parse_timespec function

[David Fifield <david () bamsoftware com>]

On Fri, Apr 02, 2010 at 04:54:38PM -0700, Fyodor wrote:
> On Fri, Apr 02, 2010 at 07:01:56PM -0400, Michael Pattrick wrote:
> > > Other scripts take time arguments in seconds, not minutes. It's not the
> > > best for this script but I'd like it if you make this script work that
> > > way too. In the future we should have a standard function for parsing a
> > > time specification like "60s" or "1m".
> >
> > I have implemented it to stay consistent with the new argument name,
> > but I don't think it works well... No one would be running a fuzzer
> > for less then one minute.
>
> Yeah, it will be better when we have a custom time parsing function
> for NSE like David suggested.  We already have one for Nmap proper.
> I've added it to docs/TODO.
>
> But for now, I think standardizing on seconds like you've done makes
> sense.  While it may be slightly annnoying to type in 1200 rather than
> 20 to run for 20 minutes, it beats having to look up the documentation
> each time or to get it wrong.

Here's a proposed function to go in stdnse.

---
-- Parses a time duration specification, which is a number followed by a
-- unit, and returns a number of seconds. The unit is optional and
-- defaults to seconds. The possible units (case-insensitive) are
-- * <code>s</code>: seconds,
-- * <code>m</code>: minutes,
-- * <code>h</code>: hours.
-- In case of a parsing error, the function returns <code>nil</code>
-- followed by an error message.
--
-- @usage
-- parse_timespec("10") --> 10
-- parse_timespec("10s") --> 10
-- parse_timespec("10m") --> 600
-- parse_timespec("10h") --> 3600
-- parse_timespec("10z") --> nil, "Can't parse time specification \"10z\" (bad unit \"z\""
--
-- @param timespec A time specification string.
-- @return A number of seconds, or <code>nil</code> followed by an error
-- message.
function parse_timespec(timespec)
  local n, unit
  local multiplier

  n, unit = string.match(timespec, "^(%d+)(.*)$")
  if not n then
    return nil, string.format("Can't parse time specification \"%s\"", timespec)
  end
  n = tonumber(n)
  assert(n)

  unit = string.lower(unit)
  if unit == "" or unit == "s" then
    multiplier = 1
  elseif unit == "m" then
    multiplier = 60
  elseif unit == "h" then
    multiplier = 60 * 60
  else
    return nil, string.format("Can't parse time specification \"%s\" (bad unit \"%s\")", timespec, unit)
  end

  return n * multiplier
end

If this looks good, I'll commit it and change scripts to use it where
appropriate.

David Fifield
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