    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017
    018package org.apache.commons.net.time;
    019
    020import java.io.IOException;
    021import java.net.DatagramPacket;
    022import java.net.InetAddress;
    023import java.util.Date;
    024
    025import org.apache.commons.net.DatagramSocketClient;
    026
    027/**
    028 * The TimeUDPClient class is a UDP implementation of a client for the
    029 * Time protocol described in RFC 868.  To use the class, merely
    030 * open a local datagram socket with
    031 * {@link org.apache.commons.net.DatagramSocketClient#open  open }
    032 * and call {@link #getTime  getTime } or
    033 * {@link #getTime  getDate } to retrieve the time. Then call
    034 * {@link org.apache.commons.net.DatagramSocketClient#close  close }
    035 * to close the connection properly.  Unlike
    036 * {@link org.apache.commons.net.time.TimeTCPClient},
    037 * successive calls to {@link #getTime  getTime } or
    038 * {@link #getDate  getDate } are permitted
    039 * without re-establishing a connection.  That is because UDP is a
    040 * connectionless protocol and the Time protocol is stateless.
    041 *
    042 *
    043 * @see TimeTCPClient
    044 */
    045
    046public final class TimeUDPClient extends DatagramSocketClient
    047{
    048    /** The default time port.  It is set to 37 according to RFC 868. */
    049    public static final int DEFAULT_PORT = 37;
    050
    051    /**
    052     * The number of seconds between 00:00 1 January 1900 and
    053     * 00:00 1 January 1970.  This value can be useful for converting
    054     * time values to other formats.
    055     */
    056    public static final long SECONDS_1900_TO_1970 = 2208988800L;
    057
    058    private final byte[] dummyData = new byte[1];
    059    private final byte[] timeData = new byte[4];
    060
    061    /**
    062     * Retrieves the time from the specified server and port and
    063     * returns it. The time is the number of seconds since
    064     * 00:00 (midnight) 1 January 1900 GMT, as specified by RFC 868.
    065     * This method reads the raw 32-bit big-endian
    066     * unsigned integer from the server, converts it to a Java long, and
    067     * returns the value.
    068     *
    069     * @param host The address of the server.
    070     * @param port The port of the service.
    071     * @return The time value retrieved from the server.
    072     * @throws IOException If an error occurs while retrieving the time.
    073     */
    074    public long getTime(final InetAddress host, final int port) throws IOException
    075    {
    076        long time;
    077        final DatagramPacket sendPacket;
    078        final DatagramPacket receivePacket;
    079
    080        sendPacket =
    081            new DatagramPacket(dummyData, dummyData.length, host, port);
    082        receivePacket = new DatagramPacket(timeData, timeData.length);
    083
    084        _socket_.send(sendPacket);
    085        _socket_.receive(receivePacket);
    086
    087        time = 0L;
    088        time |= (((timeData[0] & 0xff) << 24) & 0xffffffffL);
    089        time |= (((timeData[1] & 0xff) << 16) & 0xffffffffL);
    090        time |= (((timeData[2] & 0xff) << 8) & 0xffffffffL);
    091        time |= ((timeData[3] & 0xff) & 0xffffffffL);
    092
    093        return time;
    094    }
    095
    096    /** Same as <code> getTime(host, DEFAULT_PORT); </code>
    097     * @param host the time server
    098     * @return the time returned from the server
    099     * @throws IOException on error
    100     */
    101    public long getTime(final InetAddress host) throws IOException
    102    {
    103        return getTime(host, DEFAULT_PORT);
    104    }
    105
    106
    107    /**
    108     * Retrieves the time from the server and returns a Java Date
    109     * containing the time converted to the local time zone.
    110     *
    111     * @param host The address of the server.
    112     * @param port The port of the service.
    113     * @return A Date value containing the time retrieved from the server
    114     *     converted to the local time zone.
    115     * @throws IOException  If an error occurs while fetching the time.
    116     */
    117    public Date getDate(final InetAddress host, final int port) throws IOException
    118    {
    119        return new Date((getTime(host, port) - SECONDS_1900_TO_1970)*1000L);
    120    }
    121
    122
    123    /** Same as <code> getTime(host, DEFAULT_PORT); </code>
    124     * @param host the time server
    125     * @return the date
    126     * @throws IOException on error
    127     */
    128    public Date getDate(final InetAddress host) throws IOException
    129    {
    130        return new Date((getTime(host, DEFAULT_PORT) -
    131                         SECONDS_1900_TO_1970)*1000L);
    132    }
    133
    134}
    135