Add logging, error checking and recovery around corrupt message mappings.

Signal/src/ViewControllers/ConversationView/ConversationViewController.m

@@ -455,29 +455,11 @@ typedef enum : NSUInteger {
     [self ensureDynamicInteractions];
     [[OWSPrimaryStorage sharedManager] updateUIDatabaseConnectionToLatest];
 
-    if (thread.uniqueId.length > 0) {
-        self.messageMappings = [[YapDatabaseViewMappings alloc] initWithGroups:@[ thread.uniqueId ]
-                                                                          view:TSMessageDatabaseViewExtensionName];
-    } else {
-        OWSFail(@"uniqueId unexpectedly empty for thread: %@", thread);
-        self.messageMappings =
-            [[YapDatabaseViewMappings alloc] initWithGroups:@[] view:TSMessageDatabaseViewExtensionName];
-        return;
+    [self createNewMessageMappings];
+    if (![self reloadViewItems]) {
+        OWSFail(@"%@ failed to reload view items in configureForThread.", self.logTag);
     }
 
-    // Cells' appearance can depend on adjacent cells in both directions.
-    [self.messageMappings setCellDrawingDependencyOffsets:[NSSet setWithArray:@[
-        @(-1),
-        @(+1),
-    ]]
-                                                 forGroup:self.thread.uniqueId];
-
-    // We need to impose the range restrictions on the mappings immediately to avoid
-    // doing a great deal of unnecessary work and causing a perf hotspot.
-    [self.uiDatabaseConnection readWithBlock:^(YapDatabaseReadTransaction *transaction) {
-        [self.messageMappings updateWithTransaction:transaction];
-    }];
-    [self updateMessageMappingRangeOptions];
     [self updateShouldObserveDBModifications];
 
     self.reloadTimer = [NSTimer weakScheduledTimerWithTimeInterval:1.f
@@ -814,7 +796,9 @@ typedef enum : NSUInteger {
     // Avoid layout corrupt issues and out-of-date message subtitles.
     self.lastReloadDate = [NSDate new];
     self.collapseCutoffDate = [NSDate new];
-    [self reloadViewItems];
+    if (![self reloadViewItems]) {
+        OWSFail(@"%@ failed to reload view items in resetContentAndLayout.", self.logTag);
+    }
     [self.collectionView.collectionViewLayout invalidateLayout];
     [self.collectionView reloadData];
 }
@@ -1771,7 +1755,6 @@ typedef enum : NSUInteger {
     [self.messageMappings setRangeOptions:rangeOptions forGroup:self.thread.uniqueId];
     [self updateShowLoadMoreHeader];
     self.collapseCutoffDate = [NSDate new];
-    [self reloadViewItems];
 }
 
 #pragma mark Bubble User Actions
@@ -3241,7 +3224,7 @@ typedef enum : NSUInteger {
 {
     OWSAssertIsOnMainThread();
 
-    DDLogVerbose(@"%@ %s", self.logTag, __PRETTY_FUNCTION__);
+    DDLogInfo(@"%@ %s", self.logTag, __PRETTY_FUNCTION__);
 
     if (self.shouldObserveDBModifications) {
         // External database modifications can't be converted into incremental updates,
@@ -3250,12 +3233,14 @@ typedef enum : NSUInteger {
         //
         // We don't need to do this if we're not observing db modifications since we'll
         // do it when we resume.
-        [self resetMappings];
+        [self hardResetMappings];
     }
 }
 
 - (void)uiDatabaseWillUpdate:(NSNotification *)notification
 {
+    DDLogInfo(@"%@ %s", self.logTag, __PRETTY_FUNCTION__);
+
     // HACK to work around radar #28167779
     // "UICollectionView performBatchUpdates can trigger a crash if the collection view is flagged for layout"
     // more: https://github.com/PSPDFKit-labs/radar.apple.com/tree/master/28167779%20-%20CollectionViewBatchingIssue
@@ -3265,14 +3250,17 @@ typedef enum : NSUInteger {
     //       We want to relayout our contents using the old message mappings and
     //       view items before they are updated.
     [self.collectionView layoutIfNeeded];
-    // ENDHACK to work around radar #28167779
+    // ENDHACK to work around radar #28167779)
 }
 
 - (void)uiDatabaseDidUpdate:(NSNotification *)notification
 {
     OWSAssertIsOnMainThread();
 
+    DDLogInfo(@"%@ %s", self.logTag, __PRETTY_FUNCTION__);
+
     if (!self.shouldObserveDBModifications) {
+        DDLogInfo(@"%@ %s ignoring", self.logTag, __PRETTY_FUNCTION__);
         return;
     }
     
