rust-bindgen

An important bugfix in 1.39.0 that wasn't mentioned in the release announcement is probably: https://github.com/rust-lang/rust/pull/63402 It's important because unless rustfmt is available, bindgen would put everything onto one line: https://github.com/rust-lang/rust-bindgen/issues/1600 Rustc would generate (unrelated) warnings for the generated code but before the bugfix it'd print the entire line, hitting the maximum log size limit on CI and causing the build to fail because of that.

The Rust bindgen tool automatically generates Rust FFI bindings to C and C++ libraries. Mozilla uses bindgen a lot to interoperate between Firefox's C++ and Rust code. IIUC, Rust and C++ code can't seamlessly call each other unchanged, but bindgen adds FFI glue that makes it much easier. https://github.com/rust-lang/rust-bindgen

Rust works pretty well with C, and you could use cbindgen[0] to generate c headers for rust functions marked as extern and it would work when linked together. However, rustls doesn't seems to be providing any such function. Most of its API is rust-based, using stuff that isn't directly available in C (Option, Vec, etc.). So you would have to write at least some rust code that calls the library, and have your C code calls the rust code that you write. On the flip side, calling C code in rust is pretty easy - you have the entire libc available, and rust-bindgen[1] generate bindings for you, which in my experience works very well. So, you may also consider writing your program in rust… If that's possible. [0]: https://github.com/eqrion/cbindgen [1]: https://github.com/rust-lang/rust-bindgen

One long-standing problem is the incompatibility of Rust enum with C enum. In C, enum's are just labels for integers, similar to const int values in Rust, so C enum { A=0, B=1, C=2 } is more like Rust's enum E { A=0, B=1, C=2, Unlabeled(3..MAX_INT32), } . This slight incompatibility forces writing of converters between C enums and Rust enums. See https://github.com/rust-lang/rust-bindgen/issues/667