// TODO: decide how to call this
public void ackReceived(long messageID) {
// Remove if received acknowledgment message id contains in retained message list.
retainedMessageList.remove(messageID);
}
/**
* Record the given message ID as a retained message in the trcker.
*
* @param messageID Message ID of the retained message
*/
public void recordRetainedMessage(long messageID) {
retainedMessageList.add(messageID);
}