rack-asset-compiler

rack-asset-compiler is a Rack middleware that provides a generic interface for compiling static files, such as Sass or CoffeeScript files.

rack-asset-compiler does not use any local file storage and makes use of caching headers such as "Cache-Control" and "If-Modified-Since". This makes it ideal for running on read-only filesystem systems such as Heroku.

Installation

gem install rack-asset-compiler

Generic form

In this example, we have a set of text files with the extension .lower in the 'lowercase' directory, and we want to serve .uppercase files out of http://yourhost.com/uppercase

The compilation step is given in the form of a lambda passed as the :compiler option. This lambda will be invoked whenever a client requests a file that needs to be compiled. The source filename will be passed in and the compiled output is expected to be returned.

require 'rack/asset_compiler'

use Rack::AssetCompiler,
  :source_dir => 'lowercase',
  :url => '/uppercase',
  :content_type => 'text/plain',
  :source_extension => 'lower',
  :compiler => lambda { |source_file|
    File.read(source_file).upcase
  }

Subclassing

An alternative to passing in a lambda to the :compiler option is to subclass Rack::AssetCompiler and override the compile method.

This gem comes with two subclasses: one for compiling CoffeeScript and one for compiling Sass.

Compiling CoffeeScript

config.ru

require 'rack/coffee_compiler'

use Rack::CoffeeCompiler,
  :source_dir => 'app/coffeescripts',
  :url => '/javascripts',
  :alert_on_error => true  # Generates a window.alert on compile error.  Defaults to (RACK_ENV != 'production')

Gemfile

gem 'therubyracer'
gem 'coffee-script'

See examples/jasmine_config.rb for an example of how to use CoffeeScript with your jasmine specs.

Compiling Sass

On Rails

require 'rack/sass_compiler'

# Disable the standard Sass plugin which will write to the filesystem
Rails.application.config.middleware.delete(Sass::Plugin::Rack)

# Insert the new middleware
Rails.application.config.middleware.use Rack::SassCompiler,
  :source_dir => 'app/sass',
  :url => '/css'

The above uses the default options for the sass compiler, including the use of the scss syntax. To compile sass, or to change any of the other sass compiler options, provide the optional sass_options hash in the options hash. For example...

# Insert the new middleware
Rails.application.config.middleware.use Rack::SassCompiler,
  :source_dir => 'app/sass',
  :url => '/css'
  :sass_options => {
    :syntax => :sass,
    :style => :compressed
  }

The above would use the sass syntax compiler and output compressed CSS. See Sass Documentation for a list of options.

To make the Compass frameworks available to the SassCompiler, simply require Compass and any compass plugins. For example...

require 'compass'
require 'ninesixty' # 960.gs Compass plugin 

use Rack::SassCompiler,
  :source_dir => 'sass'
  :url => '/css'

Running without an HTTP cache

If your stack doesn't include an HTTP cache (like Varnish), the compilation step will run each time a new visitor requests a compiled resource.

An easy solution is to use Rack::Cache

require 'rack/asset_compiler'
require 'rack/cache'
use Rack::Cache # Make sure this comes first
use Rack::AssetCompiler, ...

If you're deploying to the Bamboo or Aspen stack on Heroku, you get Varnish for free. The Cedar stack on Heroku does not have Varnish, so you'll have to use Rack::Cache and/or something like Cloudfront.

If you're running locally, the user agent cache in your browser is sufficient. So you also don't need to worry about this.

Contribute

Contributions must be accompanied by passing tests. To run the test suite for the gem you need the following gems installed:

[sudo] gem install rack rack-test haml coffee-script rspec compass

After installing the required gems and before beginning development, ensure your environment is properly configured and all tests pass by running rake.

Thanks

asset-compiler was inspired by rack-coffee by Matthew Lyon

ruby 1.9.2 compatibility added by Derek Prior