====== Program architecture ======

===== Client =====

Reads keystrokes from server. Creates screenshots, detects changes in them and sends changed tiles (128x128px by default) to the server.

Two threads: GUI thread and ClientWorker, communicating with queues.

  * Queue<byte[]> received
    * filled by ClientWorker with messages from the server
    * read by GUI thread
    * contains keystrokes and mouse instructions, they are to be performed
  * Queue<byte[]> tosend
    * filled by GUI thread
    * read by ClientWorker, the messages are sent to server
    * contains bitmap tiles to be sent to the server

ClientWorker thread:
  * perform SSL handshake
  * enter an infinite loop:
    * send data from "tosend" queue
    * if some data in socket are available, put them to "received" queue

GUI thread:
  * on timer1.tick():
    * if some data (keystrokes or mouse instructions) are available in the "received" queue, process them
    * if "tosend" queue is empty (this is to prevent network congestion)
      * create screenshot
      * break it to 128x128px tiles
      * compare with previous screenshot
      * add changed tiles to "tosend" queue

===== Server =====

Displays tiles received from client. Forwards KeyPress and MouseClick events to the client.

Two threads: GUI thread and ServerWorker, communicating with queues.

  * Queue<byte[]> received
    * filled by ServerWorker with messages from the client
    * read by GUI thread
    * contains bitmap tiles to be displayed
  * Queue<byte[]> tosend
    * filled by GUI thread
    * read by ServerWorker, the messages are sent to client
    * contains keystrokes and mouse instructions

ServerWorker thread:
  * listen on socket, perform SSL handshake
  * read data from socket asynchronously, put them to "readData" queue
  * enter infinite loop:
    * read "readData" queue, put messages to "received" queue
    * if "tosend" queue is not empty, send data from it to client

GUI thread:
  * on timer1.tick():
    * get tiles from "received" queue, display them in picturebox
  * on MouseUp, MouseDown or KeyPress:
    * add the event to "tosend" queue

===== Protocol specification =====

Datagram format:
4B magic value "0x95400954", 4B length, 4B type, lengthB-4 payload

==== Message type 0x02: Client -> Server Rectangle ====

payload: 2B format, 2B xstart, 2B ystart, 2B width, 2B height, data

format: 0x1 = JPEG

Contains image data to be displayed.

==== Message type 0x01: Server -> Client Hello ====

payload: nothing

==== Message type 0x02: Server -> Client Mouse Event ====

payload: 2B X, 2B Y, 4B flags

==== Message type 0x03: Server -> Client Text Input (type 0x3) ====

payload: text to be typed on the keyboard

==== Message type 0x04: Server -> Client Force Redraw (type 0x4) ====

payload: nothing

Forces client to resend all tiles again.

===== Sources used =====

  * https://msdn.microsoft.com/en-us/library/bew39x2a%28v=vs.110%29.aspx
  * https://msdn.microsoft.com/en-us/library/fx6588te%28v=vs.110%29.aspx
  * https://stackoverflow.com/questions/2416748/how-to-simulate-mouse-click-in-c
  * https://msdn.microsoft.com/en-us/library/ms171548%28v=vs.110%29.aspx
  * http://ksvi.mff.cuni.cz/~holan/ (Czech)
  * https://stackoverflow.com/questions/5461338/how-to-create-a-jpg-image-dynamically-in-memory-with-net
  * https://stackoverflow.com/questions/362986/capture-the-screen-into-a-bitmap
  * https://msdn.microsoft.com/en-us/library/kb5kfec7%28v=vs.110%29.aspx
  * https://msdn.microsoft.com/en-us/library/5ey6h79d%28v=vs.110%29.aspx
  * https://stackoverflow.com/questions/695802/using-ssl-and-sslstream-for-peer-to-peer-authentication
  * http://blogs.msdn.com/b/joncole/archive/2007/06/13/sample-asynchronous-sslstream-client-server-implementation.aspx
  * https://msdn.microsoft.com/en-us/library/system.net.security.sslstream.aspx
  * https://www.sslshopper.com/article-most-common-openssl-commands.html
  * https://stackoverflow.com/questions/6686356/sslstream-equivelent-of-tcpclient-available