@@ -3378,14 +3366,21 @@ typedef enum : NSUInteger {
         // These errors seems to be very rare; they can only be reproduced
         // using the more extreme actions in the debug UI.
         OWSFail(@"%@ hasMalformedRowChange", self.logTag);
-        [self resetContentAndLayout];
+        [self hardResetMappings];
         [self updateLastVisibleTimestamp];
         [self scrollToBottomAnimated:NO];
         return;
     }
 
     NSUInteger oldViewItemCount = self.viewItems.count;
-    [self reloadViewItems];
+    if (![self reloadViewItems]) {
+        // These errors are rare.
+        OWSFail(@"%@ could not reload view items; hard resetting message mappings.", self.logTag);
+        [self hardResetMappings];
+        [self updateLastVisibleTimestamp];
+        [self scrollToBottomAnimated:NO];
+        return;
+    }
 
     BOOL wasAtBottom = [self isScrolledToBottom];
     // We want sending messages to feel snappy.  So, if the only
@@ -4800,6 +4795,40 @@ typedef enum : NSUInteger {
     self.previousLastTimestamp = nil;
 }
 
+- (void)createNewMessageMappings
+{
+    if (self.thread.uniqueId.length > 0) {
+        self.messageMappings = [[YapDatabaseViewMappings alloc] initWithGroups:@[ self.thread.uniqueId ]
+                                                                          view:TSMessageDatabaseViewExtensionName];
+    } else {
+        OWSFail(@"uniqueId unexpectedly empty for thread: %@", self.thread);
+        self.messageMappings =
+            [[YapDatabaseViewMappings alloc] initWithGroups:@[] view:TSMessageDatabaseViewExtensionName];
+    }
+
+    // Cells' appearance can depend on adjacent cells in both directions.
+    [self.messageMappings setCellDrawingDependencyOffsets:[NSSet setWithArray:@[
+        @(-1),
+        @(+1),
+    ]]
+                                                 forGroup:self.thread.uniqueId];
+
+    // We need to impose the range restrictions on the mappings immediately to avoid
+    // doing a great deal of unnecessary work and causing a perf hotspot.
+    [self.uiDatabaseConnection readWithBlock:^(YapDatabaseReadTransaction *transaction) {
+        [self.messageMappings updateWithTransaction:transaction];
+    }];
+    [self updateMessageMappingRangeOptions];
+}
+
+- (void)hardResetMappings
+{
+    DDLogInfo(@"%@ %s", self.logTag, __PRETTY_FUNCTION__);
+
+    [self createNewMessageMappings];
+    [self resetMappings];
+}
+
 - (void)resetMappings
 {
     // If we're entering "active" mode (e.g. view is visible and app is in foreground),
@@ -4814,7 +4843,6 @@ typedef enum : NSUInteger {
         [self updateMessageMappingRangeOptions];
     }
     self.collapseCutoffDate = [NSDate new];
-    [self reloadViewItems];
 
     [self resetContentAndLayout];
     [self ensureDynamicInteractions];
@@ -4849,7 +4877,9 @@ typedef enum : NSUInteger {
 
 // This is a key method.  It builds or rebuilds the list of
 // cell view models.
-- (void)reloadViewItems
+//
+// Returns NO on error.
+- (BOOL)reloadViewItems
 {
     NSMutableArray<ConversationViewItem *> *viewItems = [NSMutableArray new];
     NSMutableDictionary<NSString *, ConversationViewItem *> *viewItemCache = [NSMutableDictionary new];
@@ -4857,6 +4887,7 @@ typedef enum : NSUInteger {
     NSUInteger count = [self.messageMappings numberOfItemsInSection:0];
     BOOL isGroupThread = self.isGroupConversation;
 
+    __block BOOL hasError = NO;
     [self.uiDatabaseConnection readWithBlock:^(YapDatabaseReadTransaction *transaction) {
         YapDatabaseViewTransaction *viewTransaction = [transaction ext:TSMessageDatabaseViewExtensionName];
         OWSAssert(viewTransaction);
@@ -4869,6 +4900,7 @@ typedef enum : NSUInteger {
                     (unsigned long)row,
                     (unsigned long)count);
                 // TODO: Add analytics.
+                hasError = YES;
                 continue;
             }
             if (!interaction.uniqueId) {
@@ -4878,6 +4910,7 @@ typedef enum : NSUInteger {
                     (unsigned long)count,
                     interaction);
                 // TODO: Add analytics.
+                hasError = YES;
                 continue;
             }
 
@@ -5122,6 +5155,8 @@ typedef enum : NSUInteger {
 
     self.viewItems = viewItems;
     self.viewItemCache = viewItemCache;
+
+    return !hasError;
 }
 
 // Whenever an interaction is modified, we need to reload it from the DB