  def index
    html = <<~HTML
      <!DOCTYPE html>
      <html>
        <head>
        </head>
        <body>
          <div id="app"></div>
          #{js_asset "jquery-1.8.2.js"}
          #{js_asset "react.js"}
          #{js_asset "react-dom.js"}
          #{js_asset "babel.min.js"}
          #{js_asset "message-bus.js"}
          #{js_asset "application.jsx", "text/jsx"}
        </body>
      </html>
    HTML

    [200, { "content-type" => "text/html;" }, [html]]
  end
The software uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the software does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.