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Apache Commons Net library contains a collection of network utilities and protocol implementations. Supported protocols include: Echo, Finger, FTP, NNTP, NTP, POP3(S), SMTP(S), Telnet, Whois

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/*
 * 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.daytime;

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

import org.apache.commons.net.DatagramSocketClient;

/**
 * The DaytimeUDPClient class is a UDP implementation of a client for the
 * Daytime protocol described in RFC 867.  To use the class, merely
 * open a local datagram socket with
 * {@link org.apache.commons.net.DatagramSocketClient#open  open }
 * and call {@link #getTime  getTime } to retrieve the daytime
 * string, then
 * call {@link org.apache.commons.net.DatagramSocketClient#close  close }
 * to close the connection properly.  Unlike
 * {@link org.apache.commons.net.daytime.DaytimeTCPClient},
 * successive calls to {@link #getTime  getTime } are permitted
 * without re-establishing a connection.  That is because UDP is a
 * connectionless protocol and the Daytime protocol is stateless.
 * @see DaytimeTCPClient
 */
public final class DaytimeUDPClient extends DatagramSocketClient
{
    /** The default daytime port.  It is set to 13 according to RFC 867. */
    public static final int DEFAULT_PORT = 13;

    private final byte[] __dummyData = new byte[1];
    // Received dates should be less than 256 bytes
    private final byte[] __timeData = new byte[256];

    /**
     * Retrieves the time string from the specified server and port and
     * returns it.
     *
     * @param host The address of the server.
     * @param port The port of the service.
     * @return The time string.
     * @throws IOException If an error occurs while retrieving the time.
     */
    public String getTime(InetAddress host, int port) throws IOException
    {
        DatagramPacket sendPacket, receivePacket;

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

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

        return new String(receivePacket.getData(), 0, receivePacket.getLength(), getCharset()); // Java 1.6 can use getCharset()
    }

    /** Same as getTime(host, DaytimeUDPClient.DEFAULT_PORT);
     * @param host the host
     * @return  the time
     * @throws IOException on error
     */
    public String getTime(InetAddress host) throws IOException
    {
        return getTime(host, DEFAULT_PORT);
    }

}