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Building the libraries for mobile wallets on Android and iOS

Common requirements

The cryptographic library is written in Rust, and therefore the Rust compiler and Cargo is required. These are often packaged with the package manager of your choice, but can also be obtained through https://rustup.rs/

The cargo build tool depends on git to obtain dependencies from crates.io.

Certain dependencies in the crypto library have foreign code requiring a C compiler to be compiled. A compiler such as GCC works.

Android

First time setup

First time compiling the code you'll need to install the standard library for all Android architectures. This can be done using

rustup target add aarch64-linux-android armv7-linux-androideabi i686-linux-android x86_64-linux-android

This should be sufficient for modern devices, but others might be worth installing depending on min target device.

You'll also need an extension for the cargo tool to build linking against the Android NDK.

cargo install cargo-ndk

Compiling for Android requires the NDK to be available, and having an environment variable set pointing to the location of it. The SDK and NDK can be installed using Android Studio (using the SDK Manager).

Set the following variables, adjusted appropriately for the specific install:

NDK_VERSION=21.3.6528147                         # Adjust to version in ~/Android/Sdk/ndk
export ANDROID_SDK_ROOT=$HOME/Android/Sdk
export ANDROID_NDK_HOME=$ANDROID_SDK_ROOT/ndk/$NDK_VERSION

Building

You should now be able to build the libraries using the script build-android.sh located in crypto/mobile_wallet/android.

cd android
./build-android.sh

This script builds the Rust libraries for the various Android architectures, and copies the libraries into the folder mobile_wallet_lib which can be assembled into an AAR archive using Gradle:

cd mobile_wallet_lib
./gradlew build

This command invokes Gradle via the Gradle Wrapper and writes AAR files for debug/release targets to build/outputs/aar.

iOS

First time usage

To build for iOS, XCode must be installed and the license must have been accepted. This is deemed out of scope for this guide, and therefore assumed to be in working order.

First time compiling the code you'll need to install the standard library for the two iOS architectures. This can be done using

rustup target add aarch64-apple-ios aarch64-apple-ios-sim x86_64-apple-ios

This should be sufficient for modern devices, but others might be worth installing depending on min target device.

You'll also need an extension for the cargo tool to generate C headers.

cargo install cbindgen

Building

You should now be able to build the crypto library. Go to the crypto/mobile_wallet folder.

cbindgen src/lib.rs -l c > mobile_wallet.h

It will output some warnings which can mostly be ignored. We don't want C headers for the JNI methods only used on Android, and the entries are generated correctly for iOS despite missing config.

Now you have the header file required for use from Swift/ObjC.

You can now execute

./scripts/build-ios.sh

It will proceed to build the xcframework which can then be found as ios/build/libmobile_wallet.xcframework