将流式传输（utf8）数据转换为字符串的安全方法是什么？

Suppose I'm a server written in objc/swift. The client is sending me a large amount of data, which is really a large utf8 encoded string. As the server, i have my NSInputStream firing events to say it has data to read. I grab the data and build up a string with it. Suppose I'm a server written in objc/swift. The