    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    /** The default daytime port. It is set to 13 according to RFC 867. */
    037    public static final int DEFAULT_PORT = 13;
    038
    039    private final byte[] dummyData = new byte[1];
    040    // Received dates should be less than 256 bytes
    041    private final byte[] timeData = new byte[256];
    042
    043    /**
    044     * Same as <code>getTime(host, DaytimeUDPClient.DEFAULT_PORT);</code>
    045     *
    046     * @param host the host
    047     * @return the time
    048     * @throws IOException on error
    049     */
    050    public String getTime(final InetAddress host) throws IOException {
    051        return getTime(host, DEFAULT_PORT);
    052    }
    053
    054    /**
    055     * Retrieves the time string from the specified server and port and returns it.
    056     *
    057     * @param host The address of the server.
    058     * @param port The port of the service.
    059     * @return The time string.
    060     * @throws IOException If an error occurs while retrieving the time.
    061     */
    062    public String getTime(final InetAddress host, final int port) throws IOException {
    063        final DatagramPacket sendPacket;
    064        final DatagramPacket receivePacket;
    065
    066        sendPacket = new DatagramPacket(dummyData, dummyData.length, host, port);
    067        receivePacket = new DatagramPacket(timeData, timeData.length);
    068
    069        checkOpen().send(sendPacket);
    070        checkOpen().receive(receivePacket);
    071
    072        return new String(receivePacket.getData(), 0, receivePacket.getLength(), getCharset()); // Java 1.6 can use getCharset()
    073    }
    074
    075}