func (p *XdsProxy) StreamAggregatedResources(downstream DiscoveryStream) error {
	proxyLog.Debugf("accepted XDS connection from Envoy, forwarding to upstream XDS server")
	return p.handleStream(downstream)
}

func (p *XdsProxy) handleStream(downstream adsStream) error {
	con := &ProxyConnection{
		conID:           connectionNumber.Inc(),
		upstreamError:   make(chan error), // can be produced by recv and send