文盘Rust -- FFI 浅尝

rust FFI 是rust与其他语言互调的桥梁，通过FFI rust 可以有效继承 C 语言的历史资产。本期通过几个例子来聊聊rust与C 语言交互的具体步骤。

场景一调用C代码

创建工程

cargo new --bin ffi_sample

Cargo.toml 配置

[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"

编写一个简单的c程序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");

}

代码目录树

.

├── Cargo.lock

├── Cargo.toml

├── build.rs

├── sample.c

└── src

    └── main.rs

cargo run

场景二使用bindgen 通过头文件绑定c语言动态链接库

修改Cargo.toml,新增bindgen依赖

[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"

新增 sample.h 头文件

#ifndef ADD_H

#define ADD_H

int add(int a, int b);

#endif

新增 wrapper.h 头文件 wrapper.h 文件将包括所有各种头文件，这些头文件包含我们想要绑定的结构和函数的声明

#include "sample.h";

改写build.rs 编译 sample.c 生成动态链接库sample.so;通过bindgen生成rust binding c 的代码并输出到 bindings 目录

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!");

}

修改main.rs include 宏引入sample 动态链接库的binding。以前我们自己手写的C函数绑定就不需要了，看看bindings/sample_bindings.rs 的内容与我们手写的函数绑定是等效的

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);

}

代码目录树

.

├── Cargo.lock

├── Cargo.toml

├── bindings

│   └── sample_bindings.rs

├── build.rs

├── sample.c

├── sample.h

├── src

│   └── main.rs

└── wrapper.h

ffi_sample 工程的完整代码位置,读者可以clone https://github.com/jiashiwen/wenpanrust，直接运行即可

cargo run -p ffi_sample

场景三封装一个c编写的库

secp256k1是一个椭圆曲线计算的 clib，这玩意儿在密码学和隐私计算方面的常用算法，下面我们从工程方面看看封装secp256k1如何操作

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 引入 submodule

cd wrapper_secp256k1

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

工程下新建bindings目录用来存放绑定文件，该目录与src平级

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 通过

编写测试 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);

        }

    }

}

运行测试 cargo test 报错

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

报错显示找不到编译 secp256k1 相对应的库。

手动编译secp256k1

cd secp256k1_sys

./autogen.sh

./configure

make

make install

编译完成后，测试通过

其实 secp256k1 有对应的 rust wrapper,我们这里只是展示一下封装的过程。

wrapper_secp256k1 工程的完整代码位置,有兴趣的朋友可以clone https://github.com/jiashiwen/wenpanrust。通过以下操作查看运行结果：

clone 项目

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

cd wenpanrust

update submodule

git submodule init

git submodule update

编译 secp256k1

cd wrapper_secp256k1/secp256k1_sys

./autogen.sh

./configure

make

make install

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

参考资料

Rust FFI (C vs Rust)学习杂记.pdf

bindgen官方文档

 Rust FFI 编程 - bindgen 使用示例

作者：京东科技贾世闻

来源：京东云开发者社区