    001    package 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
    020    import java.io.IOException;
    021    import java.net.DatagramPacket;
    022    import java.net.InetAddress;
    023
    024    import 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
    042    public 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    }