matrix_sdk/event_cache/pagination.rs
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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.
//! A sub-object for running pagination tasks on a given room.
use std::{future::Future, ops::ControlFlow, sync::Arc, time::Duration};
use eyeball::Subscriber;
use matrix_sdk_base::deserialized_responses::SyncTimelineEvent;
use matrix_sdk_common::linked_chunk::ChunkContent;
use tokio::time::timeout;
use tracing::{debug, instrument, trace};
use super::{
paginator::{PaginationResult, PaginatorState},
room::{
events::{Gap, RoomEvents},
RoomEventCacheInner,
},
BackPaginationOutcome, Result,
};
/// An API object to run pagination queries on a [`super::RoomEventCache`].
///
/// Can be created with [`super::RoomEventCache::pagination()`].
#[allow(missing_debug_implementations)]
pub struct RoomPagination {
pub(super) inner: Arc<RoomEventCacheInner>,
}
impl RoomPagination {
/// Starts a back-pagination for the requested number of events.
///
/// This automatically takes care of waiting for a pagination token from
/// sync, if we haven't done that before.
///
/// The `until` argument is an async closure that returns a [`ControlFlow`]
/// to decide whether a new pagination must be run or not. It's helpful when
/// the server replies with e.g. a certain set of events, but we would like
/// more, or the event we are looking for isn't part of this set: in this
/// case, `until` returns [`ControlFlow::Continue`], otherwise it returns
/// [`ControlFlow::Break`]. `until` receives [`BackPaginationOutcome`] as
/// its sole argument.
///
/// # Errors
///
/// It may return an error if the pagination token used during
/// back-pagination has disappeared while we started the pagination. In
/// that case, it's desirable to call the method again.
///
/// # Example
///
/// To do a single run:
///
/// ```rust
/// use std::ops::ControlFlow;
///
/// use matrix_sdk::event_cache::{
/// BackPaginationOutcome,
/// RoomPagination,
/// TimelineHasBeenResetWhilePaginating
/// };
///
/// # async fn foo(room_pagination: RoomPagination) {
/// let result = room_pagination.run_backwards(
/// 42,
/// |BackPaginationOutcome { events, reached_start },
/// _timeline_has_been_reset: TimelineHasBeenResetWhilePaginating| async move {
/// // Do something with `events` and `reached_start` maybe?
/// let _ = events;
/// let _ = reached_start;
///
/// ControlFlow::Break(())
/// }
/// ).await;
/// # }
#[instrument(skip(self, until))]
pub async fn run_backwards<Until, Break, UntilFuture>(
&self,
batch_size: u16,
mut until: Until,
) -> Result<Break>
where
Until: FnMut(BackPaginationOutcome, TimelineHasBeenResetWhilePaginating) -> UntilFuture,
UntilFuture: Future<Output = ControlFlow<Break, ()>>,
{
let mut timeline_has_been_reset = TimelineHasBeenResetWhilePaginating::No;
loop {
if let Some(outcome) = self.run_backwards_impl(batch_size).await? {
match until(outcome, timeline_has_been_reset).await {
ControlFlow::Continue(()) => {
trace!("back-pagination continues");
timeline_has_been_reset = TimelineHasBeenResetWhilePaginating::No;
continue;
}
ControlFlow::Break(value) => return Ok(value),
}
}
timeline_has_been_reset = TimelineHasBeenResetWhilePaginating::Yes;
debug!("back-pagination has been internally restarted because of a timeline reset.");
}
}
async fn run_backwards_impl(&self, batch_size: u16) -> Result<Option<BackPaginationOutcome>> {
const DEFAULT_WAIT_FOR_TOKEN_DURATION: Duration = Duration::from_secs(3);
let prev_token = self.get_or_wait_for_token(Some(DEFAULT_WAIT_FOR_TOKEN_DURATION)).await;
let paginator = &self.inner.paginator;
paginator.set_idle_state(PaginatorState::Idle, prev_token.clone(), None)?;
// Run the actual pagination.
let PaginationResult { events, hit_end_of_timeline: reached_start } =
paginator.paginate_backward(batch_size.into()).await?;
// Make sure the `RoomEvents` isn't updated while we are saving events from
// backpagination.
