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
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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"
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编写一个简单的 c 程序 sample.c
int add(int a,int b){ return a+b;}
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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);}
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build.rs
fn main() { cc::Build::new().file("sample.c").compile("sample");}
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代码目录树
.├── Cargo.lock├── Cargo.toml├── build.rs├── sample.c└── src └── main.rs
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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
[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"
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新增 sample.h 头文件
#ifndef ADD_H#define ADD_H
int add(int a, int b);
#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
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!");}
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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
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);}
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代码目录树
.├── Cargo.lock├── Cargo.toml├── bindings│ └── sample_bindings.rs├── build.rs├── sample.c├── sample.h├── src│ └── main.rs└── 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
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
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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]
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git 引入 submodule
cd wrapper_secp256k1git 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
#include "secp256k1_sys/secp256k1/include/secp256k1.h"
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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!");}
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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); } }}
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运行测试 cargo test 报错
warning: `wrapper_secp256k1` (lib) generated 5 warningserror: 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
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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./configuremakemake 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：
git clone https://github.com/jiashiwen/wenpanrust cd wenpanrust
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git submodule init git submodule update
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cd wrapper_secp256k1/secp256k1_sys ./autogen.sh ./configure make make install
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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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