WebSocket extension instance. This instance is created for each WebSocket request, for every installed extension by WebSocketExtensionFactory.
This method is called only for a client, when it receives the WebSocket upgrade response.
This method is called on each incoming frame before handling it in WebSocket session.
This method is called on each outgoing frame and handle it before sending.
This method is called only for a server, when it receives websocket session.
List of WebSocket extension protocols which will be sent by client in headers. They are required to inform server that client wants to negotiate current extension.