}

type unwrapper interface {
	Unwrap() http.ResponseWriter
}

// headersAlreadyWritten returns true if the headers have already been written
// to this response writer. It will unwrap the ResponseWriter if possible to try
// and find a trackingResponseWriter.
func headersAlreadyWritten(w http.ResponseWriter) bool {
	for {
		if trw, ok := w.(*trackingResponseWriter); ok {