Add support for a WebSocket extension of the given extension_type.
When a WebSocket client requests an extension of extension_type, a new [class@WebsocketExtension] of type
extension_type will be created to handle the request.
Note that [class@WebsocketExtensionDeflate] is supported by default, use [[email protected]_websocket_extension] if you want to disable it.
| this |
a Server |
| extension_type |
a Type |