pr-zlib

Description

The pr-zlib library is a pure Ruby version of the zlib compression library. It consists of both a port of zlib.h and the Ruby zlib library that ships as part of the standard library.

Installation

gem install pr-zlib

Adding the trusted cert

gem cert --add <(curl -Ls https://raw.githubusercontent.com/djberg96/pr-zlib/main/certs/djberg96_pub.pem)

Synopsis

# Imitating a bit of code used in rubygems
require 'pr/zlib'
require 'stringio'

data = StringIO.new(data)
Zlib::GzipReader.new(data).read

Motivation

First, building the zlib C library on MS Windows with Visual C++ is very difficult. However, certain libraries depend on zlib, most notably rubygems. By providing a pure Ruby version we eliminate any compiler or platform compatability issues.

Second, even some Unix distributions, such as Debian, do not ship with the zlib library by default. By creating a pure Ruby version of the zlib library we eliminate the need to install a 3rd party C library, and eliminate a potential weak link in the dependency chain.

Third, by creating pure Ruby versions of the library and the interface we are more likely to receive patches, feature requests, documentation updates, etc, from the Ruby community since not everyone who knows Ruby also knows C.

Last, the zlib interface that ships as part of the stdlib is a little on the clunky side. By providing a pure Ruby version, authors can create their own interface as they see fit.

Update August 2025: Most of the original motivation for this library is no longer relevant today. Desktop users of MS Windows typically use the one-click installer which bundles the shared objects it needs. In the land of Unix, where most actual production code happens, folks use Docker images for Ruby which either already bundles everything, or they just add it to their Dockerfile.

But, hey, I paid for this and it works. Who knows, maybe it'll be nice to have around someday.

Origins

This library was the result of a small code bounty that I (Daniel Berger) funded:

https://rubytalk.org/t/bounty-pure-ruby-zlib-gzipwriter/50730

TODO

More tests, and better tests, are needed for both Rbzlib and Zlib.

Caveats

You cannot use both this library and the zlib standard library at the same time. If you try to use both there is a good chance you will get an allocation error of some sort. If you already have zlib, you do not need this library.

License

This library is covered under the same license as zlib itself. For the text of the zlib license, please see http://zlib.net/zlib_license.html.

Authors

• Park Heesob (Original C translation)
• Daniel Berger (Testing, packaging, deployment, maintenance)