middleman--middleman/lib/middleman/features/asset_host.rb

module Middleman::Features::AssetHost
  class << self
    def registered(app)
      app.after_feature_init do
        if Middleman::Server.asset_host.is_a?(Proc)
          ::Compass.configuration.asset_host(&Middleman::Server.asset_host)
        end
      end

      Middleman::Assets.register :asset_host do |path, prefix, request|
        original_output = Middleman::Assets.before(:asset_host, path, prefix, request)

        valid_extensions = %w(.png .gif .jpg .jpeg .js .css)

        asset_prefix = Middleman::Server.asset_host.call(original_output)

        File.join(asset_prefix, original_output)
      end
    end
    alias :included :registered
  end
end