WildCat's Blog

Rust for Mobile Development

Since the creation of this blog, I’ve been focusing on mobile and web development, for nearly a decade. At the same time, the popularity of Rust is growing quickly.

There’re not so much community resources about mobile development with Rust, though Mozilla has been using Rust for Firefox Android/iOS for a long time. After investigating their Rust projects, it is a good time to write a blog about it.

Is Rust ready for mobile development?

The short answer is “yes”.

Most well-known showcases of Rust are about backend development. However, you can also find many cases about its usage in the client-side development.

If you’d like to see more, here are great references:

Key pieces of the puzzle

You can write a simple Rust library with C bindings to be used in Swift/Objective-C or Java/Kotlin (JNI). However, it is not an easy way. C bindings mean a lot of boilerplate code, and it’s hard to maintain.

Fortunately, Mozilla built two key frameworks which help a lot:

Example of mobile development with Rust

I built a simple codebase for a mobile app using Rust: https://github.com/imWildCat/uniffi-rs-fullstack-examples. I believe the code explains itself. But it should be good to mention some tricks.

iOS

For iOS, you need to build the binary for each target, including simulator and device (Intel and Apple CPUs, respectively).

Usually, you need to build for this matrix:

Target CPU
Simulator x86_64
Simulator aarch64
Device x86_64
Device aarch64

For the aarch64 simulator toolchain of Rust, it is not supported by the stable channel. So, you need to install the nightly toolchain with source code. Similar things apply to most Mac Catalyst targets:

rustup toolchain install nightly
rustup target add aarch64-apple-ios-sim --toolchain nightly
rustup target add aarch64-apple-ios x86_64-apple-ios
rustup component add rust-src --toolchain nightly

(link to the source code)

More information about the platform support of Rust can be found at https://doc.rust-lang.org/nightly/rustc/platform-support.html.

Android

The only thing that we need to be carefully about is Python 2 removal on macOS 12.3. If you’d like to build Android libraries using NDK on macOS 12.3 and later, you’d better to build Python 2.x from source and link it to /usr/local/bin/python. Otherwise, the build is likely to fail. It’s sad to see that Python 2 is still a dependency of the NDK toolchain in 2022.

Summary

Although it is still an early stage of Rust development for mobile, this language has a great potential. To me, the most attractive feature is the zero-cost abstraction of Rust. This means the binary generated can be small enough and its performance is great. Since many great teams like Mozilla have been using it for mobile applications for several years, it is a good time to start using it.