RExecClientpublic class RExecClient extends org.apache.commons.net.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 {@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() }.
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| Fields Summary |
|---|
| public static final int | DEFAULT_PORTThe default rexec port. Set to 512 in BSD Unix. | | private boolean | __remoteVerificationEnabled | | 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. |
| Constructors Summary |
|---|
public RExecClient()The default RExecClient constructor. Initializes the
default port to DEFAULT_PORT .
_errorStream_ = null;
setDefaultPort(DEFAULT_PORT);
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| Methods Summary |
|---|
| java.io.InputStream | _createErrorStream()
// This can be overridden in local package to implement port range
// limitations of rcmd and rlogin
ServerSocket server;
Socket socket;
server = _socketFactory_.createServerSocket(0, 1, getLocalAddress());
_output_.write(Integer.toString(server.getLocalPort()).getBytes());
_output_.write('\0");
_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()));
| | public void | disconnect()Disconnects from the server, closing all associated open sockets and
streams.
if (_errorStream_ != null)
_errorStream_.close();
_errorStream_ = null;
super.disconnect();
| | public java.io.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.
return _errorStream_;
| | public java.io.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.
return _input_;
| | public java.io.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.
return _output_;
| | 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.
return __remoteVerificationEnabled;
| | public void | rexec(java.lang.String username, java.lang.String password, java.lang.String command, boolean separateErrorStream)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()}
.
int ch;
if (separateErrorStream)
{
_errorStream_ = _createErrorStream();
}
else
{
_output_.write('\0");
}
_output_.write(username.getBytes());
_output_.write('\0");
_output_.write(password.getBytes());
_output_.write('\0");
_output_.write(command.getBytes());
_output_.write('\0");
_output_.flush();
ch = _input_.read();
if (ch > 0)
{
StringBuffer buffer = new StringBuffer();
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.");
}
| | public void | rexec(java.lang.String username, java.lang.String password, java.lang.String command)Same as rexec(username, password, command, false);
rexec(username, password, command, false);
| | 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.
__remoteVerificationEnabled = enable;
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