Simple way to integrate Rust for cross platforms (Android, IoS, macOS, Windows, and Linux) using Flutter.

Required installation

• Rust
• Flutter

Setup

Let’s create simple app

flutter create example
cd example
cargo new rust_ffi --lib --name rust_ffi

Then create simple function

fn hai(input: &str) -> String {
    format!("Hello {} Powered by Rust", input)
}

to make sure this function works,let’s create a simple test:

#[test]
fn it_works() {
    let result = hai("Flutter");
    assert_eq!(result, "Hello Flutter Powered by Rust");
}

then run

cd rust_ffi
cargo test

Now, Time to export

‘We export the best coffee beans to the world, but we still buy Starbucks coffee… ’ it’s jokes..hahaha.

Let’s export hai function using Rust FFI

use std::{
    ffi::{CStr, CString},
    os::raw::c_char,
};

#[no_mangle]
pub extern "C" fn hello(input: *const c_char) -> *mut c_char {
    let value = unsafe { CStr::from_ptr(input).to_str().map(|s| s.to_owned()) };
    match value {
        Ok(value_ptr) => {
            let input_ptr = hai(&value_ptr);
            match CString::new(input_ptr) {
                Ok(c_str) => c_str.into_raw(),
                Err(_) => std::ptr::null_mut(),
            }
        }
        Err(_) => std::ptr::null_mut(),
    }
}

to make sure this function works,let’s create simple test

#[test]
fn test_hello() {
    let input = String::from("world");
    let c_str = CString::new(input.clone()).unwrap();
    let hai = hai(&input);
    let hello = hello(c_str.as_ptr());
    let result = unsafe { CStr::from_ptr(hello) };
    assert!(!hello.is_null());
    assert_eq!(hai, result.to_str().unwrap());
}

that’s it, simple.

Build and Share Library

Required some tools to build specific target. For example, to cross-compile to Android the Android NDK must be installed.

Let’s build for linux target

rustup target add x86_64-unknown-linux-gnu
cargo build --target x86_64-unknown-linux-gnu --release

To see a list of available targets rustup target list

How do we know builds success and Rust code can call? move into PATH ‘target/x86_64-unknown-linux-gnu/release/’ there are name file librust_ffi.so and also file name were different for other target

• .a format for IoS
• .dylib format for macOS
• .dll format for Windows

run command

nm -D target/x86_64-unknown-linux-gnu/release/librust_ffi.so | grep hello
00000000000062d0 T hello

that’s it.

Next Integration to Flutter App.