1 package org.apache.commons.net.ntp; 2 /* 3 * Licensed to the Apache Software Foundation (ASF) under one or more 4 * contributor license agreements. See the NOTICE file distributed with 5 * this work for additional information regarding copyright ownership. 6 * The ASF licenses this file to You under the Apache License, Version 2.0 7 * (the "License"); you may not use this file except in compliance with 8 * the License. You may obtain a copy of the License at 9 * 10 * http://www.apache.org/licenses/LICENSE-2.0 11 * 12 * Unless required by applicable law or agreed to in writing, software 13 * distributed under the License is distributed on an "AS IS" BASIS, 14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 15 * See the License for the specific language governing permissions and 16 * limitations under the License. 17 */ 18 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 28 * Network Time Protocol (NTP) described in RFC 1305 as well as the 29 * Simple Network Time Protocol (SNTP) in RFC-2030. To use the class, 30 * merely open a local datagram socket with <a href="#open"> open </a> 31 * and call <a href="#getTime"> getTime </a> to retrieve the time. Then call 32 * <a href="org.apache.commons.net.DatagramSocketClient.html#close"> close </a> 33 * to close the connection properly. 34 * Successive calls to <a href="#getTime"> getTime </a> are permitted 35 * without re-establishing a connection. That is because UDP is a 36 * connectionless protocol and the Network Time Protocol is stateless. 37 * 38 * @author Jason Mathews, MITRE Corp 39 * @version $Revision: 489397 $ $Date: 2006-12-21 16:28:51 +0000 (Thu, 21 Dec 2006) $ 40 ***/ 41 42 public final class NTPUDPClient extends DatagramSocketClient 43 { 44 /*** The default NTP port. It is set to 123 according to RFC 1305. ***/ 45 public static final int DEFAULT_PORT = 123; 46 47 private int _version = NtpV3Packet.VERSION_3; 48 49 /*** 50 * Retrieves the time information from the specified server and port and 51 * returns it. The time is the number of miliiseconds since 52 * 00:00 (midnight) 1 January 1900 UTC, as specified by RFC 1305. 53 * This method reads the raw NTP packet and constructs a <i>TimeInfo</i> 54 * object that allows access to all the fields of the NTP message header. 55 * <p> 56 * @param host The address of the server. 57 * @param port The port of the service. 58 * @return The time value retrieved from the server. 59 * @exception IOException If an error occurs while retrieving the time. 60 ***/ 61 public TimeInfo getTime(InetAddress host, int port) throws IOException 62 { 63 // if not connected then open to next available UDP port 64 if (!isOpen()) 65 { 66 open(); 67 } 68 69 NtpV3Packet message = new NtpV3Impl(); 70 message.setMode(NtpV3Packet.MODE_CLIENT); 71 message.setVersion(_version); 72 DatagramPacket sendPacket = message.getDatagramPacket(); 73 sendPacket.setAddress(host); 74 sendPacket.setPort(port); 75 76 NtpV3Packet recMessage = new NtpV3Impl(); 77 DatagramPacket receivePacket = recMessage.getDatagramPacket(); 78 79 /* 80 * Must minimize the time between getting the current time, 81 * timestamping the packet, and sending it out which 82 * introduces an error in the delay time. 83 * No extraneous logging and initializations here !!! 84 */ 85 TimeStamp now = TimeStamp.getCurrentTime(); 86 87 // Note that if you do not set the transmit time field then originating time 88 // in server response is all 0's which is "Thu Feb 07 01:28:16 EST 2036". 89 message.setTransmitTime(now); 90 91 _socket_.send(sendPacket); 92 _socket_.receive(receivePacket); 93 94 long returnTime = System.currentTimeMillis(); 95 // create TimeInfo message container but don't pre-compute the details yet 96 TimeInfo info = new TimeInfo(recMessage, returnTime, false); 97 98 return info; 99 } 100 101 /*** 102 * Retrieves the time information from the specified server on the 103 * default NTP port and returns it. The time is the number of miliiseconds 104 * since 00:00 (midnight) 1 January 1900 UTC, as specified by RFC 1305. 105 * This method reads the raw NTP packet and constructs a <i>TimeInfo</i> 106 * object that allows access to all the fields of the NTP message header. 107 * <p> 108 * @param host The address of the server. 109 * @return The time value retrieved from the server. 110 * @exception IOException If an error occurs while retrieving the time. 111 ***/ 112 public TimeInfo getTime(InetAddress host) throws IOException 113 { 114 return getTime(host, NtpV3Packet.NTP_PORT); 115 } 116 117 /*** 118 * Returns the NTP protocol version number that client sets on request packet 119 * that is sent to remote host (e.g. 3=NTP v3, 4=NTP v4, etc.) 120 * 121 * @return the NTP protocol version number that client sets on request packet. 122 * @see #setVersion(int) 123 ***/ 124 public int getVersion() 125 { 126 return _version; 127 } 128 129 /*** 130 * Sets the NTP protocol version number that client sets on request packet 131 * communicate with remote host. 132 * 133 * @param version the NTP protocol version number 134 ***/ 135 public void setVersion(int version) 136 { 137 _version = version; 138 } 139 140 }