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/telnet/TelnetClient.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.telnet;

import java.io.BufferedInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

/**
 * The TelnetClient class implements the simple network virtual
 * terminal (NVT) for the Telnet protocol according to RFC 854.  It
 * does not implement any of the extra Telnet options because it
 * is meant to be used within a Java program providing automated
 * access to Telnet accessible resources.
 * <p>
 * The class can be used by first connecting to a server using the
 * SocketClient
 * {@link org.apache.commons.net.SocketClient#connect connect}
 * method.  Then an InputStream and OutputStream for sending and
 * receiving data over the Telnet connection can be obtained by
 * using the {@link #getInputStream  getInputStream() } and
 * {@link #getOutputStream  getOutputStream() } methods.
 * When you finish using the streams, you must call
 * {@link #disconnect  disconnect } rather than simply
 * closing the streams.
 */

public class TelnetClient extends Telnet
{
    private static final int DEFAULT_MAX_SUBNEGOTIATION_LENGTH = 512;

    final int maxSubnegotiationLength;
    private InputStream input;
    private OutputStream output;
    protected boolean readerThread = true;
    private TelnetInputListener inputListener;

    /**
     * Default TelnetClient constructor, sets terminal-type {@code VT100}.
     */
    public TelnetClient()
    {
        this("VT100", DEFAULT_MAX_SUBNEGOTIATION_LENGTH);
    }

    /**
     * Construct an instance with the specified terminal type.
     *
     * @param termtype the terminal type to use, e.g. {@code VT100}
     */
    public TelnetClient(final String termtype)
    {
        this(termtype, DEFAULT_MAX_SUBNEGOTIATION_LENGTH);
    }

    /**
     * Construct an instance with the specified max subnegotiation
     * length and the default terminal-type {@code VT100}
     *
     * @param maxSubnegotiationLength the size of the subnegotiation buffer
     */
    public TelnetClient(final int maxSubnegotiationLength)
    {
        this("VT100", maxSubnegotiationLength);
    }


    /**
     * Construct an instance with the specified terminal type
     * and max subnegotiation length
     *
     * @param termtype the terminal type to use, e.g. {@code VT100}
     * @param maxSubnegotiationLength the size of the subnegotiation buffer
     */
    public TelnetClient(final String termtype, final int maxSubnegotiationLength)
    {
    /* TERMINAL-TYPE option (start)*/
        super(termtype);
    /* TERMINAL-TYPE option (end)*/
        this.input = null;
        this.output = null;
        this.maxSubnegotiationLength = maxSubnegotiationLength;
    }

    void flushOutputStream() throws IOException
    {
        if (_output_ == null) {
            throw new IOException("Stream closed");
        }
        _output_.flush();
    }
    void closeOutputStream() throws IOException
    {
        if (_output_ == null) {
            return;
        }
        try {
            _output_.close();
        } finally {
            _output_ = null;
        }
    }

    /**
     * Handles special connection requirements.
     *
     * @throws IOException  If an error occurs during connection setup.
     */
    @Override
    protected void _connectAction_() throws IOException
    {
        super._connectAction_();
        final TelnetInputStream tmp = new TelnetInputStream(_input_, this, readerThread);
        if(readerThread)
        {
            tmp.start();
        }
        // __input CANNOT refer to the TelnetInputStream.  We run into
        // blocking problems when some classes use TelnetInputStream, so
        // we wrap it with a BufferedInputStream which we know is safe.
        // This blocking behavior requires further investigation, but right
        // now it looks like classes like InputStreamReader are not implemented
        // in a safe manner.
        input = new BufferedInputStream(tmp);
        output = new TelnetOutputStream(this);
    }

    /**
     * Disconnects the telnet session, closing the input and output streams
     * as well as the socket.  If you have references to the
     * input and output streams of the telnet connection, you should not
     * close them yourself, but rather call disconnect to properly close
     * the connection.
     */
    @Override
    public void disconnect() throws IOException
    {
        try {
            if (input != null) {
                input.close();
            }
            if (output != null) {
                output.close();
            }
        } finally { // NET-594
            output = null;
            input = null;
            super.disconnect();
        }
    }

