code: func (s *Server) WebsocketHandler(allowedOrigins []string) http.Handler {
  	return websocket.Server{
  		Handshake: wsHandshakeValidator(allowedOrigins),
  		Handler: func(conn *websocket.Conn) {
  			codec := newWebsocketCodec(conn)
  			s.ServeCodec(codec, OptionMethodInvocation|OptionSubscriptions)
  		},
  	}
  }
docs: // WebsocketHandler returns a handler that serves JSON-RPC to WebSocket connections.
  //
  // allowedOrigins should be a comma-separated list of allowed origin URLs.
  // To allow connections with any origin, pass "*".