Wenpan Rust -- A Taste of FFI | JD Cloud Technical Team

rust FFI is a bridge for intermodulation between rust and other languages. Through FFI rust can effectively inherit the historical assets of C language. This issue uses a few examples to talk about the specific steps of rust and C language interaction.

Scenario 1 calls C code

create project

cargo new --bin ffi_sample

Cargo.toml configuration

[package]
name = "ffi_sample"
version = "0.1.0"
edition = "2021"
build = "build.rs"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[build-dependencies]
cc = "1.0.79"

[dependencies]
libc = "0.2.146"
libloading = "0.8.0"

Write a simple c program sample.c

int add(int a,int b){
    return a+b;
}

main.rs

use std::os::raw::c_int;


#[link(name = "sample")]
extern "C" {
    fn add(a: c_int, b: c_int) -> c_int;
}

fn main() {
    let r = unsafe { add(2, 18) };
    println!("{:?}", r);
}

build.rs


fn main() {
    cc::Build::new().file("sample.c").compile("sample");
}

code directory tree

.
├── Cargo.lock
├── Cargo.toml
├── build.rs
├── sample.c
└── src
    └── main.rs

cargo run

Scenario 2 Use bindgen to bind the C language dynamic link library through the header file

Modify Cargo.toml, add bindgen dependency

[package]
name = "ffi_sample"
version = "0.1.0"
edition = "2021"
build = "build.rs"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[build-dependencies]
cc = "1.0.79"
bindgen = "0.65.1"

[dependencies]
libc = "0.2.146"
libloading = "0.8.0"

Add sample.h header file

#ifndef ADD_H
#define ADD_H

int add(int a, int b);

#endif

New wrapper.h header file The wrapper.h file will include all the various header files that contain the declarations of the structures and functions we want to bind

#include "sample.h";

Rewrite build.rs and compile sample.c to generate dynamic link library sample.so ; generate rust binding c code through bindgen and output it to the bindings directory

use std::path::PathBuf;

fn main() {
    // 参考cc 文档
    println!("cargo:rerun-if-changed=sample.c");
    cc::Build::new()
        .file("sample.c")
        .shared_flag(true)
        .compile("sample.so");
    // 参考 https://doc.rust-lang.org/cargo/reference/build-scripts.html
    println!("cargo:rustc-link-lib=sample.so");
    println!("cargo:rerun-if-changed=sample.h");
    let bindings = bindgen::Builder::default()
        .header("wrapper.h")
        .parse_callbacks(Box::new(bindgen::CargoCallbacks))
        .generate()
        .expect("Unable to generate bindings");

    let out_path = PathBuf::from("bindings");
    bindings
        .write_to_file(out_path.join("sample_bindings.rs"))
        .expect("Couldn't write bindings!");
}

Modify the main.rs include macro to introduce the binding of the sample dynamic link library. In the past, we don’t need the handwritten C function bindings. Look at the content of bindings/sample_bindings.rs and our handwritten function bindings are equivalent.

include!("../bindings/sample_bindings.rs");

// #[link(name = "sample")]
// extern "C" {
//     fn add(a: c_int, b: c_int) -> c_int;
// }

fn main() {
    let r = unsafe { add(2, 18) };
    println!("{:?}", r);
}

code directory tree

.
├── Cargo.lock
├── Cargo.toml
├── bindings
│   └── sample_bindings.rs
├── build.rs
├── sample.c
├── sample.h
├── src
│   └── main.rs
└── wrapper.h

The complete code location of the ffi_sample project , readers can clone https://github.com/jiashiwen/wenpanrust and run it directly

cargo run -p ffi_sample

Scenario 3 encapsulates a library written in c

secp256k1 is a clib for elliptic curve calculation, which is a common algorithm in cryptography and privacy calculation. Let's take a look at how to package secp256k1 from an engineering perspective.

cargo new --lib wrapper_secp256k1

cargo.toml

[package]
name = "wrapper_secp256k1"
version = "0.1.0"
edition = "2021"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
[build-dependencies]
cc = "1.0.79"
bindgen = "0.65.1"

[dependencies]

git import submodule

cd wrapper_secp256k1
git submodule add https://github.com/bitcoin-core/secp256k1  wrapper_secp256k1/secp256k1_sys

Create a new bindings directory under the project to store binding files, which is at the same level as src

wrapper.h

#include "secp256k1_sys/secp256k1/include/secp256k1.h"

build.rs

use std::path::PathBuf;

fn main() {
    println!("cargo:rustc-link-lib=secp256k1");
    println!("cargo:rerun-if-changed=wrapper.h");
    let bindings = bindgen::Builder::default()
        .header("wrapper.h")
        .parse_callbacks(Box::new(bindgen::CargoCallbacks))
        .generate()
        .expect("Unable to generate bindings");

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

cargo build via

write test lib.rs

include!("../bindings/secp256k1.rs");

