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/*
* 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 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.
*
* 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.
*
* 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 separateErrorStream
* parameter of {@link #rexec rexec()} to true .
* 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, _errorStream_
* will point to an InputStream from which the standard error of the
* remote process can be read (after a call to rexec()). Otherwise,
* _errorStream_ 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
{
ServerSocket server;
Socket socket;
server = _serverSocketFactory_.createServerSocket(0, 1, getLocalAddress());
_output_.write(Integer.toString(server.getLocalPort()).getBytes("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 DEFAULT_PORT .
***/
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.
*
* 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(String username, String password,
String command, 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) {
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 rexec(username, password, command, false);
* @param username the user name
* @param password the password
* @param command the command to run
* @throws IOException if an error occurs
***/
public void rexec(String username, String password,
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(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;
}
}