RCommandClientpublic class RCommandClient extends RExecClient | RCommandClient is very similar to
{@link org.apache.commons.net.bsd.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 {@link #rcommand 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 {@link org.apache.commons.net.bsd.RExecClient#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 org.apache.commons.net.bsd.RExecClient#getInputStream 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 {@link org.apache.commons.net.bsd.RExecClient#getErrorStream getErrorStream() }
. You
can specify that a separate connection should be created for standard
error by setting the boolean separateErrorStream
parameter of {@link #rcommand rcommand() } to true .
The standard input of the remote process can be written to through
the output stream returned by
{@link org.apache.commons.net.bsd.RExecClient#getOutputStream getOutputStream() }
.
|
| Fields Summary |
|---|
| public static final int | DEFAULT_PORTThe default rshell port. Set to 514 in BSD Unix. | | public static final int | MIN_CLIENT_PORTThe smallest port number an rcmd client may use. By BSD convention
this number is 512. | | public static final int | MAX_CLIENT_PORTThe largest port number an rcmd client may use. By BSD convention
this number is 1023. |
| Constructors Summary |
|---|
public RCommandClient()The default RCommandClient constructor. Initializes the
default port to DEFAULT_PORT .
setDefaultPort(DEFAULT_PORT);
|
| Methods Summary |
|---|
| java.io.InputStream | _createErrorStream()
// Overrides method in RExecClient in order to implement proper
// port number limitations.
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()));
| | public void | connect(java.net.InetAddress host, int port, java.net.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.
Before returning, {@link org.apache.commons.net.SocketClient#_connectAction_ _connectAction_() }
is called to perform connection initialization actions.
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_();
| | public void | connect(java.net.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.
Before returning, {@link org.apache.commons.net.SocketClient#_connectAction_ _connectAction_() }
is called to perform connection initialization actions.
connect(host, port, InetAddress.getLocalHost());
| | public void | connect(java.lang.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.
Before returning, {@link org.apache.commons.net.SocketClient#_connectAction_ _connectAction_() }
is called to perform connection initialization actions.
connect(InetAddress.getByName(hostname), port, InetAddress.getLocalHost());
| | public void | connect(java.lang.String hostname, int port, java.net.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.
Before returning, {@link org.apache.commons.net.SocketClient#_connectAction_ _connectAction_() }
is called to perform connection initialization actions.
connect(InetAddress.getByName(hostname), port, localAddr);
| | public void | connect(java.net.InetAddress host, int port, java.net.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. The
local port must lie between MIN_CLIENT_PORT and
MAX_CLIENT_PORT or an IllegalArgumentException will
be thrown.
Before returning, {@link org.apache.commons.net.SocketClient#_connectAction_ _connectAction_() }
is called to perform connection initialization actions.
if (localPort < MIN_CLIENT_PORT || localPort > MAX_CLIENT_PORT)
throw new IllegalArgumentException("Invalid port number " + localPort);
super.connect(host, port, localAddr, localPort);
| | public void | connect(java.lang.String hostname, int port, java.net.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. The
local port must lie between MIN_CLIENT_PORT and
MAX_CLIENT_PORT or an IllegalArgumentException will
be thrown.
Before returning, {@link org.apache.commons.net.SocketClient#_connectAction_ _connectAction_() }
is called to perform connection initialization actions.
if (localPort < MIN_CLIENT_PORT || localPort > MAX_CLIENT_PORT)
throw new IllegalArgumentException("Invalid port number " + localPort);
super.connect(hostname, port, localAddr, localPort);
| | public void | rcommand(java.lang.String localUsername, java.lang.String remoteUsername, java.lang.String command)Same as
rcommand(localUsername, remoteUsername, command, false);
rcommand(localUsername, remoteUsername, command, false);
| | public void | rcommand(java.lang.String localUsername, java.lang.String remoteUsername, java.lang.String command, boolean separateErrorStream)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
{@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 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
{@link org.apache.commons.net.bsd.RExecClient#setRemoteVerificationEnabled setRemoteVerificationEnabled()}
.
rexec(localUsername, remoteUsername, command, separateErrorStream);
|
|
