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// Copyright 2024 The Matrix.org Foundation C.I.C.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//! The event cache is an abstraction layer, sitting between the Rust SDK and a
//! final client, that acts as a global observer of all the rooms, gathering and
//! inferring some extra useful information about each room. In particular, this
//! doesn't require subscribing to a specific room to get access to this
//! information.
//!
//! It's intended to be fast, robust and easy to maintain, having learned from
//! previous endeavours at implementing middle to high level features elsewhere
//! in the SDK, notably in the UI's Timeline object.
//!
//! See the [github issue](https://github.com/matrix-org/matrix-rust-sdk/issues/3058) for more
//! details about the historical reasons that led us to start writing this.
#![forbid(missing_docs)]
use std::{
collections::BTreeMap,
fmt::Debug,
sync::{Arc, OnceLock},
};
use eyeball::Subscriber;
use matrix_sdk_base::{
deserialized_responses::{AmbiguityChange, SyncTimelineEvent, TimelineEvent},
sync::RoomUpdates,
};
use matrix_sdk_common::executor::{spawn, JoinHandle};
use ruma::{
events::{relation::RelationType, AnySyncEphemeralRoomEvent},
serde::Raw,
EventId, OwnedEventId, OwnedRoomId, RoomId,
};
use tokio::sync::{
broadcast::{error::RecvError, Receiver},
Mutex, RwLock,
};
use tracing::{error, info_span, instrument, trace, warn, Instrument as _, Span};
use self::paginator::PaginatorError;
use crate::{client::WeakClient, Client};
mod deduplicator;
mod linked_chunk;
mod pagination;
mod room;
pub mod paginator;
pub use pagination::{RoomPagination, TimelineHasBeenResetWhilePaginating};
pub use room::RoomEventCache;
/// An error observed in the [`EventCache`].
#[derive(thiserror::Error, Debug)]
pub enum EventCacheError {
/// The [`EventCache`] instance hasn't been initialized with
/// [`EventCache::subscribe`]
#[error(
"The EventCache hasn't subscribed to sync responses yet, call `EventCache::subscribe()`"
)]
NotSubscribedYet,
/// The room hasn't been found in the client.
///
/// Technically, it's possible to request a [`RoomEventCache`] for a room
/// that is not known to the client, leading to this error.
#[error("Room {0} hasn't been found in the Client.")]
RoomNotFound(OwnedRoomId),
/// The given back-pagination token is unknown to the event cache.
#[error("The given back-pagination token is unknown to the event cache.")]
UnknownBackpaginationToken,
/// An error has been observed while back-paginating.
#[error("Error observed while back-paginating: {0}")]
BackpaginationError(#[from] PaginatorError),
/// The [`EventCache`] owns a weak reference to the [`Client`] it pertains
/// to. It's possible this weak reference points to nothing anymore, at
/// times where we try to use the client.
#[error("The owning client of the event cache has been dropped.")]
ClientDropped,
}
/// A result using the [`EventCacheError`].
pub type Result<T> = std::result::Result<T, EventCacheError>;
/// Hold handles to the tasks spawn by a [`RoomEventCache`].
pub struct EventCacheDropHandles {
/// Task that listens to room updates.
listen_updates_task: JoinHandle<()>,
/// Task that listens to updates to the user's ignored list.
ignore_user_list_update_task: JoinHandle<()>,
}
impl Debug for EventCacheDropHandles {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
f.debug_struct("EventCacheDropHandles").finish_non_exhaustive()
}
}
impl Drop for EventCacheDropHandles {
fn drop(&mut self) {
self.listen_updates_task.abort();
self.ignore_user_list_update_task.abort();
}
}
/// An event cache, providing lots of useful functionality for clients.
///
/// Cloning is shallow, and thus is cheap to do.
///
/// See also the module-level comment.
