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org.apache.commons.net.bsd
Class RCommandClient

java.lang.Object
  extended by org.apache.commons.net.SocketClient
      extended by org.apache.commons.net.bsd.RExecClient
          extended by org.apache.commons.net.bsd.RCommandClient
Direct Known Subclasses:
RLoginClient
public class RCommandClient
extends RExecClient

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 getOutputStream() .

Author:
Daniel F. Savarese
See Also:
SocketClient, RExecClient, RLoginClient

Field Summary
static int DEFAULT_PORT
          The default rshell port.
static int MAX_CLIENT_PORT
          The largest port number an rcmd client may use.
static int MIN_CLIENT_PORT
          The smallest port number an rcmd client may use.
 
Fields inherited from class org.apache.commons.net.bsd.RExecClient
_errorStream_
 
Fields inherited from class org.apache.commons.net.SocketClient
_defaultPort_, _input_, _isConnected_, _output_, _socket_, _socketFactory_, _timeout_, NETASCII_EOL
 
Constructor Summary
RCommandClient()
          The default RCommandClient constructor.
 
Method Summary
 void connect(InetAddress host, int port)
          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.
 void connect(InetAddress host, int port, InetAddress localAddr)
          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.
 void connect(InetAddress host, int port, InetAddress localAddr, int localPort)
          Opens a Socket connected to a remote host at the specified port and originating from the specified local address and port.
 void connect(String hostname, int port)
          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.
 void connect(String hostname, int port, InetAddress localAddr)
          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.
 void connect(String hostname, int port, InetAddress localAddr, int localPort)
          Opens a Socket connected to a remote host at the specified port and originating from the specified local address and port.
 void rcommand(String localUsername, String remoteUsername, String command)
          Same as rcommand(localUsername, remoteUsername, command, false);
 void rcommand(String localUsername, String remoteUsername, String command, boolean separateErrorStream)
          Remotely executes a command through the rshd daemon on the server to which the RCommandClient is connected.
 
Methods inherited from class org.apache.commons.net.bsd.RExecClient
disconnect, getErrorStream, getInputStream, getOutputStream, isRemoteVerificationEnabled, rexec, rexec, setRemoteVerificationEnabled
 
Methods inherited from class org.apache.commons.net.SocketClient
_connectAction_, 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 rshell port. Set to 514 in BSD Unix.

See Also:
Constant Field Values

MIN_CLIENT_PORT

public static final int MIN_CLIENT_PORT
The smallest port number an rcmd client may use. By BSD convention this number is 512.

See Also:
Constant Field Values

MAX_CLIENT_PORT

public static final int MAX_CLIENT_PORT
The largest port number an rcmd client may use. By BSD convention this number is 1023.

See Also:
Constant Field Values
Constructor Detail

RCommandClient

public RCommandClient()
The default RCommandClient constructor. Initializes the default port to DEFAULT_PORT .

Method Detail

connect

public void connect(InetAddress host,
                    int port,
                    InetAddress localAddr)
             throws SocketException,
                    BindException,
                    IOException
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.

Parameters:
host - The remote host.
port - The port to connect to on the remote host.
localAddr - The local address to use.
Throws:
SocketException - If the socket timeout could not be set.
BindException - If all acceptable rshell ports are in use.
IOException - If the socket could not be opened. In most cases you will only want to catch IOException since SocketException is derived from it.

connect

public void connect(InetAddress host,
                    int port)
             throws SocketException,
                    IOException
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.

Overrides:
connect in class SocketClient
Parameters:
host - The remote host.
port - The port to connect to on the remote host.
Throws:
SocketException - If the socket timeout could not be set.
BindException - If all acceptable rshell ports are in use.
IOException - If the socket could not be opened. In most cases you will only want to catch IOException since SocketException is derived from it.

connect

public void connect(String hostname,
                    int port)
             throws SocketException,
                    IOException
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.

Overrides:
connect in class SocketClient
Parameters:
hostname - The name of the remote host.
port - The port to connect to on the remote host.
Throws:
SocketException - If the socket timeout could not be set.
BindException - If all acceptable rshell ports are in use.
IOException - If the socket could not be opened. In most cases you will only want to catch IOException since SocketException is derived from it.
UnknownHostException - If the hostname cannot be resolved.

connect

public void connect(String hostname,
                    int port,
                    InetAddress localAddr)
             throws SocketException,
                    IOException
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.

Parameters:
hostname - The remote host.
port - The port to connect to on the remote host.
localAddr - The local address to use.
Throws:
SocketException - If the socket timeout could not be set.
BindException - If all acceptable rshell ports are in use.
IOException - If the socket could not be opened. In most cases you will only want to catch IOException since SocketException is derived from it.

connect

public void connect(InetAddress host,
                    int port,
                    InetAddress localAddr,
                    int localPort)
             throws SocketException,
                    IOException,
                    IllegalArgumentException
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.

Overrides:
connect in class SocketClient
Parameters:
host - The remote host.
port - The port to connect to on the remote host.
localAddr - The local address to use.
localPort - The local port to use.
Throws:
SocketException - If the socket timeout could not be set.
IOException - If the socket could not be opened. In most cases you will only want to catch IOException since SocketException is derived from it.
IllegalArgumentException - If an invalid local port number is specified.

connect

public void connect(String hostname,
                    int port,
                    InetAddress localAddr,
                    int localPort)
             throws SocketException,
                    IOException,
                    IllegalArgumentException
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.

Overrides:
connect in class SocketClient
Parameters:
hostname - The name of the remote host.
port - The port to connect to on the remote host.
localAddr - The local address to use.
localPort - The local port to use.
Throws:
SocketException - If the socket timeout could not be set.
IOException - If the socket could not be opened. In most cases you will only want to catch IOException since SocketException is derived from it.
UnknownHostException - If the hostname cannot be resolved.
IllegalArgumentException - If an invalid local port number is specified.

rcommand

public void rcommand(String localUsername,
                     String remoteUsername,
                     String command,
                     boolean separateErrorStream)
              throws IOException
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() .

Parameters:
localUsername - The user account on the local machine that is requesting the command execution.
remoteUsername - The account name on the server through which to execute the command.
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 rcommand() attempt fails. The exception will contain a message indicating the nature of the failure.

rcommand

public void rcommand(String localUsername,
                     String remoteUsername,
                     String command)
              throws IOException
Same as rcommand(localUsername, remoteUsername, command, false);

Throws:
IOException
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