Backfill room history on startup

Cargo.toml

@@ -50,7 +50,8 @@ signal-hook = "0.3.17"
 smallvec = "1.11.1"
 
 # Matrix
-eyeball-im = "0.4.1" # immutable data structures returned by matrix-sdk-ui
+eyeball = "0.8.7" # data structures observer returned by matrix-sdk-ui
+eyeball-im = "0.4.1" # immutable data structures observer returned by matrix-sdk-ui
 imbl = "2.0" # ditto
 matrix-sdk = { git = "https://github.com/matrix-org/matrix-rust-sdk.git", rev = "91e7f2f7224b8ada17ab639d60da10dad98aeaf9", features = ["eyre", "markdown"] }
 matrix-sdk-ui = { git = "https://github.com/matrix-org/matrix-rust-sdk.git", rev = "91e7f2f7224b8ada17ab639d60da10dad98aeaf9" }

src/buffers/mod.rs

@@ -28,6 +28,10 @@ pub trait Buffer: Send {
   fn short_name(&self) -> String;
   async fn poll_updates(&mut self) {}
   fn content(&self) -> Vec<ratatui::text::Text>; // TODO: make this lazy, only the last few are used
+  /// Called when the user is being showned the oldest items this buffer returned.
+  ///
+  /// This should return immediately, not waiting for anything to be loaded.
+  fn request_back_pagination(&self, num: u16) {}
 }
 
 pub struct Buffers {
@@ -69,4 +73,11 @@ impl Buffers {
       .get(self.active_index)
       .expect("Active buffer index does not exist")
   }
+
+  pub fn active_buffer_mut(&mut self) -> &mut Box<dyn Buffer> {
+    self
+      .buffers
+      .get_mut(self.active_index)
+      .expect("Active buffer index does not exist")
+  }
 }

src/buffers/room.rs

@@ -14,8 +14,8 @@
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  */
 
-use std::pin::Pin;
-use std::sync::Arc;
+use std::sync::atomic::{AtomicU16, Ordering};
+use std::sync::{Arc, OnceLock};
 
 use color_eyre::eyre::{eyre, Result};
 use eyeball_im::VectorDiff;
@@ -25,22 +25,31 @@ use matrix_sdk::async_trait;
 use matrix_sdk::ruma::OwnedRoomId;
 use matrix_sdk::Client;
 use matrix_sdk::Room;
-use matrix_sdk_ui::timeline::{RoomExt, Timeline, TimelineItem};
+use matrix_sdk_ui::timeline::{
+  BackPaginationStatus, PaginationOptions, RoomExt, Timeline, TimelineItem,
+};
 use ratatui::text::Text;
 use smallvec::SmallVec;
-use tokio::pin;
 
 use super::Buffer;
 
 pub struct SingleClientRoomBuffer {
+  room_id: OwnedRoomId,
   client: Client,
   items: imbl::vector::Vector<String>,
   // TODO: get rid of this trait object, we know it's matrix_sdk_ui::timeline::TimelineStream
-  stream: Box<dyn Stream<Item = Vec<VectorDiff<Arc<TimelineItem>>>> + Send + Unpin>,
+  stream: Box<dyn Stream<Item = Vec<VectorDiff<Arc<TimelineItem>>>> + Send + Sync + Unpin>,
+  timeline: Arc<Timeline>,
+  back_pagination_request: AtomicU16,
 }
 
 impl SingleClientRoomBuffer {
   async fn poll_updates(&mut self) {
+    let back_pagination_request = self.back_pagination_request.swap(0, Ordering::Relaxed);
+    if back_pagination_request > 0 {
+      // TODO: run this concurrently with stream.next() below
+      self.spawn_back_pagination(back_pagination_request).await;
+    }
     self.items.extend(
       self
         .stream
@@ -49,6 +58,30 @@ impl SingleClientRoomBuffer {
         .map(|change| format!("New items: {:#?}", change)),
     );
   }
+
+  async fn spawn_back_pagination(&self, num: u16) {
+    let room_id = self.room_id.clone();
+    let timeline = self.timeline.clone();
+    let mut back_pagination_status = timeline.back_pagination_status();
+    if back_pagination_status.get() == BackPaginationStatus::Paginating {
+      // We are already waiting for a backfill from the server
+      return;
+    }
+    tokio::spawn(async move {
+      tracing::info!("Starting pagination for {}", room_id);
+      timeline
+        .paginate_backwards(matrix_sdk_ui::timeline::PaginationOptions::until_num_items(
+          num, num,
+        ))
+        .await
+        .unwrap_or_else(|e| tracing::error!("Failed to paginate {} backward: {}", room_id, e));
+      tracing::info!("Ended pagination for {}", room_id);
+    });
+
+    // Wait for the task we just spawned to change the status, so we don't risk starting
+    // a new one in the meantime
+    back_pagination_status.next().await;
+  }
 }
 
 pub struct RoomBuffer {
@@ -75,7 +108,7 @@ impl RoomBuffer {
   }
 
   pub async fn add_client(&mut self, client: Client) -> Result<()> {
-    let (items, stream) = client
+    let timeline = client
       .get_room(&self.room_id)
       .ok_or_else(|| {
         tracing::error!(
@@ -88,21 +121,23 @@ impl RoomBuffer {
       })?
       .timeline_builder()
       .build()
-      .await
-      .subscribe_batched()
       .await;
+    let (items, stream) = timeline.subscribe_batched().await;
     tracing::info!(
       "Added client for {}, initial items: {:?}",
       self.room_id,
       items
     );
     self.buffers.push(SingleClientRoomBuffer {
+      room_id: self.room_id.clone(),
       client,
+      timeline: Arc::new(timeline),
       items: items // FIXME: it's always empty. why?
         .into_iter()
         .map(|item| format!("Initial item: {:#?}", item))
         .collect(),
       stream: Box::new(stream),
+      back_pagination_request: AtomicU16::new(0),
     });
     Ok(())
   }
@@ -132,7 +167,17 @@ impl Buffer for RoomBuffer {
       .unwrap_or_else(|| panic!("No sub-buffer for {}", self.room_id))
       .items
       .iter()
-      .map(|line|Text::raw(line))
+      .map(|line| Text::raw(line))
       .collect()
   }
+
+  fn request_back_pagination(&self, num: u16) {
+    // TODO: pick a client at random instead of just the first one, etc.
+    self
+      .buffers
+      .first()
+      .unwrap_or_else(|| panic!("No sub-buffer for {}", self.room_id))
+      .back_pagination_request
+      .fetch_max(num, Ordering::Relaxed);
+  }
 }

src/components/backlog.rs

@@ -34,7 +34,8 @@ impl Component for Backlog {
     let mut text_area = block.inner(area);
     block.render(area, frame.buffer_mut());
 
-    let mut items = buffers.active_buffer().content();
+    let active_buffer = buffers.active_buffer();
+    let mut items = active_buffer.content();
     items.reverse();
     for item in items {
       let widget = BottomAlignedParagraph::new(item);
@@ -42,6 +43,12 @@ impl Component for Backlog {
       assert!(area.height >= height, "{:?} {}", area, height);
       text_area.height -= height; // Remove lines at the bottom used by this paragraph
     }
+
+    // If there is empty room on screen, ask the buffer to fetch more backlog if it can
+    if text_area.height > 0 {
+      active_buffer.request_back_pagination(100);
+    }
+
     Ok(())
   }
 }