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/bsd/RCommandClient.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.bsd;

import java.io.IOException;
import java.io.InputStream;
import java.net.BindException;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.SocketException;
import java.net.UnknownHostException;
import java.nio.charset.StandardCharsets;

import org.apache.commons.net.io.SocketInputStream;

/**
 * RCommandClient is very similar to
 * {@link org.apache.commons.net.bsd.RExecClient},
 * from which it is derived, and implements the rcmd() facility that
 * first appeared in 4.2BSD Unix.  rcmd() is the facility used by the rsh
 * (rshell) and other commands to execute a command on another machine
 * from a trusted host without issuing a password.  The trust relationship
 * between two machines is established by the contents of a machine's
 * /etc/hosts.equiv file and a user's .rhosts file.  These files specify
 * from which hosts and accounts on those hosts rcmd() requests will be
 * accepted.  The only additional measure for establishing trust is that
 * all client connections must originate from a port between 512 and 1023.
 * Consequently, there is an upper limit to the number of rcmd connections
 * that can be running simultaneously.   The required ports are reserved
 * ports on Unix systems, and can only be bound by a
 * process running with root permissions (to accomplish this rsh, rlogin,
 * and related commands usualy have the suid bit set).  Therefore, on a
 * Unix system, you will only be able to successfully use the RCommandClient
 * class if the process runs as root.  However, there is no such restriction
 * on Windows95 and some other systems.  The security risks are obvious.
 * However, when carefully used, rcmd() can be very useful when used behind
 * a firewall.
 * <p>
 * As with virtually all of the client classes in org.apache.commons.net, this
 * class derives from SocketClient.  But it overrides most of its connection
 * methods so that the local Socket will originate from an acceptable
 * rshell port.  The way to use RCommandClient is to first connect
 * to the server, call the {@link #rcommand  rcommand() } method,
 * and then
 * fetch the connection's input, output, and optionally error streams.
 * Interaction with the remote command is controlled entirely through the
 * I/O streams.  Once you have finished processing the streams, you should
 * invoke {@link org.apache.commons.net.bsd.RExecClient#disconnect disconnect() }
 *  to clean up properly.
 * <p>
 * By default the standard output and standard error streams of the
 * remote process are transmitted over the same connection, readable
 * from the input stream returned by
 * {@link org.apache.commons.net.bsd.RExecClient#getInputStream getInputStream() }
 * .  However, it is
 * possible to tell the rshd daemon to return the standard error
 * stream over a separate connection, readable from the input stream
 * returned by {@link org.apache.commons.net.bsd.RExecClient#getErrorStream getErrorStream() }
 * .  You
 * can specify that a separate connection should be created for standard
 * error by setting the boolean <code> separateErrorStream </code>
 * parameter of {@link #rcommand  rcommand() } to <code> true </code>.
 * The standard input of the remote process can be written to through
 * the output stream returned by
 * {@link org.apache.commons.net.bsd.RExecClient#getOutputStream getOutputStream() }
 * .
 * @see org.apache.commons.net.SocketClient
 * @see RExecClient
 * @see RLoginClient
 */

public class RCommandClient extends RExecClient
{
    /**
     * The default rshell port.  Set to 514 in BSD Unix.
     */
    public static final int DEFAULT_PORT = 514;

    /**
     * The smallest port number an rcmd client may use.  By BSD convention
     * this number is 512.
     */
    public static final int MIN_CLIENT_PORT = 512;

    /**
     * The largest port number an rcmd client may use.  By BSD convention
     * this number is 1023.
     */
    public static final int MAX_CLIENT_PORT = 1023;

    // Overrides method in RExecClient in order to implement proper
    // port number limitations.
    @Override
    InputStream createErrorStream() throws IOException
    {
        int localPort;
        ServerSocket server;
        final Socket socket;

        localPort = MAX_CLIENT_PORT;
        server = null; // Keep compiler from barfing

        for (localPort = MAX_CLIENT_PORT; localPort >= MIN_CLIENT_PORT; --localPort)
        {
            try
            {
                server = _serverSocketFactory_.createServerSocket(localPort, 1,
                         getLocalAddress());
                break; // got a socket
            }
            catch (final SocketException e)
            {
                continue;
            }
        }

        if (server == null) {
            throw new BindException("All ports in use.");
        }

