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LibDeflate

Pure Lua compressor and decompressor with high compression ratio using DEFLATE/zlib format.

Copyright (C) 2018-2021 Haoqian He

Introduction

LibDeflate is pure Lua compressor and decompressor with high compression ratio, which compresses almost as good as zlib. The purpose of this project is to give a reasonable good compression when you only have access to a pure Lua environment, without accessing to Lua C bindings or any external Lua libraries. LibDeflate does not have any dependencies except you need to have a working Lua interpreter.

LibDeflate uses the following compression formats:

  1. DEFLATE, as defined by the specification RFC1951. DEFLATE is the default compression method of ZIP.
  2. zlib, as defined by the specification RFC1950. zlib format uses DEFLATE formats to compress data and adds several bytes as headers and checksum.

A simple C program utilizing zlib should be compatible with LibDeflate. If you are not sure how to write this program, goto the zlib repository, or read tests/zdeflate.c in this repository.

Supported Lua Versions

LibDeflate supports and is fully tested under Lua 5.1/5.2/5.3/5.4, LuaJIT 2.0/2.1, for Linux, MaxOS and Windows. Click the CI badge on the top of this README for the test results. Click the CodeCov badge to see the test coverage (should be 100%).

Documentation

Documentation is hosted on Github. Beside run as a library, LibDeflate can also be run directly in commmandline. See the documentation for detail.

Limitation

Though many performance optimization has been done in the source code, as a pure Lua implementation, the compression speed of LibDeflate is significantly slower than a C compressor. LibDeflate aims to compress small files, and it is suggested to not compress files with the order of several Megabytes. If you need to compress files hundreds of MetaBytes, please use a C compressor, or a Lua compressor with C binding.

Performance

Below is a simple benchmark compared with another pure Lua compressor LibCompress. More benchmarks can be viewed in the documentation.

<table> <thead> <tr> <th></th> <th>LibDeflate</th> <th>LibDeflate</th> <th>LibDeflate</th> <th>LibCompress</th> <th>LibCompress</th> <th>LibCompress</th> </tr> </thead> <tbody> <tr> <td></td> <td>CompressDeflate Level 1</td> <td>CompressDeflate Level 5</td> <td>CompressDeflate Level 8</td> <td>Compress</td> <td>CompressLZW</td> <td>CompressHuffman</td> </tr> <tr> <td>compress ratio</td> <td>3.15</td> <td>3.68</td> <td>3.71</td> <td>1.36</td> <td>1.20</td> <td>1.36</td> </tr> <tr> <td>compress time(ms)</td> <td>68</td> <td>116</td> <td>189</td> <td>111</td> <td>52</td> <td>50</td> </tr> <tr> <td>decompress time(ms)</td> <td>48</td> <td>30</td> <td>27</td> <td>55</td> <td>26</td> <td>59</td> </tr> <tr> <td>compress+decompress time(ms)</td> <td>116</td> <td>145</td> <td>216</td> <td>166</td> <td>78</td> <td>109</td> </tr> </tbody> </table>

LibDeflate with compression level 1 compresses as fast as LibCompress, but already produces significantly smaller data than LibCompress. High compression level takes a bit more time to get better compression.

Download And Install

Usage

local LibDeflate
if LibStub then -- You are using LibDeflate as WoW addon
	LibDeflate = LibStub:GetLibrary("LibDeflate")
else
	LibDeflate = require("LibDeflate")
end

local example_input = "12123123412345123456123456712345678123456789"

--- Compress using raw deflate format
local compress_deflate = LibDeflate:CompressDeflate(example_input)

-- decompress
local decompress_deflate = LibDeflate:DecompressDeflate(compress_deflate)

-- Check if the first return value of DecompressXXXX is non-nil to know if the
-- decompression succeeds.
if decompress_deflate == nil then
	error("Decompression fails.")
else
	-- Decompression succeeds.
	assert(example_input == decompress_deflate)
end


-- To transmit through WoW addon channel, data must be encoded so NULL ("\000")
-- is not in the data.
local data_to_trasmit_WoW_addon = LibDeflate:EncodeForWoWAddonChannel(
	compress_deflate)
-- When the receiver gets the data, decoded it first.
local data_decoded_WoW_addon = LibDeflate:DecodeForWoWAddonChannel(
	data_to_trasmit_WoW_addon)
-- Then decomrpess it
local decompress_deflate = LibDeflate:DecompressDeflate(data_decoded_WoW_addon)

assert(decompress_deflate == example_input)

-- The compressed output is not printable. EncodeForPrint will convert to
-- a printable format, in case you want to export to the user to
-- copy and paste. This encoding will make the data 25% bigger.
local printable_compressed = LibDeflate:EncodeForPrint(compress_deflate)

-- DecodeForPrint to convert back.
-- DecodeForPrint will remove prefixed and trailing control or space characters
-- in the string before decode it.
assert(LibDeflate:DecodeForPrint(printable_compressed) == compress_deflate)

See Full examples in examples/example.lua

License

LibDeflate is licensed under the zlib license. See LICENSE.txt. The "tests" folder in the repository contains some third party code and data. Their original licenses shall be complied when used.

Credits and Disclaimer

This library rewrites the code from the algorithm and the ideas of the following projects, and uses their code to help to test the correctness of this library, but their code is not included directly in the library itself. Their original licenses shall be complied when used.

  1. zlib, by Jean-loup Gailly (compression) and Mark Adler (decompression). Licensed under zlib License.
  2. puff, by Mark Adler. Licensed under zlib License.
  3. LibCompress, by jjsheets and Galmok of European Stormrage (Horde). Licensed under GPLv2.
  4. WeakAuras2. Licensed under GPLv2.