001package org.apache.commons.net.ntp; 002/* 003 * Licensed to the Apache Software Foundation (ASF) under one or more 004 * contributor license agreements. See the NOTICE file distributed with 005 * this work for additional information regarding copyright ownership. 006 * The ASF licenses this file to You under the Apache License, Version 2.0 007 * (the "License"); you may not use this file except in compliance with 008 * the License. You may obtain a copy of the License at 009 * 010 * http://www.apache.org/licenses/LICENSE-2.0 011 * 012 * Unless required by applicable law or agreed to in writing, software 013 * distributed under the License is distributed on an "AS IS" BASIS, 014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 015 * See the License for the specific language governing permissions and 016 * limitations under the License. 017 */ 018 019 020import java.io.IOException; 021import java.net.DatagramPacket; 022import java.net.InetAddress; 023 024import org.apache.commons.net.DatagramSocketClient; 025 026/** 027 * The NTPUDPClient class is a UDP implementation of a client for the 028 * Network Time Protocol (NTP) described in RFC 1305 as well as the 029 * Simple Network Time Protocol (SNTP) in RFC-2030. To use the class, 030 * merely open a local datagram socket with <a href="#open"> open </a> 031 * and call <a href="#getTime"> getTime </a> to retrieve the time. Then call 032 * <a href="org.apache.commons.net.DatagramSocketClient.html#close"> close </a> 033 * to close the connection properly. 034 * Successive calls to <a href="#getTime"> getTime </a> are permitted 035 * without re-establishing a connection. That is because UDP is a 036 * connectionless protocol and the Network Time Protocol is stateless. 037 * 038 */ 039 040public final class NTPUDPClient extends DatagramSocketClient 041{ 042 /** The default NTP port. It is set to 123 according to RFC 1305. */ 043 public static final int DEFAULT_PORT = 123; 044 045 private int version = NtpV3Packet.VERSION_3; 046 047 /** 048 * Retrieves the time information from the specified server and port and 049 * returns it. The time is the number of miliiseconds since 050 * 00:00 (midnight) 1 January 1900 UTC, as specified by RFC 1305. 051 * This method reads the raw NTP packet and constructs a <i>TimeInfo</i> 052 * object that allows access to all the fields of the NTP message header. 053 * <p> 054 * @param host The address of the server. 055 * @param port The port of the service. 056 * @return The time value retrieved from the server. 057 * @throws IOException If an error occurs while retrieving the time. 058 */ 059 public TimeInfo getTime(final InetAddress host, final int port) throws IOException 060 { 061 // if not connected then open to next available UDP port 062 if (!isOpen()) 063 { 064 open(); 065 } 066 067 final NtpV3Packet message = new NtpV3Impl(); 068 message.setMode(NtpV3Packet.MODE_CLIENT); 069 message.setVersion(version); 070 final DatagramPacket sendPacket = message.getDatagramPacket(); 071 sendPacket.setAddress(host); 072 sendPacket.setPort(port); 073 074 final NtpV3Packet recMessage = new NtpV3Impl(); 075 final DatagramPacket receivePacket = recMessage.getDatagramPacket(); 076 077 /* 078 * Must minimize the time between getting the current time, 079 * timestamping the packet, and sending it out which 080 * introduces an error in the delay time. 081 * No extraneous logging and initializations here !!! 082 */ 083 final TimeStamp now = TimeStamp.getCurrentTime(); 084 085 // Note that if you do not set the transmit time field then originating time 086 // in server response is all 0's which is "Thu Feb 07 01:28:16 EST 2036". 087 message.setTransmitTime(now); 088 089 _socket_.send(sendPacket); 090 _socket_.receive(receivePacket); 091 092 final long returnTimeMillis = System.currentTimeMillis(); 093 // create TimeInfo message container but don't pre-compute the details yet 094 return new TimeInfo(recMessage, returnTimeMillis, false); 095 } 096 097 /** 098 * Retrieves the time information from the specified server on the 099 * default NTP port and returns it. The time is the number of miliiseconds 100 * since 00:00 (midnight) 1 January 1900 UTC, as specified by RFC 1305. 101 * This method reads the raw NTP packet and constructs a <i>TimeInfo</i> 102 * object that allows access to all the fields of the NTP message header. 103 * <p> 104 * @param host The address of the server. 105 * @return The time value retrieved from the server. 106 * @throws IOException If an error occurs while retrieving the time. 107 */ 108 public TimeInfo getTime(final InetAddress host) throws IOException 109 { 110 return getTime(host, NtpV3Packet.NTP_PORT); 111 } 112 113 /** 114 * Returns the NTP protocol version number that client sets on request packet 115 * that is sent to remote host (e.g. 3=NTP v3, 4=NTP v4, etc.) 116 * 117 * @return the NTP protocol version number that client sets on request packet. 118 * @see #setVersion(int) 119 */ 120 public int getVersion() 121 { 122 return version; 123 } 124 125 /** 126 * Sets the NTP protocol version number that client sets on request packet 127 * communicate with remote host. 128 * 129 * @param version the NTP protocol version number 130 */ 131 public void setVersion(final int version) 132 { 133 this.version = version; 134 } 135 136}