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1   package org.apache.commons.net.ntp;
2   /*
3    * Licensed to the Apache Software Foundation (ASF) under one or more
4    * contributor license agreements.  See the NOTICE file distributed with
5    * this work for additional information regarding copyright ownership.
6    * The ASF licenses this file to You under the Apache License, Version 2.0
7    * (the "License"); you may not use this file except in compliance with
8    * the License.  You may obtain a copy of the License at
9    *
10   *      http://www.apache.org/licenses/LICENSE-2.0
11   *
12   * Unless required by applicable law or agreed to in writing, software
13   * distributed under the License is distributed on an "AS IS" BASIS,
14   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15   * See the License for the specific language governing permissions and
16   * limitations under the License.
17   */
18  
19  
20  import java.io.IOException;
21  import java.net.DatagramPacket;
22  import java.net.InetAddress;
23  
24  import org.apache.commons.net.DatagramSocketClient;
25  
26  /***
27   * The NTPUDPClient class is a UDP implementation of a client for the
28   * Network Time Protocol (NTP) described in RFC 1305 as well as the
29   * Simple Network Time Protocol (SNTP) in RFC-2030. To use the class,
30   * merely open a local datagram socket with <a href="#open"> open </a>
31   * and call <a href="#getTime"> getTime </a> to retrieve the time. Then call
32   * <a href="org.apache.commons.net.DatagramSocketClient.html#close"> close </a>
33   * to close the connection properly.
34   * Successive calls to <a href="#getTime"> getTime </a> are permitted
35   * without re-establishing a connection.  That is because UDP is a
36   * connectionless protocol and the Network Time Protocol is stateless.
37   *
38   * @version $Revision: 1570303 $
39   ***/
40  
41  public final class NTPUDPClient extends DatagramSocketClient
42  {
43      /*** The default NTP port.  It is set to 123 according to RFC 1305. ***/
44      public static final int DEFAULT_PORT = 123;
45  
46      private int _version = NtpV3Packet.VERSION_3;
47  
48      /***
49       * Retrieves the time information from the specified server and port and
50       * returns it. The time is the number of miliiseconds since
51       * 00:00 (midnight) 1 January 1900 UTC, as specified by RFC 1305.
52       * This method reads the raw NTP packet and constructs a <i>TimeInfo</i>
53       * object that allows access to all the fields of the NTP message header.
54       * <p>
55       * @param host The address of the server.
56       * @param port The port of the service.
57       * @return The time value retrieved from the server.
58       * @exception IOException If an error occurs while retrieving the time.
59       ***/
60      public TimeInfo getTime(InetAddress host, int port) throws IOException
61      {
62          // if not connected then open to next available UDP port
63          if (!isOpen())
64          {
65              open();
66          }
67  
68          NtpV3Packet message = new NtpV3Impl();
69          message.setMode(NtpV3Packet.MODE_CLIENT);
70          message.setVersion(_version);
71          DatagramPacket sendPacket = message.getDatagramPacket();
72          sendPacket.setAddress(host);
73          sendPacket.setPort(port);
74  
75          NtpV3Packet recMessage = new NtpV3Impl();
76          DatagramPacket receivePacket = recMessage.getDatagramPacket();
77  
78          /*
79           * Must minimize the time between getting the current time,
80           * timestamping the packet, and sending it out which
81           * introduces an error in the delay time.
82           * No extraneous logging and initializations here !!!
83           */
84          TimeStamp now = TimeStamp.getCurrentTime();
85  
86          // Note that if you do not set the transmit time field then originating time
87          // in server response is all 0's which is "Thu Feb 07 01:28:16 EST 2036".
88          message.setTransmitTime(now);
89  
90          _socket_.send(sendPacket);
91          _socket_.receive(receivePacket);
92  
93          long returnTime = System.currentTimeMillis();
94          // create TimeInfo message container but don't pre-compute the details yet
95          TimeInfo info = new TimeInfo(recMessage, returnTime, false);
96  
97          return info;
98      }
99  
100     /***
101      * Retrieves the time information from the specified server on the
102      * default NTP port and returns it. The time is the number of miliiseconds
103      * since 00:00 (midnight) 1 January 1900 UTC, as specified by RFC 1305.
104      * This method reads the raw NTP packet and constructs a <i>TimeInfo</i>
105      * object that allows access to all the fields of the NTP message header.
106      * <p>
107      * @param host The address of the server.
108      * @return The time value retrieved from the server.
109      * @exception IOException If an error occurs while retrieving the time.
110      ***/
111     public TimeInfo getTime(InetAddress host) throws IOException
112     {
113         return getTime(host, NtpV3Packet.NTP_PORT);
114     }
115 
116     /***
117      * Returns the NTP protocol version number that client sets on request packet
118      * that is sent to remote host (e.g. 3=NTP v3, 4=NTP v4, etc.)
119      *
120      * @return  the NTP protocol version number that client sets on request packet.
121      * @see #setVersion(int)
122      ***/
123     public int getVersion()
124     {
125         return _version;
126     }
127 
128     /***
129      * Sets the NTP protocol version number that client sets on request packet
130      * communicate with remote host.
131      *
132      * @param version the NTP protocol version number
133      ***/
134     public void setVersion(int version)
135     {
136         _version = version;
137     }
138 
139 }