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 * @version $Revision: 1570303 $
039 ***/
040
041public final class NTPUDPClient extends DatagramSocketClient
042{
043    /*** The default NTP port.  It is set to 123 according to RFC 1305. ***/
044    public static final int DEFAULT_PORT = 123;
045
046    private int _version = NtpV3Packet.VERSION_3;
047
048    /***
049     * Retrieves the time information from the specified server and port and
050     * returns it. The time is the number of miliiseconds since
051     * 00:00 (midnight) 1 January 1900 UTC, as specified by RFC 1305.
052     * This method reads the raw NTP packet and constructs a <i>TimeInfo</i>
053     * object that allows access to all the fields of the NTP message header.
054     * <p>
055     * @param host The address of the server.
056     * @param port The port of the service.
057     * @return The time value retrieved from the server.
058     * @exception IOException If an error occurs while retrieving the time.
059     ***/
060    public TimeInfo getTime(InetAddress host, int port) throws IOException
061    {
062        // if not connected then open to next available UDP port
063        if (!isOpen())
064        {
065            open();
066        }
067
068        NtpV3Packet message = new NtpV3Impl();
069        message.setMode(NtpV3Packet.MODE_CLIENT);
070        message.setVersion(_version);
071        DatagramPacket sendPacket = message.getDatagramPacket();
072        sendPacket.setAddress(host);
073        sendPacket.setPort(port);
074
075        NtpV3Packet recMessage = new NtpV3Impl();
076        DatagramPacket receivePacket = recMessage.getDatagramPacket();
077
078        /*
079         * Must minimize the time between getting the current time,
080         * timestamping the packet, and sending it out which
081         * introduces an error in the delay time.
082         * No extraneous logging and initializations here !!!
083         */
084        TimeStamp now = TimeStamp.getCurrentTime();
085
086        // Note that if you do not set the transmit time field then originating time
087        // in server response is all 0's which is "Thu Feb 07 01:28:16 EST 2036".
088        message.setTransmitTime(now);
089
090        _socket_.send(sendPacket);
091        _socket_.receive(receivePacket);
092
093        long returnTime = System.currentTimeMillis();
094        // create TimeInfo message container but don't pre-compute the details yet
095        TimeInfo info = new TimeInfo(recMessage, returnTime, false);
096
097        return info;
098    }
099
100    /***
101     * Retrieves the time information from the specified server on the
102     * default NTP port and returns it. The time is the number of miliiseconds
103     * since 00:00 (midnight) 1 January 1900 UTC, as specified by RFC 1305.
104     * This method reads the raw NTP packet and constructs a <i>TimeInfo</i>
105     * object that allows access to all the fields of the NTP message header.
106     * <p>
107     * @param host The address of the server.
108     * @return The time value retrieved from the server.
109     * @exception IOException If an error occurs while retrieving the time.
110     ***/
111    public TimeInfo getTime(InetAddress host) throws IOException
112    {
113        return getTime(host, NtpV3Packet.NTP_PORT);
114    }
115
116    /***
117     * Returns the NTP protocol version number that client sets on request packet
118     * that is sent to remote host (e.g. 3=NTP v3, 4=NTP v4, etc.)
119     *
120     * @return  the NTP protocol version number that client sets on request packet.
121     * @see #setVersion(int)
122     ***/
123    public int getVersion()
124    {
125        return _version;
126    }
127
128    /***
129     * Sets the NTP protocol version number that client sets on request packet
130     * communicate with remote host.
131     *
132     * @param version the NTP protocol version number
133     ***/
134    public void setVersion(int version)
135    {
136        _version = version;
137    }
138
139}