Re: [NSE] Syntax error messages and help finding them.

[Brandon Enright <bmenrigh () ucsd edu>]

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Comment inline.

On Thu, 07 Aug 2008 03:53:00 +0100 or thereabouts jah
<jah () zadkiel plus com> wrote:

> Hello,
>
> If one makes a syntax error that prevents an NSE script from loading
> one would see the following:
>
> SCRIPT ENGINE: error while initializing script rules:
> 'C:\Program Files\Nmap\dev\foo.nse' could not be loaded!
> stack traceback:
>         [C]: ?
>         [C]: ?

Yeah you aren't alone here.  I tend to learn a new language via trial
and error rather than documentation.  NSE is more like trial and
unknown and trial and unknown and trial... ;-)

I should just go read the Lua book.

> SCRIPT ENGINE: Aborting script scan.
>
> This certainly applies to windows, I don't know if there's any more
> detail shown when this happens on other OSes. I've attached a quick
> script for those that would like to find out - it uses an assignment
> operator where it should use comparison.

It's the same on all of the OSes.

> Using Nmap 4.53 the error message pointed to the actual mistake:
>
> LUA INTERPRETER in ..\nse_init.cc:760: C:\Program
> Files\Nmap\dev\foo.nse:11: 'end' expected (to close 'function' at line
>  10) near '='
> SCRIPT ENGINE: Aborting script scan.

Yeah NSE/Lua seems to be able to catch lexical and syntactic errors but
not semantic ones.

> Both of these messages are helpful, but I've often spent ages hunting
> through lines of script trying to find the source of the error and
> have wished many times for that LUA INTERPRETER message to point me
> at a mistake.

Agreed.  I sure hope is isn't a limitation of Lua.  We are dealing with
a language designed to be super compact though.

> If these two messages could be combined I think it would be really
> beneficial and especially so for users who are new to NSE scripting.
>
>
> Regards,
>
>
> jah

Yeah it sure would be nice to see semantic errors.  Even the line the
error occurred on (if the parser keeps that information from the lexer)
would be more useful than '[C]: ?'.  Perhaps Patrick or Diman can chime
in here?

Brandon

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