type Callbacks interface {
	// OnDeltaStreamOpen is called once an incremental xDS stream is open with a stream ID and the type URL (or "" for ADS).
	// Returning an error will end processing and close the stream. OnStreamClosed will still be called.
	OnDeltaStreamOpen(context.Context, int64, string) error
	// OnDeltaStreamClosed is called immediately prior to closing an xDS stream with a stream ID.
	OnDeltaStreamClosed(int64, *core.Node)
	// OnStreamDeltaRequest is called once a request is received on a stream.
	// Returning an error will end processing and close the stream. OnStreamClosed will still be called.
	OnStreamDeltaRequest(int64, *discovery.DeltaDiscoveryRequest) error
	// OnStreamDeltaResponse is called immediately prior to sending a response on a stream.
	OnStreamDeltaResponse(int64, *discovery.DeltaDiscoveryRequest, *discovery.DeltaDiscoveryResponse)
}

type Server interface {
	DeltaStreamHandler(stream stream.DeltaStream, typeURL string) error
}