//   - Exactly 0 bytes are read and EOF is hit.
//   - Exactly 1 block of zeros is read and EOF is hit.
//   - At least 2 blocks of zeros are read.
func (tr *Reader) readHeader() (*Header, *block, error) {
	// Two blocks of zero bytes marks the end of the archive.
	if _, err := io.ReadFull(tr.r, tr.blk[:]); err != nil {
		return nil, nil, err // EOF is okay here; exactly 0 bytes read
	}

		r.err = io.EOF
	}
	return r.readCloser.Close()
}

// nextSplit will attempt to skip a number of bytes and
// return the buffer until the next newline occurs.
// The last block will be sent along with an io.EOF.
func (r *Reader) nextSplit(skip int, dst []byte) ([]byte, error) {
	if cap(dst) < skip {
		dst = make([]byte, 0, skip+1024)
	}
	dst = dst[:skip]
	if skip > 0 {
		n, err := io.ReadFull(r.buf, dst)