Computer networks -- 2008-2009 -- info.uvt.ro/Sockets/UDP/Examples/Ping

Quick links: front; agenda; courses 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13; examination.

Please note that the current work serves mainly as general guidance and discussion topics, and is by no means the reference material for the course. For further information please consult the dedicated section.

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Client

import java.io.IOException;
import java.net.DatagramSocket;
import java.net.DatagramPacket;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.net.SocketException;
import java.net.UnknownHostException;


public class PingClient
{
	public static void main (String[] arguments)
	{
		if (arguments.length != 2) {
			System.err.println ("wrong arguments !!!");
			return;
		}
		
		// Selecting the arguments.
		String serverAddressAsString = arguments[0];
		String serverPortAsString = arguments[1];
		
		// Resolving the server address.
		InetAddress serverAddress;
		try {
			serverAddress = InetAddress.getByName (serverAddressAsString);
		} catch (UnknownHostException exception) {
			System.err.println ("wrong server name !!!");
			return;
		}
		
		// Parsing the server port.
		int serverPort;
		try {
			serverPort = Integer.parseInt (serverPortAsString);
		} catch (NumberFormatException exception) {
			System.err.println ("wrong server port !!!");
			return;
		}
		
		// Initializing the message to be sent.
		String message = "ping";
		
		// Creating and binding the socket.
		DatagramSocket socket;
		try {
			System.err.println ("creating and binding socket...");
			socket = new DatagramSocket ();
		} catch (SocketException exception) {
			// An unknown / unexpected network error was encountered. (Not a normal situation.)
			exception.printStackTrace (System.err);
			return;
		}
		
		// Only for debugging purposes.
		// Obtaining and printing the local socket address (the datagram source). (Which should be an instance of InetSocketAddress.)
		InetSocketAddress localSocketAddress = (InetSocketAddress) socket.getLocalSocketAddress ();
		System.err.println ("local socket address -->");
		printInetSocketAddress (localSocketAddress);
		
		// Creating the datagram destination (that is the server socket address).
		InetSocketAddress datagramDestination = new InetSocketAddress (serverAddress, serverPort);
		
		// Only for debugging purposes.
		// Printing the datagram destination address.
		System.err.println ("datagram destination -->");
		printInetSocketAddress (datagramDestination);
		
		// Creating the datagram backing buffer.
		byte[] datagramBuffer = message.getBytes ();
		int datagramBufferOffset = 0;
		int datagramBufferSize = datagramBuffer.length;
		
		// Creating the datagram.
		DatagramPacket datagram;
		try {
			System.err.println ("creating datagram...");
			datagram = new DatagramPacket (datagramBuffer, datagramBufferOffset, datagramBufferSize, datagramDestination);
		} catch (SocketException exception) {
			// An unknown / unexpected network error was encountered. (Not a normal situation.)
			exception.printStackTrace (System.err);
			return;
		}
		
		// Sending the datagram.
		try {
			System.err.println ("sending datagram...");
			socket.send (datagram);
		} catch (IOException exception) {
			// The datagram could not be sent. (Maybe destination is unreachable.)
			exception.printStackTrace (System.err);
			return;
		}
		
		// Closing the socket.
		System.err.println ("closing socket...");
		socket.close ();
	}
	
	public static void printInetSocketAddress (InetSocketAddress socketAddress)
	{
		// Obtaining the local IP address.
		InetAddress address = socketAddress.getAddress ();
		
		// Obtaining the local port.
		int port = socketAddress.getPort ();
		
		// Printing obtained information;
		printInetAddress (address);
		System.err.println ("    port = " + port);
	}
	
	public static void printInetAddress (InetAddress address)
	{
		// Obtaining the IP as a string.
		String ipAsString = address.getHostAddress ();
		
		// Obtaining the IP as an array of bytes.
		byte[] ipAsBytes = address.getAddress ();
		
		// Obtaining the reverse host name.
		String reverseName = address.getCanonicalHostName ();
		
		// Printing the default string representation.
		System.err.println ("    address = " + address);
		
		// Printing the IP as string.
		System.err.println ("    ip as string = " + ipAsString);
		
		// Printing the IP as bytes.
		System.err.println ("    ip as bytes length = " + ipAsBytes.length);
		System.err.print ("    ip as bytes =");
		for (byte b : ipAsBytes)
			System.err.print (" " + (b));
		System.err.println ();
		
		// Printing the reverse host name.
		System.err.println ("    reverse name = " + reverseName);
	}
}

