// number of files is reasonable, since a malformed archive may
	// indicate it contains up to 1 << 128 - 1 files. Since each file has a
	// header which will be _at least_ 30 bytes we can safely preallocate
	// if (data size / 30) >= end.directoryRecords.
	if end.directorySize < uint64(size) && (uint64(size)-end.directorySize)/30 >= end.directoryRecords {

//
// 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.
	if _, err := io.ReadFull(tr.r, tr.blk[:]); err != nil {