RE: NSE's garbage collection and exception handling

["Matthew Boyle" <matt_boyle32 () hotmail com>]

> From: "Kris Katterjohn" <katterjohn () gmail com>
> To: "Nmap Dev" <nmap-dev () insecure org>
> Subject: NSE's garbage collection and exception handling
> Date: Sat, 8 Sep 2007 08:52:30 -0500
>
> Hey everyone!
>
> I've been reading over the NSE guide[1] recently and got to thinking about
> something for which I couldn't find an answer: does the garbage collection
> Stoiko added (closing sockets forgotten when exiting a script) still happen
> when NSE exceptions occur[2]?
>
> All of the examples that I've seen show the "catch" function (or whatever 
> it
> happens to be called) closing the socket.  What happens if we don't have
> it?  Does the socket still get closed?  Does the script just exit normally
> after an NSE exception, and thus the sockets get closed as it would if no
> exception occurred at all?

as far as i can tell, when the exception occurs, the script is terminated 
once your catch-function returns (NSE pushes the error string onto the 
stack, then calls lua_error() 
[http://www.lua.org/manual/5.1/manual.html#lua_error].  in which case, it 
shouldn't be necessary to close the socket explicitly; the garbage collector 
should take care of that.

it would also seem that, so long as you don't need to do anything special, 
you don't need to define a catch-function.  if you just put

local try = nmap.new_try(nil);

in your script, NSE will call l_exc_do_nothing() instead.  which, uh, does 
nothing before terminating the script :-)

though some of the error messages could perhaps be a bit more explicit.  
'SCRIPT ENGINE: EOF' isn't perhaps the most descriptive ;-)

--matt

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