tags: rust ffi python

The aim here is to write a library in Rust and call it from Python using `ctypes`.

# Example 1: Hello World
`Cargo.toml`
```toml
[package]
name = "capi1"
version = "0.1.0"
edition = "2021"

[lib]
name = "capi1"
crate-type = ["rlib", "cdylib"]

[dependencies]
```
`lib.rs`
```rust
use std::ffi::{CStr,CString};
use std::os::raw::c_char;

#[no_mangle]
pub extern "C" fn hello_world() {
    println!("Hello world");
}

#[no_mangle]
pub extern "C" fn hello(s: *const c_char ) {
    if s.is_null() {
        eprintln!("Received null pointer");
        return
    }
    
    unsafe {
        match CStr::from_ptr(s).to_str() {
            Ok(rust_str) => {
                println!("Hello {rust_str}!!");
            }
            Err(e) => {
                eprintln!("Failed to convert C string to Rust string: {}",e);
            }
        }
    }
}
```
`hello.py`
```py
import ctypes

dll = ctypes.CDLL("./libcapi1.so")
hello_world = dll.hello_world
hello_world()

hello = dll.hello
hello("world".encode())
```