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    1   /*
    2    * Copyright 2001-2005 The Apache Software Foundation
    3    *
    4    * Licensed under the Apache License, Version 2.0 (the "License");
    5    * you may not use this file except in compliance with the License.
    6    * You may obtain a copy of the License at
    7    *
    8    *     http://www.apache.org/licenses/LICENSE-2.0
    9    *
    10   * Unless required by applicable law or agreed to in writing, software
    11   * distributed under the License is distributed on an "AS IS" BASIS,
    12   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    13   * See the License for the specific language governing permissions and
    14   * limitations under the License.
    15   */
    16  package org.apache.commons.net;
    17
    18  import java.io.IOException;
    19  import java.net.DatagramPacket;
    20  import java.net.InetAddress;
    21  import java.util.Date;
    22
    23  /****
    24   * The TimeUDPClient class is a UDP implementation of a client for the
    25   * Time protocol described in RFC 868.  To use the class, merely
    26   * open a local datagram socket with
    27   * {@link org.apache.commons.net.DatagramSocketClient#open  open }
    28   * and call {@link #getTime  getTime } or
    29   * {@link #getTime  getDate } to retrieve the time. Then call
    30   * {@link org.apache.commons.net.DatagramSocketClient#close  close }
    31   * to close the connection properly.  Unlike
    32   * {@link org.apache.commons.net.TimeTCPClient},
    33   * successive calls to {@link #getTime  getTime } or
    34   * {@link #getDate  getDate } are permitted
    35   * without re-establishing a connection.  That is because UDP is a
    36   * connectionless protocol and the Time protocol is stateless.
    37   * <p>
    38   * <p>
    39   * @author Daniel F. Savarese
    40   * @see TimeTCPClient
    41   ***/
    42
    43  public final class TimeUDPClient extends DatagramSocketClient
    44  {
    45      /**** The default time port.  It is set to 37 according to RFC 868. ***/
    46      public static final int DEFAULT_PORT = 37;
    47
    48      /****
    49       * The number of seconds between 00:00 1 January 1900 and
    50       * 00:00 1 January 1970.  This value can be useful for converting
    51       * time values to other formats.
    52       ***/
    53      public static final long SECONDS_1900_TO_1970 = 2208988800L;
    54
    55      private byte[] __dummyData = new byte[1];
    56      private byte[] __timeData = new byte[4];
    57
    58      /****
    59       * Retrieves the time from the specified server and port and
    60       * returns it. The time is the number of seconds since
    61       * 00:00 (midnight) 1 January 1900 GMT, as specified by RFC 868.
    62       * This method reads the raw 32-bit big-endian
    63       * unsigned integer from the server, converts it to a Java long, and
    64       * returns the value.
    65       * <p>
    66       * @param host The address of the server.
    67       * @param port The port of the service.
    68       * @return The time value retrieved from the server.
    69       * @exception IOException If an error occurs while retrieving the time.
    70       ***/
    71      public long getTime(InetAddress host, int port) throws IOException
    72      {
    73          long time;
    74          DatagramPacket sendPacket, receivePacket;
    75
    76          sendPacket =
    77              new DatagramPacket(__dummyData, __dummyData.length, host, port);
    78          receivePacket = new DatagramPacket(__timeData, __timeData.length);
    79
    80          _socket_.send(sendPacket);
    81          _socket_.receive(receivePacket);
    82
    83          time = 0L;
    84          time |= (((__timeData[0] & 0xff) << 24) & 0xffffffffL);
    85          time |= (((__timeData[1] & 0xff) << 16) & 0xffffffffL);
    86          time |= (((__timeData[2] & 0xff) << 8) & 0xffffffffL);
    87          time |= ((__timeData[3] & 0xff) & 0xffffffffL);
    88
    89          return time;
    90      }
    91
    92      /**** Same as <code> getTime(host, DEFAULT_PORT); </code> ***/
    93      public long getTime(InetAddress host) throws IOException
    94      {
    95          return getTime(host, DEFAULT_PORT);
    96      }
    97
    98
    99      /****
    100      * Retrieves the time from the server and returns a Java Date
    101      * containing the time converted to the local timezone.
    102      * <p>
    103      * @param host The address of the server.
    104      * @param port The port of the service.
    105      * @return A Date value containing the time retrieved from the server
    106      *     converted to the local timezone.
    107      * @exception IOException  If an error occurs while fetching the time.
    108      ***/
    109     public Date getDate(InetAddress host, int port) throws IOException
    110     {
    111         return new Date((getTime(host, port) - SECONDS_1900_TO_1970)*1000L);
    112     }
    113
    114
    115     /**** Same as <code> getTime(host, DEFAULT_PORT); </code> ***/
    116     public Date getDate(InetAddress host) throws IOException
    117     {
    118         return new Date((getTime(host, DEFAULT_PORT) -
    119                          SECONDS_1900_TO_1970)*1000L);
    120     }
    121
    122 }
    123