        _output_.write(Integer.toString(server.getLocalPort()).getBytes(StandardCharsets.UTF_8)); // $NON-NLS
        _output_.write(NULL_CHAR);
        _output_.flush();

        socket = server.accept();
        server.close();

        if (isRemoteVerificationEnabled() && !verifyRemote(socket))
        {
            socket.close();
            throw new IOException(
                "Security violation: unexpected connection attempt by " +
                socket.getInetAddress().getHostAddress());
        }

        return new SocketInputStream(socket, socket.getInputStream());
    }

    /**
     * The default RCommandClient constructor.  Initializes the
     * default port to <code> DEFAULT_PORT </code>.
     */
    public RCommandClient()
    {
        setDefaultPort(DEFAULT_PORT);
    }


    /**
     * Opens a Socket connected to a remote host at the specified port and
     * originating from the specified local address using a port in a range
     * acceptable to the BSD rshell daemon.
     * Before returning, {@link org.apache.commons.net.SocketClient#_connectAction_  _connectAction_() }
     * is called to perform connection initialization actions.
     *
     * @param host  The remote host.
     * @param port  The port to connect to on the remote host.
     * @param localAddr  The local address to use.
     * @throws SocketException If the socket timeout could not be set.
     * @throws BindException If all acceptable rshell ports are in use.
     * @throws IOException If the socket could not be opened.  In most
     *  cases you will only want to catch IOException since SocketException is
     *  derived from it.
     */
    public void connect(final InetAddress host, final int port, final InetAddress localAddr)
    throws SocketException, BindException, IOException
    {
        int localPort;

        localPort = MAX_CLIENT_PORT;

        for (localPort = MAX_CLIENT_PORT; localPort >= MIN_CLIENT_PORT; --localPort)
        {
            try
            {
                _socket_ =
                    _socketFactory_.createSocket(host, port, localAddr, localPort);
            }
            catch (final SocketException e)
            {
                continue;
            }
            break;
        }

        if (localPort < MIN_CLIENT_PORT) {
            throw new BindException("All ports in use or insufficient permssion.");
        }

        _connectAction_();
    }



    /**
     * Opens a Socket connected to a remote host at the specified port and
     * originating from the current host at a port in a range acceptable
     * to the BSD rshell daemon.
     * Before returning, {@link org.apache.commons.net.SocketClient#_connectAction_  _connectAction_() }
     * is called to perform connection initialization actions.
     *
     * @param host  The remote host.
     * @param port  The port to connect to on the remote host.
     * @throws SocketException If the socket timeout could not be set.
     * @throws BindException If all acceptable rshell ports are in use.
     * @throws IOException If the socket could not be opened.  In most
     *  cases you will only want to catch IOException since SocketException is
     *  derived from it.
     */
    @Override
    public void connect(final InetAddress host, final int port)
    throws SocketException, IOException
    {
        connect(host, port, InetAddress.getLocalHost());
    }


    /**
     * Opens a Socket connected to a remote host at the specified port and
     * originating from the current host at a port in a range acceptable
     * to the BSD rshell daemon.
     * Before returning, {@link org.apache.commons.net.SocketClient#_connectAction_  _connectAction_() }
     * is called to perform connection initialization actions.
     *
     * @param hostname  The name of the remote host.
     * @param port  The port to connect to on the remote host.
     * @throws SocketException If the socket timeout could not be set.
     * @throws BindException If all acceptable rshell ports are in use.
     * @throws IOException If the socket could not be opened.  In most
     *  cases you will only want to catch IOException since SocketException is
     *  derived from it.
     * @throws UnknownHostException If the hostname cannot be resolved.
     */
    @Override
    public void connect(final String hostname, final int port)
    throws SocketException, IOException, UnknownHostException
    {
        connect(InetAddress.getByName(hostname), port, InetAddress.getLocalHost());
    }


    /**
     * Opens a Socket connected to a remote host at the specified port and
     * originating from the specified local address using a port in a range
     * acceptable to the BSD rshell daemon.
     * Before returning, {@link org.apache.commons.net.SocketClient#_connectAction_  _connectAction_() }
     * is called to perform connection initialization actions.
     *
     * @param hostname  The remote host.
     * @param port  The port to connect to on the remote host.
     * @param localAddr  The local address to use.
     * @throws SocketException If the socket timeout could not be set.
     * @throws BindException If all acceptable rshell ports are in use.
     * @throws IOException If the socket could not be opened.  In most
     *  cases you will only want to catch IOException since SocketException is
     *  derived from it.
     */
    public void connect(final String hostname, final int port, final InetAddress localAddr)
    throws SocketException, IOException
    {
        connect(InetAddress.getByName(hostname), port, localAddr);
    }


