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 * https://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 Daytime protocol described in RFC 867. To use the class, merely open a local datagram
28 * socket with {@link org.apache.commons.net.DatagramSocketClient#open open} and call {@link #getTime getTime} to retrieve the daytime string, then call
29 * {@link org.apache.commons.net.DatagramSocketClient#close close} to close the connection properly. Unlike
30 * {@link org.apache.commons.net.daytime.DaytimeTCPClient}, successive calls to {@link #getTime getTime} are permitted without re-establishing a connection.
31 * That is because UDP is a connectionless protocol and the Daytime protocol is stateless.
32 *
33 * @see DaytimeTCPClient
34 */
35 public final class DaytimeUDPClient extends DatagramSocketClient {
36
37 /**
38 * The default daytime port. It is set to 13 according to RFC 867.
39 */
40 public static final int DEFAULT_PORT = 13;
41
42 private final byte[] dummyData = new byte[1];
43
44 /**
45 * Received dates should be less than 256 bytes.
46 */
47 private final byte[] timeData = new byte[256];
48
49 /**
50 * Constructs a new instance.
51 */
52 public DaytimeUDPClient() {
53 // empty
54 }
55
56 /**
57 * Gets the time string from the specified server and port and returns it.
58 * <p>
59 * Shorthand for {@code getTime(host, DaytimeUDPClient.DEFAULT_PORT);}
60 * </p>
61 *
62 * @param host the host
63 * @return the time
64 * @throws IOException on error
65 */
66 public String getTime(final InetAddress host) throws IOException {
67 return getTime(host, DEFAULT_PORT);
68 }
69
70 /**
71 * Gets the time string from the specified server and port and returns it.
72 *
73 * @param host The address of the server.
74 * @param port The port of the service.
75 * @return The time string.
76 * @throws IOException If an error occurs while retrieving the time.
77 */
78 public String getTime(final InetAddress host, final int port) throws IOException {
79 final DatagramPacket sendPacket = new DatagramPacket(dummyData, dummyData.length, host, port);
80 final DatagramPacket receivePacket = new DatagramPacket(timeData, timeData.length);
81 checkOpen().send(sendPacket);
82 checkOpen().receive(receivePacket);
83 return new String(receivePacket.getData(), 0, receivePacket.getLength(), getCharset());
84 }
85
86 }