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Developer on boarding

Introduction

This doc is a quick introduction about the project and its architecture.

Its aim is to help new developers to understand the overall project and where to start developing.

Other useful documentation:

  • all the docs in this folder!
  • the contributing doc, that you should also read carefully.

Quick introduction to Matrix

Matrix website: matrix.org, discover page. Note: Matrix.org is also hosting a homeserver (.well-known file). The reference homeserver (this is how Matrix servers are called) implementation is Synapse. But other implementations exist. The Matrix specification is here to ensure that any Matrix client, such as Element Android and its SDK can talk to any Matrix server.

Have a quick look to the client-server API documentation: Client-server documentation. Other network API exist, the list is here: (https://spec.matrix.org/latest/)

Matrix is an open source protocol. Change are possible and are tracked using this GitHub repository. Changes to the protocol are called MSC: Matrix Spec Change. These are PullRequest to this project.

Matrix object are Json data. Unstable prefixes must be used for Json keys when the MSC is not merged (i.e. accepted).

Matrix data

There are many object and data in the Matrix worlds. Let's focus on the most important and used, Room and Event

Room

Room is a place which contains ordered Events. They are identified with their room_id. Nearly all the data are stored in rooms, and shared using homeserver to all the Room Member.

Note: Spaces are also Rooms with a different type.

Event

Events are items of a Room, where data is embedded.

There are 2 types of Room Event:

  • Regular Events: contain useful content for the user (message, image, etc.), but are not necessarily displayed as this in the timeline (reaction, message edition, call signaling).
  • State Events: contain the state of the Room (name, topic, etc.). They have a non null value for the key state_key.

Also all the Room Member details are in State Events: one State Event per member. In this case, the state_key is the matrixId (= userId).

Important Fields of an Event:

  • event_id: unique across the Matrix universe;
  • room_id: the room the Event belongs to;
  • type: describe what the Event contain, especially in the content section, and how the SDK should handle this Event;
  • content: dynamic Event data; depends on the type.

So we have a triple event_id, type, state_key which uniquely defines an Event.

Sync

This is managed by the Rust SDK.

Rust SDK

The Rust SDK is hosted here: https://github.com/matrix-org/matrix-rust-sdk.

This repository contains an implementation of a Matrix client-server library written in Rust.

With some bindings we can embed this sdk inside other environments, like Swift or Kotlin, with the help of Uniffi. From these kotlin bindings we can generate native libs (.so files) and kotlin classes/interfaces.

Matrix Rust Component Kotlin

To use these bindings in an android project, we need to wrap this up into an android library (as the form of an .aar file). This is the goal of https://github.com/matrix-org/matrix-rust-components-kotlin. This repository is used for distributing kotlin releases of the Matrix Rust SDK. It'll provide the corresponding aar and also publish them on maven.

Most of the time you want to use the releases made on maven with gradle:

implementation("org.matrix.rustcomponents:sdk-android:latest-version")

You can also have access to the aars through the release page.

Building the SDK locally

If you want to make changes to the SDK or test them before integrating it with your codebase, you can build the SDK locally too.

Prerequisites:

  • Install the Android NDK (Native Development Kit). To do this from within Android Studio:
    1. Tools > SDK Manager
    2. Click the SDK Tools tab.
    3. Select the NDK (Side by side) checkbox
    4. Click OK.
    5. Click OK.
    6. When the installation is complete, click Finish.
  • Install cargo-ndk: 
    cargo install cargo-ndk
  • Install the Android Rust toolchain for your machine's hardware: 
    rustup target add aarch64-linux-android x86_64-linux-android
  • Depending on the location of the Android SDK, you may need to set ANDROID_HOME: 
    export ANDROID_HOME=$HOME/android/sdk

You can then build the Rust SDK by running the script tools/sdk/build_rust_sdk.sh and just answering the questions.

This will prompt you for the path to the Rust SDK, then build it and matrix-rust-components-kotlin, eventually producing an aar file at ./libraries/rustsdk/matrix-rust-sdk.aar, which will be picked up automatically by the Element X Android build.

Troubleshooting:

  • You may need to set ANDROID_NDK_HOME e.g export ANDROID_NDK_HOME=~/Library/Android/sdk/ndk.
  • If you get the error thread 'main' panicked at 'called Option::unwrap()on aNone value', .cargo/registry/src/index.crates.io-6f17d22bba15001f/cargo-ndk-2.11.0/src/cli.rs:345:18 try updating your Cargo NDK version. In this case, 2.11.0 is too old so cargo install cargo-ndk to install a newer version.
  • If you get the error Unsupported class file major version <n>, try changing your JVM version by setting JAVA_HOME and, if building via Android Studio, "File | Settings | Build, Execution, Deployment | Build Tools | Gradle | Gradle JDK".

