tokens = need + hdr

		} else { // part of header can be accommodated
			r.opts.HeaderSize -= b - 1
			need = 1 // to ensure we read at least one byte for every Read
			tokens = b
		}
	} else { // all tokens go towards payload
		need = int(math.Min(float64(b), float64(need)))
		tokens = need
	}

	err = r.throttle.WaitN(r.ctx, tokens)
	if err != nil {

func (r *Reader) startReaders(newReader func(io.Reader) *csv.Reader) error {
	if r.args.FileHeaderInfo != none {
		// Read column names
		// Get one line.
		b, err := r.nextSplit(0, nil)
		if err != nil {
			r.err = err
			return err
		}
		if !utf8.Valid(b) {
			return errInvalidTextEncodingError()
		}
		reader := newReader(bytes.NewReader(b))