let mut state = self.inner.state.write().await;
// Check that the previous token still exists; otherwise it's a sign that the
// room's timeline has been cleared.
let gap_identifier = if let Some(token) = prev_token {
let gap_identifier = state.events().chunk_identifier(|chunk| {
matches!(chunk.content(), ChunkContent::Gap(Gap { ref prev_token }) if *prev_token == token)
});
// The method has been called with `token` but it doesn't exist in `RoomEvents`,
// it's an error.
if gap_identifier.is_none() {
return Ok(None);
}
gap_identifier
} else {
None
};
let prev_token = paginator.prev_batch_token().map(|prev_token| Gap { prev_token });
Ok(Some(state.with_events_mut(move |room_events| {
// Note: The chunk could be empty.
//
// If there's any event, they are presented in reverse order (i.e. the first one
// should be prepended first).
let sync_events = events
.iter()
// Reverse the order of the events as `/messages` has been called with `dir=b`
// (backward). The `RoomEvents` API expects the first event to be the oldest.
.rev()
.cloned()
.map(SyncTimelineEvent::from);
// There is a `token`/gap, let's replace it by new events!
if let Some(gap_identifier) = gap_identifier {
let new_position = {
// Replace the gap by new events.
let new_chunk = room_events
.replace_gap_at(sync_events, gap_identifier)
// SAFETY: we are sure that `gap_identifier` represents a valid
// `ChunkIdentifier` for a `Gap` chunk.
.expect("The `gap_identifier` must represent a `Gap`");
new_chunk.first_position()
};
// And insert a new gap if there is any `prev_token`.
if let Some(prev_token_gap) = prev_token {
room_events
.insert_gap_at(prev_token_gap, new_position)
// SAFETY: we are sure that `new_position` represents a valid
// `ChunkIdentifier` for an `Item` chunk.
.expect("The `new_position` must represent an `Item`");
}
trace!("replaced gap with new events from backpagination");
// TODO: implement smarter reconciliation later
//let _ = self.sender.send(RoomEventCacheUpdate::Prepend { events });
return BackPaginationOutcome { events, reached_start };
}
// There is no `token`/gap identifier. Let's assume we must prepend the new
// events.
let first_event_pos = room_events.events().next().map(|(item_pos, _)| item_pos);
match first_event_pos {
// Is there a first item? Insert at this position.
Some(first_event_pos) => {
if let Some(prev_token_gap) = prev_token {
room_events
.insert_gap_at(prev_token_gap, first_event_pos)
// SAFETY: The `first_event_pos` can only be an `Item` chunk, it's
// an invariant of `LinkedChunk`. Also, it can only represent a valid
// `ChunkIdentifier` as the data structure isn't modified yet.
.expect("`first_event_pos` must point to a valid `Item` chunk when inserting a gap");
}
room_events
.insert_events_at(sync_events, first_event_pos)
// SAFETY: The `first_event_pos` can only be an `Item` chunk, it's
// an invariant of `LinkedChunk`. The chunk it points to has not been
// removed.
.expect("The `first_event_pos` must point to a valid `Item` chunk when inserting events");
}
// There is no first item. Let's simply push.
None => {
if let Some(prev_token_gap) = prev_token {
room_events.push_gap(prev_token_gap);
}
room_events.push_events(sync_events);
}
}
BackPaginationOutcome { events, reached_start }
}).await?))
}
/// Get the latest pagination token, as stored in the room events linked
/// list, or wait for it for the given amount of time.
///
/// It will only wait if we *never* saw an initial previous-batch token.
/// Otherwise, it will immediately skip.
#[doc(hidden)]
pub async fn get_or_wait_for_token(&self, wait_time: Option<Duration>) -> Option<String> {
fn get_latest(events: &RoomEvents) -> Option<String> {
events.rchunks().find_map(|chunk| match chunk.content() {
ChunkContent::Gap(gap) => Some(gap.prev_token.clone()),
ChunkContent::Items(..) => None,
})
}
{
// Scope for the lock guard.
let state = self.inner.state.read().await;
// Fast-path: we do have a previous-batch token already.
if let Some(found) = get_latest(state.events()) {
return Some(found);
}
// If we've already waited for an initial previous-batch token before,
// immediately abort.
if state.waited_for_initial_prev_token {
return None;
}
}
// If the caller didn't set a wait time, return none early.
let wait_time = wait_time?;
// Otherwise, wait for a notification that we received a previous-batch token.
