From: ts <decoux@...>
Date: 2003-08-13T18:27:00+09:00
Subject: Re: $SAFE = 5 and Safe Ruby Misleading?

>>>>> "D" == Dave Fayram <kirindave@lensmen.net> writes:

D> Which is why I'm curious what $SAFE = 4 is meant to do? It's easy to make it
D> so that code runs in a box, what's difficult is to get data out of that box.

 Try something like this

   def a_verifier(str)
      Thread.new do
         $SAFE = 4
         res = begin
                  eval str
               rescue Exception
                  $!
               end
         begin
            res = ::String.new(res.to_s)
            # add some test if you want
         rescue Exception
            "unknown error"
         end
      end.value
      # here you have a String object which is tainted
      # be carefull with it
   end

 the basic idea
   * protect it against any error to control the result
   * never trust the result : if you want a String, you explicitely create
     it with a method that you can trust (::String::new in my case)
   * never try to correct an error : in my case don't try to interpret the
     error in the second begin ... rescue ... end (it return "unknown
     error")


Guy Decoux