You can switch back to using the published version of the SDK by deleting libraries/rustsdk/matrix-rust-sdk.aar.

The Android project

The project should compile out of the box.

This Android project is a multi modules project.

  • app module is the Android application module. Other modules are libraries;
  • features modules contain some UI and can be seen as screen or flow of screens of the application;
  • libraries modules contain classes that can be useful for other modules to work.

A few details about some modules:

  • libraries-core module contains utility classes;
  • libraries-designsystem module contains Composables which can be used across the app (theme, etc.);
  • libraries-elementresources module contains resource from Element Android (mainly strings);
  • libraries-matrix module contains wrappers around the Matrix Rust SDK.

Most of the time a feature module should not know anything about other feature module. The navigation glue is currently done in the app module.

Here is the current simplified module dependency graph:

flowchart TD
    subgraph Application
    app([:app])--implementation-->appnav([:appnav])
    end
    subgraph Features
    featureapi([:features:*:api])
    featureimpl([:features:*:impl])
    end
    subgraph Libraries
        subgraph Matrix
        matrixapi([:matrix:api])
        matriximpl([:matrix:impl])
        end
    libraryarch([:libraries:architecture])
    libraryapi([:libraries:*:api])
    libraryimpl([:libraries:*:impl])
    end
    subgraph Matrix RustSdk
    RustSdk([Rust Sdk])
    end

    app--implementation-->featureimpl
    app--implementation-->libraryimpl
    appnav--implementation-->featureapi
    appnav--implementation-->libraryarch
    featureimpl--api-->featureapi
    featureimpl--implementation-->matrixapi
    featureimpl--implementation-->libraryapi
    featureimpl--implementation-->libraryarch
    matriximpl--implementation-->matrixapi
    matrixapi--api-->RustSdk
    matriximpl--api-->RustSdk
    featureapi--implementation-->libraryarch
    libraryimpl--api-->libraryapi
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Application

This Android project mainly handle the application layer of the whole software. The communication with the Matrix server, as well as the local storage, the cryptography (encryption and decryption of Event, key management, etc.) is managed by the Rust SDK.

The application is responsible to store the session credentials though.

Jetpack Compose

Compose is essentially two libraries : Compose Compiler and Compose UI. The compiler (and his runtime) is actually not specific to UI at all and offer powerful state management APIs. See https://jakewharton.com/a-jetpack-compose-by-any-other-name/

Some useful links:

About Preview

Global architecture

Main libraries and frameworks used in this application:

  • Navigation state with Appyx. Please watch this video to learn more about Appyx!
  • Dependency injection: Metro
  • Reactive State management with Compose runtime and Molecule

Some patterns are inspired by Circuit

Here are the main points:

  1. Presenter and View does not communicate with each other directly, but through State and Event
  2. Views are compose first
  3. Presenters are also compose first, and have a single present(): State method. It's using the power of compose-runtime/compiler.
  4. The point of connection between a View and a Presenter is a Node.
  5. A Node is also responsible for managing DI graph if any, see for instance LoggedInAppScopeFlowNode.
  6. A ParentNode has some children Node and only know about them.
  7. This is a single activity full compose application. The MainActivity is responsible for holding and configuring the RootNode.
  8. There is no more needs for Android Architecture Component ViewModel as configuration change should be handled by Composable if needed.

Template and naming

This documentation provides you with the steps to install and use the AS plugin for generating modules in your project. The plugin and templates will help you quickly create new features with a standardized structure.

A. Installation

Follow these steps to install and configure the plugin and templates:

  1. Install the AS plugin for generating modules : Generate Module from Template
  2. From repository root, run ./tools/templates/generate_templates.sh to generate the template zip file
  3. Import file templates in AS :
    • Navigate to File/Manage IDE Settings/Import Settings
    • Pick the tmp/file_templates.zip files
    • Click on OK
  4. Configure generate-module-from-template plugin :
    • Navigate to AS/Settings/Tools/Module Template Settings
    • Click on + / Import From File
    • Pick the tools/templates/FeatureModule.json

Everything should be ready to use.

B. Usage

Example for a new feature called RoomDetails:

  1. Right-click on the features package and click on Create Module from Template
  2. Fill the 2 text fields like so:
    • MODULE_NAME = roomdetails
    • FEATURE_NAME = RoomDetails
  3. Click on Next
  4. Verify that the structure looks ok and click on Finish
  5. The modules api/impl should be created under features/roomdetails directory.
  6. Sync project with Gradle so the modules are recognized (no need to add them to settings.gradle).
  7. You can now add more Presentation classes (Events, State, StateProvider, View, Presenter) in the impl module with the Template Presentation Classes. To use it, just right click on the package where you want to generate classes, and click on Template Presentation Classes. Fill the text field with the base name of the classes, ie RootRoomDetails in the root package.

