type Reader struct {
	args         *ReaderArgs
	readCloser   io.ReadCloser    // raw input
	buf          *bufio.Reader    // input to the splitter
	columnNames  []string         // names of columns
	nameIndexMap map[string]int64 // name to column index
	current      [][]string       // current block of results to be returned
	recordsRead  int              // number of records read in current slice
	input        chan *queueItem  // input for workers

// returns ETag of the content. Otherwise, it returns
// nil as ETag.
//
// Wrap provides an adapter for io.Reader implementations
// that don't implement the Tagger interface.
// It is mainly used to provide a high-level io.Reader
// access to the ETag computed by a low-level io.Reader:
//
//	content := etag.NewReader(r.Body, nil)
//
//	compressedContent := Compress(content)
//	encryptedContent := Encrypt(compressedContent)
//