//
// 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.
// NewReader enforces S3 compatibility strictly by ensuring caller
// does not send more content than specified size.
func NewReader(ctx context.Context, src io.Reader, size int64, md5Hex, sha256Hex string, actualSize int64) (*Reader, error) {

//
// If the current file is sparse and w is an io.WriteSeeker,
// then writeTo uses Seek to skip past holes defined in Header.SparseHoles,
// assuming that skipped regions are filled with NULs.
// This always writes the last byte to ensure w is the right size.
//
// TODO(dsnet): Re-export this when adding sparse file support.
// See https://golang.org/issue/22735