    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 */
    033public final class NTPUDPClient extends DatagramSocketClient {
    034    /** The default NTP port. It is set to 123 according to RFC 1305. */
    035    public static final int DEFAULT_PORT = 123;
    036
    037    private int version = NtpV3Packet.VERSION_3;
    038
    039    /**
    040     * Retrieves the time information from the specified server on the default NTP port and returns it. The time is the number of milliseconds since 00:00
    041     * (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
    042     * to all the fields of the NTP message header.
    043     *
    044     * @param host The address of the server.
    045     * @return The time value retrieved from the server.
    046     * @throws IOException If an error occurs while retrieving the time.
    047     */
    048    public TimeInfo getTime(final InetAddress host) throws IOException {
    049        return getTime(host, NtpV3Packet.NTP_PORT);
    050    }
    051
    052    /**
    053     * Retrieves the time information from the specified server and port and returns it. The time is the number of milliseconds since 00:00 (midnight) 1 January
    054     * 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
    055     * the NTP message header.
    056     *
    057     * @param host The address of the server.
    058     * @param port The port of the service.
    059     * @return The time value retrieved from the server.
    060     * @throws IOException If an error occurs while retrieving the time or if received packet does not match the request.
    061     */
    062    public TimeInfo getTime(final InetAddress host, final int port) throws IOException {
    063        // if not connected then open to next available UDP port
    064        if (!isOpen()) {
    065            open();
    066        }
    067
    068        final NtpV3Packet message = new NtpV3Impl();
    069        message.setMode(NtpV3Packet.MODE_CLIENT);
    070        message.setVersion(version);
    071        final DatagramPacket sendPacket = message.getDatagramPacket();
    072        sendPacket.setAddress(host);
    073        sendPacket.setPort(port);
    074
    075        final NtpV3Packet recMessage = new NtpV3Impl();
    076        final DatagramPacket receivePacket = recMessage.getDatagramPacket();
    077
    078        /*
    079         * 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
    080         * extraneous logging and initializations here !!!
    081         */
    082        final TimeStamp now = TimeStamp.getCurrentTime();
    083
    084        // Note that if you do not set the transmit time field then originating time
    085        // in server response is all 0's which is "Thu Feb 07 01:28:16 EST 2036".
    086        message.setTransmitTime(now);
    087
    088        checkOpen().send(sendPacket);
    089        checkOpen().receive(receivePacket);
    090
    091        final long returnTimeMillis = System.currentTimeMillis();
    092
    093        // Prevent invalid time information if response does not match request
    094        if (!now.equals(recMessage.getOriginateTimeStamp())) {
    095            throw new IOException("Originate time does not match the request");
    096        }
    097
    098        // create TimeInfo message container but don't pre-compute the details yet
    099        return new TimeInfo(recMessage, returnTimeMillis, false);
    100    }
    101
    102    /**
    103     * 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.)
    104     *
    105     * @return the NTP protocol version number that client sets on request packet.
    106     * @see #setVersion(int)
    107     */
    108    public int getVersion() {
    109        return version;
    110    }
    111
    112    /**
    113     * Sets the NTP protocol version number that client sets on request packet communicate with remote host.
    114     *
    115     * @param version the NTP protocol version number
    116     */
    117    public void setVersion(final int version) {
    118        this.version = version;
    119    }
    120
    121}