AnkiDroid-Backend

An interface for accessing Anki Desktop's Rust backend inside AnkiDroid. This allows AnkiDroid to re-use the computer version's business logic and webpages, instead of having to reimplement them.

This is a separate repo that gets published to a library that AnkiDroid consumes, so that AnkiDroid development is possible without a Rust toolchain installed.

Prerequisites

We assume you already have Android Studio, and are able to build the AnkiDroid project already.

The repos Anki-Android and Anki-Android-Backend should be cloned inside the same folder. Furthermore, Anki-Android-Backend should not be renamed, as this name is hard-coded in AnkiDroid gradle files. Unless stated otherwise, all commands below are supposed to be executed in the current repo.

Download Anki submodule

git submodule update --init --recursive

C toolchain

Install Xcode/Visual Studio if on macOS/Windows.

Rust

Install rustup from https://rustup.rs/

Ninja

Anki can be built with Ninja or N2. N2 gives better status output and may be installed like so:

./anki/tools/install-n2

On Windows:

bash anki/tools/install-n2

Note: n2 receives occasional mandatory updates. If you see build errors, you may need to re-run this command and re-try the build

NDK

In Android Studio, choose the Tools>SDK Manager menu option.

• In SDK tools, enable "show package details"
• Choose NDK version 27.0.12077973
• After downloading, you may need to restart Android Studio to get it to synchronize gradle.

Windows: msys2

Install msys2 into the default folder location.

After installation completes, run msys2, and run the following command:

pacman -S git rsync

When following the build steps below, make sure msys is on the path:

set PATH=%PATH%;c:\msys64\usr\bin

Building

Two main files need to be built:

• The main .aar file, which contains the backend Kotlin code, web assets, and Anki backend code compiled for Android.
• A .jar that contains the backend code compiled for the host platform, for use with Robolectric unit tests.

You should do the first build with the provided shell .sh/.bat file, as it will take care of downloading the target architecture library as well. You'll need to tell the script to use the Java libraries and NDK downloaded by Android Studio, eg on Linux:

export ANDROID_SDK_ROOT=$HOME/Android/Sdk
export ANDROID_NDK_HOME=$HOME/Android/Sdk/ndk/27.0.12077973

Or macOS:

export ANDROID_SDK_ROOT=$HOME/Library/Android/sdk
export ANDROID_NDK_HOME=$HOME/Library/Android/sdk/ndk/27.0.12077973

Or Windows using Powershell:

$env:ANDROID_NDK_HOME="$env:ANDROID_SDK_ROOT\ndk\27.0.12077973"

If you don't have Java installed, you may be able to use the version bundled with Android Studio. Eg on macOS:

export JAVA_HOME="/Applications/Android Studio.app/Contents/jre/Contents/Home"

or Windows:

set JAVA_HOME=C:\Program Files\Android\Android Studio\jre

Now build with ./build.sh or build.bat.

After you've confirmed building works, you may want to build again with the env var RELEASE=1 defined, to build a faster version.

Modify AnkiDroid to use built library

Now open the AnkiDroid project in AndroidStudio. To tell gradle to load the compiled .aar and .jar files from disk, edit local.properties in the AnkiDroid repo, and add the following line:

local_backend=true

Check Anki-AndroidBackend/gradle.properties's BACKEND_VERSION and Anki-Android/build.gradle's ext.ankidroid_backend_version. Both variables should have the same value. If it is not the case, you must edit Anki-Android's one.

After making the change, you should be able to build and run the project on an x86_64 emulator/device (arm64 on M1 Macs), and run unit tests.

Release builds

Only the current platform is built by default. In CI, the .aar and .jar files are built for multiple platforms, so one release library can be used on a variety of devices. See [.github/workflows] for how this is done.

Testing with a specific version of anki

In this section, we'll consider that you want to test AnkiDroid with the version of Anki at commit $COMMIT_IDENTIFIER from the repository some_repo.

Most of the time $SOME_REPO will simply be origin, that is, ankitects official repository, and COMMIT_IDENTIFIER could be replaced by the tag of the latest stable release. You can find the latest tag by running git tag|sort -V|tail -n1 in the anki directory.

1. run cd anki to change into the anki submodule directory,
2. run git fetch $SOME_REPO to ensure you obtain the latest change from this repo.
3. run git checkout $COMMIT_IDENTIFIER --recurse-submodules to obtain the version of the code at this particular commit.
4. move back to the root of the repo (not the submodule) and run cargo check to update our Cargo.lock with any updated versions from the submodule

Creating and Publishing a release

Let's now consider that you want to release a new version of the back-end.

1. Find the latest stable version of Anki. You can find the latest tag by running git tag|sort -V|tail -n1 in the anki directory. Let's call it version $ANKI_VERSION.
2. Ensure you are testing and building the back-end against this version (see preceding section to learn how to do it).
3. In Anki-Android-Backend/gradle.properties you will need to update VERSION_NAME. Its value is of the form $BACKEND_VERSION-$ANKI_VERSION. $ANKI_VERSION should be as defined above. $BACKEND_VERSION should be incremented compared to the last release.
4. Run the Github workflow Build release (from macOS) manually with a string argument (I typically use shipit, but any string will work) - this will trigger a full release build ready for upload to maven.
5. Check the workflow logs for the link to Maven Central where if you have a Maven Central user with permissions (like David A and Mike H - ask if you want permission) you may "close" the repository" then after a short wait "release" the repository.
6. Head over to the main Anki-Android repository and update the AnkiDroid/build.gradle file there to adopt the new backend version once it shows up in https://repo1.maven.org/maven2/io/github/david-allison/anki-android-backend/

Architecture

See ARCHITECTURE.md

License

GPL-3.0 License
AGPL-3.0 Licence (anki submodule)