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.chargen;
019
020import java.io.IOException;
021import java.net.DatagramPacket;
022import java.net.InetAddress;
023
024import org.apache.commons.net.DatagramSocketClient;
025import org.apache.commons.net.util.NetConstants;
026
027/**
028 * The CharGenUDPClient class is a UDP implementation of a client for the character generator protocol described in RFC 864. It can also be used for Systat (RFC
029 * 866), Quote of the Day (RFC 865), and netstat (port 15). All of these protocols involve sending a datagram to the appropriate port, and reading data
030 * contained in one or more reply datagrams. The chargen and quote of the day protocols only send one reply datagram containing 512 bytes or fewer. The
031 * other protocols may reply with more than one datagram, in which case you must wait for a timeout to determine that all reply datagrams have been sent.
032 * <p>
033 * To use the CharGenUDPClient class, just open a local UDP port with {@link org.apache.commons.net.DatagramSocketClient#open open} and call {@link #send send
034 * } to send the datagram that will initiate the data reply. For chargen or quote of the day, just call {@link #receive receive}, and you're done. For netstat
035 * and systat, call receive in a while loop, and catch a SocketException and InterruptedIOException to detect a timeout (don't forget to set the timeout
036 * duration beforehand). Don't forget to call {@link org.apache.commons.net.DatagramSocketClient#close close()} to clean up properly.
037 * </p>
038 *
039 * @see CharGenTCPClient
040 */
041public final class CharGenUDPClient extends DatagramSocketClient {
042
043    /** The systat port value of 11 according to RFC 866. */
044    public static final int SYSTAT_PORT = 11;
045
046    /** The netstat port value of 19. */
047    public static final int NETSTAT_PORT = 15;
048
049    /** The quote of the day port value of 17 according to RFC 865. */
050    public static final int QUOTE_OF_DAY_PORT = 17;
051
052    /** The character generator port value of 19 according to RFC 864. */
053    public static final int CHARGEN_PORT = 19;
054
055    /** The default chargen port. It is set to 19 according to RFC 864. */
056    public static final int DEFAULT_PORT = 19;
057
058    private final byte[] receiveData;
059    private final DatagramPacket receivePacket;
060    private final DatagramPacket sendPacket;
061
062    /**
063     * The default CharGenUDPClient constructor. It initializes some internal data structures for sending and receiving the necessary datagrams for the chargen
064     * and related protocols.
065     */
066    public CharGenUDPClient() {
067        // CharGen return packets have a maximum length of 512
068        receiveData = new byte[512];
069        receivePacket = new DatagramPacket(receiveData, receiveData.length);
070        sendPacket = new DatagramPacket(NetConstants.EMPTY_BTYE_ARRAY, 0);
071    }
072
073    /**
074     * Receive the reply data from the server. This will always be 512 bytes or fewer. Chargen and quote of the day only return one packet. Netstat and systat
075     * require multiple calls to receive() with timeout detection.
076     *
077     * @return The reply data from the server.
078     * @throws IOException If an error occurs while receiving the datagram.
079     */
080    public byte[] receive() throws IOException {
081        final int length;
082        final byte[] result;
083
084        checkOpen().receive(receivePacket);
085
086        result = new byte[length = receivePacket.getLength()];
087        System.arraycopy(receiveData, 0, result, 0, length);
088
089        return result;
090    }
091
092    /**
093     * Same as {@code send(host, CharGenUDPClient.DEFAULT_PORT);}
094     *
095     * @param host the destination host
096     * @throws IOException on error
097     */
098    public void send(final InetAddress host) throws IOException {
099        send(host, DEFAULT_PORT);
100    }
101
102    /**
103     * Sends the data initiation datagram. This data in the packet is ignored by the server, and merely serves to signal that the server should send its reply.
104     *
105     * @param host The address of the server.
106     * @param port The port of the service.
107     * @throws IOException If an error occurs while sending the datagram.
108     */
109    public void send(final InetAddress host, final int port) throws IOException {
110        sendPacket.setAddress(host);
111        sendPacket.setPort(port);
112        checkOpen().send(sendPacket);
113    }
114
115}