Detect client bandwidth or whether WebSocket Connection is busy

[Kjos]

I'm using Webbit for streaming video over a websocket,
I want to apply some adaptive streaming, but I am scratching my head on how I can detect the bandwidth of the user, or just whether to check when data is still outgoing.
WebsocketConnection.send(data) will return immediately afaik.

Is there a way in Webbit to check whether a connection is busy? Is that even an option?

[Kjos]

Quick update; I've just added a message from the client to the server when the FPS is too low, in which case it will lower quality in a PID loop. This seems to work well, but if there is a better way it'd be glad to hear it.
I saw writeMessage returns a Future, but I didn't check whether it has a listener for bytes sent, because I think it was protected anyway.

[Kjos]

So I've added a function to WebSocketConnection called sendFuture which returns the ChannelFuture. I then listen to operationComplete. operationComplete then sets a boolean whether the Channel is busy or not.
This doesn't work reliably however.