func (s *Storage) NewWriter(ctx context.Context) *Writer {
	return newWriter(ctx, s.objC, s.prefix)
}
func (s *Storage) NewWriter(ctx context.Context) *Writer {
	return newWriter(ctx, s.objC, s.prefix)
}
// NewWriter creates an io.WriteCloser for a stream of bytes to be chunked.
// Chunks are created based on the content, then hashed and deduplicated/uploaded to
// object storage.
// The callback arguments are the chunk hash and content.