+ /**
+ * Convert string into RFC's quoted-string or literal-c2s form
+ *
+ * @param string $string The string to convert.
+ *
+ * @return string Result string
+ */
+ function _escape($string)
+ {
+ // Some implementations doesn't allow UTF-8 characters in quoted-string
+ // It's safe to use literal-c2s
+ if (preg_match('/[^\x01-\x09\x0B-\x0C\x0E-\x7F]/', $string)) {
+ return sprintf("{%d+}\r\n%s", $this->_getLineLength($string), $string);
+ }
+
+ return '"' . addcslashes($string, '\\"') . '"';
+ }
+