Modify CloseWebSocketFrame#statusCode() to change the fetch c…

[zhangjinying]

Motivation:

According to the websocket protocol description, change the get code method in the CloseWebSocketFrame to unsigned.

Modification:

Modify changed CloseWebSocketFrame#statusCode() to change the fetch code to unsigned

Result:

Fixes #13113.

[normanmaurer]

Can you please sign our ICLA: https://netty.io/s/icla and let me know once done

[zhangjinying]

ICLA

Agreed, done

[mostroverkhov]

On the next line the spec says status code with value /code/ defined in [Section 7.4](https://www.rfc-editor.org/rfc/rfc6455#section-7.4). rfc6455 section-7.4 defines maximum value of 4999: so while this change is "formally" correct, I am wondering what library/software/user-agent is a) using status > 4999 b) using status > 32_767 which would lead to overflow with current code?

[zhangjinying]

On the next line the spec says status code with value /code/ defined in [Section 7.4](https://www.rfc-editor.org/rfc/rfc6455#section-7.4). rfc6455 section-7.4 defines maximum value of 4999: so while this change is "formally" correct, I am wondering what library/software/user-agent is a) using status > 4999 b) using status > 32_767 which would lead to overflow with current code?

Yes, but rfc6455 section-7.4 is no restriction that you cannot use more than 32_767, and custom code should not overflow if it is greater than 32_767 (according to https://www.rfc-editor.org/rfc/rfc6455#section-5.5.1the first two bytes of
the body MUST be a 2-byte unsigned integer (in network byte order)）