// Note the state lock is released while doing so, allowing other tasks to write
// into the linked chunk.
let _ = timeout(wait_time, self.inner.pagination_batch_token_notifier.notified()).await;
let mut state = self.inner.state.write().await;
let token = get_latest(state.events());
state.waited_for_initial_prev_token = true;
token
}
/// Returns a subscriber to the pagination status used for the
/// back-pagination integrated to the event cache.
pub fn status(&self) -> Subscriber<PaginatorState> {
self.inner.paginator.state()
}
/// Returns whether we've hit the start of the timeline.
///
/// This is true if, and only if, we didn't have a previous-batch token and
/// running backwards pagination would be useless.
pub fn hit_timeline_start(&self) -> bool {
self.inner.paginator.hit_timeline_start()
}
/// Returns whether we've hit the end of the timeline.
///
/// This is true if, and only if, we didn't have a next-batch token and
/// running forwards pagination would be useless.
pub fn hit_timeline_end(&self) -> bool {
self.inner.paginator.hit_timeline_end()
}
}
/// A type representing whether the timeline has been reset.
#[derive(Debug)]
pub enum TimelineHasBeenResetWhilePaginating {
/// The timeline has been reset.
Yes,
/// The timeline has not been reset.
No,
}
#[cfg(test)]
mod tests {
// Those tests require time to work, and it does not on wasm32.
#[cfg(not(target_arch = "wasm32"))]
mod time_tests {
use std::time::{Duration, Instant};
use matrix_sdk_base::RoomState;
use matrix_sdk_test::{
async_test, event_factory::EventFactory, sync_timeline_event, ALICE,
};
use ruma::room_id;
use tokio::{spawn, time::sleep};
use crate::{
deserialized_responses::SyncTimelineEvent, event_cache::room::events::Gap,
test_utils::logged_in_client,
};
#[async_test]
async fn test_wait_no_pagination_token() {
let client = logged_in_client(None).await;
let room_id = room_id!("!galette:saucisse.bzh");
client.base_client().get_or_create_room(room_id, RoomState::Joined);
let event_cache = client.event_cache();
event_cache.subscribe().unwrap();
let (room_event_cache, _drop_handlers) = event_cache.for_room(room_id).await.unwrap();
// When I only have events in a room,
room_event_cache
.inner
.state
.write()
.await
.with_events_mut(|events| {
events.push_events([SyncTimelineEvent::new(sync_timeline_event!({
"sender": "b@z.h",
"type": "m.room.message",
"event_id": "$ida",
"origin_server_ts": 12344446,
"content": { "body":"yolo", "msgtype": "m.text" },
}))])
})
.await
.unwrap();
let pagination = room_event_cache.pagination();
// If I don't wait for the backpagination token,
let found = pagination.get_or_wait_for_token(None).await;
// Then I don't find it.
assert!(found.is_none());
// Reset waited_for_initial_prev_token state.
pagination.inner.state.write().await.reset().await.unwrap();
// If I wait for a back-pagination token for 0 seconds,
let before = Instant::now();
let found = pagination.get_or_wait_for_token(Some(Duration::default())).await;
let waited = before.elapsed();
// then I don't get any,
assert!(found.is_none());
// and I haven't waited long.
assert!(waited.as_secs() < 1);
// Reset waited_for_initial_prev_token state.
pagination.inner.state.write().await.reset().await.unwrap();
// If I wait for a back-pagination token for 1 second,
let before = Instant::now();
let found = pagination.get_or_wait_for_token(Some(Duration::from_secs(1))).await;
let waited = before.elapsed();
// then I still don't get any.
assert!(found.is_none());
// and I've waited a bit.
