rust-ffi

Q: How do I install rust-ffi?

Run npx skills add https://github.com/mohitmishra786/low-level-dev-skills --skill rust-ffi in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/rust-ffi/ (personal) or .claude/skills/rust-ffi/ (project).

by mohitmishra786Backend & APIs

Rust FFI skill for C interoperability. Use when calling C libraries from Rust, generating Rust bindings with bindgen, exporting Rust functions to C with cbindgen, writing safe wrappers around unsafe FFI, or linking system and vendor libraries. Activates on queries about bindgen, cbindgen, extern "C", unsafe FFI, Rust C bindings, linking C from Rust, or sys crates.

Installs: 566
Last 24h: —
Trending rank: —
Security: Not audited

Install

Works with every agent the skills CLI supports.

npx skills add https://github.com/mohitmishra786/low-level-dev-skills --skill rust-ffi

01
Install
Run the command in your project. The CLI asks which agents to install for.
02
Describe the task
Ask your agent for something this skill covers. It loads rust-ffi automatically when relevant.
03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.

SKILL.md

The instructions your agent reads when the skill is triggered.

Rust FFI

Purpose

Guide agents through Rust's Foreign Function Interface: calling C from Rust with bindgen, exporting Rust to C with cbindgen, writing safe wrappers, linking libraries via build.rs, and structuring sys crates.

Triggers

"How do I call a C library from Rust?"
"How do I use bindgen to generate Rust bindings?"
"How do I export Rust functions to be called from C?"
"How do I write a safe wrapper around an unsafe C API?"
"How do I link a system library in Rust?"
"What is a sys crate and how do I structure one?"

Workflow

1. Calling C without bindgen (manual declarations)

// Declare external C functions manually
use std::ffi::{c_int, c_char, c_void, CStr, CString};

extern "C" {
    fn strlen(s: *const c_char) -> usize;
    fn malloc(size: usize) -> *mut c_void;
    fn free(ptr: *mut c_void);
    fn my_lib_init(config: *const c_char) -> c_int;
    fn my_lib_process(handle: *mut c_void, data: *const u8, len: usize) -> c_int;
    fn my_lib_cleanup(handle: *mut c_void);
}

// Call unsafe C function safely
fn init(config: &str) -> Result<*mut c_void, Error> {
    let c_config = CString::new(config)?;
    let result = unsafe { my_lib_init(c_config.as_ptr()) };
    if result != 0 {
        return Err(Error::InitFailed(result));
    }
    // return handle...
    todo!()
}

2. bindgen for automatic binding generation

# Cargo.toml
[build-dependencies]
bindgen = "0.70"

// build.rs
use std::path::PathBuf;

fn main() {
    println!("cargo:rerun-if-changed=wrapper.h");
    println!("cargo:rustc-link-lib=mylib");
    println!("cargo:rustc-link-search=/usr/local/lib");

    let bindings = bindgen::Builder::default()
        .header("wrapper.h")
        .clang_arg("-I/usr/local/include")
        .clang_arg("-DMYLIB_VERSION=2")
        // Only generate bindings for this library (not system headers)
        .allowlist_function("mylib_.*")
        .allowlist_type("MyLib.*")
        .allowlist_var("MYLIB_.*")
        // Derive common traits on structs
        .derive_debug(true)
        .derive_default(true)
        // Block problematic types
        .blocklist_type("__va_list_tag")
        .generate()
        .expect("Unable to generate bindings");

    let out_path = PathBuf::from(std::env::var("OUT_DIR").unwrap());
    bindings
        .write_to_file(out_path.join("bindings.rs"))
        .expect("Couldn't write bindings!");
}

// src/lib.rs — include generated bindings
#![allow(non_upper_case_globals)]
#![allow(non_camel_case_types)]
#![allow(non_snake_case)]

include!(concat!(env!("OUT_DIR"), "/bindings.rs"));

3. sys crate pattern

Structure:

mylib-sys/
├── Cargo.toml
├── build.rs        # links the library
├── wrapper.h       # C headers to translate
└── src/
    └── lib.rs      # includes generated bindings

mylib/             # safe wrapper
├── Cargo.toml
└── src/
    └── lib.rs

# mylib-sys/Cargo.toml
[package]
name = "mylib-sys"
version = "0.1.0"
links = "mylib"          # tells Cargo this crate links libmylib

[build-dependencies]
bindgen = "0.70"
pkg-config = "0.3"       # for system library detection

