# Architecture

The SDK is split into multiple layers:

```text
    WASM (external crate matrix-rust-sdk-crypto-wasm)
      /
     /     uniffi
    /     /
   /     bindings (matrix-sdk-ffi)
 crypto   |
bindings  |
   |      |
   |     UI (matrix-sdk-ui)
   |      \
   |       \
   |   main (matrix-sdk)
   | /     /
crypto    /
     \   /
      store (matrix-sdk-base, + all the store impls)
        |
      common (matrix-sdk-common)
```

Where the store implementations are `matrix-sdk-sqlite` and
`matrix-sdk-indexeddb` as well as `MemoryStore` which is defined in
`matrix-sdk-base`.

## `crates/matrix-sdk`

This is the main crate, and one that is expected to be used by most consumers.
Notable data types include:

- the `Client`, which can run room-independent requests: logging in/out,
  creating rooms, running sync, etc.
- the `Room`, which represents a room and its state (notably via the observable
  `RoomInfo`), and allows running queries that are room-specific, notably
  sending events.

## `crates/matrix-sdk-base`

A _sans I/O_ crate to represent the base data types persisted in the SDK. No
network or storage I/O happens in this crate, although it defines traits
(`StateStore` and `EventCacheStore`) representing storage backends, as well as
dummy in-memory implementations of these traits.

## `crates/matrix-sdk-common`

Common helpers used by most of the other crates; almost a leaf in the dependency
tree of our own crates (the only crate it's using is test helpers).

## `crates/matrix-sdk-crypto`

A _sans I/O_ implementation of a state machine that handles end-to-end
encryption for Matrix clients. It defines a `CryptoStore` trait representing
storage backends that will perform the actual storage I/O later, as well as a
dummy in-memory implementation of this trait.

## `crates/matrix-sdk-indexeddb`

Implementations of `EventCacheStore`, `StateStore` and `CryptoStore` for a
indexeddb backend (for use in Web browsers, via WebAssembly).

## `crates/matrix-sdk-qrcode`

Implementation of QR codes for interactive verifications, used in the crypto
crate.

## `crates/matrix-sdk-sqlite`

Implementations of `EventCacheStore`, `StateStore` and `CryptoStore` for a
SQLite backend.

## `crates/matrix-sdk-store-encryption`

Low-level primitives for encrypting/decrypting/hashing values. Store
implementations that implement encryption at rest can use those primitives.

## `crates/matrix-sdk-ui`

Very high-level primitives implementing the best practices and cutting-edge
Matrix tech:

- `EncryptionSyncService`: a specialized service running simplified sliding sync
  (MSC4186) for everything related to crypto and E2EE for the current `Client`.
- `RoomListService`: a specialized service running simplified sliding sync
  (MSC4186) for retrieving the list of current rooms, and exposing its entries.
- `SyncService`: a wrapper for the two previous services, coordinating their
  running and shutting down.
- `Timeline`: a high-level view for a `Room`'s timeline of events, grouping
  related events (aggregations) into single timeline items.

## `bindings/matrix-sdk-crypto-ffi/`

FFI bindings for the crypto crate, used in a Web browser context via
WebAssembly. These use `wasm-bindgen` to generate the bindings. These bindings
are used in Element Web and the legacy Element apps, as of 2024-11-07.

## `bindings/matrix-sdk-ffi/`

FFI bindings for important concepts in `matrix-sdk-ui` and `matrix-sdk`,
generated with [UniFFI](https://github.com/mozilla/uniffi-rs) and to be used
from other languages like Swift/Go/Kotlin. These bindings are used in the
ElementX apps, as of 2024-11-07.

## `bindings/matrix-sdk-ffi-macros/`

Macros used in `bindings/matrix-sdk-ffi`.

## `testing/matrix-sdk-test/`

Common test helpers, used by all the other crates.

## `testing/matrix-sdk-test-macros/`

Implementation of the `#[async_test]` test macro.

## `testing/matrix-sdk-integration-testing/`

Fully-fledged integration tests that require spawning a Synapse instance to run.
A docker-compose setup is provided to ease running the tests, and it is
compatible for running with Podman too.

## Inspiration

This document has been inspired by the reading of this
[blog post](https://matklad.github.io/2021/02/06/ARCHITECTURE.md.html).