thread(this);
thread.start();
}
}
public void stop()
{ if (thread != null)
{ thread.stop();
thread = null;
}
try
{ if (console != null) console.close();
if (streamOut != null) streamOut.close();
if (socket != null) socket.close();
}
catch(IOException ioe)
{ System.out.println("Error closing ..."); }
client.close();
client.stop();
}
public static void main(String args[])
{ ChatClient client = null;
if (args.length != 2)
System.out.println("Usage: java ChatClient host port");
else
client = new ChatClient(args[0], Integer.parseInt(args[1]));
}
}

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

public class ChatClientThread extends Thread
{ private Socket socket = null;
private ChatClient client = null;
private DataInputStream streamIn = null;

public ChatClientThread(ChatClient _client, Socket _socket)
{ client = _client;
socket = _socket;
open();
start();
}
public void open()
{ try
{ streamIn = new DataInputStream(socket.getInputStream());
}
catch(IOException ioe)
{ System.out.println("Error getting input stream: " + ioe);
client.stop();
}
}
public void close()
{ try
{ if (streamIn != null) streamIn.close();
}
catch(IOException ioe)
{ System.out.println("Error closing input stream: " + ioe);
}
}
public void run()
{ while (true)
{ try
{ client.handle(streamIn.readUTF());
}
catch(IOException ioe)
{ System.out.println("Listening error: " + ioe.getMessage());
client.stop();
}
}
}
}


Stage 5: Chat client moved to very simple GUI interface

import java.net.*;
import java.io.*;
import java.applet.*;
import java.awt.*;
public class ChatClient extends Applet
{ private Socket socket = null;
private DataInputStream console = null;
private DataOutputStream streamOut = null;
private ChatClientThread client = null;
private TextArea display = new TextArea();
private TextField input = new TextField();
private Button send = new Button("Send"), connect = new Button("Connect"),
quit = new Button("Bye");
private String serverName = "localhost";
private int serverPort = 4444;

public void init()
{ Panel keys = new Panel(); keys.setLayout(new GridLayout(1,2));
keys.add(quit); keys.add(connect);
Panel south = new Panel(); south.setLayout(new BorderLayout());
south.add("West", keys); south.add("Center", input); south.add("East", send);
Label title = new Label("Simple Chat Client Applet", Label.CENTER);
title.setFont(new Font("Helvetica", Font.BOLD, 14));
setLayout(new BorderLayout());
add("North", title); add("Center", display); add("South", south);
quit.disable(); send.disable(); getParameters(); }
public boolean action(Event e, Object o)
{ if (e.target == quit)
{ input.setText(".bye");
send(); quit.disable(); send.disable(); connect.enable(); }
else if (e.target == connect)
{ connect(serverName, serverPort); }
else if (e.target == send)
{ send(); input.requestFocus(); }
return true; }
public void connect(String serverName, int serverPort)
{ println("Establishing connection. Please wait ...");
try
{ socket = new Socket(serverName, serverPort);
println("Connected: " + socket);
open(); send.enable(); connect.disable(); quit.enable(); }
catch(UnknownHostException uhe)
{ println("Host unknown: " + uhe.getMessage()); }
catch(IOException ioe)
{ println("Unexpected exception: " + ioe.getMessage()); } }
private void send()
{ try
{ streamOut.writeUTF(input.getText()); streamOut.flush(); input.setText(""); }
catch(IOException ioe)
{ println("Sending error: " + ioe.getMessage()); close(); } }
public void handle(String msg)
{ if (msg.equals(".bye"))
{ println("Good bye. Press RETURN to exit ..."); close(); }
else println(msg); }
public void open()
{ try
{ streamOut = new DataOutputStream(socket.getOutputStream());
client = new ChatClientThread(this, socket); }
catch(IOException ioe)
{ println("Error opening output stream: " + ioe); } }
public void close()
{ try
{ if (streamOut != null) streamOut.close();
if (socket != null) socket.close(); }
catch(IOException ioe)
{ println("Error closing ..."); }
client.close(); client.stop(); }
private void println(String msg)
{ display.appendText(msg + "\n"); }
public void getParameters()
{ serverName = getParameter("host");
serverPort = Integer.parseInt(getParameter("port")); }

Referred :

http://pirate.shu.edu/~wachsmut/Teaching/CSAS2214/Virtual/Lectures/chat-client-server.html



2. Describe the important and distinguishing properties of Peer to Peer computing and the Grid. How is this peer to peer and the Grid architecture changing work flow and service-oriented applications?


