* have been received. If the returned list contains multiple blocks of headers the blocks will be
   * delimited by 'null'.
   *
   * @param callerIsIdle true if the caller isn't sending any more bytes until the peer responds.
   *     This is true after a `Expect-Continue` request, false for duplex requests, and false for
   *     all other requests.
   */
  @Throws(IOException::class)