Note that naming of files and classes is important, since those names are used to set up code coverage rules. For instance, presenters MUST have a suffix Presenter,states MUST have a suffix State, etc. Also we want to have a common naming along all the modules.

Push

Note Firebase is implemented, but Unified Push is not yet fully implemented on the project, so this is not possible to choose this push provider in the app at the moment.

Please see the dedicated documentation for more details.

This is the classical scenario:

  • App receives a Push. Note: Push is ignored if app is in foreground;
  • App asks the SDK to load Event data (fastlane mode). We have a change to get the data faster and display the notification faster;
  • App asks the SDK to perform a sync request.

Dependencies management

We are using Gradle version catalog on this project.

All the dependencies (including android artifact, gradle plugin, etc.) should be declared in ../gradle/libs.versions.toml file. Some dependency, mainly because they are not shared can be declared in build.gradle.kts files.

Renovate is set up on the project. This tool will automatically create Pull Request to upgrade our dependencies one by one. A dependency dashboard issue is maintained by the tool and allow to perform some actions.

Test

We have 3 tests frameworks in place, and this should be sufficient to guarantee a good code coverage and limit regressions hopefully:

Note For now we want to avoid using class mocking (with library such as mockk), because this should be not necessary. We prefer to create Fake implementation of our interfaces. Mocking can be used to mock Android framework classes though, such as Bitmap for instance.

Code coverage

kover is used to compute code coverage. Only have unit tests can produce code coverage result. Running Maestro does not participate to the code coverage results.

Kover configuration is defined in the app build.gradle.kts file.

To compute the code coverage, run:

./gradlew :app:koverHtmlReport

and open the Html report: ../app/build/reports/kover/html/index.html

To ensure that the code coverage threshold are OK, you can run

./gradlew :app:koverVerify

Note that the CI performs this check on every pull requests.

Also, if the rule Global minimum code coverage. is in error because code coverage is > maxValue, minValue and maxValue can be updated for this rule in the file build.gradle.kts (you will see further instructions there).

Other points

Logging

**Important warning: ** NEVER log private user data, or use the flag LOG_PRIVATE_DATA. Be very careful when logging data class, all the content will be output!

Timber is used to log data to logcat. We do not use directly the Log class. If possible please use a tag, as per

Timber.tag(loggerTag.value).d("my log")

because automatic tag (= class name) will not be available on the release version.

Also generally it is recommended to provide the Throwable to the Timber log functions.

Last point, note that Timber.v function may have no effect on some devices. Prefer using Timber.d and up.

Translations

Translations are handled through localazy. See the dedicated README.md file for information on how to configure new modules etc.

Rageshake

Rageshake is a feature to send bug report directly from the application. Just shake your phone and you will be prompted to send a bug report.

Bug reports can contain:

  • a screenshot of the current application state
  • the application logs from up to 15 application starts
  • the logcat logs

The data will be sent to an internal server, which is not publicly accessible. A GitHub issue will also be created to a private GitHub repository.

Rageshake can be very useful to get logs from a release version of the application.

Developer options

Warning

Developer options can result in unexpected application behavior or destructive actions. Use with caution and only if you are instructed by someone at Element or are already familiar.

These options provide advanced controls for testing and debugging. They are visible by default in debug and nightly builds but are hidden in release versions.

Enabling in release builds: Navigate to application settings and tap the version number at the bottom 7 times. After tapping, a new "Developer options" entry will appear at the bottom of the list.

The developer options include feature flags, notification/push history, Element call customization, Rust SDK log levels, per-feature tracing toggles, Showkase to debug UI components, rageshake controls, app crash controls, cache details/controls, persistent storage maintenance tasks.

Keywords: Developer settings, developer mode

Tips

  • Using logcat, filtering with Compositions can help you to understand what screen are currently displayed on your device. Searching for string displayed on the screen can also help to find the running code in the codebase.
  • When this is possible, prefer using sealed interface instead of sealed class;
  • When writing temporary code, using the string "DO NOT COMMIT" in a comment can help to avoid committing things by mistake. If committed and pushed, the CI will detect this String and will warn the user about it. (TODO Not supported yet!)
  • Very occasionally the gradle cache misbehaves and causes problems with code generation. Adding --no-build-cache to the gradlew command line can help to fix compilation issue.

Happy coding!

The team is here to support you, feel free to ask anything to other developers.

Also please feel free to update this documentation, if incomplete/wrong/obsolete/etc.

Thanks!