sub is_valid_utf8 {
   return $_[0] =~ /
      ^
      (?: [\x00-\x7F]
      |   [\xC0-\xDF] [\x80-\xBF]
      |   [\xE0-\xEF] [\x80-\xBF]{2}
      |   [\xF0-\xF7] [\x80-\xBF]{3}
      )*+
      \z
   /x
}

utf8::decode($string)
   if is_valid_utf8($string);