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_create_pubkey() {
        // secp256k1返回公钥
        let mut pubkey: secp256k1_pubkey = secp256k1_pubkey { data: [0; 64] };
        let prikey: u8 = 1;

        unsafe {
            let context = secp256k1_context_create(SECP256K1_CONTEXT_SIGN);
            assert!(!context.is_null());
            let ret = secp256k1_ec_pubkey_create(&*context, &mut pubkey, &prikey);
            assert_eq!(ret, 1);
        }
    }
}

Run the test cargo test and report an error

warning: `wrapper_secp256k1` (lib) generated 5 warnings
error: linking with `cc` failed: exit status: 1
  |
  = note: LC_ALL="C" PATH="/usr/local/Cellar/rust/1.70.0/lib/rustlib/x86_64-apple-darwin/bin:/Users/jiashiwen/local/Cellar/rust/1.70.0/lib/rustlib/x86_64-apple-darwin/lib/libobject-6d1da0e5d7930106.rlib" "/usr/local/Cellar/rust/1.70.0/lib/rustlib/x86_64-apple-darwin/lib/libmemchr-d6d74858e37ed726.rlib" "/usr/local/Cellar/rust/1.70.0/lib/rustlib/x86_64-apple-darwin/lib/libaddr2line-d75e66c6c1b76fdd.rlib" "/usr/local/Cellar/rust/1.70.0/lib/rustlib/x86_64-apple-darwin/lib/libgimli-546ea342344e3761.rlib" "/usr/local/Cellar/rust/1.70.0/lib/rustlib/x86_64-apple-darwin/lib/librustc_demangle-8ad10e36ca13f067.rlib" "/usr/local/Cellar/rust/1.70.0/lib/rustlib/x86_64-apple-darwin/lib/libstd_detect-0543b8486ac00cf6.rlib" "/usr/local/Cellar/rust/1.70.0/lib/rustlib/x86_64-apple-darwin/lib/libhashbrown-7f0d42017ce08763.rlib" "/usr/local/Cellar/rust/1.70.0/lib/rustlib/x86_64-apple-darwin/lib/libminiz_oxide-65e6b9c4725e3b7f.rlib" "/usr/local/Cellar/rust/1.70.0/lib/rustlib/x86_64-apple-darwin/lib/libadler-131157f72607aea7.rlib" "/usr/local/Cellar/rust/1.70.0/lib/rustlib/x86_64-apple-darwin/lib/librustc_std_workspace_alloc-f7d15060b16c135d.rlib" "/usr/local/Cellar/rust/1.70.0/lib/rustlib/x86_64-apple-darwin/lib/libunwind-a52bfac5ae872be2.rlib" "/usr/local/Cellar/rust/1.70.0/lib/rustlib/x86_64-apple-darwin/lib/libcfg_if-1762d9ac100ea3e7.rlib" "/usr/local/Cellar/rust/1.70.0/lib/rustlib/x86_64-apple-darwin/lib/liblibc-f8e0e4708f61f3f4.rlib" "/usr/local/Cellar/rust/1.70.0/lib/rustlib/x86_64-apple-darwin/lib/liballoc-af9a608dd9cb26b2.rlib" "/usr/local/Cellar/rust/1.70.0/lib/rustlib/x86_64-apple-darwin/lib/librustc_std_workspace_core-9777023438fd3d6a.rlib" "/usr/local/Cellar/rust/1.70.0/lib/rustlib/x86_64-apple-darwin/lib/libcore-83ca6d61eb70e9b8.rlib" "/usr/local/Cellar/rust/1.70.0/lib/rustlib/x86_64-apple-darwin/lib/libcompiler_builtins-ea2ca6e1df0449b8.rlib" "-lSystem" "-lc" "-lm" "-L" "/usr/local/Cellar/rust/1.70.0/lib/rustlib/x86_64-apple-darwin/lib" "-o" "/Users/jiashiwen/rustproject/wrapper_secp256k1/target/debug/deps/wrapper_secp256k1-4bf30c62ecfdf2a7" "-Wl,-dead_strip" "-nodefaultlibs"
  = note: ld: library not found for -lsecp256k1
          clang: error: linker command failed with exit code 1 (use -v to see invocation)


warning: `wrapper_secp256k1` (lib test) generated 5 warnings (5 duplicates)
error: could not compile `wrapper_secp256k1` (lib test) due to previous error; 5 warnings emitted

The error shows that the corresponding library for compiling secp256k1 cannot be found.

Manually compile secp256k1

cd secp256k1_sys
./autogen.sh
./configure
make
make install

After the compilation is complete, the test passes

In fact, secp256k1 has a corresponding rust wrapper , we just show the encapsulation process here.

The complete code location of the wrapper_secp256k1 project , interested friends can clone https://github.com/jiashiwen/wenpanrust. Check the running results by doing the following:

clone project

git clone https://github.com/jiashiwen/wenpanrust
cd wenpanrust

update submodule

git submodule init
git submodule update

compile secp256k1

cd wrapper_secp256k1/secp256k1_sys 
./autogen.sh
./configure
make
make install

run test
```
cargo test -p wrapper_secp256k1
```

References

Rust FFI (C vs Rust) learning miscellaneous notes.pdf
bindgen official document
Rust FFI programming - bindgen usage examples

Author: JD.com Jia Shiwen

Source: JD Cloud Developer Community