How do I use Sprockets with Sinatra without a rackup file?

Question

I'm writing a library that has an embedded Sinatra app launched via Thor. I want to mount instances of Sprockets::Environment at /css and /js and have the main app mapped to /. This would be easy using Rack::URLMap in a config.ru file, but in this case there isn't one because I'm starting the Sinatra app programmatically with Sinatra::Application.run!. How can I achieve this?

Answer 1

Actually, this is not that hard. All you need to do is assign an instance of Sprockets::Environment to a Sinatra configuration variable and define some paths to look up the assets you're interested in.

Here's a basic example:

require "sass"
require "haml"
require "erubis"
require "sinatra"
require "sprockets"

set :assets, Sprockets::Environment.new

# Configure sprockets
settings.assets.append_path "app/javascripts"
settings.assets.append_path "app/stylesheets"

# For compressed JS and CSS output
require "yui/compressor"
settings.assets.js_compressor  = YUI::JavaScriptCompressor.new
settings.assets.css_compressor = YUI::CssCompressor.new

get "/" do
  haml :index
end

get "/javascripts/:file.js" do
  content_type "application/javascript"
  settings.assets["#{params[:file]}.js"]
end

get "/stylesheets/:file.css" do
  content_type "text/css"
  settings.assets["#{params[:file]}.css"]
end

Happy sprocketing!

Answer 2

I ended up doing it by writing a custom middleware with some of the functionality from Rack::URLMap. It looks roughly like this:

require "sprockets"
require "sinatra/base"

class SprocketsMiddleware
  attr_reader :app, :prefix, :sprockets

  def initialize(app, prefix)
    @app = app
    @prefix = prefix
    @sprockets = Sprockets::Environment.new

    yield sprockets if block_given?
  end

  def call(env)
    path_info = env["PATH_INFO"]
    if path_info =~ prefix
      env["PATH_INFO"].sub!(prefix, "")
      sprockets.call(env)
    else
      app.call(env)
    end
  ensure
    env["PATH_INFO"] = path_info
  end
end

class App < Sinatra::Base
  use SprocketsMiddleware, %r{/assets} do |env|
    env.append_path "assets/css"
    env.append_path "assets/js"
  end
end

App.run!

Answer 3

Here is how I integrated Sprockets into Sinatra with Rails-like directory layout, helpers and minification for JS and CSS.

I chose to write a Sinatra extension. This extension encapsulates the configuration of sprockets (paths, minification, helpers) and can be registered by the application.

module Sinatra
  module Assets
    extend Sinatra::Extension

    configure do
      set :assets, Sprockets::Environment.new(root).tap { |assets|
        %w(assets vendor/assets).each do |base|
          %w(images javascripts stylesheets).each do |type|
            assets.append_path File.join(base, type)
          end
        end
        if production?
          assets.js_compressor = Closure::Compiler.new
          assets.css_compressor = YUI::CssCompressor.new
          uid = Digest::MD5.hexdigest(File.dirname(__FILE__))[0,8]
          assets.cache = Sprockets::Cache::FileStore.new("/tmp/sinatra-#{uid}")
        else
          assets.cache = nil
        end
      }
    end

    get "/assets/*" do
      env["PATH_INFO"].sub!(%r{^/assets}, "")
      expires Time.now + (365*24*60*60) if settings.production?
      settings.assets.call(env)
    end

    helpers do
      include Sprockets::Helpers

      Sprockets::Helpers.configure do |config|
        config.expand = development?
        config.digest = production?
      end

      def assets_environment
        settings.assets
      end
    end
  end
end

Using the extension in your application is simple:

class App < Sinatra::Base
  register Sinatra::Assets
  # ...
end

Assets can be placed in assets, or vendor/assets. For example vendor/assets/jquery.js can be referenced by logical name, i.e. http://localhost/assets/jquery.js.

In the example above I'm using sprockets-helpers which provides helpers such as javascript_tag. The configuration given above assumes that in development, you want to expand assets required by the referenced asset (resulting in multiple tags per asset).