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lloyd / easylzma

An easy to use, tiny, public domain, C wrapper library around Igor Pavlov's work that can be used to compress and extract lzma files.
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Overview

Easylzma is a C library and command line tools for LZMA compression and decompression. It uses a Igor Pavlov's reference implementation and SDK written in C.

License

All the cruft you find here is public domain. You don't have to credit anyone to use this code, but my personal request is that you mention Igor Pavlov for his hard, high quality work.

Project Goals

  1. A tiny C wrapper and portable build system around a subset of Igor Pavlov's public domain LZMA compression and decompression implementation.
  2. A tiny and straighforward API
  3. Support for multiple different prominent LZMA file formats (see section on file formats below)
  4. easy to build and use everywhere (doze and nix alike)
  5. public domain licensing through and through. (hats off to Igor)

Current State:

THIS IS A WORK IN PROGRESS. The code here should be considered pre-alpha, and this should only be used by tinkerers or hackers at this point. Once feature completion is attained this message will be updated. See the TODO file distributed with the source for remaining work to be done.

Platforms Supported

0.0.2 has been successfully compiled and run basic round trip testing on the following platforms & compilers:

Features

XXX: write me (and the code)

Usage

XXX: write me (and the code)

The Saga of LZMA File Formats, and a couple cents.

As far as I can tell, there are at least four different ways to put LZMA compressed data in a stream:

  1. The LZMA-Alone format, which consists of a 13 byte header including compression properties, dictionary size, and the uncompressed size of the file, followed by compressed data. This format has some support in Igor Pavlov's reference implementation and is in widespread use, as it's supported by lzmautils: http://tukaani.org/lzma/

    The canonical (afaict) implementation of this format (lzmautis) is BSD licensed.

  2. The lzip format (http://www.nongnu.org/lzip/lzip.html) - which includes a CRC footer and leading "magic number". The former affords data integrity gaurantees, while the latter simplifies heuristic determination of file format. This format looks to have reasonably widespread usage, though not quite as significant as LZMA-Alone.

    The only implementation of this format I can find (lzip) is GPL licensed.

  3. the xz format ( http://tukaani.org/xz/xz-file-format.txt ) which is a more complex representation that includes CRC support and a magic number. This format is to be supported by the next iteration of XZ Utils which is currently in beta. The source may be obtained here: git://ctrl.tukaani.org/xz.git

    This format will address some criticisms to the LZMA-Alone format and was developed collaboratively by Lasse Collin (the current maintainer of XZ utils) and Igor Pavlov (the author of 7zip and the refrence implementation of LZMA).

    The xz format will employ LZMA2 which consists of extensions on top of LZMA, in the xz utils maintainer's words:

    "The primary compression algorithm in .xz is currently LZMA2, which is an extension on top of the orignal LZMA to fix a few practical issues, like adding support for flushing the encoder (equivalent to zlib's Z_SYNC_FLUSH), which isn't possible with the original LZMA."

    Again, maintainers words, regarding licensing:

    "XZ Utils currently contains a zlib-like compression library and a gzip-like command line tool. It's currently under LGPLv2.1+ but I will put it into the public domain before the first stable release."

  4. The 7zip disk format which can contain multiple files possibly stored in LZMA compressed format.

Given the state of things, the goal of this project is to develop something based on the existing formats, and quickly leverage code generated by the XZ Utils project, or simply kill this thing if that project produces something that's easy to embed and has a clean API at a similar level of abstraction as easylzma.

lloyd - sometime in oh nine.