Re: [NSE][PATCH] string.to_hex() function

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

Hi Sven,

On Wed, Sep 10, 2008 at 8:25 AM, Sven Klemm <sven () c3d2 de> wrote:
> Hi everyone,
>
> I've written a to_hex() function for the lua string class.
> string.to_hex(string, separator = "", group_length = 1)
> separator and group_length are optional. Separator will be added to the
> string after each byte or after group_length bytes when group_length is
> passed.
>
> Here are a few examples:
>
> ("abc"):to_hex() => "616263"
> ("abc"):to_hex(":") => "61:62:63"
> ("abc"):to_hex(":",2) => "6162:63"
>
> I think this function is extremely useful for any script that wants to
> display hexencoded data as this function would be available on every string.
> But I am not sure myself whether it is the best way to add this
> functionality. Do you think this function should be added to string or are
> there better ways to implement this. The main reason for this patch is so we
> don't have to implement a hash_raw() and a hash_hex() function for every
> hashing algorithm but the function is surely useful in a lot of other places
> too.

This function is best not added directly to the string library. We
could add an auxiliary string library (that's done elsewhere, e.g.
[1]) for these useful string functions. I would even advocate having
it be a super class of the current string library (so strings may
index it), that is, <code>setmetatable(string, {__index =
ourlibrary})</code>.

As for the function itself, this could easily be done in Lua directly
(and would most likely be faster). Most Lua functions in C should only
be written if there is a clear speed advantage or the function must
access a C construct or API. Please see [2] for an example similar to
what you've done.


[1] http://lua-users.org/wiki/StringRecipes
These are Lua functions for string manipulation but are often included
in extension string libraries.
[2] http://seclists.org/nmap-dev/2008/q3/0688.html

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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