20 December, 2011

Remote Desktop Viewer - The cheap way [Part 1]

Microsoft RDP, RemoteFX, VNC.  That is the real stuff.  Solutions such as those will allow you to secure your connections, log you in to your desktop, compress the connection, etc.  But have you ever thought if it is possible to implement something rudimentary, totally in Java.  Actually it is possible.  But it's nothing much, and what I'll be doing here is a very, very basic implementation of an idea.  Obviously one can go on and enhance it, but it's almost totally impossible to produce a real solution, since Java does not have direct access to the OS, so for example you cannot remotely log-in, as you would for example using ssh.  Well it might be possible, but it would be an overkill.

As I said, I will simply implement an idea, so even though I know we won't be building the next Remote Desktop protocol, it is still interesting.

First we shall lay out some basic requirements.  Basically we will build a server and a client.  The server shall receive a request, it will then grab a screen shot, and send it back.  Meanwhile the client will wait for the server to reply with the image, and will then draw it.  This will go on until we disconnect.

So create three packages first, com.jf.rd, com.jf.rd.client and com.jf.rd.server.  Obviously you can name them whatever you want, but ideally you should have xxx.xxx.client and .server.

We'll start off with the server.  That way we can define what we expect from the client and what we intend to send back.

Now, in the server package create the JRDServer class.


package com.jf.rd.server;




public class JRDServer
{
public static int PORT;

public static String USER;
public static String PASS;

/**
* Parameters:
* Port, User, Password
* @param args
*/
public static void main(String[] args)
{
if (args.length < 3)
{
System.out.println("Usage: JRDServer Port User Password");
System.exit(0);
}

PORT = Integer.parseInt(args[0]);
USER = args[1];
PASS = args[2];

System.out.println("JRD Server sdtarted.  Will listen for connections on " +
"port " + PORT);

JRDServer server = new JRDServer();

server.start();
}

private ConnectionListen listen;

public JRDServer()
{
this.listen = new ConnectionListen(this);
}

public void start()
{
System.out.println("Service Thread starting...");
listen.startServer();
Thread srv = new Thread(listen);
srv.start();
}

public void stop()
{
System.out.println("Service Thread stopping...");
listen.stopServer();
listen.destroy();
}
}


This class is basically an entry point to the server.  I expect some basic Java knowledge so I will describe this only briefly.  We start the server by passing 3 arguments; the port to which we will bind, a username and a password.  The port is the real necessity, and as yet the user and password will not be really used, and will be there so that one day we can implement some sort of security.

There are also the start and stop methods.  start will initialise a listener class which will be running on a separate thread.  That way we can serve our clients in a parallel fashion and also prevent any user from blocking us to the rest of the application in a manner which will stop us from stopping the server.

stop simple stops the listener class and releases its resources.

Next up is the listening class.  This class will loop while the server is running and every time a connection is requested, an other, separate thread is created and the client is served.


package com.jf.rd.server;


import java.io.IOException;
import java.net.ServerSocket;


public class ConnectionListen implements Runnable
{
private boolean running;
private ServerSocket serv;

public ConnectionListen(JRDServer server)
{
try
{
serv = new ServerSocket(JRDServer.PORT);
}
catch (IOException e) 
{
System.err.println("The ServerSocket could not be initialised.");
System.err.println("Reason : " + e);
}
}

public void startServer()
{
running = true;
}

public void stopServer()
{
running = false;
}

@Override
public void run()
{
while (running)
{
try
{
Connection conn = new Connection(serv.accept());
Thread tr = new Thread(conn);
tr.start();
}
catch (IOException e) 
{
System.err.println("A connection could not be accepted.");
System.err.println("Reason : " + e);
}
}
}

public void destroy()
{
try
{
serv.close();
}
catch (IOException e) 
{
System.err.println("The ServerSocket was not closed.");
System.err.println("Reason : " + e);
}
}
}


This time, a server socket is passed as a variable to the constructor. This is the socket which will listen for and accept connections.  The run method, which is the implementation of the Runnable class is what will be running on a separate thread.  Therefore we can simply put a while loop and, kind of, forget about it, since it won't be blocking us (the main thread).  It shall keep on looping until the running flag is false.  So when we start the server we must set running to true and then start it.  To stop it - well - set it to false, and the looping will stop.

Of course, if we won't be listening for any more connections, we should close the server socket.

