Android Example

This example shows off how to use rust to build a native library from android and use it through an automatically generated JNI wrapper.

Project Structure

The file build.rs defines how rust_swig generates wrapper code. It automatically finds a suitable jni.h and generates a rust source file against it. Then, the script recursively looks for files ending in .rs.in in the source directory and uses rust_swig to generate a JNI wrapper both in Rust and in Java.

This build script is intended to be launched from gradle through e.g. ./gradlew aR. The gradle build files contain definitions on how to build the Rust libraries and where to find them for inclusion in the apk.

Building

Prerequisites

To build the demo, you will need the latest version of Cargo and at least rustc 1.16. You will also need to add support for android targets:

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

To link the libraries, you will need the android NDK and generate standalone toolchains for each target (edit the install dir as required):

# ARM
$ANDROID_NDK/build/tools/make-standalone-toolchain.sh --platform="android-27" --toolchain=arm-linux-androideabi-4.9 --install-dir=$ANDROID_TOOLCHAINS/android-27-arm-linux-androideabi-4.9  --arch=arm
$ANDROID_NDK/build/tools/make-standalone-toolchain.sh --platform="android-27" --toolchain=aarch64-linux-android-4.9 --install-dir=$ANDROID_TOOLCHAINS/android-27-aarch64-linux-android-4.9  --arch=aarch64

# x86
$ANDROID_NDK/build/tools/make-standalone-toolchain.sh --platform="android-27" --toolchain=x86-4.9 --install-dir=$ANDROID_TOOLCHAINS/android-27-x86-4.9  --arch=x86
$ANDROID_NDK/build/tools/make-standalone-toolchain.sh --platform="android-27" --toolchain=x86_64-4.9 --install-dir=$ANDROID_TOOLCHAINS/android-27-x86_64-4.9  --arch=x86_64

Then edit .cargo/config to point to the toolchains you just generated.

Finally, wrapping Rust around jni.h depends on bindgen, for which you will need libclang installed on your machine.

Invocation

Gradle will take care of building and deploying the Rust sources. Thus, to build the project in release mode, simply call ./gradlew androidRelease.

To build only the rust libraries for a specific target, call cargo as usual, e.g. cargo build --target arm-linux-androideabi.