def get_published_topics(subgraph='')
      code, message, topics = @proxy.getPublishedTopics(@caller_id, subgraph)
      if code == 1
        return topics
      elsif
        raise message
      end
    end
def get_published_topics(subgraph='')
      code, message, topics = @proxy.getPublishedTopics(@caller_id, subgraph)
      if code == 1
        return topics
      elsif
        raise message
      end
    end
get the all published topics
 @param [String] subgraph namespace for check
 @return [Array] topic names.
 @raise