notmandatory / uniffi-bindings-template

A starter template for creating uniffi-rs language bindings libraries.

Readme

Build the library for Android

1. Fire the buildAndroidLib gradle task in the calculator-android directory
2. Publish it to your local Maven (the library will appear at ~/.m2/repository/org/rustylibs/calculator-android/0.1.0/)

cd calculator-android
./gradlew buildAndroidLib
./gradlew publishToMavenLocal

You should then be able to use the library by adding it like any other dependency in an Android project, given you add mavenLocal() to your list of repositories to fetch dependencies from:

// build.gradle.kts
repositories {
    mavenCentral()
    mavenLocal()
}

A few important pieces of this template

The custom Gradle plugin for the Android library

This plugin lives in the calculator-android/plugins/ directory, and collects the tasks of building the native binaries, building the glue code file, and putting them all in the correct places in the library to prepare for packaging. The plugin exposes the buildAndroidLib task to the Gradle build tool.

The ffi-bindgen cli tool

The task of building language bindings using uniff-rs can be thought of as consisting of two steps: (1) building the native binaries for each target architecture, (2) building a "glue code" file in the target language, which will call the native binaries.

The calculator-ffi/ffi-bingen/ directory contains a binary package which allows us to build the glue code files for each of the bindings (calculator.kt and calculator.swift) using a well-defined uniffi-bindgen version. In general, this cli tool can simply be downloaded from crates.io, but a requirement of the uniffi-rs library is that the native binaries produced by the uniffi-rs crate use the same version for that crate as the one used in the cli bindgen tool which produces the glue code. That these two versions be the same is not enforced at build time because the processes are separate, and it is therefore common for unaware contributors/developers to have problems with libraries where the binaries where produced by a different version than the glue code was. The ffi-bindgen cli tool ensures that all contributors need not downloading the uniffi-bindgen tool and instead build the glue code using the same provided tool (ffi-bindgen).

Reducing the size of the final binaries

A special cargo profile is added with many flags turned on/off which allows to significantly reduce binary size.