NtpClient.java 8.50 KiB
package net.i2p.router.time;
/*
* Copyright (c) 2004, Adam Buckley
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* - Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
* - Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
* - Neither the name of Adam Buckley nor the names of its contributors may be
* used to endorse or promote products derived from this software without
* specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
*/
import java.io.IOException;
import java.io.InterruptedIOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.util.ArrayList;
import java.util.Collections;
/**
* NtpClient - an NTP client for Java. This program connects to an NTP server
* and prints the response to the console.
*
* The local clock offset calculation is implemented according to the SNTP
* algorithm specified in RFC 2030.
*
* Note that on windows platforms, the curent time-of-day timestamp is limited
* to an resolution of 10ms and adversely affects the accuracy of the results.
*
* @author Adam Buckley
* (minor refactoring by jrandom)
* @since 0.9.1 moved from net.i2p.time
*/
class NtpClient {
/** difference between the unix epoch and jan 1 1900 (NTP uses that) */
private final static double SECONDS_1900_TO_EPOCH = 2208988800.0;
private final static int NTP_PORT = 123;
private static final int DEFAULT_TIMEOUT = 10*1000;
/**
* Query the ntp servers, returning the current time from first one we find
*
* @return milliseconds since january 1, 1970 (UTC)
* @throws IllegalArgumentException if none of the servers are reachable
*/
public static long currentTime(String serverNames[]) {
if (serverNames == null)
throw new IllegalArgumentException("No NTP servers specified");
ArrayList<String> names = new ArrayList<String>(serverNames.length);
for (int i = 0; i < serverNames.length; i++) names.add(serverNames[i]);
Collections.shuffle(names);
for (int i = 0; i < names.size(); i++) {
long now = currentTime(names.get(i));
if (now > 0)
return now;
}
throw new IllegalArgumentException("No reachable NTP servers specified");
}
/**
* Query the ntp servers, returning the current time from first one we find
* Hack to return time and stratum
* @return time in rv[0] and stratum in rv[1]
* @throws IllegalArgumentException if none of the servers are reachable
* @since 0.7.12
*/
public static long[] currentTimeAndStratum(String serverNames[], int perServerTimeout) {
if (serverNames == null)
throw new IllegalArgumentException("No NTP servers specified");
ArrayList<String> names = new ArrayList<String>(serverNames.length);
for (int i = 0; i < serverNames.length; i++)
names.add(serverNames[i]);
Collections.shuffle(names);
for (int i = 0; i < names.size(); i++) {
long[] rv = currentTimeAndStratum(names.get(i), perServerTimeout);
if (rv != null && rv[0] > 0)
return rv;
}
throw new IllegalArgumentException("No reachable NTP servers specified");
}
/**
* Query the given NTP server, returning the current internet time
*
* @return milliseconds since january 1, 1970 (UTC), or -1 on error
*/
public static long currentTime(String serverName) {
long[] la = currentTimeAndStratum(serverName, DEFAULT_TIMEOUT);
if (la != null)
return la[0];
return -1;
}
/**
* Hack to return time and stratum
* @return time in rv[0] and stratum in rv[1], or null for error
* @since 0.7.12
*/
private static long[] currentTimeAndStratum(String serverName, int timeout) {
DatagramSocket socket = null;
try {
// Send request
socket = new DatagramSocket();
InetAddress address = InetAddress.getByName(serverName);
byte[] buf = new NtpMessage().toByteArray();
DatagramPacket packet = new DatagramPacket(buf, buf.length, address, NTP_PORT);
// Set the transmit timestamp *just* before sending the packet
// ToDo: Does this actually improve performance or not?
NtpMessage.encodeTimestamp(packet.getData(), 40,
(System.currentTimeMillis()/1000.0)
+ SECONDS_1900_TO_EPOCH);
socket.send(packet);
// Get response
packet = new DatagramPacket(buf, buf.length);
socket.setSoTimeout(timeout);
socket.receive(packet);
// Immediately record the incoming timestamp
double destinationTimestamp = (System.currentTimeMillis()/1000.0) + SECONDS_1900_TO_EPOCH;
// Process response
NtpMessage msg = new NtpMessage(packet.getData());
//double roundTripDelay = (destinationTimestamp-msg.originateTimestamp) -
// (msg.receiveTimestamp-msg.transmitTimestamp);
double localClockOffset = ((msg.receiveTimestamp - msg.originateTimestamp) +
(msg.transmitTimestamp - destinationTimestamp)) / 2;
// Stratum must be between 1 (atomic) and 15 (maximum defined value)
// Anything else is right out, treat such responses like errors
if ((msg.stratum < 1) || (msg.stratum > 15)) {
//System.out.println("Response from NTP server of unacceptable stratum " + msg.stratum + ", failing.");
return null;
}
long[] rv = new long[2];
rv[0] = (long)(System.currentTimeMillis() + localClockOffset*1000);
rv[1] = msg.stratum;
//System.out.println("host: " + address.getHostAddress() + " rtt: " + roundTripDelay + " offset: " + localClockOffset + " seconds");
return rv;
} catch (IOException ioe) {
//ioe.printStackTrace();
return null;
} finally {
if (socket != null)
socket.close();
}
}
/****
public static void main(String[] args) throws IOException {
// Process command-line args
if(args.length <= 0) {
printUsage();
return;
// args = new String[] { "ntp1.sth.netnod.se", "ntp2.sth.netnod.se" };
}
long now = currentTime(args);
System.out.println("Current time: " + new java.util.Date(now));
}
static void printUsage() {
System.out.println(
"NtpClient - an NTP client for Java.\n" +
"\n" +
"This program connects to an NTP server and prints the current time to the console.\n" +
"\n" +
"\n" +
"Usage: java NtpClient server[ server]*\n" +
"\n" +
"\n" +
"This program is copyright (c) Adam Buckley 2004 and distributed under the terms\n" +
"of the GNU General Public License. This program is distributed in the hope\n" +
"that it will be useful, but WITHOUT ANY WARRANTY; without even the implied\n" +
"warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU\n" +
"General Public License available at http://www.gnu.org/licenses/gpl.html for\n" +
"more details.");
}
****/
}