001/* 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache License, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 */ 017package examples.ntp; 018 019import org.apache.commons.net.ntp.NtpUtils; 020import org.apache.commons.net.ntp.NtpV3Impl; 021import org.apache.commons.net.ntp.NtpV3Packet; 022import org.apache.commons.net.ntp.TimeStamp; 023 024import java.io.IOException; 025import java.net.DatagramPacket; 026import java.net.DatagramSocket; 027 028/** 029 * The SimpleNTPServer class is a UDP implementation of a server for the 030 * Network Time Protocol (NTP) version 3 as described in RFC 1305. 031 * It is a minimal NTP server that doesn't actually adjust the time but 032 * only responds to NTP datagram requests with response sent back to 033 * originating host with info filled out using the current clock time. 034 * To be used for debugging or testing. 035 * 036 * To prevent this from interfering with the actual NTP service it can be 037 * run from any local port. 038 */ 039public class SimpleNTPServer implements Runnable { 040 041 private int port; 042 043 private volatile boolean running; 044 private boolean started; 045 046 private DatagramSocket socket; 047 048 /** 049 * Create SimpleNTPServer listening on default NTP port. 050 */ 051 public SimpleNTPServer() 052 { 053 this(NtpV3Packet.NTP_PORT); 054 } 055 056 /** 057 * Create SimpleNTPServer. 058 * 059 * @param port the local port the server socket is bound to, or 060 * <code>zero</code> for a system selected free port. 061 * @throws IllegalArgumentException if port number less than 0 062 */ 063 public SimpleNTPServer(int port) 064 { 065 if (port < 0) { 066 throw new IllegalArgumentException(); 067 } 068 this.port = port; 069 } 070 071 public int getPort() 072 { 073 return port; 074 } 075 076 /** 077 * Return state of whether time service is running. 078 * 079 * @return true if time service is running 080 */ 081 public boolean isRunning() 082 { 083 return running; 084 } 085 086 /** 087 * Return state of whether time service is running. 088 * 089 * @return true if time service is running 090 */ 091 public boolean isStarted() 092 { 093 return started; 094 } 095 096 /** 097 * Connect to server socket and listen for client connections. 098 * 099 * @throws IOException if an I/O error occurs when creating the socket. 100 */ 101 public void connect() throws IOException 102 { 103 if (socket == null) 104 { 105 socket = new DatagramSocket(port); 106 // port = 0 is bound to available free port 107 if (port == 0) { 108 port = socket.getLocalPort(); 109 } 110 System.out.println("Running NTP service on port " + port + "/UDP"); 111 } 112 } 113 114 /** 115 * Start time service and provide time to client connections. 116 * 117 * @throws java.io.IOException if an I/O error occurs when creating the socket. 118 */ 119 public void start() throws IOException 120 { 121 if (socket == null) 122 { 123 connect(); 124 } 125 if (!started) 126 { 127 started = true; 128 new Thread(this).start(); 129 } 130 } 131 132 /** 133 * main thread to service client connections. 134 */ 135 @Override 136 public void run() 137 { 138 running = true; 139 byte buffer[] = new byte[48]; 140 final DatagramPacket request = new DatagramPacket(buffer, buffer.length); 141 do { 142 try { 143 socket.receive(request); 144 final long rcvTime = System.currentTimeMillis(); 145 handlePacket(request, rcvTime); 146 } catch (IOException e) { 147 if (running) 148 { 149 e.printStackTrace(); 150 } 151 // otherwise socket thrown exception during shutdown 152 } 153 } while (running); 154 } 155 156 /** 157 * Handle incoming packet. If NTP packet is client-mode then respond 158 * to that host with a NTP response packet otherwise ignore. 159 * 160 * @param request incoming DatagramPacket 161 * @param rcvTime time packet received 162 * 163 * @throws IOException if an I/O error occurs. 164 */ 165 protected void handlePacket(DatagramPacket request, long rcvTime) throws IOException 166 { 167 NtpV3Packet message = new NtpV3Impl(); 168 message.setDatagramPacket(request); 169 System.out.printf("NTP packet from %s mode=%s%n", request.getAddress().getHostAddress(), 170 NtpUtils.getModeName(message.getMode())); 171 if (message.getMode() == NtpV3Packet.MODE_CLIENT) { 172 NtpV3Packet response = new NtpV3Impl(); 173 174 response.setStratum(1); 175 response.setMode(NtpV3Packet.MODE_SERVER); 176 response.setVersion(NtpV3Packet.VERSION_3); 177 response.setPrecision(-20); 178 response.setPoll(0); 179 response.setRootDelay(62); 180 response.setRootDispersion((int) (16.51 * 65.536)); 181 182 // originate time as defined in RFC-1305 (t1) 183 response.setOriginateTimeStamp(message.getTransmitTimeStamp()); 184 // Receive Time is time request received by server (t2) 185 response.setReceiveTimeStamp(TimeStamp.getNtpTime(rcvTime)); 186 response.setReferenceTime(response.getReceiveTimeStamp()); 187 response.setReferenceId(0x4C434C00); // LCL (Undisciplined Local Clock) 188 189 // Transmit time is time reply sent by server (t3) 190 response.setTransmitTime(TimeStamp.getNtpTime(System.currentTimeMillis())); 191 192 DatagramPacket dp = response.getDatagramPacket(); 193 dp.setPort(request.getPort()); 194 dp.setAddress(request.getAddress()); 195 socket.send(dp); 196 } 197 // otherwise if received packet is other than CLIENT mode then ignore it 198 } 199 200 /** 201 * Close server socket and stop listening. 202 */ 203 public void stop() 204 { 205 running = false; 206 if (socket != null) 207 { 208 socket.close(); // force closing of the socket 209 socket = null; 210 } 211 started = false; 212 } 213 214 public static void main(String[] args) 215 { 216 int port = NtpV3Packet.NTP_PORT; 217 if (args.length != 0) 218 { 219 try { 220 port = Integer.parseInt(args[0]); 221 } catch (NumberFormatException nfe) { 222 nfe.printStackTrace(); 223 } 224 } 225 SimpleNTPServer timeServer = new SimpleNTPServer(port); 226 try { 227 timeServer.start(); 228 } catch (IOException e) { 229 e.printStackTrace(); 230 } 231 } 232 233}