matrix_sdk_ui/timeline/
pagination.rs

1// Copyright 2023 The Matrix.org Foundation C.I.C.
2//
3// Licensed under the Apache License, Version 2.0 (the "License");
4// you may not use this file except in compliance with the License.
5// You may obtain a copy of the License at
6//
7//     http://www.apache.org/licenses/LICENSE-2.0
8//
9// Unless required by applicable law or agreed to in writing, software
10// distributed under the License is distributed on an "AS IS" BASIS,
11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12// See the License for the specific language governing permissions and
13// limitations under the License.
14
15use async_rx::StreamExt as _;
16use async_stream::stream;
17use futures_core::Stream;
18use futures_util::{StreamExt as _, pin_mut};
19use matrix_sdk::event_cache::{self, EventCacheError, RoomPaginationStatus};
20use tracing::{instrument, warn};
21
22use super::Error;
23use crate::timeline::{PaginationError::NotSupported, controller::TimelineFocusKind};
24
25impl super::Timeline {
26    /// Add more events to the start of the timeline.
27    ///
28    /// Returns whether we hit the start of the timeline.
29    #[instrument(skip_all, fields(room_id = ?self.room().room_id()))]
30    pub async fn paginate_backwards(&self, mut num_events: u16) -> Result<bool, Error> {
31        match self.controller.focus() {
32            TimelineFocusKind::Live { .. } => {
33                match self.controller.live_lazy_paginate_backwards(num_events).await {
34                    Some(needed_num_events) => {
35                        num_events = needed_num_events.try_into().expect(
36                            "failed to cast `needed_num_events` (`usize`) into `num_events` (`usize`)",
37                        );
38                    }
39                    None => {
40                        // We could adjust the skip count to a lower value, while passing the
41                        // requested number of events. We *may* have reached
42                        // the start of the timeline, but since
43                        // we're fulfilling the caller's request, assume it's not the case and
44                        // return false here. A subsequent call will go to
45                        // the `Some()` arm of this match, and cause a call
46                        // to the event cache's pagination.
47                        return Ok(false);
48                    }
49                }
50
51                Ok(self.live_paginate_backwards(num_events).await?)
52            }
53            TimelineFocusKind::Event { .. } => {
54                Ok(self.controller.focused_paginate_backwards(num_events).await?)
55            }
56            TimelineFocusKind::Thread { root_event_id } => Ok(self
57                .event_cache
58                .paginate_thread_backwards(root_event_id.to_owned(), num_events)
59                .await?),
60            TimelineFocusKind::PinnedEvents { .. } => Err(Error::PaginationError(NotSupported)),
61        }
62    }
63
64    /// Add more events to the end of the timeline.
65    ///
66    /// Returns whether we hit the end of the timeline.
67    #[instrument(skip_all, fields(room_id = ?self.room().room_id()))]
68    pub async fn paginate_forwards(&self, num_events: u16) -> Result<bool, Error> {
69        if self.controller.is_live() {
70            Ok(true)
71        } else {
72            Ok(self.controller.focused_paginate_forwards(num_events).await?)
73        }
74    }
75
76    /// Paginate backwards in live mode.
77    ///
78    /// This can only be called when the timeline is in live mode, not focused
79    /// on a specific event.
80    ///
81    /// Returns whether we hit the start of the timeline.
82    async fn live_paginate_backwards(&self, batch_size: u16) -> event_cache::Result<bool> {
83        loop {
84            match self.event_cache.pagination().run_backwards_once(batch_size).await {
85                Ok(outcome) => {
86                    // As an exceptional contract, restart the back-pagination if we received an
87                    // empty chunk.
88                    if outcome.reached_start || !outcome.events.is_empty() {
89                        if outcome.reached_start {
90                            self.controller.insert_timeline_start_if_missing().await;
91                        }
92                        return Ok(outcome.reached_start);
93                    }
94                }
95
96                Err(EventCacheError::AlreadyBackpaginating) => {
97                    // Treat an already running pagination exceptionally, returning false so that
98                    // the caller retries later.
99                    warn!("Another pagination request is already happening, returning early");
100                    return Ok(false);
101                }
102
103                // Propagate other errors as such.
104                Err(err) => return Err(err),
105            }
106        }
107    }
108
109    /// Subscribe to the back-pagination status of a live timeline.
110    ///
111    /// This will return `None` if the timeline is in the focused mode.
112    ///
113    /// Note: this may send multiple Paginating/Idle sequences during a single
114    /// call to [`Self::paginate_backwards()`].
115    pub async fn live_back_pagination_status(
116        &self,
117    ) -> Option<(RoomPaginationStatus, impl Stream<Item = RoomPaginationStatus> + use<>)> {
118        if !self.controller.is_live() {
119            return None;
120        }
121
122        let pagination = self.event_cache.pagination();
123
124        let mut status = pagination.status();
125
126        let current_value = self.controller.map_pagination_status(status.next_now()).await;
127
128        let controller = self.controller.clone();
129        let stream = Box::pin(stream! {
130            let status_stream = status.dedup();
131
132            pin_mut!(status_stream);
133
134            while let Some(state) = status_stream.next().await {
135                let state = controller.map_pagination_status(state).await;
136
137                match state {
138                    RoomPaginationStatus::Idle { hit_timeline_start } => {
139                        if hit_timeline_start {
140                            controller.insert_timeline_start_if_missing().await;
141                        }
142                    }
143                    RoomPaginationStatus::Paginating => {}
144                }
145
146                yield state;
147            }
148        });
149
150        Some((current_value, stream))
151    }
152}
matrix_sdk_ui/timeline/pagination.rs

matrix_sdk_ui/timeline/
pagination.rs
