// It is mainly used to provide a high-level io.Reader
// access to the ETag computed by a low-level io.Reader:
//
//	content := etag.NewReader(r.Body, nil)
//
//	compressedContent := Compress(content)
//	encryptedContent := Encrypt(compressedContent)
//
//	// Now, we need an io.Reader that can access
//	// the ETag computed over the content.
//	reader := etag.Wrap(encryptedContent, content)

		// jar tool) don't properly set the storage method on directories
		// resulting in a file with compressed size > 0 but uncompressed size ==
		// 0. We still want to fail when a directory has associated uncompressed
		// data, but we are tolerant of cases where the uncompressed size is
		// zero but compressed size is not.
		if f.UncompressedSize64 != 0 {
			return &dirReader{ErrFormat}, nil
		} else {