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 * @author Jason Mathews, MITRE Corp
039 * @version $Revision: 489397 $ $Date: 2006-12-21 16:28:51 +0000 (Thu, 21 Dec 2006) $
040 ***/
041
042public final class NTPUDPClient extends DatagramSocketClient
043{
044    /*** The default NTP port.  It is set to 123 according to RFC 1305. ***/
045    public static final int DEFAULT_PORT = 123;
046
047    private int _version = NtpV3Packet.VERSION_3;
048
049    /***
050     * Retrieves the time information from the specified server and port and
051     * returns it. The time is the number of miliiseconds since
052     * 00:00 (midnight) 1 January 1900 UTC, as specified by RFC 1305.
053     * This method reads the raw NTP packet and constructs a <i>TimeInfo</i>
054     * object that allows access to all the fields of the NTP message header.
055     * <p>
056     * @param host The address of the server.
057     * @param port The port of the service.
058     * @return The time value retrieved from the server.
059     * @exception IOException If an error occurs while retrieving the time.
060     ***/
061    public TimeInfo getTime(InetAddress host, int port) throws IOException
062    {
063        // if not connected then open to next available UDP port
064        if (!isOpen())
065        {
066            open();
067        }
068
069        NtpV3Packet message = new NtpV3Impl();
070        message.setMode(NtpV3Packet.MODE_CLIENT);
071        message.setVersion(_version);
072        DatagramPacket sendPacket = message.getDatagramPacket();
073        sendPacket.setAddress(host);
074        sendPacket.setPort(port);
075
076        NtpV3Packet recMessage = new NtpV3Impl();
077        DatagramPacket receivePacket = recMessage.getDatagramPacket();
078
079        /*
080         * Must minimize the time between getting the current time,
081         * timestamping the packet, and sending it out which
082         * introduces an error in the delay time.
083         * No extraneous logging and initializations here !!!
084         */
085        TimeStamp now = TimeStamp.getCurrentTime();
086
087        // Note that if you do not set the transmit time field then originating time
088        // in server response is all 0's which is "Thu Feb 07 01:28:16 EST 2036".
089        message.setTransmitTime(now);
090
091        _socket_.send(sendPacket);
092        _socket_.receive(receivePacket);
093
094        long returnTime = System.currentTimeMillis();
095        // create TimeInfo message container but don't pre-compute the details yet
096        TimeInfo info = new TimeInfo(recMessage, returnTime, false);
097
098        return info;
099    }
100
101    /***
102     * Retrieves the time information from the specified server on the
103     * default NTP port and returns it. The time is the number of miliiseconds
104     * since 00:00 (midnight) 1 January 1900 UTC, as specified by RFC 1305.
105     * This method reads the raw NTP packet and constructs a <i>TimeInfo</i>
106     * object that allows access to all the fields of the NTP message header.
107     * <p>
108     * @param host The address of the server.
109     * @return The time value retrieved from the server.
110     * @exception IOException If an error occurs while retrieving the time.
111     ***/
112    public TimeInfo getTime(InetAddress host) throws IOException
113    {
114        return getTime(host, NtpV3Packet.NTP_PORT);
115    }
116
117    /***
118     * Returns the NTP protocol version number that client sets on request packet
119     * that is sent to remote host (e.g. 3=NTP v3, 4=NTP v4, etc.)
120     *
121     * @return  the NTP protocol version number that client sets on request packet.
122     * @see #setVersion(int)
123     ***/
124    public int getVersion()
125    {
126        return _version;
127    }
128
129    /***
130     * Sets the NTP protocol version number that client sets on request packet
131     * communicate with remote host.
132     *
133     * @param version the NTP protocol version number
134     ***/
135    public void setVersion(int version)
136    {
137        _version = version;
138    }
139
140}