如何使用python wasmtime调用rust生成的wasm库

时间:2023-02-02 huzhenwei 人气:0

本文介绍了使用python wasmtime来访问rust库的便捷方法，步骤极其简练，可以在生产环境中使用。

安装rust target wasm32-wasi

使用如下命令安装wasm32-wasi，用于便捷地将rust编译为wasm字节码。

rustup target add wasm32-wasi

编写rust库

使用cargo创建rust库

cd /mnt/d/workspace/rust
cargo new --lib wasmlib

编辑Cargo.toml文件

cd wasmlib
echo "[lib]" >> Cargo.toml
echo "crate-type = ['cdylib']" >> Cargo.toml

编辑rust源文件
编辑src/lib.rs, 修改文件内容如下

#[no_mangle]
pub extern "C" fn add(a: i32, b: i32) -> i32 {
    a + b
}

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

    #[test]
    fn it_works() {
        let result = add(2, 2);
        assert_eq!(result, 4);
    }
}

将rust库编译为wasm字节码

将rust库编译为wasm字节码

cargo build --release --target wasm32-wasi

查看生成的wasm文件

cd target/wasm32-wasi/release
ls

结果如下，其中wasmlib.wasm就是wasm字节码文件：

build  deps  examples  incremental  wasmlib.d  wasmlib.wasm

安装python wasmtime库

pip3 install wasmtime

测试使用python wasmtime调用rust库（wasm字节码）

hzw@hzwwin:/mnt/d/workspace/rust/wasmlib/target/wasm32-wasi/release$ python3
Python 3.10.4 (main, Apr  2 2022, 09:04:19) [GCC 11.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import wasmtime.loader
>>> import wasmlib # 不需要加.wasm扩展名
>>> dir(wasmlib)
['__doc__', '__file__', '__loader__', '__name__', '__package__', '__spec__', 'add', 'memory']
>>> wasmlib.add(2, 2)
4
>>> wasmlib.add(2, 4)
6
>>> wasmlib.add("a", "b")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/hzw/.local/lib/python3.10/site-packages/wasmtime/loader.py", line 89, in <lambda>
    item = lambda *args,func=func: func(store, *args)  # noqa
  File "/home/hzw/.local/lib/python3.10/site-packages/wasmtime/_func.py", line 83, in __call__
    param_vals = [Val._convert(ty, params[i]) for i, ty in enumerate(param_tys)]
  File "/home/hzw/.local/lib/python3.10/site-packages/wasmtime/_func.py", line 83, in <listcomp>
    param_vals = [Val._convert(ty, params[i]) for i, ty in enumerate(param_tys)]
  File "/home/hzw/.local/lib/python3.10/site-packages/wasmtime/_value.py", line 154, in _convert
    raise TypeError("don't know how to convert %r to %s" % (val, ty))
TypeError: don't know how to convert 'a' to i32

参考链接

https://docs.wasmtime.dev/

http://pypi.org/project/wasmtime/

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