assert!(waited.as_secs() < 2);
assert!(waited.as_secs() >= 1);
}
#[async_test]
async fn test_wait_for_pagination_token_already_present() {
let client = logged_in_client(None).await;
let room_id = room_id!("!galette:saucisse.bzh");
client.base_client().get_or_create_room(room_id, RoomState::Joined);
let event_cache = client.event_cache();
event_cache.subscribe().unwrap();
let (room_event_cache, _drop_handlers) = event_cache.for_room(room_id).await.unwrap();
let expected_token = "old".to_owned();
// When I have events and multiple gaps, in a room,
{
room_event_cache
.inner
.state
.write()
.await
.with_events_mut(|room_events| {
room_events.push_gap(Gap { prev_token: expected_token.clone() });
room_events.push_events([SyncTimelineEvent::new(sync_timeline_event!({
"sender": "b@z.h",
"type": "m.room.message",
"event_id": "$ida",
"origin_server_ts": 12344446,
"content": { "body":"yolo", "msgtype": "m.text" },
}))]);
})
.await
.unwrap();
}
let pagination = room_event_cache.pagination();
// If I don't wait for a back-pagination token,
let found = pagination.get_or_wait_for_token(None).await;
// Then I get it.
assert_eq!(found.as_ref(), Some(&expected_token));
// If I wait for a back-pagination token for 0 seconds,
let before = Instant::now();
let found = pagination.get_or_wait_for_token(Some(Duration::default())).await;
let waited = before.elapsed();
// then I do get one.
assert_eq!(found.as_ref(), Some(&expected_token));
// and I haven't waited long.
assert!(waited.as_millis() < 100);
// If I wait for a back-pagination token for 1 second,
let before = Instant::now();
let found = pagination.get_or_wait_for_token(Some(Duration::from_secs(1))).await;
let waited = before.elapsed();
// then I do get one.
assert_eq!(found, Some(expected_token));
// and I haven't waited long.
assert!(waited.as_millis() < 100);
}
#[async_test]
async fn test_wait_for_late_pagination_token() {
let client = logged_in_client(None).await;
let room_id = room_id!("!galette:saucisse.bzh");
client.base_client().get_or_create_room(room_id, 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 expected_token = "old".to_owned();
let before = Instant::now();
let cloned_expected_token = expected_token.clone();
let cloned_room_event_cache = room_event_cache.clone();
let insert_token_task = spawn(async move {
// If a backpagination token is inserted after 400 milliseconds,
sleep(Duration::from_millis(400)).await;
cloned_room_event_cache
.inner
.state
.write()
.await
.with_events_mut(|events| {
events.push_gap(Gap { prev_token: cloned_expected_token })
})
.await
.unwrap();
});
let pagination = room_event_cache.pagination();
// Then first I don't get it (if I'm not waiting,)
let found = pagination.get_or_wait_for_token(None).await;
assert!(found.is_none());
// And if I wait for the back-pagination token for 600ms,
let found = pagination.get_or_wait_for_token(Some(Duration::from_millis(600))).await;
let waited = before.elapsed();
// then I do get one eventually.
assert_eq!(found, Some(expected_token));
// and I have waited between ~400 and ~1000 milliseconds.
assert!(waited.as_secs() < 1);
assert!(waited.as_millis() >= 400);
// The task succeeded.
insert_token_task.await.unwrap();
}
#[async_test]
async fn test_get_latest_token() {
let client = logged_in_client(None).await;
let room_id = room_id!("!galette:saucisse.bzh");
client.base_client().get_or_create_room(room_id, 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 old_token = "old".to_owned();
let new_token = "new".to_owned();
// Assuming a room event cache that contains both an old and a new pagination
// token, and events in between,
room_event_cache
.inner
.state
.write()
.await
.with_events_mut(|events| {
let f = EventFactory::new().room(room_id).sender(*ALICE);
// This simulates a valid representation of a room: first group of gap+events
// were e.g. restored from the cache; second group of gap+events was received
// from a subsequent sync.
events.push_gap(Gap { prev_token: old_token });
events.push_events([f.text_msg("oldest from cache").into()]);
events.push_gap(Gap { prev_token: new_token.clone() });
events.push_events([f.text_msg("sync'd gappy timeline").into()]);
})
.await
.unwrap();
let pagination = room_event_cache.pagination();
// Retrieving the pagination token will return the most recent one, not the old
// one.
let found = pagination.get_or_wait_for_token(None).await;
assert_eq!(found, Some(new_token));
}
}
}