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}