From 6a8230239b13b52d6b2622afdffd4d56726964c3 Mon Sep 17 00:00:00 2001
From: SpiritCroc <dev@spiritcroc.de>
Date: Mon, 21 Mar 2022 10:46:59 +0100
Subject: [PATCH] Avoid inconsistent timelines by db insertions before fully
 loaded chunk

---
 .../session/room/timeline/TimelineChunk.kt    | 25 +++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/room/timeline/TimelineChunk.kt b/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/room/timeline/TimelineChunk.kt
index 368979d73e..1bd541c2a9 100644
--- a/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/room/timeline/TimelineChunk.kt
+++ b/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/room/timeline/TimelineChunk.kt
@@ -430,6 +430,31 @@ internal class TimelineChunk(private val chunkEntity: ChunkEntity,
     private fun handleDatabaseChangeSet(results: RealmResults<TimelineEventEntity>, changeSet: OrderedCollectionChangeSet) {
         val insertions = changeSet.insertionRanges
         for (range in insertions) {
+            // Check if the insertion's displayIndices match our expectations - or skip this insertion.
+            // Inconsistencies (missing messages) can happen otherwise if we get insertions before having loaded all timeline events of the chunk.
+            if (builtEvents.isNotEmpty()) {
+                // Check consistency to item before insertions
+                if (range.startIndex > 0) {
+                    val firstInsertion = results[range.startIndex]!!
+                    val lastBeforeInsertion = builtEvents[range.startIndex-1]
+                    if (firstInsertion.displayIndex+1 != lastBeforeInsertion.displayIndex) {
+                        Timber.i("handleDatabaseChangeSet: skip insertion at ${range.startIndex}/${builtEvents.size}, " +
+                                "displayIndex mismatch at ${range.startIndex}: ${firstInsertion.displayIndex} -> ${lastBeforeInsertion.displayIndex}")
+                        continue
+                    }
+                }
+                // Check consistency to item after insertions
+                if (range.startIndex < builtEvents.size) {
+                    val lastInsertion = results[range.startIndex+range.length-1]!!
+                    val firstAfterInsertion = builtEvents[range.startIndex]
+                    if (firstAfterInsertion.displayIndex+1 != lastInsertion.displayIndex) {
+                        Timber.i("handleDatabaseChangeSet: skip insertion at ${range.startIndex}/${builtEvents.size}, " +
+                                "displayIndex mismatch at ${range.startIndex+range.length}: " +
+                                "${firstAfterInsertion.displayIndex} -> ${lastInsertion.displayIndex}")
+                        continue
+                    }
+                }
+            }
             val newItems = results
                     .subList(range.startIndex, range.startIndex + range.length)
                     .map { it.buildAndDecryptIfNeeded() }