TimeUDPClient.java

  1. /*
  2.  * Licensed to the Apache Software Foundation (ASF) under one or more
  3.  * contributor license agreements.  See the NOTICE file distributed with
  4.  * this work for additional information regarding copyright ownership.
  5.  * The ASF licenses this file to You under the Apache License, Version 2.0
  6.  * (the "License"); you may not use this file except in compliance with
  7.  * the License.  You may obtain a copy of the License at
  8.  *
  9.  *      https://www.apache.org/licenses/LICENSE-2.0
  10.  *
  11.  * Unless required by applicable law or agreed to in writing, software
  12.  * distributed under the License is distributed on an "AS IS" BASIS,
  13.  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  14.  * See the License for the specific language governing permissions and
  15.  * limitations under the License.
  16.  */

  18. package org.apache.commons.net.time;

  20. import java.io.IOException;
  21. import java.net.DatagramPacket;
  22. import java.net.InetAddress;
  23. import java.util.Date;

  25. import org.apache.commons.net.DatagramSocketClient;

  27. /**
  28.  * The TimeUDPClient class is a UDP implementation of a client for the Time protocol described in RFC 868. To use the class, merely open a local datagram socket
  29.  * with {@link org.apache.commons.net.DatagramSocketClient#open open} and call {@link #getTime getTime} or {@link #getTime getDate} to retrieve the time.
  30.  * Then call {@link org.apache.commons.net.DatagramSocketClient#close close} to close the connection properly. Unlike
  31.  * {@link org.apache.commons.net.time.TimeTCPClient}, successive calls to {@link #getTime getTime} or {@link #getDate getDate} are permitted without
  32.  * re-establishing a connection. That is because UDP is a connectionless protocol and the Time protocol is stateless.
  33.  *
  34.  *
  35.  * @see TimeTCPClient
  36.  */
  37. public final class TimeUDPClient extends DatagramSocketClient {

  39.     /** The default time port. It is set to 37 according to RFC 868. */
  40.     public static final int DEFAULT_PORT = 37;

  42.     /**
  43.      * The number of seconds between 00:00 1 January 1900 and 00:00 1 January 1970. This value can be useful for converting time values to other formats.
  44.      */
  45.     public static final long SECONDS_1900_TO_1970 = 2208988800L;

  47.     static long toTime(final byte[] timeData) {
  48.         long time = 0L;
  49.         time |= (timeData[0] & 0xff) << 24 & 0xffffffffL;
  50.         time |= (timeData[1] & 0xff) << 16 & 0xffffffffL;
  51.         time |= (timeData[2] & 0xff) << 8 & 0xffffffffL;
  52.         time |= timeData[3] & 0xff & 0xffffffffL;
  53.         return time;
  54.     }

  56.     /**
  57.      * Constructs a new instance.
  58.      */
  59.     public TimeUDPClient() {
  60.         // empty
  61.     }

  63.     /**
  64.      * Gets the time from a server and returns a Java Date containing the time converted to the local time zone.
  65.      *
  66.      * @param host the time-server
  67.      * @return the date
  68.      * @throws IOException on error
  69.      */
  70.     public Date getDate(final InetAddress host) throws IOException {
  71.         return new Date((getTime(host, DEFAULT_PORT) - SECONDS_1900_TO_1970) * 1000L);
  72.     }

  74.     /**
  75.      * Gets the time from a server and returns a Java Date containing the time converted to the local time zone.
  76.      *
  77.      * @param host The address of the server.
  78.      * @param port The port of the service.
  79.      * @return A Date value containing the time retrieved from the server converted to the local time zone.
  80.      * @throws IOException If an error occurs while fetching the time.
  81.      */
  82.     public Date getDate(final InetAddress host, final int port) throws IOException {
  83.         return new Date((getTime(host, port) - SECONDS_1900_TO_1970) * 1000L);
  84.     }

  86.     /**
  87.      * Gets the time from the specified server and default port.
  88.      *
  89.      * @param host the time-server
  90.      * @return the time returned from the server
  91.      * @throws IOException on error
  92.      */
  93.     public long getTime(final InetAddress host) throws IOException {
  94.         return getTime(host, DEFAULT_PORT);
  95.     }

  97.     /**
  98.      * Gets the time from the specified server and port. The time is the number of seconds since 00:00 (midnight) 1 January 1900 GMT, as
  99.      * specified by RFC 868. This method reads the raw 32-bit big-endian unsigned integer from the server, converts it to a Java long, and returns the value.
  100.      *
  101.      * @param host The address of the server.
  102.      * @param port The port of the service.
  103.      * @return The time value retrieved from the server.
  104.      * @throws IOException If an error occurs while retrieving the time.
  105.      */
  106.     public long getTime(final InetAddress host, final int port) throws IOException {
  107.         final byte[] dummyData = new byte[1];
  108.         final byte[] timeData = new byte[4];

  110.         final DatagramPacket sendPacket = new DatagramPacket(dummyData, dummyData.length, host, port);
  111.         final DatagramPacket receivePacket = new DatagramPacket(timeData, timeData.length);

  113.         checkOpen().send(sendPacket);
  114.         checkOpen().receive(receivePacket);

  116.         return toTime(timeData);
  117.     }

  119. }
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