    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.ntp;
    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 Network Time Protocol (NTP) described in RFC 1305 as well as the Simple Network Time
    028 * Protocol (SNTP) in RFC-2030. To use the class, merely open a local datagram socket with <a href="#open"> open </a> and call <a href="#getTime"> getTime </a>
    029 * to retrieve the time. Then call <a href="org.apache.commons.net.DatagramSocketClient.html#close"> close </a> to close the connection properly. Successive
    030 * calls to <a href="#getTime"> getTime </a> are permitted without re-establishing a connection. That is because UDP is a connectionless protocol and the
    031 * Network Time Protocol is stateless.
    032 *
    033 */
    034
    035public final class NTPUDPClient extends DatagramSocketClient {
    036    /** The default NTP port. It is set to 123 according to RFC 1305. */
    037    public static final int DEFAULT_PORT = 123;
    038
    039    private int version = NtpV3Packet.VERSION_3;
    040
    041    /**
    042     * Retrieves the time information from the specified server on the default NTP port and returns it. The time is the number of miliiseconds since 00:00
    043     * (midnight) 1 January 1900 UTC, as specified by RFC 1305. This method reads the raw NTP packet and constructs a <i>TimeInfo</i> object that allows access
    044     * to all the fields of the NTP message header.
    045     * <p>
    046     *
    047     * @param host The address of the server.
    048     * @return The time value retrieved from the server.
    049     * @throws IOException If an error occurs while retrieving the time.
    050     */
    051    public TimeInfo getTime(final InetAddress host) throws IOException {
    052        return getTime(host, NtpV3Packet.NTP_PORT);
    053    }
    054
    055    /**
    056     * Retrieves the time information from the specified server and port and returns it. The time is the number of miliiseconds since 00:00 (midnight) 1 January
    057     * 1900 UTC, as specified by RFC 1305. This method reads the raw NTP packet and constructs a <i>TimeInfo</i> object that allows access to all the fields of
    058     * the NTP message header.
    059     * <p>
    060     *
    061     * @param host The address of the server.
    062     * @param port The port of the service.
    063     * @return The time value retrieved from the server.
    064     * @throws IOException If an error occurs while retrieving the time or if received packet does not match the request.
    065     */
    066    public TimeInfo getTime(final InetAddress host, final int port) throws IOException {
    067        // if not connected then open to next available UDP port
    068        if (!isOpen()) {
    069            open();
    070        }
    071
    072        final NtpV3Packet message = new NtpV3Impl();
    073        message.setMode(NtpV3Packet.MODE_CLIENT);
    074        message.setVersion(version);
    075        final DatagramPacket sendPacket = message.getDatagramPacket();
    076        sendPacket.setAddress(host);
    077        sendPacket.setPort(port);
    078
    079        final NtpV3Packet recMessage = new NtpV3Impl();
    080        final DatagramPacket receivePacket = recMessage.getDatagramPacket();
    081
    082        /*
    083         * Must minimize the time between getting the current time, timestamping the packet, and sending it out which introduces an error in the delay time. No
    084         * extraneous logging and initializations here !!!
    085         */
    086        final TimeStamp now = TimeStamp.getCurrentTime();
    087
    088        // Note that if you do not set the transmit time field then originating time
    089        // in server response is all 0's which is "Thu Feb 07 01:28:16 EST 2036".
    090        message.setTransmitTime(now);
    091
    092        _socket_.send(sendPacket);
    093        _socket_.receive(receivePacket);
    094
    095        final long returnTimeMillis = System.currentTimeMillis();
    096
    097        // Prevent invalid time information if response does not match request
    098        if (!now.equals(recMessage.getOriginateTimeStamp())) {
    099            throw new IOException("Originate time does not match the request");
    100        }
    101
    102        // create TimeInfo message container but don't pre-compute the details yet
    103        return new TimeInfo(recMessage, returnTimeMillis, false);
    104    }
    105
    106    /**
    107     * Returns the NTP protocol version number that client sets on request packet that is sent to remote host (e.g. 3=NTP v3, 4=NTP v4, etc.)
    108     *
    109     * @return the NTP protocol version number that client sets on request packet.
    110     * @see #setVersion(int)
    111     */
    112    public int getVersion() {
    113        return version;
    114    }
    115
    116    /**
    117     * Sets the NTP protocol version number that client sets on request packet communicate with remote host.
    118     *
    119     * @param version the NTP protocol version number
    120     */
    121    public void setVersion(final int version) {
    122        this.version = version;
    123    }
    124
    125}