001 package org.apache.commons.net.ntp;
002 /*
003 * Copyright 2001-2005 The Apache Software Foundation
004 *
005 * Licensed under the Apache License, Version 2.0 (the "License");
006 * you may not use this file except in compliance with the License.
007 * 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
018 import java.io.IOException;
019 import java.net.DatagramPacket;
020 import java.net.InetAddress;
021 import org.apache.commons.net.DatagramSocketClient;
022
023 /***
024 * The NTPUDPClient class is a UDP implementation of a client for the
025 * Network Time Protocol (NTP) described in RFC 1305 as well as the
026 * Simple Network Time Protocol (SNTP) in RFC-2030. To use the class,
027 * merely open a local datagram socket with <a href="#open"> open </a>
028 * and call <a href="#getTime"> getTime </a> to retrieve the time. Then call
029 * <a href="org.apache.commons.net.DatagramSocketClient.html#close"> close </a>
030 * to close the connection properly.
031 * Successive calls to <a href="#getTime"> getTime </a> are permitted
032 * without re-establishing a connection. That is because UDP is a
033 * connectionless protocol and the Network Time Protocol is stateless.
034 *
035 * @author Jason Mathews, MITRE Corp
036 * @version $Revision: 165675 $ $Date: 2005-05-02 21:09:55 +0100 (Mon, 02 May 2005) $
037 ***/
038
039 public final class NTPUDPClient extends DatagramSocketClient
040 {
041 /*** The default NTP port. It is set to 123 according to RFC 1305. ***/
042 public static final int DEFAULT_PORT = 123;
043
044 private int _version = NtpV3Packet.VERSION_3;
045
046 /***
047 * Retrieves the time information from the specified server and port and
048 * returns it. The time is the number of miliiseconds since
049 * 00:00 (midnight) 1 January 1900 UTC, as specified by RFC 1305.
050 * This method reads the raw NTP packet and constructs a <i>TimeInfo</i>
051 * object that allows access to all the fields of the NTP message header.
052 * <p>
053 * @param host The address of the server.
054 * @param port The port of the service.
055 * @return The time value retrieved from the server.
056 * @exception IOException If an error occurs while retrieving the time.
057 ***/
058 public TimeInfo getTime(InetAddress host, int port) throws IOException
059 {
060 // if not connected then open to next available UDP port
061 if (!isOpen())
062 {
063 open();
064 }
065
066 NtpV3Packet message = new NtpV3Impl();
067 message.setMode(NtpV3Packet.MODE_CLIENT);
068 message.setVersion(_version);
069 DatagramPacket sendPacket = message.getDatagramPacket();
070 sendPacket.setAddress(host);
071 sendPacket.setPort(port);
072
073 NtpV3Packet recMessage = new NtpV3Impl();
074 DatagramPacket receivePacket = recMessage.getDatagramPacket();
075
076 /*
077 * Must minimize the time between getting the current time,
078 * timestamping the packet, and sending it out which
079 * introduces an error in the delay time.
080 * No extraneous logging and initializations here !!!
081 */
082 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 _socket_.send(sendPacket);
089 _socket_.receive(receivePacket);
090
091 long returnTime = System.currentTimeMillis();
092 // create TimeInfo message container but don't pre-compute the details yet
093 TimeInfo info = new TimeInfo(recMessage, returnTime, false);
094
095 return info;
096 }
097
098 /***
099 * Retrieves the time information from the specified server on the
100 * default NTP port and returns it. The time is the number of miliiseconds
101 * since 00:00 (midnight) 1 January 1900 UTC, as specified by RFC 1305.
102 * This method reads the raw NTP packet and constructs a <i>TimeInfo</i>
103 * object that allows access to all the fields of the NTP message header.
104 * <p>
105 * @param host The address of the server.
106 * @return The time value retrieved from the server.
107 * @exception IOException If an error occurs while retrieving the time.
108 ***/
109 public TimeInfo getTime(InetAddress host) throws IOException
110 {
111 return getTime(host, NtpV3Packet.NTP_PORT);
112 }
113
114 /***
115 * Returns the NTP protocol version number that client sets on request packet
116 * that is sent to remote host (e.g. 3=NTP v3, 4=NTP v4, etc.)
117 *
118 * @return the NTP protocol version number that client sets on request packet.
119 * @see #setVersion(int)
120 ***/
121 public int getVersion()
122 {
123 return _version;
124 }
125
126 /***
127 * Sets the NTP protocol version number that client sets on request packet
128 * communicate with remote host.
129 *
130 * @param version the NTP protocol version number
131 ***/
132 public void setVersion(int version)
133 {
134 _version = version;
135 }
136
137 }