// of the read content as ETag. Optionally, it also computes
// the SHA256 checksum of the content.
//
// If the reference values for the ETag and content SHA26
// are not empty then it will check whether the computed
// match the reference values.
type Reader struct {
	src         io.Reader
	bytesRead   int64
	expectedMin int64
	expectedMax int64

	size       int64
	actualSize int64

		hdr, rawHdr, err := tr.readHeader()
		if err != nil {
			return nil, err
		}
		if err := tr.handleRegularFile(hdr); err != nil {
			return nil, err
		}
		format.mayOnlyBe(hdr.Format)

		// Check for PAX/GNU special headers and files.
		switch hdr.Typeflag {
		case TypeXHeader, TypeXGlobalHeader:
			format.mayOnlyBe(FormatPAX)
			paxHdrs, err = parsePAX(tr)
			if err != nil {
				return nil, err
			}