From: Robin Stocker <robin-lists-ruby-talk@...>
Date: 2005-06-05T21:25:57+09:00
Subject: Re: [QUIZ] [Solution] Whiteout (#34)

Hi,


Here's my solution for Ruby Quiz #34. It's my first one :)


Well, it's pretty simple..

To find out whether the file was run directly or required:
- if __FILE__ == $0

When whiteout is run directly, it does the following for each ARGV:
- Leaves the shebang intact
- Adds the "require 'whiteout'"
- Converts the rest of the file to whitespace

The conversion to whitespace is done like this:
- Chars in like "\n" and "\r" are ignored
- Each byte is converted to its bit representation
- So we have something like 01100001
- Then, it is converted to whitespace
- 0 results in a " " (space)
- 1 results in a "\t" (tab)

When whiteout was required:
- Opens the file of $0
- Skips to after the require line
- Decodes the whitespace to code
- Runs the code with eval


I don't like the opening of $0 and the eval part.
Also, the encoding to whitespace could be made more efficient in size by 
adding more whitespace characters to the "code table".

I'm curious to see the other, probably cleaner solutions.

Bye,
  Robin

PS: Here's the code:


#!/usr/bin/ruby


#
# This is my solution for Ruby Quiz #34, Whiteout.
# Author::  Robin Stocker
#


#
# The Whiteout module includes all functionality like:
# - whiten
# - run
# - encode
# - decode
#
module Whiteout

   @@bit_to_code = { '0' => " ", '1' => "\t" }
   @@code_to_bit = @@bit_to_code.invert
   @@chars_to_ignore = [ "\n", "\r" ]

   #
   # Whitens the content of a file specified by _filename_.
   # It leaves the shebang intact, if there is one.
   # At the beginning of the file it inserts the require 'whiteout'.
   # See #encode for details about how the whitening works.
   #
   def Whiteout.whiten( filename )
     code = ''
     File.open( filename, 'r' ) do |file|
       file.each_line do |line|
         if code.empty?
           # Add shebang if there is one.
           code << line if line =~ /#!\s*.+/
           code << "#{$/}require 'whiteout'#{$/}"
         else
           code << encode( line )
         end
       end
     end
     File.open( filename, 'w' ) do |file|
       file.write( code )
     end
   end

   #
   # Reads the file _filename_, decodes and runs it through eval.
   #
   def Whiteout.run( filename )
     text = ''
     File.open( filename, 'r' ) do |file|
       decode = false
       file.each_line do |line|
         if not decode
           # We don't want to decode the "require 'whiteout'",
           # so start decoding not before we passed it.
           decode = true if line =~ /require 'whiteout'/
         else
           text << decode( line )
         end
       end
     end
     # Run the code!
     eval text
   end

   #
   # Encodes text to "whitecode". It works like this:
   # - Chars in @@char_to_ignore are ignored
   # - Each byte is converted to its bit representation,
   #   so that we have something like 01100001
   # - Then, it is converted to whitespace according to @@bit_to_code
   # - 0 results in a " " (space)
   # - 1 results in a "\t" (tab)
   #
   def Whiteout.encode( text )
     white = ''
     text.scan(/./m) do |char|
       if @@chars_to_ignore.include?( char )
         white << char
       else
         char.unpack('B8').first.scan(/./) do |bit|
           code = @@bit_to_code[bit]
           white << code
         end
       end
     end
     return white
   end

   #
   # Does the inverse of #encode, it takes "white"
   # and returns the decoded text.
   #
   def Whiteout.decode( white )
     text = ''
     char = ''
     white.scan(/./m) do |code|
       if @@chars_to_ignore.include?( code )
         text << code
       else
         char << @@code_to_bit[code]
         if char.length == 8
           text << [char].pack("B8")
           char = ''
         end
       end
     end
     return text
   end

end


#
# And here's the logic part of whiteout.
# If it was run directly, whites out the files in ARGV.
# And if it was required, decodes the whitecode and runs it.
#
if __FILE__ == $0
   ARGV.each do |filename|
     Whiteout.whiten( filename )
   end
else
   Whiteout.run( $0 )
end