Fix accessing messages with invalid index (#663)

Author: laevandus

CHANGELOG.md

@@ -9,6 +9,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 - Fix message long press taking too much time to show actions [#648](https://github.com/GetStream/stream-chat-swiftui/pull/648)
 - Fix rendering link attachment preview with other attachment types [#659](https://github.com/GetStream/stream-chat-swiftui/pull/659)
 - Fix not using colors from the palette in some of the poll views [#661](https://github.com/GetStream/stream-chat-swiftui/pull/661)
+- Fix a rare crash when handling list change in the `ChatChannelViewModel` [#663](https://github.com/GetStream/stream-chat-swiftui/pull/663)
 ### 🔄 Changed
 - Message composer now uses `.uploadFile` capability when showing attachment picker icon [#646](https://github.com/GetStream/stream-chat-swiftui/pull/646)
 - `ChannelInfoView` now uses `.updateChannelMembers` capability to show "Add Users" button [#651](https://github.com/GetStream/stream-chat-swiftui/pull/651)
@@ -59,8 +60,8 @@ _September 12, 2024_
 
 ### 🔄 Changed
 - Improved subtitle info in pinned messages view [#594](https://github.com/GetStream/stream-chat-swiftui/pull/594)
-- The `image(for channel: ChatChannel)` in `ChannelHeaderLoader` is now open [#595](https://github.com/GetStream/stream-chat-swiftui/pull/595) 
-- FlagMessage Action is now only shown if the user has a permission to perform the action [#599](https://github.com/GetStream/stream-chat-swiftui/pull/599) 
+- The `image(for channel: ChatChannel)` in `ChannelHeaderLoader` is now open [#595](https://github.com/GetStream/stream-chat-swiftui/pull/595)
+- FlagMessage Action is now only shown if the user has a permission to perform the action [#599](https://github.com/GetStream/stream-chat-swiftui/pull/599)
 
 ### 🐞 Fixed
 - Typing users did not update reliably in the message list [#591](https://github.com/GetStream/stream-chat-swiftui/pull/591)

Sources/StreamChatSwiftUI/ChatChannel/ChatChannelViewModel.swift

@@ -709,19 +709,18 @@ open class ChatChannelViewModel: ObservableObject, MessagesDataSource {
                  .remove(_, index: _):
                 return true
             case let .update(message, index: index):
-                let animateReactions = message.reactionScoresId != messages[index.row].reactionScoresId
+                guard index.row >= messages.startIndex, index.row < messages.endIndex else { continue }
+                let existingDisplayedMessage = messages[index.row]
+                let animateReactions = message.reactionScoresId != existingDisplayedMessage.reactionScoresId
                     && utils.messageListConfig.messageDisplayOptions.shouldAnimateReactions
-                if index.row < messages.count,
-                   message.messageId != messages[index.row].messageId
+                if animateReactions,
+                   message.messageId != existingDisplayedMessage.messageId
                    || message.type == .ephemeral
                    || !message.linkAttachments.isEmpty {
-                    if index.row < messages.count
-                        && animateReactions {
-                        animateChanges = message.linkAttachments.isEmpty
-                    }
+                    animateChanges = message.linkAttachments.isEmpty
                 }
-            default:
-                break
+            case .move(_, fromIndex: _, toIndex: _):
+                continue
             }
         }
 

StreamChatSwiftUITests/Tests/ChatChannel/ChatChannelViewModel_Tests.swift

@@ -489,6 +489,30 @@ class ChatChannelViewModel_Tests: StreamChatTestCase {
         // Then
         XCTAssert(shouldJump == false)
     }
+    
+    func test_chatChannelVM_crashWhenIndexAccess() {
+        // Given
+        let message1 = ChatMessage.mock()
+        let message2 = ChatMessage.mock()
+        let message3 = ChatMessage.mock()
+        let channelController = makeChannelController(messages: [message1, message2])
+        let viewModel = ChatChannelViewModel(channelController: channelController)
+        let newMessages = LazyCachedMapCollection(elements: [message1, message2, message3])
+        
+        // When
+        viewModel.dataSource(
+            channelDataSource: ChatChannelDataSource(controller: channelController),
+            didUpdateMessages: newMessages,
+            changes: [
+                .insert(message3, index: IndexPath(row: 2, section: 0)),
+                .update(message3, index: IndexPath(row: 2, section: 0)),
+                .update(message3, index: IndexPath(row: 3, section: 0)) // intentionally invalid path
+            ]
+        )
+        
+        // Then
+        XCTAssertEqual(3, viewModel.messages.count)
+    }
 
     // MARK: - private