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
040    /** The default time port. It is set to 37 according to RFC 868. */
041    public static final int DEFAULT_PORT = 37;
042
043    /**
044     * 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.
045     */
046    public static final long SECONDS_1900_TO_1970 = 2208988800L;
047
048    static long toTime(final byte[] timeData) {
049        long time = 0L;
050        time |= (timeData[0] & 0xff) << 24 & 0xffffffffL;
051        time |= (timeData[1] & 0xff) << 16 & 0xffffffffL;
052        time |= (timeData[2] & 0xff) << 8 & 0xffffffffL;
053        time |= timeData[3] & 0xff & 0xffffffffL;
054        return time;
055    }
056
057    /**
058     * Same as <code>getTime(host, DEFAULT_PORT);</code>
059     *
060     * @param host the time-server
061     * @return the date
062     * @throws IOException on error
063     */
064    public Date getDate(final InetAddress host) throws IOException {
065        return new Date((getTime(host, DEFAULT_PORT) - SECONDS_1900_TO_1970) * 1000L);
066    }
067
068    /**
069     * Retrieves the time from the server and returns a Java Date containing the time converted to the local time zone.
070     *
071     * @param host The address of the server.
072     * @param port The port of the service.
073     * @return A Date value containing the time retrieved from the server converted to the local time zone.
074     * @throws IOException If an error occurs while fetching the time.
075     */
076    public Date getDate(final InetAddress host, final int port) throws IOException {
077        return new Date((getTime(host, port) - SECONDS_1900_TO_1970) * 1000L);
078    }
079
080    /**
081     * Same as <code>getTime(host, DEFAULT_PORT);</code>
082     *
083     * @param host the time-server
084     * @return the time returned from the server
085     * @throws IOException on error
086     */
087    public long getTime(final InetAddress host) throws IOException {
088        return getTime(host, DEFAULT_PORT);
089    }
090
091    /**
092     * 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
093     * 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.
094     *
095     * @param host The address of the server.
096     * @param port The port of the service.
097     * @return The time value retrieved from the server.
098     * @throws IOException If an error occurs while retrieving the time.
099     */
100    public long getTime(final InetAddress host, final int port) throws IOException {
101        final byte[] dummyData = new byte[1];
102        final byte[] timeData = new byte[4];
103
104        final DatagramPacket sendPacket = new DatagramPacket(dummyData, dummyData.length, host, port);
105        final DatagramPacket receivePacket = new DatagramPacket(timeData, timeData.length);
106
107        checkOpen().send(sendPacket);
108        checkOpen().receive(receivePacket);
109
110        return toTime(timeData);
111    }
112
113}