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
018package org.apache.commons.net.daytime;
019
020import java.io.IOException;
021import java.net.DatagramPacket;
022import java.net.InetAddress;
023
024import org.apache.commons.net.DatagramSocketClient;
025
026/**
027 * 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
028 * socket with {@link org.apache.commons.net.DatagramSocketClient#open open } and call {@link #getTime getTime } to retrieve the daytime string, then call
029 * {@link org.apache.commons.net.DatagramSocketClient#close close } to close the connection properly. Unlike
030 * {@link org.apache.commons.net.daytime.DaytimeTCPClient}, successive calls to {@link #getTime getTime } are permitted without re-establishing a connection.
031 * That is because UDP is a connectionless protocol and the Daytime protocol is stateless.
032 *
033 * @see DaytimeTCPClient
034 */
035public final class DaytimeUDPClient extends DatagramSocketClient {
036
037    /**
038     * The default daytime port. It is set to 13 according to RFC 867.
039     */
040    public static final int DEFAULT_PORT = 13;
041
042    private final byte[] dummyData = new byte[1];
043
044    /**
045     * Received dates should be less than 256 bytes.
046     */
047    private final byte[] timeData = new byte[256];
048
049    /**
050     * Shorthand for <code>getTime(host, DaytimeUDPClient.DEFAULT_PORT);</code>
051     *
052     * @param host the host
053     * @return the time
054     * @throws IOException on error
055     */
056    public String getTime(final InetAddress host) throws IOException {
057        return getTime(host, DEFAULT_PORT);
058    }
059
060    /**
061     * Gets the time string from the specified server and port and returns it.
062     *
063     * @param host The address of the server.
064     * @param port The port of the service.
065     * @return The time string.
066     * @throws IOException If an error occurs while retrieving the time.
067     */
068    public String getTime(final InetAddress host, final int port) throws IOException {
069        final DatagramPacket sendPacket = new DatagramPacket(dummyData, dummyData.length, host, port);
070        final DatagramPacket receivePacket = new DatagramPacket(timeData, timeData.length);
071        checkOpen().send(sendPacket);
072        checkOpen().receive(receivePacket);
073        return new String(receivePacket.getData(), 0, receivePacket.getLength(), getCharset());
074    }
075
076}