element-x-android/docs/_developer_onboarding.md

Developer on boarding

• Introduction
  • Quick introduction to Matrix
    • Matrix data
      • Room
      • Event
    • Sync
  • The Android project
  • Application
    • Anvil
      • Node
    • Other frameworks
  • Push
  • Dependencies management
  • Test
  • Other points
    • Logging
    • Rageshake
  • Tips
• Happy coding!

Introduction

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

It's 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.

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 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.

Here is the current module dependency graph:

Application

(Note: to update)

This is the UI part of the project.

There are two variants of the application: Gplay and Fdroid.

The main difference is about using Firebase on Gplay variant, to have Push from Google Services. FDroid variant cannot contain closed source dependency.

Fdroid is using background polling to lack the missing of Pushed. Now a solution using UnifiedPush has ben added to the project. See refer to the dedicated documentation for more details.

Anvil

TODO

Node

TODO

Other frameworks

• Dependency injection is managed by Dagger (SDK) and Hilt (App);

Push

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

TODO Update All the dependencies are declared in build.gradle files. But some versions are declared in this dedicated file.

When adding a new dependency, you will have to update the file dependencies_groups.gradle to allow the dependency to be downloaded from the artifact repository. Sometimes sub-dependencies need to be added too, until the project can compile.

Dependabot is set up on the project. This tool will automatically create Pull Request to upgrade our dependencies one by one. dependencies_group, gradle files, Dependabot, etc.

Test

Please refer to this dedicated document.

TODO add link to the dedicated screenshot test documentation

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, not that Timber.v function may have no effect on some devices. Prefer using Timber.d and up.

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 report can contain:

• a screenshot of the current application state
• the application logs from up to 15 application starts
• the logcat logs
• the key share history (crypto data)

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.

Tips

• Element Android has a developer mode in the Settings/Advanced settings. Other useful options are available here;
• Show hidden Events can also help to debug feature. When developer mode is enabled, it is possible to view the source (= the Json content) of any Events;
• Type /devtools in a Room composer to access a developer menu. There are some other entry points. Developer mode has to be enabled;
• Hidden debug menu: when developer mode is enabled and on debug build, there are some extra screens that can be accessible using the green wheel. In those screens, it will be possible to toggle some feature flags;
• Using logcat, filtering with onResume 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.

Happy coding!

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

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

Thanks!