001 package org.apache.commons.net.ntp;
002 /*
003 * Licensed to the Apache Software Foundation (ASF) under one or more
004 * contributor license agreements. See the NOTICE file distributed with
005 * this work for additional information regarding copyright ownership.
006 * The ASF licenses this file to You under the Apache License, Version 2.0
007 * (the "License"); you may not use this file except in compliance with
008 * the License. You may obtain a copy of the License at
009 *
010 * http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018
019
020 import java.io.IOException;
021 import java.net.DatagramPacket;
022 import java.net.InetAddress;
023
024 import org.apache.commons.net.DatagramSocketClient;
025
026 /***
027 * The NTPUDPClient class is a UDP implementation of a client for the
028 * Network Time Protocol (NTP) described in RFC 1305 as well as the
029 * Simple Network Time Protocol (SNTP) in RFC-2030. To use the class,
030 * merely open a local datagram socket with <a href="#open"> open </a>
031 * and call <a href="#getTime"> getTime </a> to retrieve the time. Then call
032 * <a href="org.apache.commons.net.DatagramSocketClient.html#close"> close </a>
033 * to close the connection properly.
034 * Successive calls to <a href="#getTime"> getTime </a> are permitted
035 * without re-establishing a connection. That is because UDP is a
036 * connectionless protocol and the Network Time Protocol is stateless.
037 *
038 * @author Jason Mathews, MITRE Corp
039 * @version $Revision: 1299238 $
040 ***/
041
042 public final class NTPUDPClient extends DatagramSocketClient
043 {
044 /*** The default NTP port. It is set to 123 according to RFC 1305. ***/
045 public static final int DEFAULT_PORT = 123;
046
047 private int _version = NtpV3Packet.VERSION_3;
048
049 /***
050 * Retrieves the time information from the specified server and port and
051 * returns it. The time is the number of miliiseconds since
052 * 00:00 (midnight) 1 January 1900 UTC, as specified by RFC 1305.
053 * This method reads the raw NTP packet and constructs a <i>TimeInfo</i>
054 * object that allows access to all the fields of the NTP message header.
055 * <p>
056 * @param host The address of the server.
057 * @param port The port of the service.
058 * @return The time value retrieved from the server.
059 * @exception IOException If an error occurs while retrieving the time.
060 ***/
061 public TimeInfo getTime(InetAddress host, int port) throws IOException
062 {
063 // if not connected then open to next available UDP port
064 if (!isOpen())
065 {
066 open();
067 }
068
069 NtpV3Packet message = new NtpV3Impl();
070 message.setMode(NtpV3Packet.MODE_CLIENT);
071 message.setVersion(_version);
072 DatagramPacket sendPacket = message.getDatagramPacket();
073 sendPacket.setAddress(host);
074 sendPacket.setPort(port);
075
076 NtpV3Packet recMessage = new NtpV3Impl();
077 DatagramPacket receivePacket = recMessage.getDatagramPacket();
078
079 /*
080 * Must minimize the time between getting the current time,
081 * timestamping the packet, and sending it out which
082 * introduces an error in the delay time.
083 * No extraneous logging and initializations here !!!
084 */
085 TimeStamp now = TimeStamp.getCurrentTime();
086
087 // Note that if you do not set the transmit time field then originating time
088 // in server response is all 0's which is "Thu Feb 07 01:28:16 EST 2036".
089 message.setTransmitTime(now);
090
091 _socket_.send(sendPacket);
092 _socket_.receive(receivePacket);
093
094 long returnTime = System.currentTimeMillis();
095 // create TimeInfo message container but don't pre-compute the details yet
096 TimeInfo info = new TimeInfo(recMessage, returnTime, false);
097
098 return info;
099 }
100
101 /***
102 * Retrieves the time information from the specified server on the
103 * default NTP port and returns it. The time is the number of miliiseconds
104 * since 00:00 (midnight) 1 January 1900 UTC, as specified by RFC 1305.
105 * This method reads the raw NTP packet and constructs a <i>TimeInfo</i>
106 * object that allows access to all the fields of the NTP message header.
107 * <p>
108 * @param host The address of the server.
109 * @return The time value retrieved from the server.
110 * @exception IOException If an error occurs while retrieving the time.
111 ***/
112 public TimeInfo getTime(InetAddress host) throws IOException
113 {
114 return getTime(host, NtpV3Packet.NTP_PORT);
115 }
116
117 /***
118 * Returns the NTP protocol version number that client sets on request packet
119 * that is sent to remote host (e.g. 3=NTP v3, 4=NTP v4, etc.)
120 *
121 * @return the NTP protocol version number that client sets on request packet.
122 * @see #setVersion(int)
123 ***/
124 public int getVersion()
125 {
126 return _version;
127 }
128
129 /***
130 * Sets the NTP protocol version number that client sets on request packet
131 * communicate with remote host.
132 *
133 * @param version the NTP protocol version number
134 ***/
135 public void setVersion(int version)
136 {
137 _version = version;
138 }
139
140 }