case debugIsOutgoingClosed:
		// params: muxID uint64, isClosed func(bool)
		muxID := args[0].(uint64)
		resp := args[1].(func(b bool))
		mid, ok := c.outgoing.Load(muxID)
		if !ok || mid == nil {
			resp(true)
			return
		}
		mid.respMu.Lock()
		resp(mid.closed)
		mid.respMu.Unlock()
	}
}

// wsWriter writes websocket messages.
type wsWriter struct {
	tmp [ws.MaxHeaderSize]byte
}