#[derive(Clone)]
pub struct EventCache {
/// Reference to the inner cache.
inner: Arc<EventCacheInner>,
}
impl Debug for EventCache {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
f.debug_struct("EventCache").finish_non_exhaustive()
}
}
impl EventCache {
/// Create a new [`EventCache`] for the given client.
pub(crate) fn new(client: WeakClient) -> Self {
Self {
inner: Arc::new(EventCacheInner {
client,
multiple_room_updates_lock: Default::default(),
by_room: Default::default(),
drop_handles: Default::default(),
all_events: Default::default(),
}),
}
}
/// Starts subscribing the [`EventCache`] to sync responses, if not done
/// before.
///
/// Re-running this has no effect if we already subscribed before, and is
/// cheap.
pub fn subscribe(&self) -> Result<()> {
let client = self.inner.client()?;
let _ = self.inner.drop_handles.get_or_init(|| {
// Spawn the task that will listen to all the room updates at once.
let listen_updates_task = spawn(Self::listen_task(
self.inner.clone(),
client.subscribe_to_all_room_updates(),
));
let ignore_user_list_update_task = spawn(Self::ignore_user_list_update_task(
self.inner.clone(),
client.subscribe_to_ignore_user_list_changes(),
));
Arc::new(EventCacheDropHandles { listen_updates_task, ignore_user_list_update_task })
});
Ok(())
}
/// Try to find an event by its ID in all the rooms.
// Note: replace this with a select-by-id query when this is implemented in a
// store.
pub async fn event(&self, event_id: &EventId) -> Option<SyncTimelineEvent> {
self.inner
.all_events
.read()
.await
.events
.get(event_id)
.map(|(_room_id, event)| event.clone())
}
/// Clear all the events from the immutable event cache.
///
/// This keeps all the rooms along with their internal events linked chunks,
/// but it clears the side immutable cache for events.
///
/// As such, it doesn't emit any [`RoomEventCacheUpdate`], and it's expected
/// to be only useful in testing contexts.
// Note: replace this with a remove query when this is implemented in a
// store.
#[cfg(any(test, feature = "testing"))]
pub async fn empty_immutable_cache(&self) {
self.inner.all_events.write().await.events.clear();
}
#[instrument(skip_all)]
async fn ignore_user_list_update_task(
inner: Arc<EventCacheInner>,
mut ignore_user_list_stream: Subscriber<Vec<String>>,
) {
let span = info_span!(parent: Span::none(), "ignore_user_list_update_task");
span.follows_from(Span::current());
async move {
while ignore_user_list_stream.next().await.is_some() {
inner.clear_all_rooms().await;
}
}
.instrument(span)
.await;
}
#[instrument(skip_all)]
async fn listen_task(
inner: Arc<EventCacheInner>,
mut room_updates_feed: Receiver<RoomUpdates>,
) {
trace!("Spawning the listen task");
loop {
match room_updates_feed.recv().await {
Ok(updates) => {
if let Err(err) = inner.handle_room_updates(updates).await {
match err {
EventCacheError::ClientDropped => {
// The client has dropped, exit the listen task.
break;
}
err => {
error!("Error when handling room updates: {err}");
}
}
}
}
Err(RecvError::Lagged(num_skipped)) => {
// Forget everything we know; we could have missed events, and we have
// no way to reconcile at the moment!
// TODO: implement Smart Matching™,
warn!(num_skipped, "Lagged behind room updates, clearing all rooms");
inner.clear_all_rooms().await;
}
Err(RecvError::Closed) => {
// The sender has shut down, exit.
break;
}
}
}
}
/// Return a room-specific view over the [`EventCache`].
pub(crate) async fn for_room(
&self,
room_id: &RoomId,
) -> Result<(RoomEventCache, Arc<EventCacheDropHandles>)> {
let Some(drop_handles) = self.inner.drop_handles.get().cloned() else {
return Err(EventCacheError::NotSubscribedYet);
};
let room = self.inner.for_room(room_id).await?;
Ok((room, drop_handles))
}
/// Add an initial set of events to the event cache, reloaded from a cache.
///
/// TODO: temporary for API compat, as the event cache should take care of
/// its own store.
