rust FFI 是rust與其他語言互調的橋梁，通過FFI rust 可以有效繼承 C 語言的歷史資產。本期通過幾個例子來聊聊rust與 C 語言交互的具體步驟。

場景一 調用C代碼

創建工程

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cargo new --bin ffi_sample

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Cargo.toml 配置

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[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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編寫一個簡單的c程序sample.c

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

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main.rs

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use std::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

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

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代碼目錄樹

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

cargo run

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場景二? 使用bindgen 通過頭文件綁定c語言動態鏈接庫

修改Cargo.toml,新增bindgen依賴

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[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 頭文件

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#ifndef ADD_H
#define ADD_H


int add(int a, int b);


#endif

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新增 wrapper.h 頭文件

wrapper.h 文件將包括所有各種頭文件，這些頭文件包含我們想要綁定的結構和函數的聲明

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#include "sample.h";

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改寫build.rs

編譯 sample.c 生成動態鏈接庫sample.so;通過bindgen生成rust binding c 的代碼并輸出到 bindings 目錄

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use std::PathBuf;


fn main() {
    // 參考cc 文檔
    println!("cargo:rerun-if-changed=sample.c");
    cc::new()
        .file("sample.c")
        .shared_flag(true)
        .compile("sample.so");
    // 參考 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::default()
        .header("wrapper.h")
        .parse_callbacks(Box::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 動態鏈接庫的binding。以前我們自己手寫的C函數綁定就不需要了，看看bindings/sample_bindings.rs 的內容與我們手寫的函數綁定是等效的

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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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代碼目錄樹

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.
├── 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 工程的完整代碼：https://github.com/jiashiwen/wenpanrust/tree/main/ffi_sample,讀者可以clone https://github.com/jiashiwen/wenpanrust，直接運行即可

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cargo run -p ffi_sample

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場景三 封裝一個c編寫的庫

secp256k1是一個橢圓曲線計算的 clib，這玩意兒在密碼學和隱私計算方面的常用算法，下面我們從工程方面看看封裝secp256k1如何操作

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cargo new --lib wrapper_secp256k1

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cargo.toml

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[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

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

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工程下新建bindings目錄用來存放綁定文件，該目錄與src平級

wrapper.h

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

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build.rs

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use std::path::PathBuf;


fn main() {
    println!("cargo:rustc-link-lib=secp256k1");
    println!("cargo:rerun-if-changed=wrapper.h");
    let bindings = bindgen::default()
        .header("wrapper.h")
        .parse_callbacks(Box::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 通過

編寫測試 lib.rs

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


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


    #[test]
    fn test_create_pubkey() {
        // secp256k1返回公鑰
        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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運行測試 cargo test 報錯

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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

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報錯顯示找不到編譯 secp256k1 相對應的庫。

手動編譯secp256k1

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

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編譯完成后，測試通過

其實 secp256k1 有對應的 [rust wrapper](https://github.com/rust-bitcoin/rust-secp256k1),我們這里只是展示一下封裝的過程。

wrapper_secp256k1 工程的完整代碼：https://github.com/jiashiwen/wenpanrust/tree/main/wrapper_secp256k1,有興趣的朋友可以clone https://github.com/jiashiwen/wenpanrust。通過以下操作查看運行結果：

clone 項目

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

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update submodule

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  git submodule init
  git submodule update

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編譯 secp256k1

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

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run test

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  cargo test -p wrapper_secp256k1

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　　審核編輯：湯梓紅