Re: Detecting/parsing a hex string

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

On Wed, Oct 8, 2008 at 12:22 PM, David Fifield <david () bamsoftware com> wrote:
> On Wed, Oct 08, 2008 at 11:41:36AM -0600, Patrick Donnelly wrote:
> > On Wed, Oct 8, 2008 at 5:25 AM, Ron <ron () skullsecurity net> wrote:
> > > Hi all,
> > >
> > > I need to detect whether or not a string is an ascii representation of a hex
> > > string (eg, "12ab3d1a3badabeea1...."), and, if it is, to convert it to a
> > > binary string. Is there an easy way to do that (maybe with
> > > bin.pack/bin.unpack)?
> > >
> > > Thanks,
> > > Ron
> >
> > a = "414243"
> > if string.find(a, "^%x+$") then
> >   a = string.gsub(a, "%x%x", function(a) return
> > string.char(tonumber(a, 16)) end) --> a = "ABC"
> > end
>
> I suspect this won't work when the string is long enough to overflow the
> capacity of a double, which a 128-bit key will be.
>
> Better than checking first whether the operation will produce an error
> is just to do the operation and catch any error produced. However (from
> reading the source code), bin.unpack appears to ignore non-hex
> characters in a hex conversion:
>
>      for (ii = 0; ii < l; ii++) {
>        if (isxdigit(a[ii])) {
>          ...
>        } else if (isspace(a[ii])) {
>          /* ignore */
>        } else {
>          /* err ... ignore too*/
>        }
>      }
>
> I think that's a bug that should be fixed.

The code I gave works on two characters at a time...


-- 
-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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