+function reverse_feed_permalink($description)
+{
+ return preg_replace('@— <a href="([^"]+)" title="[^"]+">(\w+)</a>$@im', '— [$2]($1)', $description);
+}
+
+/**
+ * Replace not whitelisted protocols with http:// in given description.
+ *
+ * @param string $description input description text.
+ * @param array $allowedProtocols list of allowed protocols.
+ *
+ * @return string $description without malicious link.
+ */
+function filter_protocols($description, $allowedProtocols)
+{
+ return preg_replace_callback(
+ '#]\((.*?)\)#is',
+ function ($match) use ($allowedProtocols) {
+ return ']('. whitelist_protocols($match[1], $allowedProtocols) .')';
+ },
+ $description
+ );
+}
+