RBzip2 is a gem providing various implementations of the bzip2 algorithm used for compression and decompression. Currently, it includes a FFI-based implementation and a pure Ruby implementation that's slower but works on any Ruby VM. Additionally, there's a JRuby specific implementation that's based on Commons Compress.

The pure Ruby implementations is based on the code of the Apache Commons Compress project and adds a straight Ruby-like API. There are no external dependencies like other gems or libraries. Therefore it will run on any Ruby implementation and the respective operating systems supported by those implementations.

The FFI implementation is using libbz2 and provides fast performance on platforms where both libbz2 and FFI are available. It is derived from this Gist by Brian Lopez.

The Java-based implementation can use the Commons Compress Java library if it is available in the classpath.


  • Compression of raw data into bzip2 compressed IOs (like File or StringIO)
  • Decompression of bzip2 compressed IOs (like File or StringIO)


require 'rbzip2'


data = some_data
file = File.new 'somefile.bz2'      # open the target file
bz2  = RBzip2.default_adapter::Compressor.new file  # wrap the file into the compressor
bz2.write data                      # write the raw data to the compressor
bz2.close                           # finish compression (important!)


file = File.new 'somefile.bz2'        # open a compressed file
bz2  = RBzip2.default_adapter::Decompressor.new file  # wrap the file into the decompressor
data = io.read                        # read data into a string

Future plans

  • Simple decompression of strings
  • Simple creation of compressed files
  • Two-way compressed IO that will (de)compress as you read/write


To install RBzip2 as a Ruby gem use the following command:

$ gem install rbzip2

To use it as a dependency managed by Bundler add the following to your Gemfile:

gem 'rbzip2'

If you want to use the FFI implementation on any non-JRuby VM, be sure to also install the ffi gem.


The bzip2-ruby gem is a Ruby binding to libbz2 and offers best performance, but it is only available for MRI < 2.0.0 and Rubinius.

The FFI implementation binds to libbz2 as well and has almost the same performance as bzip2-ruby.

The Java implementation uses a native Java library and is slower by a factor of about 2/10 while compressing/decompressing.

The pure Ruby implementation of RBzip2 is inherently slower than bzip2-ruby. Currently, this is a plain port of Apache Commons' Java code to Ruby and no effort has been made to optimize it. That's why the Ruby implementation of RBzip2 is slower by a factor of about 130/100 while compressing/decompressing (on Ruby 1.9.3). Ruby 1.8.7 is even slower.


This code is free software; you can redistribute it and/or modify it under the terms of the new BSD License. A copy of this license can be found in the included LICENSE file.


  • Sebastian Staudt -- koraktor(at)gmail.com
  • Brian Lopez -- seniorlopez(at)gmail.com

See Also