private function get_contact_vcard($source, $cid, &$filename = null)
    {
        $rcmail  = rcmail::get_instance();
        $source  = $rcmail->get_address_book($source);
        $contact = $source->get_record($cid, true);

        if ($contact) {
            $fieldmap = $source ? $source->vcard_map : null;

            if (empty($contact['vcard'])) {
                $vcard = new rcube_vcard('', RCUBE_CHARSET, false, $fieldmap);
                $vcard->reset();

                foreach ($contact as $key => $values) {
                    list($field, $section) = explode(':', $key);
                    // avoid unwanted casting of DateTime objects to an array
                    // (same as in rcube_contacts::convert_save_data())
                    if (is_object($values) && is_a($values, 'DateTime')) {
                        $values = array($values);
                    }

                    foreach ((array) $values as $value) {
                        if (is_array($value) || is_a($value, 'DateTime') || @strlen($value)) {
                            $vcard->set($field, $value, strtoupper($section));
                        }
                    }
                }

                $contact['vcard'] = $vcard->export();
            }

            $name     = rcube_addressbook::compose_list_name($contact);
            $filename = (self::parse_filename($name) ?: 'contact') . '.vcf';

            // fix folding and end-of-line chars
            $vcard = preg_replace('/\r|\n\s+/', '', $contact['vcard']);
            $vcard = preg_replace('/\n/', rcube_vcard::$eol, $vcard);

            return rcube_vcard::rfc2425_fold($vcard) . rcube_vcard::$eol;
        }
    }