panda.net.time.TimeUDPClient Maven / Gradle / Ivy

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Panda Nets is a client side library of many basic Internet protocols.
There is a newer version: 1.8.0
package panda.net.time;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.InetAddress;
import java.util.Date;

import panda.net.DatagramSocketClient;

/***
 * The TimeUDPClient class is a UDP implementation of a client for the Time protocol described in
 * RFC 868. To use the class, merely open a local datagram socket with
 * {@link panda.net.DatagramSocketClient#open open } and call {@link #getTime getTime } or
 * {@link #getTime getDate } to retrieve the time. Then call
 * {@link panda.net.DatagramSocketClient#close close } to close the connection properly. Unlike
 * {@link panda.net.time.TimeTCPClient}, successive calls to {@link #getTime getTime } or
 * {@link #getDate getDate } are permitted without re-establishing a connection. That is because UDP
 * is a connectionless protocol and the Time protocol is stateless.
 * 
 * @see TimeTCPClient
 ***/

public final class TimeUDPClient extends DatagramSocketClient {
	/*** The default time port. It is set to 37 according to RFC 868. ***/
	public static final int DEFAULT_PORT = 37;

	/***
	 * The number of seconds between 00:00 1 January 1900 and 00:00 1 January 1970. This value can
	 * be useful for converting time values to other formats.
	 ***/
	public static final long SECONDS_1900_TO_1970 = 2208988800L;

	private final byte[] __dummyData = new byte[1];
	private final byte[] __timeData = new byte[4];

	/***
	 * Retrieves the time from the specified server and port and returns it. The time is the number
	 * of seconds since 00:00 (midnight) 1 January 1900 GMT, as specified by RFC 868. This method
	 * reads the raw 32-bit big-endian unsigned integer from the server, converts it to a Java long,
	 * and returns the value.
	 * 
	 * @param host The address of the server.
	 * @param port The port of the service.
	 * @return The time value retrieved from the server.
	 * @exception IOException If an error occurs while retrieving the time.
	 ***/
	public long getTime(InetAddress host, int port) throws IOException {
		long time;
		DatagramPacket sendPacket, receivePacket;

		sendPacket = new DatagramPacket(__dummyData, __dummyData.length, host, port);
		receivePacket = new DatagramPacket(__timeData, __timeData.length);

		_socket_.send(sendPacket);
		_socket_.receive(receivePacket);

		time = 0L;
		time |= (((__timeData[0] & 0xff) << 24) & 0xffffffffL);
		time |= (((__timeData[1] & 0xff) << 16) & 0xffffffffL);
		time |= (((__timeData[2] & 0xff) << 8) & 0xffffffffL);
		time |= ((__timeData[3] & 0xff) & 0xffffffffL);

		return time;
	}

	/***
	 * Same as  getTime(host, DEFAULT_PORT); 
	 * 
	 * @param host the time server
	 * @return the time returned from the server
	 * @throws IOException on error
	 ***/
	public long getTime(InetAddress host) throws IOException {
		return getTime(host, DEFAULT_PORT);
	}

	/***
	 * Retrieves the time from the server and returns a Java Date containing the time converted to
	 * the local timezone.
	 * 
	 * @param host The address of the server.
	 * @param port The port of the service.
	 * @return A Date value containing the time retrieved from the server converted to the local
	 *         timezone.
	 * @exception IOException If an error occurs while fetching the time.
	 ***/
	public Date getDate(InetAddress host, int port) throws IOException {
		return new Date((getTime(host, port) - SECONDS_1900_TO_1970) * 1000L);
	}

	/***
	 * Same as  getTime(host, DEFAULT_PORT); 
	 * 
	 * @param host the time server
	 * @return the date
	 * @throws IOException on error
	 ***/
	public Date getDate(InetAddress host) throws IOException {
		return new Date((getTime(host, DEFAULT_PORT) - SECONDS_1900_TO_1970) * 1000L);
	}

}