Send telnet commands with org.apache.commons.net.telnet

Question

I'm using org.apache.commons.net.telnet library to establish a connection with my Telnet server which has a slightly different implementation than the standard RFC 854, but nothing too scary.

Actually, the only way for me to establish a connection to this remote telnet server is to utilize the org.apache.commons.net.telnet, since the pure Java Socket didn't work.

I'm stucked with this library since I can't figure out a way to send commans with it using sendCommand method, which accepts a byte (not byte[]) for it's one and only argument.

I convert my String command into a byte[] array but I can't pass that as an argument...

This is my code so far:

import org.apache.commons.net.io.Util;
import org.apache.commons.net.telnet.TelnetClient;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

public class Telnet {

    public static void main(String[] args) {
        TelnetClient telnet;

        telnet = new TelnetClient();

        try {
            telnet.connect("17.16.15.14", 12345);

            byte[] cmd = "root".getBytes();

            telnet.sendCommand(cmd); // this is where I'm stuck
        } catch (IOException e) {
            e.printStackTrace();
            System.exit(1);
        }

        readWrite(telnet.getInputStream(), telnet.getOutputStream(),
                System.in, System.out);

        try {
            telnet.disconnect();
        } catch (IOException e) {
            e.printStackTrace();
            System.exit(1);
        }

        System.exit(0);
    }

    public static final void readWrite(final InputStream remoteInput,
                                       final OutputStream remoteOutput,
                                       final InputStream localInput,
                                       final OutputStream localOutput)
    {
        Thread reader, writer;

        reader = new Thread()
        {
            @Override
            public void run()
            {
                int ch;

                try
                {
                    while (!interrupted() && (ch = localInput.read()) != -1)
                    {
                        remoteOutput.write(ch);
                        remoteOutput.flush();
                    }
                }
                catch (IOException e)
                {
                    //e.printStackTrace();
                }
            }
        }
        ;


        writer = new Thread()
        {
            @Override
            public void run()
            {
                try
                {
                    Util.copyStream(remoteInput, localOutput);
                }
                catch (IOException e)
                {
                    e.printStackTrace();
                    System.exit(1);
                }
            }
        };


        writer.setPriority(Thread.currentThread().getPriority() + 1);

        writer.start();
        reader.setDaemon(true);
        reader.start();

        try
        {
            writer.join();
            reader.interrupt();
        }
        catch (InterruptedException e)
        {
            // Ignored
        }
    }
}

Long story short: How can I send commands using this library?

Answer 1

You can write data using the OutputStream returned from getOutputStream, e.g. telnet.getOutputStream().write(cmd);. You might need to call .flush() on the OutputStream too