commons-net.jar is the bytecode of Apache Commons Net library, which implements the client side of many basic Internet protocols.

Apache Commons Net Source Code files are provided in the binary packge (commons-net-3.8.0-bin.zip). You can download it at Apache Commons Net Website.

The source code of commons-net-3.8.0.jar is provided below:

⏎ org/apache/commons/net/chargen/CharGenUDPClient.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.commons.net.chargen;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.InetAddress;

import org.apache.commons.net.DatagramSocketClient;
import org.apache.commons.net.util.NetConstants;

/**
 * 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 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 contained in one or more reply
 * datagrams.  The chargen and quote of the day protocols only send
 * one reply datagram containing 512 bytes or less of data.  The 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.
 * <p>
 * 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 } 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 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 duration beforehand).  Don't forget to call
 * {@link org.apache.commons.net.DatagramSocketClient#close  close() }
 * to clean up properly.
 *
 * @see CharGenTCPClient
 */

public final class CharGenUDPClient extends DatagramSocketClient
{
    /** The systat port value of 11 according to RFC 866. */
    public static final int SYSTAT_PORT = 11;
    /** The netstat port value of 19. */
    public static final int NETSTAT_PORT = 15;
    /** The quote of the day port value of 17 according to RFC 865. */
    public static final int QUOTE_OF_DAY_PORT = 17;
    /** The character generator port value of 19 according to RFC 864. */
    public static final int CHARGEN_PORT = 19;
    /** The default chargen port.  It is set to 19 according to RFC 864. */
    public static final int DEFAULT_PORT = 19;

    private final byte[] receiveData;
    private final DatagramPacket receivePacket;
    private final DatagramPacket sendPacket;

    /**
     * The default CharGenUDPClient constructor.  It initializes some internal
     * data structures for sending and receiving the necessary datagrams for
     * the chargen and related protocols.
     */
    public CharGenUDPClient()
    {
        // CharGen return packets have a maximum length of 512
        receiveData = new byte[512];
        receivePacket = new DatagramPacket(receiveData, receiveData.length);
        sendPacket = new DatagramPacket(NetConstants.EMPTY_BTYE_ARRAY, 0);
    }


    /**
     * 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.
     *
     * @param host The address of the server.
     * @param port The port of the service.
     * @throws IOException If an error occurs while sending the datagram.
     */
    public void send(final InetAddress host, final int port) throws IOException
    {
        sendPacket.setAddress(host);
        sendPacket.setPort(port);
        _socket_.send(sendPacket);
    }

    /** Same as <code>send(host, CharGenUDPClient.DEFAULT_PORT);</code>
     * @param host the destination host
     * @throws IOException on error
     */
    public void send(final InetAddress host) throws IOException
    {
        send(host, DEFAULT_PORT);
    }

    /**
     * Receive the reply data from the server.  This will always be 512 bytes
     * or less.  Chargen and quote of the day only return one packet.  Netstat
     * and systat require multiple calls to receive() with timeout detection.
     *
     * @return The reply data from the server.
     * @throws IOException If an error occurs while receiving the datagram.
     */
    public byte[] receive() throws IOException
    {
        final int length;
        final byte[] result;

        _socket_.receive(receivePacket);

        result = new byte[length = receivePacket.getLength()];
        System.arraycopy(receiveData, 0, result, 0, length);

        return result;
    }

}

⏎ org/apache/commons/net/chargen/CharGenUDPClient.java

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File name: commons-net-3.8.0-sources.jar
File size: 437325 bytes
Release date: 2020-01-22
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