Patch Rack::File to look for pre-gzipped files (mimic nginx's gzip_static behavior)

static_gzip.rb

# Patch Rack::File to support pre-gzipped files
module Rack
  class File
    def _call_with_static_gzip(env)
      @path_info = Utils.unescape(env["PATH_INFO"])
      return forbidden  if @path_info.include? ".."

      @path = F.join(@root, @path_info) + '.gz'
      if F.file?(@path) && F.readable?(@path)
        serving
      else
        _call_without_static_gzip(env)
      end
    end
    alias_method_chain :_call, :static_gzip

    def serving_with_static_gzip
      res = serving_without_static_gzip
      if @path.end_with?('.gz')
        headers = res[1]
        headers['Content-Encoding'] = 'gzip'
        headers['Content-Type'] = Mime.mime_type(F.extname(@path.sub(/.gz$/, '')), headers['Content-Type'])
      end
      res
    end
    alias_method_chain :serving, :static_gzip
  end
end

module ActionDispatch
  class Static
    def file_exist?(path)
      full_path = File.join(@file_server.root, ::Rack::Utils.unescape(path))
      [full_path, full_path + '.gz'].any? do |_full_path|
        File.file?(_full_path) && File.readable?(_full_path)
      end
    end
  end
end