panda.net.ntp.NTPUDPClient Maven / Gradle / Ivy
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package panda.net.ntp;
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.InetAddress;
import panda.net.DatagramSocketClient;
/***
* 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.
* @exception IOException If an error occurs while retrieving the time.
***/
public TimeInfo getTime(InetAddress host, int port) throws IOException {
// if not connected then open to next available UDP port
if (!isOpen()) {
open();
}
NtpV3Packet message = new NtpV3Impl();
message.setMode(NtpV3Packet.MODE_CLIENT);
message.setVersion(_version);
DatagramPacket sendPacket = message.getDatagramPacket();
sendPacket.setAddress(host);
sendPacket.setPort(port);
NtpV3Packet recMessage = new NtpV3Impl();
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 !!!
*/
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);
long returnTime = System.currentTimeMillis();
// create TimeInfo message container but don't pre-compute the details yet
TimeInfo info = new TimeInfo(recMessage, returnTime, false);
return info;
}
/***
* 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.
* @exception IOException If an error occurs while retrieving the time.
***/
public TimeInfo getTime(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(int version) {
_version = version;
}
}