// mylib-sys/build.rs
fn main() {
    // Try pkg-config first
    if let Ok(lib) = pkg_config::probe_library("mylib") {
        for path in lib.include_paths {
            println!("cargo:include={}", path.display());
        }
        return;
    }

    // Fallback: compile from vendored source
    cc::Build::new()
        .file("vendor/mylib/src/mylib.c")
        .include("vendor/mylib/include")
        .compile("mylib");

    println!("cargo:rerun-if-changed=vendor/mylib/src/mylib.c");
}

4. Writing safe wrappers

// mylib/src/lib.rs
use mylib_sys as ffi;
use std::ffi::{CStr, CString};

pub struct MyLib {
    handle: *mut ffi::mylib_t,
}

// Safety: handle is not shared across threads
unsafe impl Send for MyLib {}
unsafe impl Sync for MyLib {}

impl MyLib {
    pub fn new(config: &str) -> Result<Self, Error> {
        let c_config = CString::new(config).map_err(|_| Error::InvalidConfig)?;
        let handle = unsafe { ffi::mylib_create(c_config.as_ptr()) };
        if handle.is_null() {
            return Err(Error::InitFailed);
        }
        Ok(Self { handle })
    }

    pub fn process(&mut self, data: &[u8]) -> Result<usize, Error> {
        let result = unsafe {
            ffi::mylib_process(self.handle, data.as_ptr(), data.len())
        };
        if result < 0 {
            return Err(Error::ProcessFailed(result));
        }
        Ok(result as usize)
    }
}

impl Drop for MyLib {
    fn drop(&mut self) {
        unsafe { ffi::mylib_destroy(self.handle) };
    }
}

5. Exporting Rust to C with cbindgen

# Cargo.toml
[build-dependencies]
cbindgen = "0.27"

// src/lib.rs — exported Rust API
#[no_mangle]
pub extern "C" fn mylib_create(config: *const std::ffi::c_char) -> *mut MyLib {
    // ...
    Box::into_raw(Box::new(instance))
}

#[no_mangle]
pub extern "C" fn mylib_destroy(ptr: *mut MyLib) {
    if !ptr.is_null() {
        unsafe { drop(Box::from_raw(ptr)) };
    }
}

#[no_mangle]
pub extern "C" fn mylib_process(
    ptr: *mut MyLib,
    data: *const u8,
    len: usize,
) -> std::ffi::c_int {
    let lib = unsafe { &mut *ptr };
    match lib.process(unsafe { std::slice::from_raw_parts(data, len) }) {
        Ok(n) => n as std::ffi::c_int,
        Err(_) => -1,
    }
}

// build.rs
fn main() {
    let crate_dir = std::env::var("CARGO_MANIFEST_DIR").unwrap();
    cbindgen::Builder::new()
        .with_crate(crate_dir)
        .with_language(cbindgen::Language::C)
        .generate()
        .expect("Unable to generate C bindings")
        .write_to_file("include/mylib.h");
}

6. Linking libraries in build.rs

// build.rs — common patterns
fn main() {
    // Static library
    println!("cargo:rustc-link-lib=static=mylib");
    println!("cargo:rustc-link-search=native=/path/to/lib");

    // Dynamic library
    println!("cargo:rustc-link-lib=dylib=mylib");

    // Framework (macOS)
    println!("cargo:rustc-link-lib=framework=CoreFoundation");

    // Build C source with cc crate
    cc::Build::new()
        .file("src/helper.c")
        .flag("-std=c11")
        .compile("helper");
}

For bindgen and cbindgen configuration details, see references/bindgen-cbindgen.md.

Related skills

Use skills/rust/rustc-basics for RUSTFLAGS affecting FFI builds
Use skills/rust/cargo-workflows for build.rs integration and sys crate layout
Use skills/zig/zig-cinterop for Zig's equivalent C interop approach
Use skills/binaries/dynamic-linking for dynamic library linking details

FAQ

What does the rust-ffi skill do?

How do I install rust-ffi?

Run npx skills add https://github.com/mohitmishra786/low-level-dev-skills --skill rust-ffi in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/rust-ffi/ (personal) or .claude/skills/rust-ffi/ (project).

Which AI agents can use rust-ffi?

Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.

Is rust-ffi safe to install?

No partner security audit is available yet. Skills can run commands and scripts, so read the SKILL.md and any bundled files before installing.

Who maintains rust-ffi?

It is published by mohitmishra786 in mohitmishra786/low-level-dev-skills. It has 566 recorded installs.