func (s *Stack) IterateBackward(handler func(depth int, header io.Reader, body io.Reader) bool) error {
	s.guard.Lock()
	defer s.guard.Unlock()
	if s.depth == 0 {
		return nil
	}
	file, err := s.getFile()
	if err != nil {
		return err
	}
	defer file.Seek(0, os.SEEK_END)
	var (
		currentBlock       fileBlock // Current block description
		currentBlockOffset uint64    // Current block offset from begining of file
	)
	currentBlock = s.currentBlock
	currentBlockOffset = uint64(s.currentBlockPos)
	depth := s.depth
	for {
		body := io.NewSectionReader(file, int64(currentBlock.DataPoint), int64(currentBlock.DataSize))
		header := io.NewSectionReader(file, int64(currentBlock.HeaderPoint), int64(currentBlock.HeaderSize))
		// invoke block processor
		if handler != nil && !handler(depth, header, body) {
			return nil
		}
		if currentBlock.PrevBlock > currentBlockOffset {
			log.Printf("Danger back-ref link: prev block %v has greater index then current %v", currentBlock.PrevBlock, currentBlockOffset)
		}

		depth--
		if currentBlock.PrevBlock == currentBlockOffset {
			// First block has prev block = 0
			break
		}
		currentBlockOffset = currentBlock.PrevBlock
		currentBlock, err = readBlockAt(file, int64(currentBlock.PrevBlock))
		if err != nil {
			return err
		}
	}
	if depth != 0 {
		log.Println("Broker back path detected at", depth, "depth index")
	}
	return nil
}
func (s *Stack) IterateBackward(handler func(depth int, header io.Reader, body io.Reader) bool) error {
	s.guard.Lock()
	defer s.guard.Unlock()
	if s.depth == 0 {
		return nil
	}
	file, err := s.getFile()
	if err != nil {
		return err
	}
	defer file.Seek(0, os.SEEK_END)
	var (
		currentBlock       fileBlock // Current block description
		currentBlockOffset uint64    // Current block offset from begining of file
	)
	currentBlock = s.currentBlock
	currentBlockOffset = uint64(s.currentBlockPos)
	depth := s.depth
	for {
		body := io.NewSectionReader(file, int64(currentBlock.DataPoint), int64(currentBlock.DataSize))
		header := io.NewSectionReader(file, int64(currentBlock.HeaderPoint), int64(currentBlock.HeaderSize))
		// invoke block processor
		if handler != nil && !handler(depth, header, body) {
			return nil
		}
		if currentBlock.PrevBlock > currentBlockOffset {
			log.Printf("Danger back-ref link: prev block %v has greater index then current %v", currentBlock.PrevBlock, currentBlockOffset)
		}

		depth--
		if currentBlock.PrevBlock == currentBlockOffset {
			// First block has prev block = 0
			break
		}
		currentBlockOffset = currentBlock.PrevBlock
		currentBlock, err = readBlockAt(file, int64(currentBlock.PrevBlock))
		if err != nil {
			return err
		}
	}
	if depth != 0 {
		log.Println("Broker back path detected at", depth, "depth index")
	}
	return nil
}
// IterateBackward - iterate over hole stack segment-by-segment from end to begining