Connection: add 'uidvalidity' event for unsolicited, untagged OK responses with uidvalidity text code

README.md

@@ -325,6 +325,8 @@ Connection Events
 
 * **expunge**(< _integer_ >seqno) - Emitted when a message was expunged externally. `seqno` is the sequence number (instead of the unique UID) of the message that was expunged. If you are caching sequence numbers, all sequence numbers higher than this value **MUST** be decremented by 1 in order to stay synchronized with the server and to keep correct continuity.
 
+* **uidvalidity**(< _integer_ >uidvalidity) - Emitted if the UID validity value for the currently open mailbox changes during the current session.
+
 * **update**(< _integer_ >seqno, < _object_ >info) - Emitted when message metadata (e.g. flags) changes externally.
 
 * **error**(< _Error_ >err) - Emitted when an error occurs. The 'source' property will be set to indicate where the error originated from.

lib/Connection.js

@@ -1014,7 +1014,9 @@ Connection.prototype._resUntagged = function(info) {
         for (i = 0, len = keywords.length; i < len; ++i)
           permFlags.splice(permFlags.indexOf(keywords[i]), 1);
       }
-    }
+    } else if (typeof info.textCode === 'string'
+               && info.textCode.toUpperCase() === 'UIDVALIDITY')
+      this.emit('uidvalidity', info.text);
   } else if (type === 'list') {
     if (this.delimiter === undefined)
       this.delimiter = info.text.delimiter;