esp-v2 websocket messages filtering

[shunsuke_w]

In esp-v2, Is it possible to apply envoy filters over WebSocket frames/messages?
Such as rate limiting.
Or they are not applied once connection is upgraded.
https://github.com/GoogleCloudPlatform/esp-v2 

Thank you

(Because no category exists for cloud-endpoints, esp-v2, I posted the qudstion here)