// if sha256Hex is not the empty string.
//
// If size resp. actualSize is unknown at the time of calling
// NewReader then it should be set to -1.
// When size is >=0 it *must* match the amount of data provided by r.
//
// NewReader may try merge the given size, MD5 and SHA256 values
// into src - if src is a Reader - to avoid computing the same
// checksums multiple times.

// Reader.Next advances to the next file in the archive (including the first),
// and then Reader can be treated as an io.Reader to access the file's data.
type Reader struct {
	r    io.Reader
	pad  int64      // Amount of padding (ignored) after current file entry
	curr fileReader // Reader for current file entry
	blk  block      // Buffer to use as temporary local storage

	// err is a persistent error.