func GenerateETag(fileSize, fileName, modTime string) string {
	etag := fileSize + fileName + modTime
	return base64.StdEncoding.EncodeToString([]byte(etag))
}
func GenerateETag(fileSize, fileName, modTime string) string {
	etag := fileSize + fileName + modTime
	return base64.StdEncoding.EncodeToString([]byte(etag))
}
// GenerateETag generates an ETag based on size, filename and file modification time