From: Ara.T.Howard@...
Date: 2005-06-09T23:30:28+09:00
Subject: Re: [SUMMARY] Whiteout (#34)

On Thu, 9 Jun 2005, Ruby Quiz wrote:

> Does this library have any practical value?  Probably not.  It's been suggested
> in the Perl community that hacks like this are a good minor deterrent to those
> trying to read source code you would rather keep hidden, but it must be stressed
> that this is no form of serious security.  Regardless, it's a fun little toy to
> play with.
>
> It was mentioned in the discussion that Perl, where ACME::Bleach comes from,
> includes a framework for source filtering.  It can be used to make modules that
> modify source code much as we are doing in this quiz.  Perl's Switch.pm is a
> good example of this, but ironically ACME::Bleach is not.
>
> That naturally leads to the question, can you build source filters in Ruby?
> Clearly we can build ACME::Bleach, but not all source filters are as simple I'm
> afraid.  Consider this:
>
> 	#!/usr/local/bin/ruby -w
>
> 	require "fix_my_broken_syntax"
>
> 	invalid++
>
> Now the thought here is that fix_my_broken_syntax.rb will read my source, change
> it so that it does something valid, eval() it, and exit() before the invalid
> code is an issue.  Here's a trivial example of fix_my_broken_syntax.rb:
>
> 	#!/usr/local/bin/ruby -w
>
> 	puts "Fixed!"
> 	exit
>
> Does that work?  Unfortunately, no:
>
> 	$ ruby invalid.rb
> 	invalid.rb:5: syntax error
> 	invalid++
> 	         ^
>
> Ruby never gets to loading the library, because it's not happy with the syntax
> of the first file.  That makes writing a source filter for anything that isn't
> valid Ruby syntax complicated and if it is valid Ruby syntax, you can probably
> just code it up in Ruby to begin with.


a hack but:

   harp:~ > cat fix_my_broken_syntax.rb
   src = open($0).read
   src.gsub! %r/([_a-z][_a-zA-Z]*)\+\+/, '((\1+=1;\1 - 1))'
   eval src
   exit


   harp:~ > cat a.rb
   #!/usr/local/bin/ruby -r./fix_my_broken_syntax.rb
   n = 41
   p n++
   p n


   harp:~ > ./a.rb
   41
   42


cheers.

-a
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