Returning filename and filesize in info.json response

[heliumcell]

I need to return the filename and the filesize in bytes in the info.json response. The feels like something that is doable, as at the very least the server "knows" the filename at the point that it is responding to the request, and it should be able to get the filesize I should think, However I am not seeing a straightforward way of doing this. I was trying to see if I could sneak it into the delegates extra responses, but I'm not seeing a way to do it and the documentation isn't helping. Thoughts?