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Overview
Until the final migration to rust crypto sdk, the Element Android project will support two different SDK as a product flavor.
The matrix-sdk-android module is defining a new flavor dimension crypto, with two flavors kotlinCrypto and rustCrypto.
The crypto module cannot be changed at runtime, it's a build time configuration. The app supports migration from kotlinCrypto to rustCrypto but not the other
way around.
The code that is not shared between the flavors is located in dedicated source sets (src/kotlinCrypto/, src/rustCrypto/). Some tests are also extracted
in different source sets because they were accessing internal API and won't work with the rust crypto sdk.
Noticeable changes
As a general rule, if you stick to the kotlinCrypto the app should behave as it was before the integration of favours.
There is a noticeable exception though:
In order to integrate the rust crypto several APIs had to be migrated from callback code to suspendable code. This change
impacted a lot the key verification engine (user and device verification), so this part has been refactored for kotlinCrypto. The UI is also impacted,
the verification flows now match the web experience.
TLDR; Verification UI and engine has been refactored.
Testing with a local rust aar
In order to run a custom rust SDK branch you can follow the direction in the bindings repository
in order to build the matrix-rust-sdk-crypto.aar.
Copy this lib in library/rustCrypto/, and rename it matrix-rust-sdk-crypto.aar.
Then go to matrix-sdk-android/build.gradle and toggle the comments between the following lines.
rustCryptoImplementation("org.matrix.rustcomponents:crypto-android:0.3.1")
// rustCryptoApi project(":library:rustCrypto")
Changes in CI
The workflow files have been updated to use the kotlinCrypto flavor, e.g
assembleGplayNightly => assembleGplayKotlinCryptoNightly
So building the unsigned release kotlin crypto apk is now:
> ./gradlew assembleGplayKotlinCryptoRelease
An additional workflow has been added to build the rustCrypto flavor (elementr.yml, Build debug APKs ER).
Database migration from kotlin to rust
With the kotlin flavor, the crypto information are persisted in the crypto realm database. With the rust flavor, the crypto information are in a sqllite database.
The migration is handled when injecting @SessionRustFilesDirectory in the olmMachine.
When launching the first time after migration, the app will detect that there is no rust data repository and it will
create one. If there is an existing realm database, the data will then migrated to rust. See ExtractMigrationDataUseCase.
This will extract your device keys, account secrets, active olm and megolm sessions.
There is no inverse migration for now, as there is not yet rust pickle to olm pickle support in the sdk.
If you migrate your app to rust, and want to revert to kotlin you have to logout then login again.