serving (Rack::File)

    # File lib/rack/file.rb, line 55
        def serving
          if size = F.size?(@path)
            body = self
          else
            body = [F.read(@path)]
            size = body.first.size
          end

          [200, {
            "Last-Modified"  => F.mtime(@path).httpdate,
            "Content-Type"   => Mime.mime_type(F.extname(@path), 'text/plain'),
            "Content-Length" => size.to_s
          }, body]
        end