Building cross-platform Rust for Web, Android and iOS – a minimal example

One of the advantages of writing code in Rust is that it can be re-used in other places. Both iOS and Android allow using native libraries within your apps, and Rust compiles to native. Web pages can now use WebAssembly (WASM), and Rust can compile to WASM.

So, it should be easy, right?

Well, in practice it seems a little tricky, so I created a small example project to explain it to myself, so maybe it’s helpful to you too.

The full code is at gitlab.com/andybalaam/example-rust-bindings, but here is the general idea:

  • crates/example-rust-bindings – the real Rust code
  • bindings/ffi – uniffi code to build shared objects for Android and iOS
  • bindings/wasm – wasm_bingen code to build WASM for Web
  • examples/example-android – an Android app that generates a Kotlin wrapper, and runs the code in the shared object
  • examples/example-ios – an iOS XCode project where we generate Swift bindings, so we can call the code in the shared object
  • examples/example-web – a web page that imports the WASM and runs it

Steps for WASM

Proof that I did this on Web - Firefox showing "This string is from Rust!"

Variation: if you modify the build script in package.json to call wasm-pack with --target node instead of --target web you can generate code suitable for using from a NodeJS module.

Steps for Android

Proof that I did this on Android: Android emulator showing a label "This string is from Rust!"

Steps for iOS

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