type Callbacks interface {
	// OnStreamOpen is called once an 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.
	OnStreamOpen(context.Context, int64, string) error
	// OnStreamClosed is called immediately prior to closing an xDS stream with a stream ID.
	OnStreamClosed(int64)
	// OnStreamRequest 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.
	OnStreamRequest(int64, *discovery.DiscoveryRequest) error
	// OnStreamResponse is called immediately prior to sending a response on a stream.
	OnStreamResponse(int64, *discovery.DiscoveryRequest, *discovery.DiscoveryResponse)
}

type Server interface {
	StreamHandler(stream Stream, typeURL string) error
}

type Stream interface {
	grpc.ServerStream

	Send(*discovery.DiscoveryResponse) error
	Recv() (*discovery.DiscoveryRequest, error)
}