repository: deduplicate index loading implementation

internal/repository/repository.go

@@ -434,88 +434,35 @@ func (r *Repository) SaveFullIndex(ctx context.Context) error {
 	return r.saveIndex(ctx, r.idx.FinalizeFullIndexes()...)
 }
 
-const loadIndexParallelism = 4
-
 // LoadIndex loads all index files from the backend in parallel and stores them
 // in the master index. The first error that occurred is returned.
 func (r *Repository) LoadIndex(ctx context.Context) error {
 	debug.Log("Loading index")
 
-	// track spawned goroutines using wg, create a new context which is
-	// cancelled as soon as an error occurs.
-	wg, ctx := errgroup.WithContext(ctx)
-
-	type FileInfo struct {
-		restic.ID
-		Size int64
-	}
-	ch := make(chan FileInfo)
-	indexCh := make(chan *Index)
-
-	// send list of index files through ch, which is closed afterwards
-	wg.Go(func() error {
-		defer close(ch)
-		return r.List(ctx, restic.IndexFile, func(id restic.ID, size int64) error {
-			select {
-			case <-ctx.Done():
-				return nil
-			case ch <- FileInfo{id, size}:
-			}
-			return nil
-		})
-	})
-
-	// a worker receives an index ID from ch, loads the index, and sends it to indexCh
-	worker := func() error {
-		var buf []byte
-		for fi := range ch {
-			var err error
-			buf, err = r.LoadAndDecrypt(ctx, buf[:0], restic.IndexFile, fi.ID)
-			if err != nil {
-				return errors.Wrapf(err, "unable to load index %s", fi.ID.Str())
-			}
-			idx, _, err := DecodeIndex(buf, fi.ID)
-			if err != nil {
-				return errors.Wrapf(err, "unable to decode index %s", fi.ID.Str())
-			}
-
-			select {
-			case indexCh <- idx:
-			case <-ctx.Done():
-			}
-		}
-
-		return nil
-	}
-
-	// run workers on ch
-	wg.Go(func() error {
-		defer close(indexCh)
-		return RunWorkers(loadIndexParallelism, worker)
-	})
-
-	// receive decoded indexes
 	validIndex := restic.NewIDSet()
-	wg.Go(func() error {
-		for idx := range indexCh {
+	err := ForAllIndexes(ctx, r, func(id restic.ID, idx *Index, oldFormat bool, err error) error {
+		if err != nil {
+			return err
+		}
+
 		ids, err := idx.IDs()
-			if err == nil {
+		if err != nil {
+			return err
+		}
+
 		for _, id := range ids {
 			validIndex.Insert(id)
 		}
-			}
-
 		r.idx.Insert(idx)
-		}
-		r.idx.MergeFinalIndexes()
 		return nil
 	})
 
-	err := wg.Wait()
 	if err != nil {
 		return errors.Fatal(err.Error())
 	}
 
+	r.idx.MergeFinalIndexes()
+
 	// remove index files from the cache which have been removed in the repo
 	return r.PrepareCache(validIndex)
 }