From 25505d6e8aaeb1e5dddd3e32e5b4afe28317126b Mon Sep 17 00:00:00 2001
From: Benoit Marty <benoit@matrix.org>
Date: Tue, 15 Sep 2026 10:00:43 +0200
Subject: [PATCH] Do not automatically restart the sync in case it is
 Terminated. Also simplify the computation of the backoff delay.

---
 .../appnav/session/SyncOrchestrator.kt        | 25 ++++++++++---------
 .../android/appnav/SyncOrchestratorTest.kt    | 25 +++----------------
 2 files changed, 16 insertions(+), 34 deletions(-)

diff --git a/appnav/src/main/kotlin/io/element/android/appnav/session/SyncOrchestrator.kt b/appnav/src/main/kotlin/io/element/android/appnav/session/SyncOrchestrator.kt
index 786365b7be..9863f75410 100644
--- a/appnav/src/main/kotlin/io/element/android/appnav/session/SyncOrchestrator.kt
+++ b/appnav/src/main/kotlin/io/element/android/appnav/session/SyncOrchestrator.kt
@@ -138,7 +138,7 @@ class SyncOrchestrator(
                 SyncStateAction.StopSync
             } else if (syncState == SyncState.Idle && isAppActive && isNetworkAvailable) {
                 SyncStateAction.StartSync
-            } else if (syncState.isDead() && isAppActive && isNetworkAvailable) {
+            } else if (syncState == SyncState.Error && isAppActive && isNetworkAvailable) {
                 // The sync service has given up, for instance because the homeserver has expired our sliding sync
                 // session and answered 400 M_UNKNOWN_POS. Nothing else will ever restart it, so do it from here,
                 // else the application is stuck until its data is cleared.
@@ -184,8 +184,18 @@ class SyncOrchestrator(
 @VisibleForTesting
 internal val FIRST_RESTART_DELAY = 1.seconds
 
+/**
+ * Exponential backoff, from [FIRST_RESTART_DELAY], doubling on every attempt, up to [FIRST_RESTART_DELAY * 32].
+ */
 @VisibleForTesting
-internal val MAX_RESTART_DELAY = 30.seconds
+internal val RESTART_BACKOFF_DELAYS = listOf(
+    FIRST_RESTART_DELAY,
+    FIRST_RESTART_DELAY * 2,
+    FIRST_RESTART_DELAY * 4,
+    FIRST_RESTART_DELAY * 8,
+    FIRST_RESTART_DELAY * 16,
+    FIRST_RESTART_DELAY * 32,
+)
 
 /**
  * Duration during which the sync service has to stay running before the restart backoff is reset.
@@ -193,17 +203,8 @@ internal val MAX_RESTART_DELAY = 30.seconds
 @VisibleForTesting
 internal val RESTART_BACKOFF_RESET_DELAY = 30.seconds
 
-/**
- * Return true if the sync service has stopped and will not restart by itself.
- */
-private fun SyncState.isDead() = this == SyncState.Error || this == SyncState.Terminated
-
-/**
- * Exponential backoff, from [FIRST_RESTART_DELAY], doubling on every attempt, up to [MAX_RESTART_DELAY].
- */
 private fun restartDelay(attempt: Int): Duration {
-    val exponent = attempt.coerceIn(0, 5)
-    return (FIRST_RESTART_DELAY * (1 shl exponent)).coerceAtMost(MAX_RESTART_DELAY)
+    return RESTART_BACKOFF_DELAYS[attempt.coerceIn(0, RESTART_BACKOFF_DELAYS.lastIndex)]
 }
 
 private enum class SyncStateAction {
diff --git a/appnav/src/test/kotlin/io/element/android/appnav/SyncOrchestratorTest.kt b/appnav/src/test/kotlin/io/element/android/appnav/SyncOrchestratorTest.kt
index 9475399a85..af53c68b3d 100644
--- a/appnav/src/test/kotlin/io/element/android/appnav/SyncOrchestratorTest.kt
+++ b/appnav/src/test/kotlin/io/element/android/appnav/SyncOrchestratorTest.kt
@@ -9,7 +9,7 @@
 package io.element.android.appnav
 
 import io.element.android.appnav.session.FIRST_RESTART_DELAY
-import io.element.android.appnav.session.MAX_RESTART_DELAY
+import io.element.android.appnav.session.RESTART_BACKOFF_DELAYS
 import io.element.android.appnav.session.RESTART_BACKOFF_RESET_DELAY
 import io.element.android.appnav.session.SyncOrchestrator
 import io.element.android.features.networkmonitor.api.NetworkStatus
@@ -441,25 +441,6 @@ class SyncOrchestratorTest {
         startSyncRecorder.assertions().isCalledOnce()
     }
 
-    @Test
-    fun `when the sync service is terminated, it will be restarted after a delay`() = runTest {
-        val startSyncRecorder = lambdaRecorder<Result<Unit>> { Result.success(Unit) }
-        val syncService = FakeSyncService(initialSyncState = SyncState.Terminated).apply {
-            startSyncLambda = startSyncRecorder
-        }
-        val syncOrchestrator = createSyncOrchestrator(
-            matrixClient = FakeMatrixClient(syncService = syncService),
-            networkMonitor = FakeNetworkMonitor(initialStatus = NetworkStatus.Connected),
-            appForegroundStateService = FakeAppForegroundStateService(initialForegroundValue = true),
-        )
-
-        // We start observing
-        syncOrchestrator.observeStates()
-
-        advanceTimeBy(FIRST_RESTART_DELAY * 2)
-        startSyncRecorder.assertions().isCalledOnce()
-    }
-
     @Test
     fun `when the sync service keeps dying, the delay between the restarts increases`() = runTest {
         val startSyncRecorder = lambdaRecorder<Result<Unit>> { Result.success(Unit) }
@@ -538,7 +519,7 @@ class SyncOrchestratorTest {
         // We start observing
         syncOrchestrator.observeStates()
 
-        advanceTimeBy(MAX_RESTART_DELAY * 2)
+        advanceTimeBy(RESTART_BACKOFF_DELAYS.last() * 2)
         startSyncRecorder.assertions().isNeverCalled()
     }
 
@@ -557,7 +538,7 @@ class SyncOrchestratorTest {
         // We start observing
         syncOrchestrator.observeStates()
 
-        advanceTimeBy(MAX_RESTART_DELAY * 2)
+        advanceTimeBy(RESTART_BACKOFF_DELAYS.last() * 2)
         startSyncRecorder.assertions().isNeverCalled()
     }