Refactor metadata read code

src/internal/m365/collection/groups/collection.go

@@ -179,7 +179,16 @@ func (col *prefetchCollection[C, I]) streamItems(ctx context.Context, errs *faul
 			defer wg.Done()
 			defer func() { <-semaphoreCh }()
 
-			col.stream <- data.NewDeletedItem(id)
+			// This is a no-op for conversations, as there is no way to detect
+			// deleted items in a conversation. It might be added in the future
+			// if graph supports it, so make sure we put up both .data and .meta
+			// files for deletions.
+			if col.getAndAugment.supportsItemMetadata() {
+				col.stream <- data.NewDeletedItem(id + metadata.DataFileSuffix)
+				col.stream <- data.NewDeletedItem(id + metadata.MetaFileSuffix)
+			} else {
+				col.stream <- data.NewDeletedItem(id)
+			}
 
 			atomic.AddInt64(&streamedItems, 1)
 			col.Counter.Inc(count.StreamItemsRemoved)
@@ -203,6 +212,18 @@ func (col *prefetchCollection[C, I]) streamItems(ctx context.Context, errs *faul
 			defer wg.Done()
 			defer func() { <-semaphoreCh }()
 
+			ictx := clues.Add(
+				ctx,
+				"item_id", id,
+				"parent_path", path.LoggableDir(col.LocationPath().String()))
+
+			// Conversation posts carry a .data suffix, while channel messages
+			// don't have any suffix. Metadata files are only supported for conversations.
+			dataFile := id
+			if col.getAndAugment.supportsItemMetadata() {
+				dataFile += metadata.DataFileSuffix
+			}
+
 			writer := kjson.NewJsonSerializationWriter()
 			defer writer.Close()
 
@@ -237,24 +258,48 @@ func (col *prefetchCollection[C, I]) streamItems(ctx context.Context, errs *faul
 
 			info.ParentPath = col.LocationPath().String()
 
-			storeItem, err := data.NewPrefetchedItemWithInfo(
+			dataItem, err := data.NewPrefetchedItemWithInfo(
 				io.NopCloser(bytes.NewReader(itemData)),
-				id,
+				dataFile,
 				details.ItemInfo{Groups: info})
 			if err != nil {
-				err := clues.StackWC(ctx, err).Label(fault.LabelForceNoBackupCreation)
-				el.AddRecoverable(ctx, err)
+				err := clues.StackWC(ictx, err).Label(fault.LabelForceNoBackupCreation)
+				el.AddRecoverable(ictx, err)
 
 				return
 			}
 
-			col.stream <- storeItem
+			// Handle metadata before data so that if metadata file fails,
+			// we are not left with an orphaned data file. No op for channel
+			// messages.
+			if col.getAndAugment.supportsItemMetadata() {
+				metaFile := id + metadata.MetaFileSuffix
+
+				// Use modTime from item info as it's the latest.
+				metaItem, err := downloadItemMeta[C, I](
+					ictx,
+					col.getAndAugment,
+					col.contains,
+					metaFile,
+					info.Modified,
+					el)
+				if err != nil {
+					return
+				}
+
+				col.stream <- metaItem
+			}
+
+			// Add data file to collection only if the metadata file(if any) was
+			// successfully added. This also helps to maintain consistency between
+			// prefetch & lazy fetch collection behaviors.
+			col.stream <- dataItem
 
 			atomic.AddInt64(&streamedItems, 1)
 			atomic.AddInt64(&totalBytes, info.Size)
 
 			if col.Counter.Inc(count.StreamItemsAdded)%1000 == 0 {
-				logger.Ctx(ctx).Infow("item stream progress", "stats", col.Counter.Values())
+				logger.Ctx(ictx).Infow("item stream progress", "stats", col.Counter.Values())
 			}
 
 			col.Counter.Add(count.StreamBytesAdded, info.Size)
@@ -401,29 +446,18 @@ func (col *lazyFetchCollection[C, I]) streamItems(ctx context.Context, errs *fau
 				dataFile += metadata.DataFileSuffix
 				metaFile := id + metadata.MetaFileSuffix
 
-				itemMeta, _, err := col.getAndAugment.getItemMetadata(
+				metaItem, err := downloadItemMeta[C, I](
 					ictx,
-					col.contains.container)
-				if err != nil {
-					errs.AddRecoverable(ctx, clues.StackWC(ctx, err))
-
-					return
-				}
-
-				// Skip adding progress reader for metadata files. It doesn't add
-				// much value.
-				storeItem, err := data.NewPrefetchedItem(
-					itemMeta,
+					col.getAndAugment,
+					col.contains,
 					metaFile,
-					// Use the same last modified time as post's.
-					modTime)
+					modTime,
+					el)
 				if err != nil {
-					errs.AddRecoverable(ctx, clues.StackWC(ctx, err))
-
 					return
 				}
 
-				col.stream <- storeItem
+				col.stream <- metaItem
 			}
 
 			col.stream <- data.NewLazyItemWithInfo(
@@ -519,3 +553,36 @@ func (lig *lazyItemGetter[C, I]) GetData(
 		false,
 		nil
 }
+
+func downloadItemMeta[C graph.GetIDer, I groupsItemer](
+	ctx context.Context,
+	gim getItemMetadataer[C, I],
+	c container[C],
+	metaFile string,
+	modTime time.Time,
+	errs *fault.Bus,
+) (data.Item, error) {
+	itemMeta, _, err := gim.getItemMetadata(
+		ctx,
+		c.container)
+	if err != nil {
+		errs.AddRecoverable(ctx, clues.StackWC(ctx, err))
+
+		return nil, err
+	}
+
+	// Skip adding progress reader for metadata files. It doesn't add
+	// much value.
+	storeItem, err := data.NewPrefetchedItem(
+		itemMeta,
+		metaFile,
+		// Use the same last modified time as post's.
+		modTime)
+	if err != nil {
+		errs.AddRecoverable(ctx, clues.StackWC(ctx, err))
+
+		return nil, err
+	}
+
+	return storeItem, nil
+}