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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   * @author Jason Mathews, MITRE Corp
39   * @version $Revision: 1299238 $
40   ***/
41  
42  public final class NTPUDPClient extends DatagramSocketClient
43  {
44      /*** The default NTP port.  It is set to 123 according to RFC 1305. ***/
45      public static final int DEFAULT_PORT = 123;
46  
47      private int _version = NtpV3Packet.VERSION_3;
48  
49      /***
50       * Retrieves the time information from the specified server and port and
51       * returns it. The time is the number of miliiseconds since
52       * 00:00 (midnight) 1 January 1900 UTC, as specified by RFC 1305.
53       * This method reads the raw NTP packet and constructs a <i>TimeInfo</i>
54       * object that allows access to all the fields of the NTP message header.
55       * <p>
56       * @param host The address of the server.
57       * @param port The port of the service.
58       * @return The time value retrieved from the server.
59       * @exception IOException If an error occurs while retrieving the time.
60       ***/
61      public TimeInfo getTime(InetAddress host, int port) throws IOException
62      {
63          // if not connected then open to next available UDP port
64          if (!isOpen())
65          {
66              open();
67          }
68  
69          NtpV3Packet message = new NtpV3Impl();
70          message.setMode(NtpV3Packet.MODE_CLIENT);
71          message.setVersion(_version);
72          DatagramPacket sendPacket = message.getDatagramPacket();
73          sendPacket.setAddress(host);
74          sendPacket.setPort(port);
75  
76          NtpV3Packet recMessage = new NtpV3Impl();
77          DatagramPacket receivePacket = recMessage.getDatagramPacket();
78  
79          /*
80           * Must minimize the time between getting the current time,
81           * timestamping the packet, and sending it out which
82           * introduces an error in the delay time.
83           * No extraneous logging and initializations here !!!
84           */
85          TimeStamp now = TimeStamp.getCurrentTime();
86  
87          // Note that if you do not set the transmit time field then originating time
88          // in server response is all 0's which is "Thu Feb 07 01:28:16 EST 2036".
89          message.setTransmitTime(now);
90  
91          _socket_.send(sendPacket);
92          _socket_.receive(receivePacket);
93  
94          long returnTime = System.currentTimeMillis();
95          // create TimeInfo message container but don't pre-compute the details yet
96          TimeInfo info = new TimeInfo(recMessage, returnTime, false);
97  
98          return info;
99      }
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 }