Writing Rust bindings for arbitrary C data structures is not hard. You just need to make sure every part of your safe Rust API code upholds the necessary invariants. (Sometimes that's non-trivial, but a little thinking will always yield a solution: if C code can do it, then it can be done, and if it can be done, then it can be done in Rust.)
Calling the C function is not the problem here. It is dealing with the big data structure this function returns in a Rust-friendly manner.
This is something Protobuf does very well, at the cost of performance.