This is a demo of how to use Rust code in a React Native app using Expo Modules

Check out the acommpanying video tutorial 🎥

Questions or feedback? Reach out to me on Farcaster at @typeof.eth

• Create expo project
  • npx create-expo-app -t expo-template-blank-typescript expo-rust-demo
  • cd my-app
• Create expo module
  • npx create-expo-module my-rust-module --local
  • Accept default answers
  • This creates a /modules folder with some boilerplate code
• Prebuild expo module
  • npx expo prebuild
  • Accept default answers
• Create rust project at root
  • cargo new --lib native_rust_lib
  • Write Rust function
  • Add #[no_mangle] and pub extern "C" directives to function
  • Add crate-type = ["staticlib"] to Cargo.toml (See /rust directory for example)

• Install Rust iOS targets
  • rustup target add aarch64-apple-ios aarch64-apple-ios-sim
• Compile Rust code for iOS
  • cargo build --release --target aarch64-apple-ios
  • cargo build --release --target aarch64-apple-ios-sim
• Generate .h file for Rust code
  • cbindgen --lang c --crate native_rust_lib --output native_rust_lib.h
  • Note: This requires the cbindgen package to be installed. If you don't have it, you can install it with cargo install cbindgen
• Copy compiled Rust code to expo module
  • Note: Right now I've only got this working for the simulator target. To get this working on an actual device, we'll need to figure out what the current target is and conditionally use either the ios or ios-sim build
  • Create a new folder at /modules/my-rust-module/ios/rust
  • Copy the libnative_rust_lib.a file from /target/aarch64-apple-ios-sim/release to /modules/my-rust-module/ios/rust
  • Copy the native_rust_lib.h file from /target/aarch64-apple-ios-sim/release to /modules/my-rust-module/ios/rust
• Update modules/my-rust-module/ios/MyModule.podspec to include Rust code
  • Add s.vendored_libraries = 'libnative_rust_lib.a'
• Update native swift code to use Rust code
  • Add method to call Rust function in MyModule.swift
• Add export that calls native module from /modules/my-rust-module/index.ts
  • See getKey() in /modules/if-rust/index.ts for example
• Update podfile
  • pod install --project-directory=ios
• Import module in RN front-end and use them
• Start app in iOS simluator
  • npm run ios

• Install Rust Android targets
  • rustup target add aarch64-linux-android armv7-linux-androideabi i686-linux-android x86_64-linux-android
• Add jni = "0.21.1" dependency to Cargo.toml
• Add "cdylib" to crate-type in Cargo.toml to create a dynamic library
• Install cargo-ndk
  • cargo install cargo-ndk
• Build Rust code for Android
  • cargo ndk --target aarch64-linux-android --platform 31 -- build --release
  • cargo ndk --target armv7-linux-androideabi --platform 31 -- build --release
  • cargo ndk --target i686-linux-android --platform 31 -- build --release
  • cargo ndk --target x86_64-linux-android --platform 31 -- build --release
• Move compiled Rust code to expo module
  • Create a new folder at /modules/my-rust-module/android/src/main/jniLibs
  • Copy the .so files from /target/aarch64-linux-android/release to /modules/my-rust-module/android/src/main/jniLibs/arm64-v8a
  • Copy the .so files from /target/armv7-linux-androideabi/release to /modules/my-rust-module/android/src/main/jniLibs/armeabi-v7a
  • Copy the .so files from /target/i686-linux-android/release to /modules/my-rust-module/android/src/main/jniLibs/x86
  • Copy the .so files from /target/x86_64-linux-android/release to /modules/my-rust-module/android/src/main/jniLibs/x86_64
• Update MyRustModule.kt to use Rust code
  • Load library in MyRustModule.kt
  • Add function type to MyRustModule.kt
  • Define function in MyRustModule.kt
• Start app in Android emulator
  • npm run android