    /**
     * Opens a Socket connected to a remote host at the specified port and
     * originating from the specified local address and port. The
     * local port must lie between <code> MIN_CLIENT_PORT </code> and
     * <code> MAX_CLIENT_PORT </code> or an IllegalArgumentException will
     * be thrown.
     * Before returning, {@link org.apache.commons.net.SocketClient#_connectAction_  _connectAction_() }
     * is called to perform connection initialization actions.
     *
     * @param host  The remote host.
     * @param port  The port to connect to on the remote host.
     * @param localAddr  The local address to use.
     * @param localPort  The local port to use.
     * @throws SocketException If the socket timeout could not be set.
     * @throws IOException If the socket could not be opened.  In most
     *  cases you will only want to catch IOException since SocketException is
     *  derived from it.
     * @throws IllegalArgumentException If an invalid local port number
     *            is specified.
     */
    @Override
    public void connect(final InetAddress host, final int port,
                        final InetAddress localAddr, final int localPort)
    throws SocketException, IOException, IllegalArgumentException
    {
        if (localPort < MIN_CLIENT_PORT || localPort > MAX_CLIENT_PORT) {
            throw new IllegalArgumentException("Invalid port number " + localPort);
        }
        super.connect(host, port, localAddr, localPort);
    }


    /**
     * Opens a Socket connected to a remote host at the specified port and
     * originating from the specified local address and port. The
     * local port must lie between <code> MIN_CLIENT_PORT </code> and
     * <code> MAX_CLIENT_PORT </code> or an IllegalArgumentException will
     * be thrown.
     * Before returning, {@link org.apache.commons.net.SocketClient#_connectAction_  _connectAction_() }
     * is called to perform connection initialization actions.
     *
     * @param hostname  The name of the remote host.
     * @param port  The port to connect to on the remote host.
     * @param localAddr  The local address to use.
     * @param localPort  The local port to use.
     * @throws SocketException If the socket timeout could not be set.
     * @throws IOException If the socket could not be opened.  In most
     *  cases you will only want to catch IOException since SocketException is
     *  derived from it.
     * @throws UnknownHostException If the hostname cannot be resolved.
     * @throws IllegalArgumentException If an invalid local port number
     *            is specified.
     */
    @Override
    public void connect(final String hostname, final int port,
                        final InetAddress localAddr, final int localPort)
    throws SocketException, IOException, IllegalArgumentException, UnknownHostException
    {
        if (localPort < MIN_CLIENT_PORT || localPort > MAX_CLIENT_PORT) {
            throw new IllegalArgumentException("Invalid port number " + localPort);
        }
        super.connect(hostname, port, localAddr, localPort);
    }


    /**
     * Remotely executes a command through the rshd daemon on the server
     * to which the RCommandClient is connected.  After calling this method,
     * you may interact with the remote process through its standard input,
     * output, and error streams.  You will typically be able to detect
     * the termination of the remote process after reaching end of file
     * on its standard output (accessible through
     * {@link #getInputStream  getInputStream() }.  Disconnecting
     * from the server or closing the process streams before reaching
     * end of file will not necessarily terminate the remote process.
     * <p>
     * If a separate error stream is requested, the remote server will
     * connect to a local socket opened by RCommandClient, providing an
     * independent stream through which standard error will be transmitted.
     * The local socket must originate from a secure port (512 - 1023),
     * and rcommand() ensures that this will be so.
     * RCommandClient will also do a simple security check when it accepts a
     * connection for this error stream.  If the connection does not originate
     * from the remote server, an IOException will be thrown.  This serves as
     * a simple protection against possible hijacking of the error stream by
     * an attacker monitoring the rexec() negotiation.  You may disable this
     * behavior with
     * {@link org.apache.commons.net.bsd.RExecClient#setRemoteVerificationEnabled setRemoteVerificationEnabled()}
     * .
     * <p>
     * @param localUsername  The user account on the local machine that is
     *        requesting the command execution.
     * @param remoteUsername  The account name on the server through which to
     *        execute the command.
     * @param command   The command, including any arguments, to execute.
     * @param separateErrorStream True if you would like the standard error
     *        to be transmitted through a different stream than standard output.
     *        False if not.
     * @throws IOException If the rcommand() attempt fails.  The exception
     *            will contain a message indicating the nature of the failure.
     */
    public void rcommand(final String localUsername, final String remoteUsername,
                         final String command, final boolean separateErrorStream)
    throws IOException
    {
        rexec(localUsername, remoteUsername, command, separateErrorStream);
    }


    /**
     * Same as
     * <code> rcommand(localUsername, remoteUsername, command, false); </code>
     * @param localUsername the local user
     * @param remoteUsername the remote user
     * @param command the command
     * @throws IOException on error
     */
    public void rcommand(final String localUsername, final String remoteUsername,
                         final String command)
    throws IOException
    {
        rcommand(localUsername, remoteUsername, command, false);
    }

}

⏎ org/apache/commons/net/bsd/RCommandClient.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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