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 *      https://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     * Constructs a new instance.
041     */
042    public NTPUDPClient() {
043        // empty
044    }
045
046    /**
047     * Gets 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
048     * (midnight) 1 January 1900 UTC, as specified by RFC 1305. This method reads the raw NTP packet and constructs a <em>TimeInfo</em> object that allows
049     * access to all the fields of the NTP message header.
050     *
051     * @param host The address of the server.
052     * @return The time value retrieved from the server.
053     * @throws IOException If an error occurs while retrieving the time.
054     */
055    public TimeInfo getTime(final InetAddress host) throws IOException {
056        return getTime(host, NtpV3Packet.NTP_PORT);
057    }
058
059    /**
060     * Gets 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
061     * 1900 UTC, as specified by RFC 1305. This method reads the raw NTP packet and constructs a <em>TimeInfo</em> object that allows access to all the fields
062     * of the NTP message header.
063     *
064     * @param host The address of the server.
065     * @param port The port of the service.
066     * @return The time value retrieved from the server.
067     * @throws IOException If an error occurs while retrieving the time or if received packet does not match the request.
068     */
069    public TimeInfo getTime(final InetAddress host, final int port) throws IOException {
070        // if not connected then open to next available UDP port
071        if (!isOpen()) {
072            open();
073        }
074
075        final NtpV3Packet message = new NtpV3Impl();
076        message.setMode(NtpV3Packet.MODE_CLIENT);
077        message.setVersion(version);
078        final DatagramPacket sendPacket = message.getDatagramPacket();
079        sendPacket.setAddress(host);
080        sendPacket.setPort(port);
081
082        final NtpV3Packet recMessage = new NtpV3Impl();
083        final DatagramPacket receivePacket = recMessage.getDatagramPacket();
084
085        /*
086         * 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
087         * extraneous logging and initializations here !!!
088         */
089        final TimeStamp now = TimeStamp.getCurrentTime();
090
091        // Note that if you do not set the transmit time field then originating time
092        // in server response is all 0's which is "Thu Feb 07 01:28:16 EST 2036".
093        message.setTransmitTime(now);
094
095        checkOpen().send(sendPacket);
096        checkOpen().receive(receivePacket);
097
098        final long returnTimeMillis = System.currentTimeMillis();
099
100        // Prevent invalid time information if response does not match request
101        if (!now.equals(recMessage.getOriginateTimeStamp())) {
102            throw new IOException("Originate time does not match the request");
103        }
104
105        // create TimeInfo message container but don't pre-compute the details yet
106        return new TimeInfo(recMessage, returnTimeMillis, false);
107    }
108
109    /**
110     * Gets 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.)
111     *
112     * @return the NTP protocol version number that client sets on request packet.
113     * @see #setVersion(int)
114     */
115    public int getVersion() {
116        return version;
117    }
118
119    /**
120     * Sets the NTP protocol version number that client sets on request packet communicate with remote host.
121     *
122     * @param version the NTP protocol version number
123     */
124    public void setVersion(final int version) {
125        this.version = version;
126    }
127
128}