CI_Form_validation::prep_url PHP Method

    public function prep_url($str = '')
    {
        if ($str === 'http://' or $str === '') {
            return '';
        }
        if (strpos($str, 'http://') !== 0 && strpos($str, 'https://') !== 0) {
            return 'http://' . $str;
        }
        return $str;
    }