    /**
     * Returns the telnet connection output stream.  You should not close the
     * stream when you finish with it.  Rather, you should call
     * {@link #disconnect  disconnect }.
     *
     * @return The telnet connection output stream.
     */
    public OutputStream getOutputStream()
    {
        return output;
    }

    /**
     * Returns the telnet connection input stream.  You should not close the
     * stream when you finish with it.  Rather, you should call
     * {@link #disconnect  disconnect }.
     *
     * @return The telnet connection input stream.
     */
    public InputStream getInputStream()
    {
        return input;
    }

    /**
     * Returns the state of the option on the local side.
     *
     * @param option - Option to be checked.
     *
     * @return The state of the option on the local side.
     */
    public boolean getLocalOptionState(final int option)
    {
        /* BUG (option active when not already acknowledged) (start)*/
        return stateIsWill(option) && requestedWill(option);
        /* BUG (option active when not already acknowledged) (end)*/
    }

    /**
     * Returns the state of the option on the remote side.
     *
     * @param option - Option to be checked.
     *
     * @return The state of the option on the remote side.
     */
    public boolean getRemoteOptionState(final int option)
    {
        /* BUG (option active when not already acknowledged) (start)*/
        return stateIsDo(option) && requestedDo(option);
        /* BUG (option active when not already acknowledged) (end)*/
    }
    /* open TelnetOptionHandler functionality (end)*/

    /* Code Section added for supporting AYT (start)*/

    /**
     * Sends an Are You There sequence and waits for the result.
     *
     * @param timeout - Time to wait for a response (millis.)
     *
     * @return true if AYT received a response, false otherwise
     *
     * @throws InterruptedException on error
     * @throws IllegalArgumentException on error
     * @throws IOException on error
     */
    public boolean sendAYT(final long timeout)
    throws IOException, IllegalArgumentException, InterruptedException
    {
        return _sendAYT(timeout);
    }
    /* Code Section added for supporting AYT (start)*/

    /**
     * Sends a protocol-specific subnegotiation message to the remote peer.
     * {@link TelnetClient} will add the IAC SB &amp; IAC SE framing bytes;
     * the first byte in {@code message} should be the appropriate telnet
     * option code.
     *
     * <p>
     * This method does not wait for any response. Subnegotiation messages
     * sent by the remote end can be handled by registering an approrpriate
     * {@link TelnetOptionHandler}.
     * </p>
     *
     * @param message option code followed by subnegotiation payload
     * @throws IllegalArgumentException if {@code message} has length zero
     * @throws IOException if an I/O error occurs while writing the message
     * @since 3.0
     */
    public void sendSubnegotiation(final int[] message)
    throws IOException, IllegalArgumentException
    {
        if (message.length < 1) {
            throw new IllegalArgumentException("zero length message");
        }
        _sendSubnegotiation(message);
    }

    /**
     * Sends a command byte to the remote peer, adding the IAC prefix.
     *
     * <p>
     * This method does not wait for any response. Messages
     * sent by the remote end can be handled by registering an approrpriate
     * {@link TelnetOptionHandler}.
     * </p>
     *
     * @param command the code for the command
     * @throws IOException if an I/O error occurs while writing the message
     * @throws IllegalArgumentException  on error
     * @since 3.0
     */
    public void sendCommand(final byte command)
    throws IOException, IllegalArgumentException
    {
        _sendCommand(command);
    }

    /* open TelnetOptionHandler functionality (start)*/

    /**
     * Registers a new TelnetOptionHandler for this telnet client to use.
     *
     * @param opthand - option handler to be registered.
     *
     * @throws InvalidTelnetOptionException on error
     * @throws IOException on error
     */
    @Override
    public void addOptionHandler(final TelnetOptionHandler opthand)
    throws InvalidTelnetOptionException, IOException
    {
        super.addOptionHandler(opthand);
    }
    /* open TelnetOptionHandler functionality (end)*/

