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    
018    package org.apache.commons.net.bsd;
019    
020    import java.io.IOException;
021    import java.io.InputStream;
022    import java.io.OutputStream;
023    import java.net.ServerSocket;
024    import java.net.Socket;
025    
026    import org.apache.commons.net.SocketClient;
027    import 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    
067    public 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                StringBuilder buffer = new StringBuilder();
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