Evalhook v0.3.0 released and shikashi works on Heroku

Evalhook is a vital dependency of shikashi gem, provide the feature of execute managed ruby code in the way of allow "hooks" of common events like method calls, system calls, assignment of global variables and constants, etc...

Fixed Issues

With this release, problems of compatibility of actual version of shikashi (v0.3.1 at the moment of writing this post) were solved. The most important change was refactor of the hooking to make it more portable, less prone to error and implemented in pure ruby (the C extension was removed from the gem). this implies that now shikashi works on heroku and possibly in other environments

Update/Install

To update current installation of evalhook gem, run in terminal:

gem install evalhook

NOTE: To update the gem on heroku you must change Gemfile and Gemfile.lock files, then push this files to your application git repository, setting the content of Gemfile to something like that:

source :rubygems

gem 'shikashi'
gem 'evalhook', '0.3.0'
gem 'partialruby', '0.1.0'

Fundamentals

The most important concept behind evalhook is the AST hook technique which consist in change the Abstract Syntax Tree before it is interpreted and executed (view this other post for more info)

In previous versions of evalhook, the method to implement the AST hook was change the internal structures (representations of AST) on the version 1.8 of Matz Ruby Interpreter. This implementation breaks the encapsulation of MRI and depends on the specific implementation of that ruby interpreter making a very poor portability and being prone to error (e.g. the ruby interpreter crashes in heroku)

The reimplementation of the evalhook core is based on partialruby, a "para-interpreter" which executes ruby code by emulating it using ruby. Partialruby also exports the hooking services needed by evalhook thus avoiding the need for "hacks" to implement that service in a interpreter that does not have that. This concept is much more portable and theoretically should work with any interpreter of ruby 1.8 code.

Links

Shikashi Project description: http://tario-project.blogspot.com/2011/03/shikashi-flexible-sandbox-for-ruby.html
AST Hook fundamentals: http://tario-project.blogspot.com/2011/03/how-tree-hooks-works-and-what-are.html
Evalhook on Github https://github.com/tario/evalhook
Shikashi on Github: https://github.com/tario/shikashi
Heroku; http://heroku.com