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.ntp;
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 Network Time Protocol (NTP) described in RFC 1305 as well as the Simple Network Time
28 * Protocol (SNTP) in RFC-2030. To use the class, merely open a local datagram socket with <a href="#open"> open </a> and call <a href="#getTime"> getTime </a>
29 * to retrieve the time. Then call <a href="org.apache.commons.net.DatagramSocketClient.html#close"> close </a> to close the connection properly. Successive
30 * calls to <a href="#getTime"> getTime </a> are permitted without re-establishing a connection. That is because UDP is a connectionless protocol and the
31 * Network Time Protocol is stateless.
32 */
33 public final class NTPUDPClient extends DatagramSocketClient {
34 /** The default NTP port. It is set to 123 according to RFC 1305. */
35 public static final int DEFAULT_PORT = 123;
36
37 private int version = NtpV3Packet.VERSION_3;
38
39 /**
40 * Constructs a new instance.
41 */
42 public NTPUDPClient() {
43 // empty
44 }
45
46 /**
47 * Gets the time information from the specified server on the default NTP port and returns it. The time is the number of milliseconds since 00:00
48 * (midnight) 1 January 1900 UTC, as specified by RFC 1305. This method reads the raw NTP packet and constructs a <em>TimeInfo</em> object that allows
49 * access to all the fields of the NTP message header.
50 *
51 * @param host The address of the server.
52 * @return The time value retrieved from the server.
53 * @throws IOException If an error occurs while retrieving the time.
54 */
55 public TimeInfo getTime(final InetAddress host) throws IOException {
56 return getTime(host, NtpV3Packet.NTP_PORT);
57 }
58
59 /**
60 * Gets the time information from the specified server and port and returns it. The time is the number of milliseconds since 00:00 (midnight) 1 January
61 * 1900 UTC, as specified by RFC 1305. This method reads the raw NTP packet and constructs a <em>TimeInfo</em> object that allows access to all the fields
62 * of the NTP message header.
63 *
64 * @param host The address of the server.
65 * @param port The port of the service.
66 * @return The time value retrieved from the server.
67 * @throws IOException If an error occurs while retrieving the time or if received packet does not match the request.
68 */
69 public TimeInfo getTime(final InetAddress host, final int port) throws IOException {
70 // if not connected then open to next available UDP port
71 if (!isOpen()) {
72 open();
73 }
74
75 final NtpV3Packet message = new NtpV3Impl();
76 message.setMode(NtpV3Packet.MODE_CLIENT);
77 message.setVersion(version);
78 final DatagramPacket sendPacket = message.getDatagramPacket();
79 sendPacket.setAddress(host);
80 sendPacket.setPort(port);
81
82 final NtpV3Packet recMessage = new NtpV3Impl();
83 final DatagramPacket receivePacket = recMessage.getDatagramPacket();
84
85 /*
86 * Must minimize the time between getting the current time, timestamping the packet, and sending it out which introduces an error in the delay time. No
87 * extraneous logging and initializations here !!!
88 */
89 final TimeStamp now = TimeStamp.getCurrentTime();
90
91 // Note that if you do not set the transmit time field then originating time
92 // in server response is all 0's which is "Thu Feb 07 01:28:16 EST 2036".
93 message.setTransmitTime(now);
94
95 checkOpen().send(sendPacket);
96 checkOpen().receive(receivePacket);
97
98 final long returnTimeMillis = System.currentTimeMillis();
99
100 // Prevent invalid time information if response does not match request
101 if (!now.equals(recMessage.getOriginateTimeStamp())) {
102 throw new IOException("Originate time does not match the request");
103 }
104
105 // create TimeInfo message container but don't pre-compute the details yet
106 return new TimeInfo(recMessage, returnTimeMillis, false);
107 }
108
109 /**
110 * Gets the NTP protocol version number that client sets on request packet that is sent to remote host (e.g. 3=NTP v3, 4=NTP v4, etc.)
111 *
112 * @return the NTP protocol version number that client sets on request packet.
113 * @see #setVersion(int)
114 */
115 public int getVersion() {
116 return version;
117 }
118
119 /**
120 * Sets the NTP protocol version number that client sets on request packet communicate with remote host.
121 *
122 * @param version the NTP protocol version number
123 */
124 public void setVersion(final int version) {
125 this.version = version;
126 }
127
128 }