001    /*
002     * Licensed to the Apache Software Foundation (ASF) under one or more
003     * contributor license agreements.  See the NOTICE file distributed with
004     * this work for additional information regarding copyright ownership.
005     * The ASF licenses this file to You under the Apache License, Version 2.0
006     * (the "License"); you may not use this file except in compliance with
007     * the License.  You may obtain a copy of the License at
008     *
009     *      http://www.apache.org/licenses/LICENSE-2.0
010     *
011     * Unless required by applicable law or agreed to in writing, software
012     * distributed under the License is distributed on an "AS IS" BASIS,
013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014     * See the License for the specific language governing permissions and
015     * limitations under the License.
016     */
017    
018    package org.apache.commons.net.time;
019    
020    import java.io.IOException;
021    import java.net.DatagramPacket;
022    import java.net.InetAddress;
023    import java.util.Date;
024    
025    import org.apache.commons.net.DatagramSocketClient;
026    
027    /***
028     * The TimeUDPClient class is a UDP implementation of a client for the
029     * Time protocol described in RFC 868.  To use the class, merely
030     * open a local datagram socket with
031     * {@link org.apache.commons.net.DatagramSocketClient#open  open }
032     * and call {@link #getTime  getTime } or
033     * {@link #getTime  getDate } to retrieve the time. Then call
034     * {@link org.apache.commons.net.DatagramSocketClient#close  close }
035     * to close the connection properly.  Unlike
036     * {@link org.apache.commons.net.time.TimeTCPClient},
037     * successive calls to {@link #getTime  getTime } or
038     * {@link #getDate  getDate } are permitted
039     * without re-establishing a connection.  That is because UDP is a
040     * connectionless protocol and the Time protocol is stateless.
041     * <p>
042     * <p>
043     * @author Daniel F. Savarese
044     * @see TimeTCPClient
045     ***/
046    
047    public final class TimeUDPClient extends DatagramSocketClient
048    {
049        /*** The default time port.  It is set to 37 according to RFC 868. ***/
050        public static final int DEFAULT_PORT = 37;
051    
052        /***
053         * The number of seconds between 00:00 1 January 1900 and
054         * 00:00 1 January 1970.  This value can be useful for converting
055         * time values to other formats.
056         ***/
057        public static final long SECONDS_1900_TO_1970 = 2208988800L;
058    
059        private final byte[] __dummyData = new byte[1];
060        private final byte[] __timeData = new byte[4];
061    
062        /***
063         * Retrieves the time from the specified server and port and
064         * returns it. The time is the number of seconds since
065         * 00:00 (midnight) 1 January 1900 GMT, as specified by RFC 868.
066         * This method reads the raw 32-bit big-endian
067         * unsigned integer from the server, converts it to a Java long, and
068         * returns the value.
069         * <p>
070         * @param host The address of the server.
071         * @param port The port of the service.
072         * @return The time value retrieved from the server.
073         * @exception IOException If an error occurs while retrieving the time.
074         ***/
075        public long getTime(InetAddress host, int port) throws IOException
076        {
077            long time;
078            DatagramPacket sendPacket, receivePacket;
079    
080            sendPacket =
081                new DatagramPacket(__dummyData, __dummyData.length, host, port);
082            receivePacket = new DatagramPacket(__timeData, __timeData.length);
083    
084            _socket_.send(sendPacket);
085            _socket_.receive(receivePacket);
086    
087            time = 0L;
088            time |= (((__timeData[0] & 0xff) << 24) & 0xffffffffL);
089            time |= (((__timeData[1] & 0xff) << 16) & 0xffffffffL);
090            time |= (((__timeData[2] & 0xff) << 8) & 0xffffffffL);
091            time |= ((__timeData[3] & 0xff) & 0xffffffffL);
092    
093            return time;
094        }
095    
096        /*** Same as <code> getTime(host, DEFAULT_PORT); </code> ***/
097        public long getTime(InetAddress host) throws IOException
098        {
099            return getTime(host, DEFAULT_PORT);
100        }
101    
102    
103        /***
104         * Retrieves the time from the server and returns a Java Date
105         * containing the time converted to the local timezone.
106         * <p>
107         * @param host The address of the server.
108         * @param port The port of the service.
109         * @return A Date value containing the time retrieved from the server
110         *     converted to the local timezone.
111         * @exception IOException  If an error occurs while fetching the time.
112         ***/
113        public Date getDate(InetAddress host, int port) throws IOException
114        {
115            return new Date((getTime(host, port) - SECONDS_1900_TO_1970)*1000L);
116        }
117    
118    
119        /*** Same as <code> getTime(host, DEFAULT_PORT); </code> ***/
120        public Date getDate(InetAddress host) throws IOException
121        {
122            return new Date((getTime(host, DEFAULT_PORT) -
123                             SECONDS_1900_TO_1970)*1000L);
124        }
125    
126    }
127