Server

import java.io.IOException;
import java.net.DatagramSocket;
import java.net.DatagramPacket;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.net.SocketException;
import java.net.UnknownHostException;


public class PingServer
{
	public static void main (String[] arguments)
	{
		if (arguments.length != 1) {
			System.err.println ("wrong arguments !!!");
			return;
		}
		
		// Selecting the arguments.
		String serverPortAsString = arguments[0];
		
		// Parsing the server port.
		int serverPort;
		try {
			serverPort = Integer.parseInt (serverPortAsString);
		} catch (NumberFormatException exception) {
			System.err.println ("wrong server port !!!");
			return;
		}
		
		// Creating and binding the socket.
		DatagramSocket socket;
		try {
			System.err.println ("creating and binding socket...");
			socket = new DatagramSocket (serverPort);
		} catch (SocketException exception) {
			// The socket can not be created or bound. (Maybe the port is already in use.)
			exception.printStackTrace (System.err);
			return;
		}
		
		// Only for debugging purposes.
		// Obtaining and printing the local socket address (the datagram destination). (Which should be an instance of InetSocketAddress.)
		InetSocketAddress localSocketAddress = (InetSocketAddress) socket.getLocalSocketAddress ();
		System.err.println ("local socket address -->");
		printInetSocketAddress (localSocketAddress);
		
		// Set a maximum datagram backing buffer size.
		int datagramBufferSize = 2048;
		
		// Create the datagram backing buffer.
		byte[] datagramBuffer = new byte [datagramBufferSize];
		int datagramBufferOffset = 0;
		
		// Create the datagram. (We can reuse the same datagram for all receives.)
		DatagramPacket datagram = new DatagramPacket (datagramBuffer, datagramBufferOffset, datagramBufferSize);
		
		// Set a maximum message counter.
		int counter = 10;
		
		// Wait for new datagrams.
		while (counter > 0) {
			
			// Receiving the datagram.
			try {
				System.err.println ("receiving datagram...");
				socket.receive (datagram);
			} catch (IOException exception) {
				// An unknown / unexpected network error was encountered. (Not a normal situation.)
				exception.printStackTrace (System.err);
				return;
			}
			
			// Obtaining the datagram source address. (Which should be an instance of InetSocketAddress.)
			InetSocketAddress datagramSource = (InetSocketAddress) datagram.getSocketAddress ();
			
			// Only for debugging purposes.
			// Printing the datagram source address.
			System.err.println ("datagram source -->");
			printInetSocketAddress (datagramSource);
			
			// Obtaining the datagram actual length (how much data was received, or how much of the backing buffer was used).
			int datagramBufferUsed = datagram.getLength ();
			
			// Decoding the message (which should be a string).
			String message = new String (datagramBuffer, datagramBufferOffset, datagramBufferUsed);
			
			System.err.println ("received -->");
			System.err.println ("    message = " + message);
			
			counter--;
		}
		
		// Closing the socket.
		System.err.println ("closing socket...");
		socket.close ();
	}
	
	public static void printInetSocketAddress (InetSocketAddress socketAddress)
	{
		// Obtaining the local IP address.
		InetAddress address = socketAddress.getAddress ();
		
		// Obtaining the local port.
		int port = socketAddress.getPort ();
		
		// Printing obtained information;
		printInetAddress (address);
		System.err.println ("    port = " + port);
	}
	
	public static void printInetAddress (InetAddress address)
	{
		// Obtaining the IP as a string.
		String ipAsString = address.getHostAddress ();
		
		// Obtaining the IP as an array of bytes.
		byte[] ipAsBytes = address.getAddress ();
		
		// Obtaining the reverse host name.
		String reverseName = address.getCanonicalHostName ();
		
		// Printing the default string representation.
		System.err.println ("    address = " + address);
		
		// Printing the IP as string.
		System.err.println ("    ip as string = " + ipAsString);
		
		// Printing the IP as bytes.
		System.err.println ("    ip as bytes length = " + ipAsBytes.length);
		System.err.print ("    ip as bytes =");
		for (byte b : ipAsBytes)
			System.err.print (" " + (b));
		System.err.println ();
		
		// Printing the reverse host name.
		System.err.println ("    reverse name = " + reverseName);
	}
}

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• conf. dr. Victoria Iordan, iordan@info.uvt.ro
• Ciprian Dorin Craciun, ccraciun@info.uvt.ro
• Marian Neagul, marian@info.uvt.ro