package primer56;

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

public class UDPPoke {

	private int bufferSize; // in bytes
	private DatagramSocket socket;
	private DatagramPacket outgoing;
	
	public UDPPoke(InetAddress host, int port, int bufferSize,
			int timeout) throws SocketException{
		outgoing = new DatagramPacket(new byte[1], 1, host, port);
		this.bufferSize = bufferSize;
		socket = new DatagramSocket();
		socket.connect(host, port);
		socket.setSoTimeout(timeout);
	}
	
	public UDPPoke(InetAddress host, int port, int bufferSize) 
		throws SocketException{
		this(host, port, bufferSize, 30000);
	}
	
	public UDPPoke(InetAddress host, int port) throws SocketException{
		this(host, port, 8192, 30000);
	}
	
	public byte[] poke() throws IOException{
		
		byte[] response = null;
		try{
			socket.send(outgoing);
			DatagramPacket incoming =
				new DatagramPacket(new byte[bufferSize], bufferSize);
			// next line blocks until the response is received
			socket.receive(incoming);
			int numBytes = incoming.getLength();
			response = new byte[numBytes];
			System.arraycopy(incoming.getData(), 0, response, 0, numBytes);
		}catch(IOException ex){
			// response will be null
		}
		
		// may return null
		return response;
	}
	
	public static void main(String[] args) {
		
		InetAddress host;
		int port = 0;
		
		try{
			host = InetAddress.getByName(args[0]);
			port = Integer.parseInt(args[1]);
			if(port < 1 || port > 65535) throw new Exception();
		}catch(Exception ex){
			System.out.println("Usage: java UDPPoke host port");
			return;
		}
		
		try{
			UDPPoke poker = new UDPPoke(host, port);
			byte[] response = poker.poke();
			if(response == null){
				System.out.println("No response within alloted time");
				return;
			}
			
			String result = "";
			try{
				result = new String(response,"ASCII");
			}catch(UnsupportedEncodingException e){
				// try a different encoding
				result = new String(response, "8859_1");
			}
			System.out.println(result);
		}catch(Exception ex){
			System.err.println(ex);
			ex.printStackTrace();
		}
		

	}// end main()

}