LuaSrcDiet

• LuaSrcDiet | FeaturesAndUsage | PerformanceStats | TechNotes
  • Introduction | LuaSrcDiet and Obfuscation | What's New | Acknowledgements

Introduction

local function calc_indent(s)
  local col = 0
  for i = 1, #s do
    local c = sub(s, i, i)
    col = col + 1
    if c == "\t" then  -- tab
      while col % 8 > 0 do col = col + 1 end
    end
  end--for
  return math.floor(col / 8)
end

into a more compact or 'squeezed' form (minus a lot of unnecessary characters) like this:

local function _(l)local e=0
for o=1,#l do
local n=n(l,o,o)e=e+1
if n=="\t"then
while e%8>0 do e=e+1 end
end
end
return r.floor(e/8)end

and still be able to run normally under standard Lua 5.1.

LuaSrcDiet reduces the size of Lua 5.1.x source files by aggressively removing all unnecessary whitespace and comments, optimizing constant tokens, and renaming local variables to shorter names. For example, LuaSrcDiet squeezes its own sources from 156KB down to 42KB. Further bzip2 or lzma compression can bring the file size further down to under 13KB. That's 12X reduction in size, if you don't mind the decompression and compilation time.

LuaSrcDiet is broadly similar to Luiz's lstrip (tar.gz link) for Lua 5.1, which can be found on Luiz's Libraries and tools for Lua page. LuaSrcDiet with its modified Lua source code lexer and parser allows most optimization options to be enabled or disabled separately, and can do a bit more like renaming local variable names.

There is also Matthew Wild's squish, which incorporates LuaSrcDiet and offers more code compression options. squish goes beyond what LuaSrcDiet does, as the latter (as a matter of policy) only sticks to source code readable by standard Lua binaries.

LuaSrcDiet and Obfuscation

• LuaSrcDiet can be used as a weak obfuscator. However, note that the structure and arrangement of the source code stays exactly the same, so do not depend on such a weak form of obfuscation if you really needed heavy-duty obfuscation.
• LuaSrcDiet was written for the purpose of comparing minimum-sized sources with binary chunks, their compressibility, and the parsing performance of the Lua interpreter. I don't care one iota about obfuscation, it's compression I'm interested in.
• This is experimental software. If you want to use it for important stuff, be sure to apply source and binary equivalence checking. I'm not, of course, responsible for anything you do.
• Treat it like a text filter tool or a compiler. There is no legal requirement to acknowledge LuaSrcDiet or to place its copyright notice anywhere for the source code you processed. Your app is stuff you wrote, LuaSrcDiet is stuff I wrote. Simples.
• Obfuscation cannot be defined precisely so we are dealing with subjective judgements. I think it's fair if people want to apply a mild deterrent against casual plagiarism. Those desperate for original sources should instead turn their energies towards Open Source or Free Software.

What's New

Version 0.12.1 (2012-04-07):

• BUG FIX: Long comment adds an extra 2 characters when using --keep option.
• Faster function call syntax sugar optimization using a one-pass token deletion loop.

Version 0.12.0 (2011-09-13):

• Added convenient single-file versions of LuaSrcDiet in various sizes.
• BUG FIX: String optimization of "\ddd" -- "\00101" was incorrectly optimized to "\101".
• Added --opt-srcequiv: Source equivalence checking. Tries hard to compare 'before' and 'after' lexer token streams for equivalence.
• Added --opt-binequiv: Binary chunk equivalence checking. Tries hard to compare 'before' and 'after' binary chunks for equivalence.
• When using --opt-eols, the last EOL character is now removed.
• --opt-experimental: Turns on a few experimental optimizations:
  • Semicolon (';') operator removal (deleted or turned into whitespace).
  • Function call syntax sugar optimization. E.g. f("string") is turned into f"string"
• Plugins are now embedded into single-file versions.
• First release of completed documentation files.
• New Makefile and numerous minor updates.
• Old code for Lua 5.0 removed (the last working version can be found in the previous release.)

Version 0.11.2 (2008-06-08):

• Improved local variable name allocation, better reuse leading to less identifiers used.
• Added experimental --plugin option with an example plugin script.
• Added a SLOC plugin to count SLOC for Lua 5.1 source files.
• Added a HTML plugin to see globals and locals marked.

Version 0.11.1 (2008-06-03):

• Fixed a local variable rename bug that generates names that are keywords.
• Added --opt-entropy option for locals variables to reduce symbol entropy.
• Implemented --detail info for strings, numbers and local variables
• Added explanatory notes on local variable optimization.

Version 0.11.0 (2008-05-28):

• Local variable name optimization.
• Many options and sample output added.

Version 0.10.2 (2008-05-27):

• Aggressive optimizations for string and number tokens.
• Minor bug fixes.

Version 0.10.1 (2008-05-25):

• Totally rewritten for Lua 5.1.x.

Acknowledgements