001package org.apache.commons.net.ntp;
002/*
003 * Licensed to the Apache Software Foundation (ASF) under one or more
004 * contributor license agreements.  See the NOTICE file distributed with
005 * this work for additional information regarding copyright ownership.
006 * The ASF licenses this file to You under the Apache License, Version 2.0
007 * (the "License"); you may not use this file except in compliance with
008 * the License.  You may obtain a copy of the License at
009 *
010 *      http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018
019
020import java.io.IOException;
021import java.net.DatagramPacket;
022import java.net.InetAddress;
023
024import org.apache.commons.net.DatagramSocketClient;
025
026/**
027 * The NTPUDPClient class is a UDP implementation of a client for the
028 * Network Time Protocol (NTP) described in RFC 1305 as well as the
029 * Simple Network Time Protocol (SNTP) in RFC-2030. To use the class,
030 * merely open a local datagram socket with <a href="#open"> open </a>
031 * and call <a href="#getTime"> getTime </a> to retrieve the time. Then call
032 * <a href="org.apache.commons.net.DatagramSocketClient.html#close"> close </a>
033 * to close the connection properly.
034 * Successive calls to <a href="#getTime"> getTime </a> are permitted
035 * without re-establishing a connection.  That is because UDP is a
036 * connectionless protocol and the Network Time Protocol is stateless.
037 *
038 */
039
040public final class NTPUDPClient extends DatagramSocketClient
041{
042    /** The default NTP port.  It is set to 123 according to RFC 1305. */
043    public static final int DEFAULT_PORT = 123;
044
045    private int version = NtpV3Packet.VERSION_3;
046
047    /**
048     * Retrieves the time information from the specified server and port and
049     * returns it. The time is the number of miliiseconds since
050     * 00:00 (midnight) 1 January 1900 UTC, as specified by RFC 1305.
051     * This method reads the raw NTP packet and constructs a <i>TimeInfo</i>
052     * object that allows access to all the fields of the NTP message header.
053     * <p>
054     * @param host The address of the server.
055     * @param port The port of the service.
056     * @return The time value retrieved from the server.
057     * @throws IOException If an error occurs while retrieving the time.
058     */
059    public TimeInfo getTime(final InetAddress host, final int port) throws IOException
060    {
061        // if not connected then open to next available UDP port
062        if (!isOpen())
063        {
064            open();
065        }
066
067        final NtpV3Packet message = new NtpV3Impl();
068        message.setMode(NtpV3Packet.MODE_CLIENT);
069        message.setVersion(version);
070        final DatagramPacket sendPacket = message.getDatagramPacket();
071        sendPacket.setAddress(host);
072        sendPacket.setPort(port);
073
074        final NtpV3Packet recMessage = new NtpV3Impl();
075        final DatagramPacket receivePacket = recMessage.getDatagramPacket();
076
077        /*
078         * Must minimize the time between getting the current time,
079         * timestamping the packet, and sending it out which
080         * introduces an error in the delay time.
081         * No extraneous logging and initializations here !!!
082         */
083        final TimeStamp now = TimeStamp.getCurrentTime();
084
085        // Note that if you do not set the transmit time field then originating time
086        // in server response is all 0's which is "Thu Feb 07 01:28:16 EST 2036".
087        message.setTransmitTime(now);
088
089        _socket_.send(sendPacket);
090        _socket_.receive(receivePacket);
091
092        final long returnTimeMillis = System.currentTimeMillis();
093        // create TimeInfo message container but don't pre-compute the details yet
094        return new TimeInfo(recMessage, returnTimeMillis, false);
095    }
096
097    /**
098     * Retrieves the time information from the specified server on the
099     * default NTP port and returns it. The time is the number of miliiseconds
100     * since 00:00 (midnight) 1 January 1900 UTC, as specified by RFC 1305.
101     * This method reads the raw NTP packet and constructs a <i>TimeInfo</i>
102     * object that allows access to all the fields of the NTP message header.
103     * <p>
104     * @param host The address of the server.
105     * @return The time value retrieved from the server.
106     * @throws IOException If an error occurs while retrieving the time.
107     */
108    public TimeInfo getTime(final InetAddress host) throws IOException
109    {
110        return getTime(host, NtpV3Packet.NTP_PORT);
111    }
112
113    /**
114     * Returns the NTP protocol version number that client sets on request packet
115     * that is sent to remote host (e.g. 3=NTP v3, 4=NTP v4, etc.)
116     *
117     * @return  the NTP protocol version number that client sets on request packet.
118     * @see #setVersion(int)
119     */
120    public int getVersion()
121    {
122        return version;
123    }
124
125    /**
126     * Sets the NTP protocol version number that client sets on request packet
127     * communicate with remote host.
128     *
129     * @param version the NTP protocol version number
130     */
131    public void setVersion(final int version)
132    {
133        this.version = version;
134    }
135
136}