// As recommended by the HTTP RFC and implemented in Firefox, the max age of a document
        // should be defaulted to 10% of the document's age at the time it was served. Default
        // expiration dates aren't used for URIs containing a query.
        val servedMillis = servedDate?.time ?: sentRequestMillis
        val delta = servedMillis - lastModified!!.time
        return if (delta > 0L) delta / 10 else 0L
      }

    sink.writeUtf8(content)
    sink.close()
  }

  /**
   * @param delta the offset from the current date to use. Negative values yield dates in the past;
   * positive values yield dates in the future.
   */
  private fun formatDate(
    delta: Long,
    timeUnit: TimeUnit,
  ): String {
    return formatDate(Date(System.currentTimeMillis() + timeUnit.toMillis(delta)))