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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.daytime;
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 DaytimeUDPClient class is a UDP implementation of a client for the
28   * Daytime protocol described in RFC 867.  To use the class, merely
29   * open a local datagram socket with
30   * {@link org.apache.commons.net.DatagramSocketClient#open  open }
31   * and call {@link #getTime  getTime } to retrieve the daytime
32   * string, then
33   * call {@link org.apache.commons.net.DatagramSocketClient#close  close }
34   * to close the connection properly.  Unlike
35   * {@link org.apache.commons.net.daytime.DaytimeTCPClient},
36   * successive calls to {@link #getTime  getTime } are permitted
37   * without re-establishing a connection.  That is because UDP is a
38   * connectionless protocol and the Daytime protocol is stateless.
39   * @see DaytimeTCPClient
40   */
41  public final class DaytimeUDPClient extends DatagramSocketClient
42  {
43      /** The default daytime port.  It is set to 13 according to RFC 867. */
44      public static final int DEFAULT_PORT = 13;
45  
46      private final byte[] __dummyData = new byte[1];
47      // Received dates should be less than 256 bytes
48      private final byte[] __timeData = new byte[256];
49  
50      /**
51       * Retrieves the time string from the specified server and port and
52       * returns it.
53       * <p>
54       * @param host The address of the server.
55       * @param port The port of the service.
56       * @return The time string.
57       * @exception IOException If an error occurs while retrieving the time.
58       */
59      public String getTime(InetAddress host, int port) throws IOException
60      {
61          DatagramPacket sendPacket, receivePacket;
62  
63          sendPacket =
64              new DatagramPacket(__dummyData, __dummyData.length, host, port);
65          receivePacket = new DatagramPacket(__timeData, __timeData.length);
66  
67          _socket_.send(sendPacket);
68          _socket_.receive(receivePacket);
69  
70          return new String(receivePacket.getData(), 0, receivePacket.getLength(), getCharsetName()); // Java 1.6 can use getCharset()
71      }
72  
73      /** Same as <code>getTime(host, DaytimeUDPClient.DEFAULT_PORT);</code> */
74      public String getTime(InetAddress host) throws IOException
75      {
76          return getTime(host, DEFAULT_PORT);
77      }
78  
79  }
80