# LibDeflate

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

Copyright (C) 2018-2019 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 Travis CI(Linux/MaxOS) and Appveyor(Windows) badge on the top of this README for the test results. Click the CodeCov badge to see the test coverage (should be 100%). Note at the time of this release, Lua 5.4 final is not released yet. For Lua 5.4, This library is tested with its first beta version.

## 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.

- Interpreter: Lua 5.1.5
- Input data: WeakAuras2 String, Size: 132462 bytes

| LibDeflate | LibDeflate | LibDeflate | LibCompress | LibCompress | LibCompress
--- | --- | --- | --- | --- | --- | ---
| CompressDeflate Level 1 | CompressDeflate Level 5 | CompressDeflate Level 8 | Compress | CompressLZW | CompressHuffman
compress ratio | 3.15 | 3.68 | 3.71 | 1.36 | 1.20 | 1.36
compress time(ms) | 70 | 120 | 200 | 127 | 58 | 64
decompress time(ms) | 35 | 32 | 32 | 62 | 36 | 62
compress+decompress time(ms) | 105 | 152 | 232 | 189 | 94 | 126

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

- The official repository locates on Github. LibDeflate.lua is the only file of LibDeflate. Copy the file to your LUA_PATH to install it.

- To download as a World of Warcraft library, goto LibDeflate Curseforge Page

- You can also install via Luarocks using the command "luarocks install libdeflate"

- To use after installation, `<code>require(&quot;LibDeflate&quot;)</code>` (case sensitive) in your Lua interpreter, or `<code>LibStub:GetLibrary(&quot;LibDeflate&quot;)</code>` (case sensitive) for World of Warcraft.

## 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 GNU Lesser General Public License Version 3 or later.

## Credits and Disclaimer

The following projects are used to the help to test the correctness of this program. The code of the main program (LibDeflate.lua) does not use their code directly, but uses their ideas and algorithms. Their original licenses shall be comply 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.

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