close message if
this was not already sent and wait for the close reply.
| Code | - is the numerical code indicating the close status. This is 16-bit integer. The codes are defined in section 7.4.1. Defined Status Codes of RFC6455. Notably, 1000 indicates a normal closure. |
| Data | - is currently interpreted as text. |
websocket_error(unexpected_message, Reply) if
the other side did not send a close message in reply.