#[instrument(skip(self, events))]
pub async fn add_initial_events(
&self,
room_id: &RoomId,
events: Vec<SyncTimelineEvent>,
prev_batch: Option<String>,
) -> Result<()> {
let room_cache = self.inner.for_room(room_id).await?;
// We could have received events during a previous sync; remove them all, since
// we can't know where to insert the "initial events" with respect to
// them.
room_cache
.inner
.replace_all_events_by(events, prev_batch, Default::default(), Default::default())
.await?;
Ok(())
}
}
type AllEventsMap = BTreeMap<OwnedEventId, (OwnedRoomId, SyncTimelineEvent)>;
type RelationsMap = BTreeMap<OwnedEventId, BTreeMap<OwnedEventId, RelationType>>;
/// Cache wrapper containing both copies of received events and lists of event
/// ids related to them.
#[derive(Default, Clone)]
struct AllEventsCache {
/// A cache of received events mapped by their event id.
events: AllEventsMap,
/// A cache of related event ids for an event id. The key is the original
/// event id and the value a list of event ids related to it.
relations: RelationsMap,
}
struct EventCacheInner {
/// A weak reference to the inner client, useful when trying to get a handle
/// on the owning client.
client: WeakClient,
/// A lock used when many rooms must be updated at once.
///
/// [`Mutex`] is “fair”, as it is implemented as a FIFO. It is important to
/// ensure that multiple updates will be applied in the correct order, which
/// is enforced by taking this lock when handling an update.
// TODO: that's the place to add a cross-process lock!
multiple_room_updates_lock: Mutex<()>,
/// Lazily-filled cache of live [`RoomEventCache`], once per room.
by_room: RwLock<BTreeMap<OwnedRoomId, RoomEventCache>>,
/// All events, keyed by event id.
///
/// Since events are immutable in Matrix, this is append-only — events can
/// be updated, though (e.g. if it was encrypted before, and
/// successfully decrypted later).
///
/// This is shared between the [`EventCacheInner`] singleton and all
/// [`RoomEventCacheInner`] instances.
all_events: Arc<RwLock<AllEventsCache>>,
/// Handles to keep alive the task listening to updates.
drop_handles: OnceLock<Arc<EventCacheDropHandles>>,
}
impl EventCacheInner {
fn client(&self) -> Result<Client> {
self.client.get().ok_or(EventCacheError::ClientDropped)
}
/// Clears all the room's data.
async fn clear_all_rooms(&self) {
// Note: one must NOT clear the `by_room` map, because if something subscribed
// to a room update, they would never get any new update for that room, since
// re-creating the `RoomEventCache` would create a new unrelated sender.
// Note 2: we don't need to clear the [`Self::events`] map, because events are
// immutable in the Matrix protocol.
let rooms = self.by_room.write().await;
for room in rooms.values() {
// Notify all the observers that we've lost track of state. (We ignore the
// error if there aren't any.)
let _ = room.inner.sender.send(RoomEventCacheUpdate::Clear);
// Clear all the room state.
room.inner.state.write().await.reset();
}
}
/// Handles a single set of room updates at once.
#[instrument(skip(self, updates))]
async fn handle_room_updates(&self, updates: RoomUpdates) -> Result<()> {
// First, take the lock that indicates we're processing updates, to avoid
// handling multiple updates concurrently.
let _lock = self.multiple_room_updates_lock.lock().await;
// Left rooms.
for (room_id, left_room_update) in updates.leave {
let room = self.for_room(&room_id).await?;
if let Err(err) = room.inner.handle_left_room_update(left_room_update).await {
// Non-fatal error, try to continue to the next room.
error!("handling left room update: {err}");
}
}
// Joined rooms.
for (room_id, joined_room_update) in updates.join {
let room = self.for_room(&room_id).await?;
if let Err(err) = room.inner.handle_joined_room_update(joined_room_update).await {
// Non-fatal error, try to continue to the next room.
error!("handling joined room update: {err}");
}
}
// Invited rooms.
// TODO: we don't anything with `updates.invite` at this point.
Ok(())
}
/// Return a room-specific view over the [`EventCache`].
