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 *      http://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.bsd;
019
020import java.io.IOException;
021import java.io.InputStream;
022import java.io.OutputStream;
023import java.net.ServerSocket;
024import java.net.Socket;
025
026import org.apache.commons.net.SocketClient;
027import org.apache.commons.net.io.SocketInputStream;
028
029/***
030 * RExecClient implements the rexec() facility that first appeared in
031 * 4.2BSD Unix.  This class will probably only be of use for connecting
032 * to Unix systems and only when the rexecd daemon is configured to run,
033 * which is a rarity these days because of the security risks involved.
034 * However, rexec() can be very useful for performing administrative tasks
035 * on a network behind a firewall.
036 * <p>
037 * As with virtually all of the client classes in org.apache.commons.net, this
038 * class derives from SocketClient, inheriting its connection methods.
039 * The way to use RExecClient is to first connect
040 * to the server, call the {@link #rexec  rexec() } method, and then
041 * fetch the connection's input, output, and optionally error streams.
042 * Interaction with the remote command is controlled entirely through the
043 * I/O streams.  Once you have finished processing the streams, you should
044 * invoke {@link #disconnect  disconnect() } to clean up properly.
045 * <p>
046 * By default the standard output and standard error streams of the
047 * remote process are transmitted over the same connection, readable
048 * from the input stream returned by
049 * {@link #getInputStream  getInputStream() }.  However, it is
050 * possible to tell the rexecd daemon to return the standard error
051 * stream over a separate connection, readable from the input stream
052 * returned by {@link #getErrorStream  getErrorStream() }.  You
053 * can specify that a separate connection should be created for standard
054 * error by setting the boolean <code> separateErrorStream </code>
055 * parameter of {@link #rexec  rexec() } to <code> true </code>.
056 * The standard input of the remote process can be written to through
057 * the output stream returned by
058 * {@link #getOutputStream  getOutputSream() }.
059 * <p>
060 * <p>
061 * @author Daniel F. Savarese
062 * @see SocketClient
063 * @see RCommandClient
064 * @see RLoginClient
065 ***/
066
067public class RExecClient extends SocketClient
068{
069    /***
070     * The default rexec port.  Set to 512 in BSD Unix.
071     ***/
072    public static final int DEFAULT_PORT = 512;
073
074    private boolean __remoteVerificationEnabled;
075
076    /***
077     * If a separate error stream is requested, <code>_errorStream_</code>
078     * will point to an InputStream from which the standard error of the
079     * remote process can be read (after a call to rexec()).  Otherwise,
080     * <code> _errorStream_ </code> will be null.
081     ***/
082    protected InputStream _errorStream_;
083
084    // This can be overridden in local package to implement port range
085    // limitations of rcmd and rlogin
086    InputStream _createErrorStream() throws IOException
087    {
088        ServerSocket server;
089        Socket socket;
090
091        server = _serverSocketFactory_.createServerSocket(0, 1, getLocalAddress());
092
093        _output_.write(Integer.toString(server.getLocalPort()).getBytes());
094        _output_.write('\0');
095        _output_.flush();
096
097        socket = server.accept();
098        server.close();
099
100        if (__remoteVerificationEnabled && !verifyRemote(socket))
101        {
102            socket.close();
103            throw new IOException(
104                "Security violation: unexpected connection attempt by " +
105                socket.getInetAddress().getHostAddress());
106        }
107
108        return (new SocketInputStream(socket, socket.getInputStream()));
109    }
110
111
112    /***
113     * The default RExecClient constructor.  Initializes the
114     * default port to <code> DEFAULT_PORT </code>.
115     ***/
116    public RExecClient()
117    {
118        _errorStream_ = null;
119        setDefaultPort(DEFAULT_PORT);
120    }
121
122
123    /***
124     * Returns the InputStream from which the standard outputof the remote
125     * process can be read.  The input stream will only be set after a
126     * successful rexec() invocation.
127     * <p>
128     * @return The InputStream from which the standard output of the remote
129     * process can be read.
130     ***/
131    public InputStream getInputStream()
132    {
133        return _input_;
134    }
135
136
137    /***
138     * Returns the OutputStream through which the standard input of the remote
139     * process can be written.  The output stream will only be set after a
140     * successful rexec() invocation.
141     * <p>
142     * @return The OutputStream through which the standard input of the remote
143     * process can be written.
