The library nmap provides an exception handling mechanism for NSE scripts, which is designed to help with networking I/O tasks.
The exception handling mechanism from the nmap library works as expected. We wrap the code that we want to monitor for exceptions inside a nmap.try() call. The first value returned by the function indicates the completion status. If it returns false or nil, the second returned value must be an error string. The rest of the return values in a successful execution can be set and used as you wish. The catch function defined by nmap.new_try() will execute when an exception is raised.
The following example is a code snippet of the script mysql-vuln-cve2012-2122.nse ( http://nmap.org/nsedoc/scripts/mysql-vuln-cve2012-2122.html ). In this script, a catch function performs some simple garbage collection if a socket is left open:
local catch = function() socket:close() end local try = nmap.new_try(catch) … try( socket:connect(host, port) ) ...