Peer-to-peer networks
The traditional client-server Internet model ("client" asks for and receives information from "server") is beginning to give some ground to peer-to-peer (P2P) networking - where all network participants are approximately equal. The primary advantage of P2P networks is that large numbers of people share the burden of providing computing resources (processor time and disk space), administration effort, creativity and legal liability. It's relatively easy to be anonymous in such an environment and it's harder for opponents of a P2P service to bring it down.

Napster was one of the best-known examples to date, though it's not a completely P2P system because users register their file libraries with a central server when they log on to the service. Because of this central link, it was possible for opponents to force Napster to stop facilitating free music downloads. This was done by legal action on behalf of the music industry, to protect copyright infringement. However, true P2P networks such as Kaaza and Morpheus now operate with impunity, because there is no central server, They are now generating traffic many times the rate of Napster at its peak.

P2P has some limitations
P2P does have problems. The primary disadvantage is the tendency of computers at the edge of the network to fade in and out of availability. Also, accountability for the actions of network participants could be a difficult problem. Several high-profile implementations have shown that architecture, security, and systems management issues are difficult to control. For these reasons, system managers often prefer to operate P2P systems as separate isolated entities. But, doing so is often impossible for practical applications.

The increasing reach of P2P beyond the desktop and into distributed computing fringe may further magnify these stumbling blocks. But that will not hold back the rising tide of P2P implementations. Dramatic cost savings and the ability to do parallel processing will continue to drive P2P use higher.


Grid Computing
Grid Computing can be defined as applying resources from many computers in a network to a single problem, usually one that requires a large number of processing cycles or access to large amounts of data.

The computational power grid is analogous to electric power grid. It allows the coupling of geographically distributed resources to offer consistent and inexpensive access to resources irrespective of their physical location or access point. The Internet or dedicated networks can be used to interconnect a wide variety of distributed computational resources (such as supercomputers, computer clusters, storage systems, data sources) and present them as a single, unified resource.

At its core, Grid Computing enables devices-regardless of their operating characteristics-to be virtually shared, managed and accessed across an enterprise, industry or workgroup. This virtualization of resources places all of the necessary access, data and processing power at the fingertips of those who need to rapidly solve complex business problems, conduct compute-intensive research and data analysis, and operate in real-time.

A company with slightly fewer than 2,000 desktop computers can harvest nearly 1 teraflop (one trillion floating-point operations per second) of computing capacity. Even better, the company can capture that power from computers it already owns that sit idle at night and work at less than full capacity during the day.

Universities and research institutions have long used grid-computing technology, but recently it is also making fast inroads into the business market. IBM has recently come up with operating standards that will generate many new business applications and will cause wide proliferation.


Resource location or discovery is a key issue for Grid systems in which applications are composed of hardware and software resources that need to be located. Classical approaches to Grid resource location are either centralized or hierarchical and will prove inefficient as the scale of Grid systems rapidly increases. On the other hand, the Peer-to-Peer (P2P) paradigm emerged as a successful model that achieves scalability in distributed systems. One possibility would be to borrow existing methods from the P2P paradigm and to adopt them to Grid systems taking into consideration the existing differences. Several such attempts have been made during the last couple of years. The architecture has a 3-layered hierarchical configuration-procedure-layer, role-layer, and actor-layer-and the three workflow knowledge models-ICN-based model, role-based model, and actor-based model-are the workflow knowledge representations on Grid/P2P nodes in the corresponding layers, respectively

Referred : http://www.jimpinto.com/writings/grid.html


3. Frameworks for development. Compare and contrast any TWO of:


Java
.NET
Ruby on Rails
Turbo Gears
Google Gears
AJAX frameworks

Comparing Java with .Net