rust-ffi_skill

Overview

This skill is an FFI cross-language interop expert for Rust, covering C/C++ bindings, bindgen, cbindgen, PyO3, JNI, memory layout, data conversion, and safe FFI patterns. It guides selection of tools, applies proven safety patterns, and helps design tested, maintainable interfaces between Rust and other languages. The focus is on practical fixes, clear ownership, and minimizing unsafe surface area.

How this skill works

The skill inspects FFI boundaries, type mappings, and safety invariants and recommends concrete changes: generated bindings (bindgen/cbindgen), high-level wrappers, and ABI-stable exports. It validates pointer lifetimes, string conversions, panic handling, and memory ownership protocols, and suggests testing strategies like Miri and valgrind. It also proposes language-specific bridges (PyO3, jni, cxx, napi-rs) when appropriate.

When to use it

• When exposing Rust libraries to C or C++ consumers
• When calling existing C/C++ libraries from Rust (bindgen)
• When building Python, Java, Node, or C# extensions from Rust
• When diagnosing crashes or undefined behavior at FFI boundaries
• When preparing cross-platform or cross-ABI builds and headers

Best practices

• Minimize unsafe: encapsulate unsafe calls in small, well-documented functions
• Document safety invariants: pointer validity, ownership, lifetimes, and thread assumptions
• Use CStr/CString for string conversions and validate encodings
• Mark exported functions #[no_mangle] extern "C" and use cbindgen for headers
• Catch panics at FFI boundaries with catch_unwind to avoid UB
• Test thoroughly: Miri for UB detection, valgrind for leaks, and cross-target builds

Example use cases

• Auto-generate Rust bindings for a C library with bindgen and wrap them in safe APIs
• Export a Rust API to C consumers using cbindgen and #[no_mangle] extern "C" functions with documented ownership
• Build a Python extension using PyO3 that safely shares memory buffers between Rust and Python
• Integrate a C++ class via cxx::bridge and provide a lightweight Rust wrapper for ergonomic use
• Implement callback-based C APIs by passing a boxed UserData pointer and restoring it safely in the callback