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

1. cargo new --bin ffi_sample

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Cargo.toml 配置

1. [package]
2. name = "ffi_sample"
3. version = "0.1.0"
4. edition = "2021"
5. build = "build.rs"
7. # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
9. [build-dependencies]
10. cc = "1.0.79"
12. [dependencies]
13. libc = "0.2.146"
14. libloading = "0.8.0"

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编写一个简单的c程序sample.c

1. int add(int a,int b){
2.     return a+b;
3. }

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main.rs

1. use std::os::raw::c_int;
4. #[link(name = "sample")]
5. extern "C" {
6.     fn add(a: c_int, b: c_int) -> c_int;
7. }
9. fn main() {
10.     let r = unsafe { add(2, 18) };
11.     println!("{:?}", r);
12. }

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build.rs

1. fn main() {
2.     cc::Build::new().file("sample.c").compile("sample");
3. }

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代码目录树

1. .
2. ├── Cargo.lock
3. ├── Cargo.toml
4. ├── build.rs
5. ├── sample.c
6. └── src
7.    └── main.rs

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1. cargo run

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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

1. [package]
2. name = "ffi_sample"
3. version = "0.1.0"
4. edition = "2021"
5. build = "build.rs"
7. # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
9. [build-dependencies]
10. cc = "1.0.79"
11. bindgen = "0.65.1"
13. [dependencies]
14. libc = "0.2.146"
15. libloading = "0.8.0"

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新增 sample.h 头文件

1. #ifndef ADD_H
2. #define ADD_H
4. int add(int a, int b);
6. #endif

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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

1. #include "sample.h";

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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

1. use std::path::PathBuf;
3. fn main() {
4.     // 参考cc 文档
5.     println!("cargo:rerun-if-changed=sample.c");
6.     cc::Build::new()
7.         .file("sample.c")
8.         .shared_flag(true)
9.         .compile("sample.so");
10.     // 参考 https://doc.rust-lang.org/cargo/reference/build-scripts.html
11.     println!("cargo:rustc-link-lib=sample.so");
12.     println!("cargo:rerun-if-changed=sample.h");
13.     let bindings = bindgen::Builder::default()
14.         .header("wrapper.h")
15.         .parse_callbacks(Box::new(bindgen::CargoCallbacks))
16.         .generate()
17.         .expect("Unable to generate bindings");
19.     let out_path = PathBuf::from("bindings");
20.     bindings
21.         .write_to_file(out_path.join("sample_bindings.rs"))
22.         .expect("Couldn't write bindings!");
23. }

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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

1. include!("../bindings/sample_bindings.rs");
3. // #[link(name = "sample")]
4. // extern "C" {
5. //     fn add(a: c_int, b: c_int) -> c_int;
6. // }
8. fn main() {
9.     let r = unsafe { add(2, 18) };
10.     println!("{:?}", r);
11. }

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代码目录树

1. .
2. ├── Cargo.lock
3. ├── Cargo.toml
4. ├── bindings
5. │   └── sample_bindings.rs
6. ├── build.rs
7. ├── sample.c
8. ├── sample.h
9. ├── src
10. │   └── main.rs
11. └── wrapper.h

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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

1. cargo run -p ffi_sample

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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

1. cargo new --lib wrapper_secp256k1

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cargo.toml

1. [package]
2. name = "wrapper_secp256k1"
3. version = "0.1.0"
4. edition = "2021"
6. # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
7. [build-dependencies]
8. cc = "1.0.79"
9. bindgen = "0.65.1"
11. [dependencies]

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git 引入 submodule

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

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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

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

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build.rs

1. use std::path::PathBuf;
3. fn main() {
4.     println!("cargo:rustc-link-lib=secp256k1");
5.     println!("cargo:rerun-if-changed=wrapper.h");
6.     let bindings = bindgen::Builder::default()
7.         .header("wrapper.h")
8.         .parse_callbacks(Box::new(bindgen::CargoCallbacks))
9.         .generate()
10.         .expect("Unable to generate bindings");
12.     let out_path = PathBuf::from("bindings");
13.     bindings
14.         .write_to_file(out_path.join("bindings.rs"))
15.         .expect("Couldn't write bindings!");
16. }

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cargo build 通过
编写测试 lib.rs

1. include!("../bindings/secp256k1.rs");
3. #[cfg(test)]
4. mod tests {
5.     use super::*;
7.     #[test]
8.     fn test_create_pubkey() {
9.         // secp256k1返回公钥
10.         let mut pubkey: secp256k1_pubkey = secp256k1_pubkey { data: [0; 64] };
11.         let prikey: u8 = 1;
13.         unsafe {
14.             let context = secp256k1_context_create(SECP256K1_CONTEXT_SIGN);
15.             assert!(!context.is_null());
16.             let ret = secp256k1_ec_pubkey_create(&*context, &mut pubkey, &prikey);
17.             assert_eq!(ret, 1);
18.         }
19.     }
20. }

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运行测试 cargo test 报错

1. warning: `wrapper_secp256k1` (lib) generated 5 warnings
2. error: linking with `cc` failed: exit status: 1
3.   |
4.   = 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"
5.   = note: ld: library not found for -lsecp256k1
6.           clang: error: linker command failed with exit code 1 (use -v to see invocation)
9. warning: `wrapper_secp256k1` (lib test) generated 5 warnings (5 duplicates)
10. error: could not compile `wrapper_secp256k1` (lib test) due to previous error; 5 warnings emitted

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报错显示找不到编译 secp256k1 相对应的库。
手动编译secp256k1

1. cd secp256k1_sys
2. ./autogen.sh
3. ./configure
4. make
5. make install

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

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• update submodule
  1. git submodule init
  2. git submodule update

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• 编译 secp256k1
  1. cd wrapper_secp256k1/secp256k1_sys
  2. ./autogen.sh
  3. ./configure
  4. make
  5. make install  

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• run test
  1. cargo test -p wrapper_secp256k1

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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

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