Re: [NSE][PATCH] only show script errors in verbose mode

["Patrick Donnelly" <batrick.donnelly () gmail com>]

On Thu, Sep 25, 2008 at 10:52 PM, David Fifield <david () bamsoftware com> wrote:
> Yes, now we're getting somewhere. Maybe we shouldn't use newproxy if
> it's not documented, but the technique of using a userdata to represent
> a unique type sounds perfect. I can't see the rest of the
> implementation, so maybe you can provide a sketch of it.

Basically, I would see us having a register_error function somewhere
that would associate a string error identifier with the unique
userdata object. The package.errors table would have the string
associated with the userdata and vice versa, literally:

package.errors.MISSING_SYSTEM_DEPENDENCY = newproxy()
package.errors[package.errors.MISSING_SYSTEM_DEPENDENCY] =
"MISSING_SYSTEM_DEPENDENCY"

So, when we catch an error in C via pcall we can quickly identify the
type of error. Internally we may have a "degree of severity" (or
perhaps simply verbosity) which we use to notify the user.

> Where does the error get raised and how?

The error would be raised by the C module (possibly by a script or Lua
module, doesn't matter too much). The module could quickly check if a
dependency is missing (e.g. OpenSSL) and raise the error.

> Is there a way to associate a different string with each instance of an error?

Yes, as shown above.

> The more I think about it, the more I think it would be good to display
> the require errors whenever a script is requested specifically. So
>
> nmap --script=default
>
> would hide the SSH-hostkey error, while
>
> nmap --script=SSH-hostkey.nse
>
> would show it. Is there a nice way to differentiate between scripts
> loaded by name (or directory) and scripts loaded implicitly through a
> category? We might want to handle warnings for the two cases
> differently. This isn't urgent, just something to think about.

In the current implementation of the script engine, this is a pretty
difficult thing to do (or rather, keep track of).

Cheers,

-- 
-Patrick Donnelly

"One of the lessons of history is that nothing is often a good thing
to do and always a clever thing to say."

-Will Durant

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