FFI Questions (Wrapping C++ code, and callbacks)

So, I’m not new to Haskell, but I’ve never worked much with the C FFI. I figured a fun place to start would be adding some really basic Botan.TLS bindings to the botan-bindings package, just to see how rough it would be (to be clear, this isn’t in any sort of shape to be reviewed for inclusion, and I haven’t talked with @ApothecaLabs at all to even see if he’s interested, I’m just doing it to learn, and also my C++ experience is a few decades out of date…). I wound up with a TLS echo server tha...