Finally, the Connection class is created.  Once this is done, the server is basically complete.  Now I should explain what will happen when this is actually run.  Any client that shall connect to this server will receive a byte stream resulting from a screenshot.  It is irrelevant if the client is a web browser, a mobile app or a simple socket.  Also, we won't be checking what the client is actually requesting, so as you can see, the username and password are irrelevant.   That means that you should either practice, and implement an authentication system (easily done) or simply avoid running this server if you fear someone might connect to it and, sort of, spy on you (aye, this is easier).

So, to the connection class.

package com.jf.rd.server;


import java.awt.AlphaComposite;
import java.awt.Dimension;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.RenderingHints;
import java.awt.Robot;
import java.awt.Toolkit;
import java.awt.image.BufferedImage;
import java.io.BufferedInputStream;
import java.io.InputStream;
import java.io.PrintStream;
import java.net.Socket;


import javax.imageio.ImageIO;


public class Connection implements Runnable
{
private static final int IMG_WIDTH  = 960;
private static final int IMG_HEIGHT = 600;

private Socket connSock;
private static final int BUF_SIZE = 2048;
static final byte[] EOL =
{ (byte) '\r', (byte) '\n' };
private byte[] buf;


public Connection(Socket connSock)
{
this.connSock = connSock;
buf = new byte[BUF_SIZE];
}


@Override
public void run()
{
try
{
InputStream is = new BufferedInputStream(connSock.getInputStream());
PrintStream ps = new PrintStream(connSock.getOutputStream());


for (int i = 0; i < BUF_SIZE; i++)
buf[i] = 0;


int nread = 0, r = 0;


outerloop: while (nread < BUF_SIZE)
{
r = is.read(buf, nread, BUF_SIZE - nread);
if (r == -1) return;
int i = nread;
nread += r;
for (; i < nread; i++)
{
if (buf[i] == (byte) '\n' || buf[i] == (byte) '\r')
break outerloop;
}
}


System.out.println("Done reading.");


Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
Rectangle screenRectangle = new Rectangle(screenSize);
Robot robot = new Robot();
BufferedImage image = robot.createScreenCapture(screenRectangle);
int type = image.getType() == 0? BufferedImage.TYPE_INT_ARGB : image.getType();
image = resizeImage(image, type);

ImageIO.write(image, "JPG", connSock.getOutputStream());


ps.flush();


connSock.close();
}
catch (Exception e)
{
System.err.println("Error, somewhere...");
e.printStackTrace();
}
}


private static BufferedImage resizeImage(BufferedImage originalImage,
int type)
{
BufferedImage resizedImage = new BufferedImage(IMG_WIDTH, IMG_HEIGHT, type);
Graphics2D g = resizedImage.createGraphics();
g.drawImage(originalImage, 0, 0, IMG_WIDTH, IMG_HEIGHT, null);
g.dispose();
g.setComposite(AlphaComposite.Src);
 
g.setRenderingHint(RenderingHints.KEY_INTERPOLATION,
RenderingHints.VALUE_INTERPOLATION_BILINEAR);
g.setRenderingHint(RenderingHints.KEY_RENDERING,
RenderingHints.VALUE_RENDER_QUALITY);
g.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
 
return resizedImage;
}


}


There it is then.  The Main screen grabber and sender.  We're not doing much here;  just receiving a request and then write "Done reading" when the process finishes, and then a picture is sent.  The resizeImage method is used to reduce the size of the image so that we do not send an image the size of your screen resolution.  That would be slow and besides, you can also specify what "resolution" you intend to receive.  The socket is also closed here, that's important too.  The lines between printing "done reading" and ImageIO.write are grabbing the screen using the AWT (Advanced Window Toolkit), so what this means is that you must have an OS that supports GUI (i.e. not headless, as it is known) and you must be logged in basically, since it grabs the screen as seen by the current user.  Therefore apart from the fact that we cannot remotely login, we also can't turn off the video card.  You can turn off the screen, obviously (lol).

That was part one of this, erm, tutorial, or whatever it is.  I like doing these sort of mini programs when I am trying to solve other problems, that's why they are not at the bleeding edge of technology.  And then, when I'm done, I just write something about it, maybe someone out there learns something hehe.

The next thing we'll do, is build a client application.  I currently plan on supporting only viewing, but eventually, we might spice it up a bit by adding cursor support so that you may click on the client and it will then be forwarded to the server and eventually consumed by the OS that is hosting the server.

Also, the second part will probably come out either just before 2012, or probably in the first week of January, so until then, Merry Christmas and a Happy New Year! :D