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TimeServer.javaAPI DocExample2853Sun Apr 28 15:07:42 BST 2002com.ronsoft.books.nio.channels

TimeServer

public class TimeServer extends Object
Provide RFC 868 time service (http://www.ietf.org/rfc/rfc0868.txt). This code implements an RFC 868 listener to provide time service. The defined port for time service is 37. On most unix systems, root privilege is required to bind to ports below 1024. You can either run this code as root or provide another port number on the command line. Use "-p port#" with TimeClient if you choose an alternate port. Note: The familiar rdate command on unix will probably not work with this server. Most versions of rdate use TCP rather than UDP to request the time. Created: April 2002
author
Ron Hitchens (ron@ronsoft.com)
version
$Id: TimeServer.java,v 1.1 2002/04/28 22:07:43 ron Exp $

Fields Summary
private static final int
DEFAULT_TIME_PORT
private static final long
DIFF_1900
protected DatagramChannel
channel
Constructors Summary
public TimeServer(int port)


	   
		 
	
		this.channel = DatagramChannel.open();
		this.channel.socket().bind (new InetSocketAddress (port));

		System.out.println ("Listening on port " + port
			+ " for time requests");
Methods Summary
public voidlisten()

		// allocate a buffer to hold a long value
		ByteBuffer longBuffer = ByteBuffer.allocate (8);

		// assure big-endian (network) byte order
		longBuffer.order (ByteOrder.BIG_ENDIAN);
		// zero the whole buffer to be sure
		longBuffer.putLong (0, 0);
		// position to first byte of the low-order 32 bits
		longBuffer.position (4);

		// slice the buffer, gives view of the low-order 32 bits
		ByteBuffer buffer = longBuffer.slice();	

		while (true) {
			buffer.clear();

			SocketAddress sa = this.channel.receive (buffer);

			if (sa == null) {
				continue;	// defensive programming
			}
			// ignore content of recived datagram per rfc 868

			System.out.println ("Time request from " + sa);

			buffer.clear();		// sets pos/limit correctly

			// set 64-bit value, slice buffer sees low 32 bits
			longBuffer.putLong (0,
				(System.currentTimeMillis() / 1000) + DIFF_1900);

			this.channel.send (buffer, sa);
		}
public static voidmain(java.lang.String[] argv)

		int port = DEFAULT_TIME_PORT;

		if (argv.length > 0) {
			port = Integer.parseInt (argv [0]);
		}

		try {
			TimeServer server = new TimeServer (port);

			server.listen();
		} catch (SocketException e) {
			System.out.println ("Can't bind to port " + port
				+ ", try a different one");
			
		}