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}