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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  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  package org.apache.commons.net.time;
19  
20  import java.io.IOException;
21  import java.net.DatagramPacket;
22  import java.net.InetAddress;
23  import java.util.Date;
24  
25  import org.apache.commons.net.DatagramSocketClient;
26  
27  /***
28   * The TimeUDPClient class is a UDP implementation of a client for the
29   * Time protocol described in RFC 868.  To use the class, merely
30   * open a local datagram socket with
31   * {@link org.apache.commons.net.DatagramSocketClient#open  open }
32   * and call {@link #getTime  getTime } or
33   * {@link #getTime  getDate } to retrieve the time. Then call
34   * {@link org.apache.commons.net.DatagramSocketClient#close  close }
35   * to close the connection properly.  Unlike
36   * {@link org.apache.commons.net.time.TimeTCPClient},
37   * successive calls to {@link #getTime  getTime } or
38   * {@link #getDate  getDate } are permitted
39   * without re-establishing a connection.  That is because UDP is a
40   * connectionless protocol and the Time protocol is stateless.
41   * <p>
42   * <p>
43   * @see TimeTCPClient
44   ***/
45  
46  public final class TimeUDPClient extends DatagramSocketClient
47  {
48      /*** The default time port.  It is set to 37 according to RFC 868. ***/
49      public static final int DEFAULT_PORT = 37;
50  
51      /***
52       * The number of seconds between 00:00 1 January 1900 and
53       * 00:00 1 January 1970.  This value can be useful for converting
54       * time values to other formats.
55       ***/
56      public static final long SECONDS_1900_TO_1970 = 2208988800L;
57  
58      private final byte[] __dummyData = new byte[1];
59      private final byte[] __timeData = new byte[4];
60  
61      /***
62       * Retrieves the time from the specified server and port and
63       * returns it. The time is the number of seconds since
64       * 00:00 (midnight) 1 January 1900 GMT, as specified by RFC 868.
65       * This method reads the raw 32-bit big-endian
66       * unsigned integer from the server, converts it to a Java long, and
67       * returns the value.
68       * <p>
69       * @param host The address of the server.
70       * @param port The port of the service.
71       * @return The time value retrieved from the server.
72       * @exception IOException If an error occurs while retrieving the time.
73       ***/
74      public long getTime(InetAddress host, int port) throws IOException
75      {
76          long time;
77          DatagramPacket sendPacket, receivePacket;
78  
79          sendPacket =
80              new DatagramPacket(__dummyData, __dummyData.length, host, port);
81          receivePacket = new DatagramPacket(__timeData, __timeData.length);
82  
83          _socket_.send(sendPacket);
84          _socket_.receive(receivePacket);
85  
86          time = 0L;
87          time |= (((__timeData[0] & 0xff) << 24) & 0xffffffffL);
88          time |= (((__timeData[1] & 0xff) << 16) & 0xffffffffL);
89          time |= (((__timeData[2] & 0xff) << 8) & 0xffffffffL);
90          time |= ((__timeData[3] & 0xff) & 0xffffffffL);
91  
92          return time;
93      }
94  
95      /*** Same as <code> getTime(host, DEFAULT_PORT); </code> ***/
96      public long getTime(InetAddress host) throws IOException
97      {
98          return getTime(host, DEFAULT_PORT);
99      }
100 
101 
102     /***
103      * Retrieves the time from the server and returns a Java Date
104      * containing the time converted to the local timezone.
105      * <p>
106      * @param host The address of the server.
107      * @param port The port of the service.
108      * @return A Date value containing the time retrieved from the server
109      *     converted to the local timezone.
110      * @exception IOException  If an error occurs while fetching the time.
111      ***/
112     public Date getDate(InetAddress host, int port) throws IOException
113     {
114         return new Date((getTime(host, port) - SECONDS_1900_TO_1970)*1000L);
115     }
116 
117 
118     /*** Same as <code> getTime(host, DEFAULT_PORT); </code> ***/
119     public Date getDate(InetAddress host) throws IOException
120     {
121         return new Date((getTime(host, DEFAULT_PORT) -
122                          SECONDS_1900_TO_1970)*1000L);
123     }
124 
125 }
126