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 *      https://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     * Constructs a new instance.
051     */
052    public DaytimeUDPClient() {
053        // empty
054    }
055
056    /**
057     * Gets the time string from the specified server and port and returns it.
058     * <p>
059     * Shorthand for {@code getTime(host, DaytimeUDPClient.DEFAULT_PORT);}
060     * </p>
061     *
062     * @param host the host
063     * @return the time
064     * @throws IOException on error
065     */
066    public String getTime(final InetAddress host) throws IOException {
067        return getTime(host, DEFAULT_PORT);
068    }
069
070    /**
071     * Gets the time string from the specified server and port and returns it.
072     *
073     * @param host The address of the server.
074     * @param port The port of the service.
075     * @return The time string.
076     * @throws IOException If an error occurs while retrieving the time.
077     */
078    public String getTime(final InetAddress host, final int port) throws IOException {
079        final DatagramPacket sendPacket = new DatagramPacket(dummyData, dummyData.length, host, port);
080        final DatagramPacket receivePacket = new DatagramPacket(timeData, timeData.length);
081        checkOpen().send(sendPacket);
082        checkOpen().receive(receivePacket);
083        return new String(receivePacket.getData(), 0, receivePacket.getLength(), getCharset());
084    }
085
086}