///
/// It may not be found, if the room isn't known to the client, in which
/// case it'll return None.
async fn for_room(&self, room_id: &RoomId) -> Result<RoomEventCache> {
// Fast path: the entry exists; let's acquire a read lock, it's cheaper than a
// write lock.
let by_room_guard = self.by_room.read().await;
match by_room_guard.get(room_id) {
Some(room) => Ok(room.clone()),
None => {
// Slow-path: the entry doesn't exist; let's acquire a write lock.
drop(by_room_guard);
let mut by_room_guard = self.by_room.write().await;
// In the meanwhile, some other caller might have obtained write access and done
// the same, so check for existence again.
if let Some(room) = by_room_guard.get(room_id) {
return Ok(room.clone());
}
let room_event_cache = RoomEventCache::new(
self.client.clone(),
room_id.to_owned(),
self.all_events.clone(),
);
by_room_guard.insert(room_id.to_owned(), room_event_cache.clone());
Ok(room_event_cache)
}
}
}
}
/// The result of a single back-pagination request.
#[derive(Debug)]
pub struct BackPaginationOutcome {
/// Did the back-pagination reach the start of the timeline?
pub reached_start: bool,
/// All the events that have been returned in the back-pagination
/// request.
///
/// Events are presented in reverse order: the first element of the vec,
/// if present, is the most "recent" event from the chunk (or
/// technically, the last one in the topological ordering).
///
/// Note: they're not deduplicated (TODO: smart reconciliation).
pub events: Vec<TimelineEvent>,
}
/// An update related to events happened in a room.
#[derive(Debug, Clone)]
pub enum RoomEventCacheUpdate {
/// The room has been cleared from events.
Clear,
/// The fully read marker has moved to a different event.
MoveReadMarkerTo {
/// Event at which the read marker is now pointing.
event_id: OwnedEventId,
},
/// The members have changed.
UpdateMembers {
/// Collection of ambiguity changes that room member events trigger.
///
/// This is a map of event ID of the `m.room.member` event to the
/// details of the ambiguity change.
ambiguity_changes: BTreeMap<OwnedEventId, AmbiguityChange>,
},
/// The room has received new timeline events.
AddTimelineEvents {
/// All the new events that have been added to the room's timeline.
events: Vec<SyncTimelineEvent>,
/// Where the events are coming from.
origin: EventsOrigin,
},
/// The room has received new ephemeral events.
AddEphemeralEvents {
/// XXX: this is temporary, until read receipts are handled in the event
/// cache
events: Vec<Raw<AnySyncEphemeralRoomEvent>>,
},
}
/// Indicate where events are coming from.
#[derive(Debug, Clone)]
pub enum EventsOrigin {
/// Events are coming from a sync.
Sync,
}
#[cfg(test)]
mod tests {
use assert_matches::assert_matches;
use futures_util::FutureExt as _;
use matrix_sdk_base::sync::{JoinedRoomUpdate, RoomUpdates, Timeline};
use matrix_sdk_test::async_test;
use ruma::{event_id, room_id, serde::Raw, user_id};
use serde_json::json;
use super::{EventCacheError, RoomEventCacheUpdate};
use crate::test_utils::{assert_event_matches_msg, events::EventFactory, logged_in_client};
#[async_test]
async fn test_must_explicitly_subscribe() {
let client = logged_in_client(None).await;
let event_cache = client.event_cache();
// If I create a room event subscriber for a room before subscribing the event
// cache,
let room_id = room_id!("!omelette:fromage.fr");
let result = event_cache.for_room(room_id).await;
// Then it fails, because one must explicitly call `.subscribe()` on the event
// cache.
assert_matches!(result, Err(EventCacheError::NotSubscribedYet));
}
#[async_test]
async fn test_uniq_read_marker() {
let client = logged_in_client(None).await;
let room_id = room_id!("!galette:saucisse.bzh");
client.base_client().get_or_create_room(room_id, matrix_sdk_base::RoomState::Joined);
let event_cache = client.event_cache();
event_cache.subscribe().unwrap();
let (room_event_cache, _drop_handles) = event_cache.for_room(room_id).await.unwrap();
let (events, mut stream) = room_event_cache.subscribe().await.unwrap();
assert!(events.is_empty());
// When sending multiple times the same read marker event,…
let read_marker_event = Raw::from_json_string(
json!({
"content": {
"event_id": "$crepe:saucisse.bzh"
},
"room_id": "!galette:saucisse.bzh",
"type": "m.fully_read"
})
.to_string(),
)
.unwrap();
let account_data = vec![read_marker_event; 100];
room_event_cache
.inner
.handle_joined_room_update(JoinedRoomUpdate { account_data, ..Default::default() })
.await
.unwrap();
// … there's only one read marker update.
