MqttServer 事件

当客户端连接时，触发的验证事件
Validation event triggered when the client connects

当客户端进行文件操作时，校验客户端合法性的事件，操作码具体查看的常量值
When client performing file operations, it is an event to verify the legitimacy of the client. For the operation code, check the constant value of

当收到客户端发来的MqttClientApplicationMessage消息时触发
Triggered when a MqttClientApplicationMessage message is received from the client

Mqtt的客户端连接上来时触发
Triggered when Mqtt client connects

Mqtt的客户端下线时触发
Triggered when Mqtt client connects

订阅主题事件，当客户端订阅主题时触发，返回 0 标识订阅通过，返回 其他值标识订阅失败
Subscribe to the topic event. This triggers when the client subscribes to the topic. Returns 0 to indicate successful subscription, and returns other values to indicate subscription failure.

文件变化的事件，当文件上传的时候，文件下载的时候，文件被删除的时候触发。
The file change event is triggered when the file is uploaded, when the file is downloaded, or when the file is deleted.

当客户端连接时，服务器决定是否需要重定向地址操作，通常用于服务器程序迁移，负载均衡操作