GitHub HTML pipeline for adding asset fingerprints to image links

image_asset_path_filter.rb

module HTML
  class Pipeline

    class ImageAssetPathFilter < HTML::Pipeline::Filter
      def call
        doc.search("img").each do |img|
          next if img['src'].nil?

          src = img['src'].strip

          if src.start_with?('/')
            # stripping `/assets/` from the URL enables asset fingerprinting in production
            img["src"] = ActionController::Base.helpers.asset_path(src.gsub(/^\/assets\//, ''))
          end
        end

        doc
      end

    end
  end
end