Prevent sync errors from crashing the app

Reader/CoreData/Item+CoreDataProperties.swift

@@ -19,6 +19,7 @@ extension Item {
     @NSManaged public var author: String?
     @NSManaged public var content: String?
     @NSManaged public var id: String?
+    @NSManaged public var needsReadStateSync: Bool
     @NSManaged public var published: Date?
     @NSManaged public var read: Bool
     @NSManaged public var title: String?

Reader/CoreData/Reader.xcdatamodeld/Reader.xcdatamodel/contents

@@ -17,6 +17,7 @@
         <attribute name="author" optional="YES" attributeType="String"/>
         <attribute name="content" optional="YES" attributeType="String"/>
         <attribute name="id" attributeType="String"/>
+        <attribute name="needsReadStateSync" attributeType="Boolean" defaultValueString="NO" usesScalarValueType="YES"/>
         <attribute name="published" optional="YES" attributeType="Date" usesScalarValueType="NO"/>
         <attribute name="read" attributeType="Boolean" usesScalarValueType="YES"/>
         <attribute name="title" optional="YES" attributeType="String"/>
@@ -29,7 +30,7 @@
     <elements>
         <element name="Feed" positionX="-54" positionY="9" width="128" height="119"/>
         <element name="Group" positionX="-63" positionY="-18" width="128" height="74"/>
-        <element name="Item" positionX="-45" positionY="63" width="128" height="149"/>
+        <element name="Item" positionX="-45" positionY="63" width="128" height="164"/>
         <element name="SyncState" positionX="-63" positionY="90" width="128" height="44"/>
     </elements>
 </model>

Reader/FervorController.swift

@@ -55,29 +55,59 @@ class FervorController {
         accessToken = token.accessToken
     }
     
-    func syncAll() async {
+    func syncAll() async throws {
         logger.info("Syncing groups and feeds")
-        async let groups = try! client.groups()
+        async let groups = try client.groups()
-        async let feeds = try! client.feeds()
+        async let feeds = try client.feeds()
-        try! await persistentContainer.sync(serverGroups: groups, serverFeeds: feeds)
+        try await persistentContainer.sync(serverGroups: groups, serverFeeds: feeds)
         
-        let lastSync = try! await persistentContainer.lastSyncDate()
+        let lastSync = try await persistentContainer.lastSyncDate()
         logger.info("Syncing items with last sync date: \(String(describing: lastSync), privacy: .public)")
-        let update = try! await client.syncItems(lastSync: lastSync)
+        let update = try await client.syncItems(lastSync: lastSync)
-        try! await persistentContainer.syncItems(update)
+        try await persistentContainer.syncItems(update)
-        try! await persistentContainer.updateLastSyncDate(update.syncTimestamp)
+        try await persistentContainer.updateLastSyncDate(update.syncTimestamp)
     }
     
     @MainActor
     func syncReadToServer() async throws {
         var count = 0
-        for case let item as Item in self.persistentContainer.viewContext.updatedObjects {
+        // todo: there should be a batch update api endpoint
-            count += 1
+        for case let item as Item in persistentContainer.viewContext.updatedObjects {
             let f = item.read ? client.read(item:) : client.unread(item:)
-            let _ = try await f(item.id!)
+            do {
+                let _ = try await f(item.id!)
+                count += 1
+            } catch {
+                logger.error("Failed to sync read state: \(error.localizedDescription, privacy: .public)")
+                item.needsReadStateSync = true
+            }
         }
+        
+        // try to sync items which failed last time
+        let req = Item.fetchRequest()
+        req.predicate = NSPredicate(format: "needsReadStateSync = YES")
+        if let needsSync = try? persistentContainer.viewContext.fetch(req) {
+            for item in needsSync {
+                let f = item.read ? client.read(item:) : client.unread(item:)
+                do {
+                    let _ = try await f(item.id!)
+                    count += 1
+                    item.needsReadStateSync = false
+                } catch {
+                    logger.error("Failed to sync read state again: \(error.localizedDescription, privacy: .public)")
+                    item.needsReadStateSync = true
+                    // todo: this should probably fail after a certain number of attempts
+                }
+            }
+        }
+        
         logger.info("Synced \(count, privacy: .public) read/unread to server")
-        try self.persistentContainer.viewContext.save()
+        
+        do {
+            try persistentContainer.viewContext.save()
+        } catch {
+            logger.error("Failed to save view context: \(error.localizedDescription, privacy: .public)")
+        }
     }
     
 }

Reader/SceneDelegate.swift

@@ -6,12 +6,15 @@
 //
 
 import UIKit
+import OSLog
 
 class SceneDelegate: UIResponder, UIWindowSceneDelegate {
 
     var window: UIWindow?
 
     private(set) var fervorController: FervorController!
+    
+    private let logger = Logger(subsystem: Bundle.main.bundleIdentifier!, category: "SceneDelegate")
 
     func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
         // Use this method to optionally configure and attach the UIWindow `window` to the provided UIWindowScene `scene`.
@@ -51,7 +54,11 @@ class SceneDelegate: UIResponder, UIWindowSceneDelegate {
         // This may occur due to temporary interruptions (ex. an incoming phone call).
         
         Task(priority: .userInitiated) {
-            try await self.fervorController?.syncReadToServer()
+            do {
+                try await self.fervorController?.syncReadToServer()
+            } catch {
+                logger.error("Unable to sync read state to server: \(error.localizedDescription, privacy: .public)")
+            }
         }
     }
 
@@ -74,7 +81,11 @@ class SceneDelegate: UIResponder, UIWindowSceneDelegate {
         window!.rootViewController = nav
             
         Task(priority: .userInitiated) {
-            await self.fervorController.syncAll()
+            do {
+                try await self.fervorController.syncAll()
+            } catch {
+                logger.error("Unable to sync from server: \(error.localizedDescription, privacy: .public)")
+            }
         }
     }