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1   package org.apache.commons.net.ntp;
2   /*
3    * Copyright 2001-2005 The Apache Software Foundation
4    *
5    * Licensed under the Apache License, Version 2.0 (the "License");
6    * you may not use this file except in compliance with the License.
7    * You may obtain a copy of the License at
8    *
9    *     http://www.apache.org/licenses/LICENSE-2.0
10   *
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  
18  import java.io.IOException;
19  import java.net.DatagramPacket;
20  import java.net.InetAddress;
21  import org.apache.commons.net.DatagramSocketClient;
22  
23  /***
24   * The NTPUDPClient class is a UDP implementation of a client for the
25   * Network Time Protocol (NTP) described in RFC 1305 as well as the
26   * Simple Network Time Protocol (SNTP) in RFC-2030. To use the class,
27   * merely open a local datagram socket with <a href="#open"> open </a>
28   * and call <a href="#getTime"> getTime </a> to retrieve the time. Then call
29   * <a href="org.apache.commons.net.DatagramSocketClient.html#close"> close </a>
30   * to close the connection properly.
31   * Successive calls to <a href="#getTime"> getTime </a> are permitted
32   * without re-establishing a connection.  That is because UDP is a
33   * connectionless protocol and the Network Time Protocol is stateless.
34   *
35   * @author Jason Mathews, MITRE Corp
36   * @version $Revision: 165675 $ $Date: 2005-05-02 15:09:55 -0500 (Mon, 02 May 2005) $
37   ***/
38  
39  public final class NTPUDPClient extends DatagramSocketClient
40  {
41      /*** The default NTP port.  It is set to 123 according to RFC 1305. ***/
42      public static final int DEFAULT_PORT = 123;
43  
44      private int _version = NtpV3Packet.VERSION_3;
45  
46      /***
47       * Retrieves the time information from the specified server and port and
48       * returns it. The time is the number of miliiseconds since
49       * 00:00 (midnight) 1 January 1900 UTC, as specified by RFC 1305.
50       * This method reads the raw NTP packet and constructs a <i>TimeInfo</i>
51       * object that allows access to all the fields of the NTP message header.
52       * <p>
53       * @param host The address of the server.
54       * @param port The port of the service.
55       * @return The time value retrieved from the server.
56       * @exception IOException If an error occurs while retrieving the time.
57       ***/
58      public TimeInfo getTime(InetAddress host, int port) throws IOException
59      {
60          // if not connected then open to next available UDP port
61          if (!isOpen())
62          {
63              open();
64          }
65  
66          NtpV3Packet message = new NtpV3Impl();
67          message.setMode(NtpV3Packet.MODE_CLIENT);
68          message.setVersion(_version);
69          DatagramPacket sendPacket = message.getDatagramPacket();
70          sendPacket.setAddress(host);
71          sendPacket.setPort(port);
72  
73          NtpV3Packet recMessage = new NtpV3Impl();
74          DatagramPacket receivePacket = recMessage.getDatagramPacket();
75  
76          /*
77           * Must minimize the time between getting the current time,
78           * timestamping the packet, and sending it out which
79           * introduces an error in the delay time.
80           * No extraneous logging and initializations here !!!
81           */
82          TimeStamp now = TimeStamp.getCurrentTime();
83  
84          // Note that if you do not set the transmit time field then originating time
85          // in server response is all 0's which is "Thu Feb 07 01:28:16 EST 2036".
86          message.setTransmitTime(now);
87  
88          _socket_.send(sendPacket);
89          _socket_.receive(receivePacket);
90  
91          long returnTime = System.currentTimeMillis();
92          // create TimeInfo message container but don't pre-compute the details yet
93          TimeInfo info = new TimeInfo(recMessage, returnTime, false);
94  
95          return info;
96      }
97  
98      /***
99       * 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 }