/*
 * 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.
 */

package org.apache.commons.net.time;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.InetAddress;
import java.util.Date;

import org.apache.commons.net.DatagramSocketClient;

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 with  open and call  getTime or  getDate to retrieve the time. Then call  close to close the connection properly. Unlike TimeTCPClient, successive calls to  getTime or  getDate are permitted without re-establishing a connection. That is because UDP is a connectionless protocol and the Time protocol is stateless. 
See Also:
TimeTCPClient/***
 * 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 with
 * {@link org.apache.commons.net.DatagramSocketClient#open  open }
 * and call {@link #getTime  getTime } or
 * {@link #getTime  getDate } to retrieve the time. Then call
 * {@link org.apache.commons.net.DatagramSocketClient#close  close }
 * to close the connection properly.  Unlike
 * {@link org.apache.commons.net.time.TimeTCPClient},
 * successive calls to {@link #getTime  getTime } or
 * {@link #getDate  getDate } are permitted
 * without re-establishing a connection.  That is because UDP is a
 * connectionless protocol and the Time protocol is stateless.
 *
 *
 * @see TimeTCPClient
 ***/

public final class TimeUDPClient extends DatagramSocketClient
{
    
The default time port.  It is set to 37 according to RFC 868. /*** The default time port.  It is set to 37 according to RFC 868. ***/
    public static final int DEFAULT_PORT = 37;

    
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.
/***
     * 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.
     ***/
    public static final long SECONDS_1900_TO_1970 = 2208988800L;

    private final byte[] __dummyData = new byte[1];
    private final byte[] __timeData = new byte[4];

    
Retrieves the time from the specified server and port and
returns it. The time is the number of seconds since
00:00 (midnight) 1 January 1900 GMT, as 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.
Params:
host – The address of the server.
port – The port of the service.
Throws:
IOException – If an error occurs while retrieving the time.
Returns:
The time value retrieved from the server./***
     * Retrieves the time from the specified server and port and
     * returns it. The time is the number of seconds since
     * 00:00 (midnight) 1 January 1900 GMT, as 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.
     *
     * @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 long getTime(InetAddress host, int port) throws IOException
    {
        long time;
        DatagramPacket sendPacket, receivePacket;

        sendPacket =
            new DatagramPacket(__dummyData, __dummyData.length, host, port);
        receivePacket = new DatagramPacket(__timeData, __timeData.length);

        _socket_.send(sendPacket);
        _socket_.receive(receivePacket);

        time = 0L;
        time |= (((__timeData[0] & 0xff) << 24) & 0xffffffffL);
        time |= (((__timeData[1] & 0xff) << 16) & 0xffffffffL);
        time |= (((__timeData[2] & 0xff) << 8) & 0xffffffffL);
        time |= ((__timeData[3] & 0xff) & 0xffffffffL);

        return time;
    }

    
Same as  getTime(host, DEFAULT_PORT); 
Params:
host – the time server
Throws:
IOException – on error
Returns:
the time returned from the server/*** Same as <code> getTime(host, DEFAULT_PORT); </code>
     * @param host the time server
     * @return the time returned from the server
     * @throws IOException on error
     ***/
    public long getTime(InetAddress host) throws IOException
    {
        return getTime(host, DEFAULT_PORT);
    }


    
Retrieves the time from the server and returns a Java Date
containing the time converted to the local timezone.
Params:
host – The address of the server.
port – The port of the service.
Throws:
IOException –  If an error occurs while fetching the time.
Returns:
A Date value containing the time retrieved from the server
    converted to the local timezone./***
     * Retrieves the time from the server and returns a Java Date
     * containing the time converted to the local timezone.
     *
     * @param host The address of the server.
     * @param port The port of the service.
     * @return A Date value containing the time retrieved from the server
     *     converted to the local timezone.
     * @throws IOException  If an error occurs while fetching the time.
     ***/
    public Date getDate(InetAddress host, int port) throws IOException
    {
        return new Date((getTime(host, port) - SECONDS_1900_TO_1970)*1000L);
    }


    
Same as  getTime(host, DEFAULT_PORT); 
Params:
host – the time server
Throws:
IOException – on error
Returns:
the date/*** Same as <code> getTime(host, DEFAULT_PORT); </code>
     * @param host the time server
     * @return the date
     * @throws IOException on error
     ***/
    public Date getDate(InetAddress host) throws IOException
    {
        return new Date((getTime(host, DEFAULT_PORT) -
                         SECONDS_1900_TO_1970)*1000L);
    }

}