From 108174e04036bf59a1d3cedee30df9c526f46d15 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?K=C3=A9vin=20Commaille?= <zecakeh@tedomum.fr>
Date: Thu, 24 Apr 2025 09:40:39 +0200
Subject: [PATCH] session: Sleep between failed sync attempts

---
 src/session/model/session.rs | 68 +++++++++++++++++++++++++++---------
 1 file changed, 52 insertions(+), 16 deletions(-)

diff --git a/src/session/model/session.rs b/src/session/model/session.rs
index cb870c89..ab1f77c7 100644
--- a/src/session/model/session.rs
+++ b/src/session/model/session.rs
@@ -13,7 +13,7 @@ use ruma::{
     },
     assign,
 };
-use tokio::task::AbortHandle;
+use tokio::{task::AbortHandle, time::sleep};
 use tokio_stream::wrappers::BroadcastStream;
 use tracing::{debug, error, info};
 
@@ -38,7 +38,13 @@ use crate::{
 const SESSION_PROFILE_KEY: &str = "session_profile";
 /// The number of consecutive missed synchronizations before the session is
 /// marked as offline.
-const MISSED_SYNC_MAX_COUNT: u8 = 3;
+///
+/// Note that this is set to `2`, but the count begins at `0` so this would
+/// match the third missed synchronization.
+const MISSED_SYNC_OFFLINE_COUNT: usize = 2;
+/// The delays in seconds to wait for when a sync fails, depending on the number
+/// of missed attempts.
+const MISSED_SYNC_DELAYS: &[u64] = &[1, 5, 10, 20, 30];
 
 /// The state of the session.
 #[derive(Debug, Default, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, glib::Enum)]
@@ -104,8 +110,8 @@ mod imp {
         homeserver_reachable_source: RefCell<Option<glib::SourceId>>,
         /// The number of missed synchonizations in a row.
         ///
-        /// Capped at `MISSED_SYNC_MAX_COUNT - 1`.
-        missed_sync_count: Cell<u8>,
+        /// Capped at `MISSED_SYNC_DELAYS.len() - 1`.
+        missed_sync_count: Cell<usize>,
     }
 
     #[glib::object_subclass]
@@ -272,6 +278,8 @@ mod imp {
                         #[weak(rename_to = imp)]
                         self,
                         move || {
+                            imp.homeserver_reachable_source.take();
+
                             spawn!(async move {
                                 imp.update_homeserver_reachable().await;
                             });
@@ -429,13 +437,24 @@ mod imp {
                 while let Some(response) = sync_stream.next().await {
                     let obj_weak = obj_weak.clone();
                     let ctx = glib::MainContext::default();
-                    ctx.spawn(async move {
-                        spawn!(async move {
-                            if let Some(obj) = obj_weak.upgrade() {
-                                obj.imp().handle_sync_response(response);
-                            }
-                        });
-                    });
+                    let delay = ctx
+                        .spawn(async move {
+                            spawn!(async move {
+                                if let Some(obj) = obj_weak.upgrade() {
+                                    obj.imp().handle_sync_response(response)
+                                } else {
+                                    None
+                                }
+                            })
+                            .await
+                            .expect("task was not aborted")
+                        })
+                        .await
+                        .expect("task was not aborted");
+
+                    if let Some(delay) = delay {
+                        sleep(delay).await;
+                    }
                 }
             })
             .abort_handle();
@@ -444,7 +463,13 @@ mod imp {
         }
 
         /// Handle the response received via sync.
-        fn handle_sync_response(&self, response: Result<SyncResponse, matrix_sdk::Error>) {
+        ///
+        /// Returns the delay to wait for before making the next sync, if
+        /// necessary.
+        fn handle_sync_response(
+            &self,
+            response: Result<SyncResponse, matrix_sdk::Error>,
+        ) -> Option<Duration> {
             let obj = self.obj();
             let session_id = obj.session_id();
             debug!(session = session_id, "Received sync response");
@@ -460,16 +485,27 @@ mod imp {
 
                     self.set_offline(false);
                     self.missed_sync_count.set(0);
+
+                    None
                 }
                 Err(error) => {
-                    let missed_sync_count = self.missed_sync_count.get() + 1;
+                    let missed_sync_count = self.missed_sync_count.get();
 
-                    if missed_sync_count >= MISSED_SYNC_MAX_COUNT {
+                    // If there are too many failed attempts, mark the session as offline.
+                    if missed_sync_count == MISSED_SYNC_OFFLINE_COUNT {
                         self.set_offline(true);
-                    } else {
-                        self.missed_sync_count.set(missed_sync_count);
                     }
+
+                    // Increase the count of missed syncs, if we have not reached the maximum value.
+                    if missed_sync_count < 4 {
+                        self.missed_sync_count.set(missed_sync_count + 1);
+                    }
+
                     error!(session = session_id, "Could not perform sync: {error}");
+
+                    // Sleep a little between attempts.
+                    let delay = MISSED_SYNC_DELAYS[missed_sync_count];
+                    Some(Duration::from_secs(delay))
                 }
             }
         }