ExoPlayer access values from custom DataSource

Question

I have a custom HttpDataSource called MyDataSource. To use it with SimpleExoPlayer I do:

MediaSource mediaSource = new ProgressiveMediaSource.Factory(
        () -> {
            return (HttpDataSource)new MyDataSource(/* some parameters */);
        }
).createMediaSource(uri);

Then later when I have MediaSource mediaSource, I want to access inner values from MyDataSource. How can I do that? I cannot cast (MyDataSource) mediaSource. I can however cast it into (ProgressiveMediaSource)mediaSource - however it's useless, because I cannot get any values from MyDataSource, or access the inner MyDataSource in any way.

Thank you.