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 Time protocol described in RFC 868. To use the class, merely open a local datagram socket
29 * with {@link org.apache.commons.net.DatagramSocketClient#open open } and call {@link #getTime getTime } or {@link #getTime getDate } to retrieve the time.
30 * Then call {@link org.apache.commons.net.DatagramSocketClient#close close } to close the connection properly. Unlike
31 * {@link org.apache.commons.net.time.TimeTCPClient}, successive calls to {@link #getTime getTime } or {@link #getDate getDate } are permitted without
32 * re-establishing a connection. That is because UDP is a connectionless protocol and the Time protocol is stateless.
33 *
34 *
35 * @see TimeTCPClient
36 */
37
38 public final class TimeUDPClient extends DatagramSocketClient {
39
40 /** The default time port. It is set to 37 according to RFC 868. */
41 public static final int DEFAULT_PORT = 37;
42
43 /**
44 * The number of seconds between 00:00 1 January 1900 and 00:00 1 January 1970. This value can be useful for converting time values to other formats.
45 */
46 public static final long SECONDS_1900_TO_1970 = 2208988800L;
47
48 static long toTime(final byte[] timeData) {
49 long time = 0L;
50 time |= (timeData[0] & 0xff) << 24 & 0xffffffffL;
51 time |= (timeData[1] & 0xff) << 16 & 0xffffffffL;
52 time |= (timeData[2] & 0xff) << 8 & 0xffffffffL;
53 time |= timeData[3] & 0xff & 0xffffffffL;
54 return time;
55 }
56
57 /**
58 * Same as <code>getTime(host, DEFAULT_PORT);</code>
59 *
60 * @param host the time-server
61 * @return the date
62 * @throws IOException on error
63 */
64 public Date getDate(final InetAddress host) throws IOException {
65 return new Date((getTime(host, DEFAULT_PORT) - SECONDS_1900_TO_1970) * 1000L);
66 }
67
68 /**
69 * Retrieves the time from the server and returns a Java Date containing the time converted to the local time zone.
70 *
71 * @param host The address of the server.
72 * @param port The port of the service.
73 * @return A Date value containing the time retrieved from the server converted to the local time zone.
74 * @throws IOException If an error occurs while fetching the time.
75 */
76 public Date getDate(final InetAddress host, final int port) throws IOException {
77 return new Date((getTime(host, port) - SECONDS_1900_TO_1970) * 1000L);
78 }
79
80 /**
81 * Same as <code>getTime(host, DEFAULT_PORT);</code>
82 *
83 * @param host the time-server
84 * @return the time returned from the server
85 * @throws IOException on error
86 */
87 public long getTime(final InetAddress host) throws IOException {
88 return getTime(host, DEFAULT_PORT);
89 }
90
91 /**
92 * Retrieves the time from the specified server and port and returns it. The time is the number of seconds since 00:00 (midnight) 1 January 1900 GMT, as
93 * specified by RFC 868. This method reads the raw 32-bit big-endian unsigned integer from the server, converts it to a Java long, and returns the value.
94 *
95 * @param host The address of the server.
96 * @param port The port of the service.
97 * @return The time value retrieved from the server.
98 * @throws IOException If an error occurs while retrieving the time.
99 */
100 public long getTime(final InetAddress host, final int port) throws IOException {
101 final byte[] dummyData = new byte[1];
102 final byte[] timeData = new byte[4];
103
104 final DatagramPacket sendPacket = new DatagramPacket(dummyData, dummyData.length, host, port);
105 final DatagramPacket receivePacket = new DatagramPacket(timeData, timeData.length);
106
107 checkOpen().send(sendPacket);
108 checkOpen().receive(receivePacket);
109
110 return toTime(timeData);
111 }
112
113 }