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}