if _, err := io.ReadFull(r, buf[off:12]); err != nil {
		return err
	}
	b := readBuf(buf[:12])
	if b.uint32() != f.CRC32 {
		return ErrChecksum
	}

	// The two sizes that follow here can be either 32 bits or 64 bits
	// but the spec is not very clear on this and different
	// interpretations has been made causing incompatibilities. We
	// already have the sizes from the central directory so we can
	// just ignore these.

	lastErr  error           // last error reported, if this non-nil all reads will fail.
	m        *Monitor
	opts     *MonitorReaderOptions
}

// BucketOptions represents the bucket and optionally its replication target pair.
type BucketOptions struct {
	Name           string
	ReplicationARN string // This is optional, and not mandatory.
}

// header in case further processing is required.
//
// The err will be set to io.EOF only when one of the following occurs:
//   - 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.