org.apache.commons.net.bsd
Class RExecClient

java.lang.Object
  org.apache.commons.net.SocketClient
      org.apache.commons.net.bsd.RExecClient

Direct Known Subclasses:

RCommandClient

public class RExecClient
extends SocketClient

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 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 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 rexecd 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 rexec() 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 Also:

SocketClient, RCommandClient, RLoginClient

Field Summary

protected InputStream	_errorStream_ 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()).
static int	DEFAULT_PORT The default rexec port.

Fields inherited from class org.apache.commons.net.SocketClient

_defaultPort_, _input_, _isConnected_, _output_, _socket_, _socketFactory_, _timeout_, NETASCII_EOL

Constructor Summary

RExecClient()
The default RExecClient constructor.

Method Summary

void	disconnect() Disconnects from the server, closing all associated open sockets and streams.
InputStream	getErrorStream() 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.
InputStream	getInputStream() Returns the InputStream from which the standard outputof the remote process can be read.
OutputStream	getOutputStream() Returns the OutputStream through which the standard input of the remote process can be written.
boolean	isRemoteVerificationEnabled() Return whether or not verification of the remote host providing a separate error stream is enabled.
void	rexec(String username, String password, String command) Same as rexec(username, password, command, false);
void	rexec(String username, String password, String command, boolean separateErrorStream) Remotely executes a command through the rexecd daemon on the server to which the RExecClient is connected.
void	setRemoteVerificationEnabled(boolean enable) 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.

Methods inherited from class org.apache.commons.net.SocketClient

_connectAction_, connect, connect, connect, connect, connect, connect, getDefaultPort, getDefaultTimeout, getLocalAddress, getLocalPort, getRemoteAddress, getRemotePort, getSoLinger, getSoTimeout, getTcpNoDelay, isConnected, setDefaultPort, setDefaultTimeout, setSocketFactory, setSoLinger, setSoTimeout, setTcpNoDelay, verifyRemote

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

DEFAULT_PORT

public static final int DEFAULT_PORT

The default rexec port. Set to 512 in BSD Unix.

See Also:

Constant Field Values

_errorStream_

protected InputStream _errorStream_

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.

Constructor Detail

RExecClient

public RExecClient()

The default RExecClient constructor. Initializes the default port to DEFAULT_PORT .

Method Detail

getInputStream

public InputStream getInputStream()

Returns the InputStream from which the standard outputof the remote process can be read. The input stream will only be set after a successful rexec() invocation.

Returns:

The InputStream from which the standard output of the remote process can be read.

getOutputStream

public OutputStream getOutputStream()

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.

Returns:

The OutputStream through which the standard input of the remote process can be written.

getErrorStream

public InputStream getErrorStream()

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.

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.

rexec

public void rexec(String username,
                  String password,
                  String command,
                  boolean separateErrorStream)
           throws IOException

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 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 setRemoteVerificationEnabled() .

Parameters:

username - The account name on the server through which to execute the command.

password - The plain text password of the user account.

command - The command, including any arguments, to execute.

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.

rexec

public void rexec(String username,
                  String password,
                  String command)
           throws IOException

Same as rexec(username, password, command, false);

Throws:

IOException

disconnect

public void disconnect()
                throws IOException

Disconnects from the server, closing all associated open sockets and streams.

Overrides:

disconnect in class SocketClient

Throws:

IOException - If there an error occurs while disconnecting.

setRemoteVerificationEnabled

public final void setRemoteVerificationEnabled(boolean enable)

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.

Parameters:

enable - True to enable verification, false to disable verification.

isRemoteVerificationEnabled

public final boolean isRemoteVerificationEnabled()

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.

Returns:

True if verification is enabled, false if not.