    /**
     * Unregisters a  TelnetOptionHandler.
     *
     * @param optcode - Code of the option to be unregistered.
     *
     * @throws InvalidTelnetOptionException on error
     * @throws IOException on error
     */
    @Override
    public void deleteOptionHandler(final int optcode)
    throws InvalidTelnetOptionException, IOException
    {
        super.deleteOptionHandler(optcode);
    }

    /* Code Section added for supporting spystreams (start)*/
    /**
     * Registers an OutputStream for spying what's going on in
     * the TelnetClient session.
     *
     * @param spystream - OutputStream on which session activity
     * will be echoed.
     */
    public void registerSpyStream(final OutputStream  spystream)
    {
        super._registerSpyStream(spystream);
    }

    /**
     * Stops spying this TelnetClient.
     *
     */
    public void stopSpyStream()
    {
        super._stopSpyStream();
    }
    /* Code Section added for supporting spystreams (end)*/

    /**
     * Registers a notification handler to which will be sent
     * notifications of received telnet option negotiation commands.
     *
     * @param notifhand - TelnetNotificationHandler to be registered
     */
    @Override
    public void registerNotifHandler(final TelnetNotificationHandler  notifhand)
    {
        super.registerNotifHandler(notifhand);
    }

    /**
     * Unregisters the current notification handler.
     *
     */
    @Override
    public void unregisterNotifHandler()
    {
        super.unregisterNotifHandler();
    }

    /**
     * Sets the status of the reader thread.
     *
     * <p>
     * When enabled, a seaparate internal reader thread is created for new
     * connections to read incoming data as it arrives. This results in
     * immediate handling of option negotiation, notifications, etc.
     * (at least until the fixed-size internal buffer fills up).
     * Otherwise, no thread is created an all negotiation and option
     * handling is deferred until a read() is performed on the
     * {@link #getInputStream input stream}.
     * </p>
     *
     * <p>
     * The reader thread must be enabled for {@link TelnetInputListener}
     * support.
     * </p>
     *
     * <p>
     * When this method is invoked, the reader thread status will apply to all
     * subsequent connections; the current connection (if any) is not affected.
     * </p>
     *
     * @param flag true to enable the reader thread, false to disable
     * @see #registerInputListener
     */
    public void setReaderThread(final boolean flag)
    {
        readerThread = flag;
    }

    /**
     * Gets the status of the reader thread.
     *
     * @return true if the reader thread is enabled, false otherwise
     */
    public boolean getReaderThread()
    {
        return readerThread;
    }

    /**
     * Register a listener to be notified when new incoming data is
     * available to be read on the {@link #getInputStream input stream}.
     * Only one listener is supported at a time.
     *
     * <p>
     * More precisely, notifications are issued whenever the number of
     * bytes available for immediate reading (i.e., the value returned
     * by {@link InputStream#available}) transitions from zero to non-zero.
     * Note that (in general) multiple reads may be required to empty the
     * buffer and reset this notification, because incoming bytes are being
     * added to the internal buffer asynchronously.
     * </p>
     *
     * <p>
     * Notifications are only supported when a {@link #setReaderThread
     * reader thread} is enabled for the connection.
     * </p>
     *
     * @param listener listener to be registered; replaces any previous
     * @since 3.0
     */
    public synchronized void registerInputListener(final TelnetInputListener listener)
    {
        this.inputListener = listener;
    }

    /**
     * Unregisters the current {@link TelnetInputListener}, if any.
     *
     * @since 3.0
     */
    public synchronized void unregisterInputListener()
    {
        this.inputListener = null;
    }

    // Notify input listener
    void notifyInputListener() {
        final TelnetInputListener listener;
        synchronized (this) {
            listener = this.inputListener;
        }
        if (listener != null) {
            listener.telnetInputAvailable();
        }
    }
}

⏎ org/apache/commons/net/telnet/TelnetClient.java

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