The application is presumably working, so there is nothing to debug, really.
Still, let's use this starter project to learn the basics of debugging.
Place a breakpoint on the s=sock.getdata(sock.txfree) line. To do so, double click on the empty border to the left of this line.
A small red circle will appear there. That's your breakpoint.
Breakpoints can also be "toggled" (added/removed) by pressing [F9].
Press [F5] if you haven't yet started the execution.
Send something from I/O NINJA. The execution will BREAK at your breakpoint.
Now select Debug > Add to Watch List and add the variable s to the watch.
S is a string, in this application all received TCP data passes through it.
At first the variable is empty — this is because the "yellow line" (the execution pointer) hasn't been executed yet.
- Press [F8] to execute a single line of code. The yellow line will move, and the Watch pane will show you the new value of s. It will contain the string you've sent from NINJA.
- Press [F5] to resume the execution.