alvinalexander.com | career | drupal | java | mac | mysql | perl | scala | uml | unix  

What this is

This file is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Other links

The source code

/*
 * Copyright 2001-2004 The Apache Software Foundation
 *
 * Licensed 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 org.apache.commons.net.io.SocketInputStream;

/***
 * RCommandClient is very similar to
 *  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.
 * 

* 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 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 * 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 * * 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 * getErrorStream() . You * can specify that a separate connection should be created for standard * error by setting the boolean separateErrorStream * parameter of rcommand() to true . * The standard input of the remote process can be written to through * the output stream returned by * * getOutputSream() . *

*

* @author Daniel F. Savarese * @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. InputStream _createErrorStream() throws IOException { int localPort; ServerSocket server; Socket socket; localPort = MAX_CLIENT_PORT; server = null; // Keep compiler from barfing for (localPort = MAX_CLIENT_PORT; localPort >= MIN_CLIENT_PORT; --localPort) { try { server = _socketFactory_.createServerSocket(localPort, 1, getLocalAddress()); } catch (SocketException e) { continue; } break; } if (localPort < MIN_CLIENT_PORT) throw new BindException("All ports in use."); _output_.write(Integer.toString(server.getLocalPort()).getBytes()); _output_.write('\0'); _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 DEFAULT_PORT . ***/ 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, _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. * @exception SocketException If the socket timeout could not be set. * @exception BindException If all acceptable rshell ports are in use. * @exception 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(InetAddress host, int port, 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 (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, _connectAction_() * is called to perform connection initialization actions. *

* @param host The remote host. * @param port The port to connect to on the remote host. * @exception SocketException If the socket timeout could not be set. * @exception BindException If all acceptable rshell ports are in use. * @exception 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(InetAddress host, 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, _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. * @exception SocketException If the socket timeout could not be set. * @exception BindException If all acceptable rshell ports are in use. * @exception IOException If the socket could not be opened. In most * cases you will only want to catch IOException since SocketException is * derived from it. * @exception UnknownHostException If the hostname cannot be resolved. ***/ public void connect(String hostname, int port) throws SocketException, IOException { 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, _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. * @exception SocketException If the socket timeout could not be set. * @exception BindException If all acceptable rshell ports are in use. * @exception 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(String hostname, int port, 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 MIN_CLIENT_PORT and * MAX_CLIENT_PORT or an IllegalArgumentException will * be thrown. * Before returning, _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. * @exception SocketException If the socket timeout could not be set. * @exception IOException If the socket could not be opened. In most * cases you will only want to catch IOException since SocketException is * derived from it. * @exception IllegalArgumentException If an invalid local port number * is specified. ***/ public void connect(InetAddress host, int port, InetAddress localAddr, 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 MIN_CLIENT_PORT and * MAX_CLIENT_PORT or an IllegalArgumentException will * be thrown. * Before returning, _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. * @exception SocketException If the socket timeout could not be set. * @exception IOException If the socket could not be opened. In most * cases you will only want to catch IOException since SocketException is * derived from it. * @exception UnknownHostException If the hostname cannot be resolved. * @exception IllegalArgumentException If an invalid local port number * is specified. ***/ public void connect(String hostname, int port, InetAddress localAddr, int localPort) throws SocketException, IOException, IllegalArgumentException { 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 * 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 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 * * setRemoteVerificationEnabled(). *

* @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. * @exception IOException If the rcommand() attempt fails. The exception * will contain a message indicating the nature of the failure. ***/ public void rcommand(String localUsername, String remoteUsername, String command, boolean separateErrorStream) throws IOException { rexec(localUsername, remoteUsername, command, separateErrorStream); } /*** * Same as * rcommand(localUsername, remoteUsername, command, false); ***/ public void rcommand(String localUsername, String remoteUsername, String command) throws IOException { rcommand(localUsername, remoteUsername, command, false); } }

... this post is sponsored by my books ...

#1 New Release!

FP Best Seller

 

new blog posts

 

Copyright 1998-2021 Alvin Alexander, alvinalexander.com
All Rights Reserved.

A percentage of advertising revenue from
pages under the /java/jwarehouse URI on this website is
paid back to open source projects.