assert_matches!(
stream.recv().await.unwrap(),
RoomEventCacheUpdate::MoveReadMarkerTo { .. }
);
assert!(stream.recv().now_or_never().is_none());
}
#[async_test]
async fn test_get_event_by_id() {
let client = logged_in_client(None).await;
let room_id1 = room_id!("!galette:saucisse.bzh");
let room_id2 = room_id!("!crepe:saucisse.bzh");
let event_cache = client.event_cache();
event_cache.subscribe().unwrap();
// Insert two rooms with a few events.
let f = EventFactory::new().room(room_id1).sender(user_id!("@ben:saucisse.bzh"));
let eid1 = event_id!("$1");
let eid2 = event_id!("$2");
let eid3 = event_id!("$3");
let joined_room_update1 = JoinedRoomUpdate {
timeline: Timeline {
events: vec![
f.text_msg("hey").event_id(eid1).into(),
f.text_msg("you").event_id(eid2).into(),
],
..Default::default()
},
..Default::default()
};
let joined_room_update2 = JoinedRoomUpdate {
timeline: Timeline {
events: vec![f.text_msg("bjr").event_id(eid3).into()],
..Default::default()
},
..Default::default()
};
let mut updates = RoomUpdates::default();
updates.join.insert(room_id1.to_owned(), joined_room_update1);
updates.join.insert(room_id2.to_owned(), joined_room_update2);
// Have the event cache handle them.
event_cache.inner.handle_room_updates(updates).await.unwrap();
// Now retrieve all the events one by one.
let found1 = event_cache.event(eid1).await.unwrap();
assert_event_matches_msg(&found1, "hey");
let found2 = event_cache.event(eid2).await.unwrap();
assert_event_matches_msg(&found2, "you");
let found3 = event_cache.event(eid3).await.unwrap();
assert_event_matches_msg(&found3, "bjr");
// An unknown event won't be found.
assert!(event_cache.event(event_id!("$unknown")).await.is_none());
// Can also find events in a single room.
client.base_client().get_or_create_room(room_id1, matrix_sdk_base::RoomState::Joined);
let room1 = client.get_room(room_id1).unwrap();
let (room_event_cache, _drop_handles) = room1.event_cache().await.unwrap();
let found1 = room_event_cache.event(eid1).await.unwrap();
assert_event_matches_msg(&found1, "hey");
let found2 = room_event_cache.event(eid2).await.unwrap();
assert_event_matches_msg(&found2, "you");
// Retrieving the event with id3 from the room which doesn't contain it will
// fail…
assert!(room_event_cache.event(eid3).await.is_none());
// …but it doesn't fail at the client-wide level.
assert!(event_cache.event(eid3).await.is_some());
}
#[async_test]
async fn test_save_event_and_clear() {
let client = logged_in_client(None).await;
let room_id = room_id!("!galette:saucisse.bzh");
let event_cache = client.event_cache();
event_cache.subscribe().unwrap();
let f = EventFactory::new().room(room_id).sender(user_id!("@ben:saucisse.bzh"));
let event_id = event_id!("$1");
client.base_client().get_or_create_room(room_id, matrix_sdk_base::RoomState::Joined);
let room = client.get_room(room_id).unwrap();
let (room_event_cache, _drop_handles) = room.event_cache().await.unwrap();
room_event_cache.save_event(f.text_msg("hey there").event_id(event_id).into()).await;
// Retrieving the event at the room-wide cache works.
assert!(room_event_cache.event(event_id).await.is_some());
// Also at the client level.
assert!(event_cache.event(event_id).await.is_some());
event_cache.empty_immutable_cache().await;
// After clearing, both fail to find the event.
assert!(room_event_cache.event(event_id).await.is_none());
assert!(event_cache.event(event_id).await.is_none());
}
}