org.rx.third.apache.ntp.NTPUDPClient Maven / Gradle / Ivy
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package org.rx.third.apache.ntp;
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.InetAddress;
/**
* 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 Protocol (SNTP) in RFC-2030. To use the class,
* merely open a local datagram socket with open
* and call getTime to retrieve the time. Then call
* close
* to close the connection properly.
* Successive calls to getTime are permitted
* without re-establishing a connection. That is because UDP is a
* connectionless protocol and the Network Time Protocol is stateless.
*
*/
public final class NTPUDPClient extends DatagramSocketClient
{
/** The default NTP port. It is set to 123 according to RFC 1305. */
public static final int DEFAULT_PORT = 123;
private int version = NtpV3Packet.VERSION_3;
/**
* Retrieves the time information from the specified server and port and
* returns it. The time is the number of miliiseconds since
* 00:00 (midnight) 1 January 1900 UTC, as specified by RFC 1305.
* This method reads the raw NTP packet and constructs a TimeInfo
* object that allows access to all the fields of the NTP message header.
*
* @param host The address of the server.
* @param port The port of the service.
* @return The time value retrieved from the server.
* @throws IOException If an error occurs while retrieving the time.
*/
public TimeInfo getTime(final InetAddress host, final int port) throws IOException
{
// if not connected then open to next available UDP port
if (!isOpen())
{
open();
}
final NtpV3Packet message = new NtpV3Impl();
message.setMode(NtpV3Packet.MODE_CLIENT);
message.setVersion(version);
final DatagramPacket sendPacket = message.getDatagramPacket();
sendPacket.setAddress(host);
sendPacket.setPort(port);
final NtpV3Packet recMessage = new NtpV3Impl();
final DatagramPacket receivePacket = recMessage.getDatagramPacket();
/*
* 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 extraneous logging and initializations here !!!
*/
final TimeStamp now = TimeStamp.getCurrentTime();
// Note that if you do not set the transmit time field then originating time
// in server response is all 0's which is "Thu Feb 07 01:28:16 EST 2036".
message.setTransmitTime(now);
_socket_.send(sendPacket);
_socket_.receive(receivePacket);
final long returnTimeMillis = System.currentTimeMillis();
// create TimeInfo message container but don't pre-compute the details yet
return new TimeInfo(recMessage, returnTimeMillis, false);
}
/**
* Retrieves the time information from the specified server on the
* default NTP port and returns it. The time is the number of miliiseconds
* since 00:00 (midnight) 1 January 1900 UTC, as specified by RFC 1305.
* This method reads the raw NTP packet and constructs a TimeInfo
* object that allows access to all the fields of the NTP message header.
*
* @param host The address of the server.
* @return The time value retrieved from the server.
* @throws IOException If an error occurs while retrieving the time.
*/
public TimeInfo getTime(final InetAddress host) throws IOException
{
return getTime(host, NtpV3Packet.NTP_PORT);
}
/**
* Returns 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.)
*
* @return the NTP protocol version number that client sets on request packet.
* @see #setVersion(int)
*/
public int getVersion()
{
return version;
}
/**
* Sets the NTP protocol version number that client sets on request packet
* communicate with remote host.
*
* @param version the NTP protocol version number
*/
public void setVersion(final int version)
{
this.version = version;
}
}