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/RExecClient.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.io.OutputStream;
import java.net.ServerSocket;
import java.net.Socket;
import java.nio.charset.StandardCharsets;

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

/**
 * RExecClient implements the rexec() facility that first appeared in
 * 4.2BSD Unix.  This class will probably only be of use for connecting
 * to Unix systems and only when the rexecd daemon is configured to run,
 * which is a rarity these days because of the security risks involved.
 * However, rexec() can be very useful for performing administrative tasks
 * on a network behind a firewall.
 * <p>
 * As with virtually all of the client classes in org.apache.commons.net, this
 * class derives from SocketClient, inheriting its connection methods.
 * The way to use RExecClient is to first connect
 * to the server, call the {@link #rexec  rexec()} 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 #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 #getInputStream  getInputStream()}.  However, it is
 * possible to tell the rexecd daemon to return the standard error
 * stream over a separate connection, readable from the input stream
 * returned by {@link #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 #rexec  rexec()} to <code> true </code>.
 * The standard input of the remote process can be written to through
 * the output stream returned by
 * {@link #getOutputStream  getOutputSream()}.
 *
 * @see SocketClient
 * @see RCommandClient
 * @see RLoginClient
 */

public class RExecClient extends SocketClient
{
    /**
     * @since 3.3
     */
    protected static final char NULL_CHAR = '\0';

    /**
     * The default rexec port.  Set to 512 in BSD Unix.
     */
    public static final int DEFAULT_PORT = 512;

    private boolean remoteVerificationEnabled;

    /**
     * If a separate error stream is requested, <code>_errorStream_</code>
     * will point to an InputStream from which the standard error of the
     * remote process can be read (after a call to rexec()).  Otherwise,
     * <code> _errorStream_ </code> will be null.
     */
    protected InputStream _errorStream_;

    // This can be overridden in local package to implement port range
    // limitations of rcmd and rlogin
    InputStream createErrorStream() throws IOException
    {
        final ServerSocket server;
        final Socket socket;

        server = _serverSocketFactory_.createServerSocket(0, 1, getLocalAddress());

        _output_.write(Integer.toString(server.getLocalPort()).getBytes(StandardCharsets.UTF_8)); // $NON-NLS-1$
        _output_.write(NULL_CHAR);
        _output_.flush();

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

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

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


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


    /**
     * Returns the InputStream from which the standard output of the remote
     * process can be read.  The input stream will only be set after a
     * successful rexec() invocation.
     *
     * @return The InputStream from which the standard output of the remote
     * process can be read.
     */
    public InputStream getInputStream()
    {
        return _input_;
    }


    /**
     * Returns the OutputStream through which the standard input of the remote
     * process can be written.  The output stream will only be set after a
     * successful rexec() invocation.
     *
     * @return The OutputStream through which the standard input of the remote
     * process can be written.
     */
    public OutputStream getOutputStream()
    {
        return _output_;
    }


    /**
     * Returns the InputStream from which the standard error of the remote
     * process can be read if a separate error stream is requested from
     * the server.  Otherwise, null will be returned.  The error stream
     * will only be set after a successful rexec() invocation.
     *
     * @return The InputStream from which the standard error of the remote
     * process can be read if a separate error stream is requested from
     * the server.  Otherwise, null will be returned.
     */
    public InputStream getErrorStream()
    {
        return _errorStream_;
    }


    /**
     * Remotely executes a command through the rexecd daemon on the server
     * to which the RExecClient 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 RExecClient, providing an
     * independent stream through which standard error will be transmitted.
     * RExecClient will 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 #setRemoteVerificationEnabled setRemoteVerificationEnabled()}
     * .
     *
     * @param username  The account name on the server through which to execute
     *                  the command.
     * @param password  The plain text password of the user account.
     * @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 rexec() attempt fails.  The exception
     *            will contain a message indicating the nature of the failure.
     */
    public void rexec(final String username, final String password,
                      final String command, final boolean separateErrorStream)
    throws IOException
    {
        int ch;

        if (separateErrorStream)
        {
            _errorStream_ = createErrorStream();
        }
        else
        {
            _output_.write(NULL_CHAR);
        }

        _output_.write(username.getBytes(getCharset()));
        _output_.write(NULL_CHAR);
        _output_.write(password.getBytes(getCharset()));
        _output_.write(NULL_CHAR);
        _output_.write(command.getBytes(getCharset()));
        _output_.write(NULL_CHAR);
        _output_.flush();

        ch = _input_.read();
        if (ch > 0) {
            final StringBuilder buffer = new StringBuilder();

            while ((ch = _input_.read()) != -1 && ch != '\n') {
                buffer.append((char)ch);
            }

            throw new IOException(buffer.toString());
        } else if (ch < 0) {
            throw new IOException("Server closed connection.");
        }
    }


    /**
     * Same as <code> rexec(username, password, command, false); </code>
     * @param username the user name
     * @param password the password
     * @param command the command to run
     * @throws IOException if an error occurs
     */
    public void rexec(final String username, final String password,
                      final String command)
    throws IOException
    {
        rexec(username, password, command, false);
    }

    /**
     * Disconnects from the server, closing all associated open sockets and
     * streams.
     *
     * @throws IOException If there an error occurs while disconnecting.
     */
    @Override
    public void disconnect() throws IOException
    {
        if (_errorStream_ != null) {
            _errorStream_.close();
        }
        _errorStream_ = null;
        super.disconnect();
    }


    /**
     * Enable or disable verification that the remote host connecting to
     * create a separate error stream is the same as the host to which
     * the standard out stream is connected.  The default is for verification
     * to be enabled.  You may set this value at any time, whether the
     * client is currently connected or not.
     *
     * @param enable True to enable verification, false to disable verification.
     */
    public final void setRemoteVerificationEnabled(final boolean enable)
    {
        remoteVerificationEnabled = enable;
    }

    /**
     * Return whether or not verification of the remote host providing a
     * separate error stream is enabled.  The default behavior is for
     * verification to be enabled.
     *
     * @return True if verification is enabled, false if not.
     */
    public final boolean isRemoteVerificationEnabled()
    {
        return remoteVerificationEnabled;
    }

}

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