peerPrefix      = "peer"
	peerPrefixS3    = "peerS3"
	healPrefix      = "heal"
)

func init() {
	// Static check if we exceed 255 handler ids.
	// Extend the type to uint16 when hit.
	if handlerLast > 255 {
		panic(fmt.Sprintf("out of handler IDs. %d > %d", handlerLast, 255))
	}
}

func (h HandlerID) valid() bool {
	return h != handlerInvalid && h < handlerLast
}

// 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.