    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 Time protocol described in RFC 868. To use the class, merely open a local datagram socket
    029 * with {@link org.apache.commons.net.DatagramSocketClient#open open } and call {@link #getTime getTime } or {@link #getTime getDate } to retrieve the time.
    030 * Then call {@link org.apache.commons.net.DatagramSocketClient#close close } to close the connection properly. Unlike
    031 * {@link org.apache.commons.net.time.TimeTCPClient}, successive calls to {@link #getTime getTime } or {@link #getDate getDate } are permitted without
    032 * re-establishing a connection. That is because UDP is a connectionless protocol and the Time protocol is stateless.
    033 *
    034 *
    035 * @see TimeTCPClient
    036 */
    037
    038public final class TimeUDPClient extends DatagramSocketClient {
    039    /** The default time port. It is set to 37 according to RFC 868. */
    040    public static final int DEFAULT_PORT = 37;
    041
    042    /**
    043     * 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.
    044     */
    045    public static final long SECONDS_1900_TO_1970 = 2208988800L;
    046
    047    private final byte[] dummyData = new byte[1];
    048    private final byte[] timeData = new byte[4];
    049
    050    /**
    051     * Same as <code> getTime(host, DEFAULT_PORT); </code>
    052     *
    053     * @param host the time-server
    054     * @return the date
    055     * @throws IOException on error
    056     */
    057    public Date getDate(final InetAddress host) throws IOException {
    058        return new Date((getTime(host, DEFAULT_PORT) - SECONDS_1900_TO_1970) * 1000L);
    059    }
    060
    061    /**
    062     * Retrieves the time from the server and returns a Java Date containing the time converted to the local time zone.
    063     *
    064     * @param host The address of the server.
    065     * @param port The port of the service.
    066     * @return A Date value containing the time retrieved from the server converted to the local time zone.
    067     * @throws IOException If an error occurs while fetching the time.
    068     */
    069    public Date getDate(final InetAddress host, final int port) throws IOException {
    070        return new Date((getTime(host, port) - SECONDS_1900_TO_1970) * 1000L);
    071    }
    072
    073    /**
    074     * Same as <code> getTime(host, DEFAULT_PORT); </code>
    075     *
    076     * @param host the time-server
    077     * @return the time returned from the server
    078     * @throws IOException on error
    079     */
    080    public long getTime(final InetAddress host) throws IOException {
    081        return getTime(host, DEFAULT_PORT);
    082    }
    083
    084    /**
    085     * 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
    086     * 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.
    087     *
    088     * @param host The address of the server.
    089     * @param port The port of the service.
    090     * @return The time value retrieved from the server.
    091     * @throws IOException If an error occurs while retrieving the time.
    092     */
    093    public long getTime(final InetAddress host, final int port) throws IOException {
    094        final DatagramPacket sendPacket = new DatagramPacket(dummyData, dummyData.length, host, port);
    095        final DatagramPacket receivePacket = new DatagramPacket(timeData, timeData.length);
    096
    097        checkOpen().send(sendPacket);
    098        checkOpen().receive(receivePacket);
    099
    100        long time = 0L;
    101        time |= (timeData[0] & 0xff) << 24 & 0xffffffffL;
    102        time |= (timeData[1] & 0xff) << 16 & 0xffffffffL;
    103        time |= (timeData[2] & 0xff) << 8 & 0xffffffffL;
    104        time |= timeData[3] & 0xff & 0xffffffffL;
    105
    106        return time;
    107    }
    108
    109}