flask-socketio 一直发请求polling 无法使用websoket 模式

客端一直请求 无法启用websocket模式 一直时 polling长轮询模式

 /socket.io/?EIO=4&transport=polling&t=O7SEpD7&sid=pgxihJ9EenZAtnYEAAA

还有异常提示

The WebSocket transport is not available, 
you must install a WebSocket server that is compatible with your async mode to enable it.
 See the documentation for details. (further occurrences of this error will be logged with level INFO)

 原因是flask run 开发方式运行 服务端不支持websocket ,可以安装simple-websocket 以支持  

github 地址 https://github.com/dpallot/simple-websocket-server