private val bytesLeft: Long
    get() = if (limit == -1L) -1L else (limit - byteCount)

  fun hasNext(): Boolean = peekHeader() != null

  /**
   * Returns the next header to process unless this scope is exhausted.
   *
   * This returns null if:
   *
   *  * The stream is exhausted.
   *  * We've read all of the bytes of an object whose length is known.