144     ***/
145    public OutputStream getOutputStream()
146    {
147        return _output_;
148    }
149
150
151    /***
152     * Returns the InputStream from which the standard error of the remote
153     * process can be read if a separate error stream is requested from
154     * the server.  Otherwise, null will be returned.  The error stream
155     * will only be set after a successful rexec() invocation.
156     * <p>
157     * @return The InputStream from which the standard error of the remote
158     * process can be read if a separate error stream is requested from
159     * the server.  Otherwise, null will be returned.
160     ***/
161    public InputStream getErrorStream()
162    {
163        return _errorStream_;
164    }
165
166
167    /***
168     * Remotely executes a command through the rexecd daemon on the server
169     * to which the RExecClient is connected.  After calling this method,
170     * you may interact with the remote process through its standard input,
171     * output, and error streams.  You will typically be able to detect
172     * the termination of the remote process after reaching end of file
173     * on its standard output (accessible through
174     * {@link #getInputStream  getInputStream() }.    Disconnecting
175     * from the server or closing the process streams before reaching
176     * end of file will not necessarily terminate the remote process.
177     * <p>
178     * If a separate error stream is requested, the remote server will
179     * connect to a local socket opened by RExecClient, providing an
180     * independent stream through which standard error will be transmitted.
181     * RExecClient will do a simple security check when it accepts a
182     * connection for this error stream.  If the connection does not originate
183     * from the remote server, an IOException will be thrown.  This serves as
184     * a simple protection against possible hijacking of the error stream by
185     * an attacker monitoring the rexec() negotiation.  You may disable this
186     * behavior with {@link #setRemoteVerificationEnabled setRemoteVerificationEnabled()}
187     * .
188     * <p>
189     * @param username  The account name on the server through which to execute
190     *                  the command.
191     * @param password  The plain text password of the user account.
192     * @param command   The command, including any arguments, to execute.
193     * @param separateErrorStream True if you would like the standard error
194     *        to be transmitted through a different stream than standard output.
195     *        False if not.
196     * @exception IOException If the rexec() attempt fails.  The exception
197     *            will contain a message indicating the nature of the failure.
198     ***/
199    public void rexec(String username, String password,
200                      String command, boolean separateErrorStream)
201    throws IOException
202    {
203        int ch;
204
205        if (separateErrorStream)
206        {
207            _errorStream_ = _createErrorStream();
208        }
209        else
210        {
211            _output_.write('\0');
212        }
213
214        _output_.write(username.getBytes());
215        _output_.write('\0');
216        _output_.write(password.getBytes());
217        _output_.write('\0');
218        _output_.write(command.getBytes());
219        _output_.write('\0');
220        _output_.flush();
221
222        ch = _input_.read();
223        if (ch > 0)
224        {
225            StringBuffer buffer = new StringBuffer();
226
227            while ((ch = _input_.read()) != -1 && ch != '\n')
228                buffer.append((char)ch);
229
230            throw new IOException(buffer.toString());
231        }
232        else if (ch < 0)
233        {
234            throw new IOException("Server closed connection.");
235        }
236    }
237
238
239    /***
240     * Same as <code> rexec(username, password, command, false); </code>
241     ***/
242    public void rexec(String username, String password,
243                      String command)
244    throws IOException
245    {
246        rexec(username, password, command, false);
247    }
248
249    /***
250     * Disconnects from the server, closing all associated open sockets and
251     * streams.
252     * <p>
253     * @exception IOException If there an error occurs while disconnecting.
254     ***/
255    @Override
256    public void disconnect() throws IOException
257    {
258        if (_errorStream_ != null)
259            _errorStream_.close();
260        _errorStream_ = null;
261        super.disconnect();
262    }
263
264
265    /***
266     * Enable or disable verification that the remote host connecting to
267     * create a separate error stream is the same as the host to which
268     * the standard out stream is connected.  The default is for verification
269     * to be enabled.  You may set this value at any time, whether the
270     * client is currently connected or not.
271     * <p>
272     * @param enable True to enable verification, false to disable verification.
273     ***/
274    public final void setRemoteVerificationEnabled(boolean enable)
275    {
276        __remoteVerificationEnabled = enable;
277    }
278
279    /***
280     * Return whether or not verification of the remote host providing a
281     * separate error stream is enabled.  The default behavior is for
282     * verification to be enabled.
283     * <p>
284     * @return True if verification is enabled, false if not.
285     ***/
286    public final boolean isRemoteVerificationEnabled()
287    {
288        return __remoteVerificationEnabled;
289    }
290
291}
292