repair pack: extract the repair logic into the repository package

Currently, the cmd/restic package contains a significant amount of code
that modifies repository internals. This code should in the mid-term
move into the repository package.

internal/repository/repair_pack.go

@@ -0,0 +1,88 @@
+package repository
+
+import (
+	"context"
+	"errors"
+	"io"
+
+	"github.com/restic/restic/internal/restic"
+	"github.com/restic/restic/internal/ui/progress"
+	"golang.org/x/sync/errgroup"
+)
+
+func RepairPacks(ctx context.Context, repo *Repository, ids restic.IDSet, printer progress.Printer) error {
+	wg, wgCtx := errgroup.WithContext(ctx)
+	repo.StartPackUploader(wgCtx, wg)
+	repo.DisableAutoIndexUpdate()
+
+	printer.P("salvaging intact data from specified pack files")
+	bar := printer.NewCounter("pack files")
+	bar.SetMax(uint64(len(ids)))
+	defer bar.Done()
+
+	wg.Go(func() error {
+		// examine all data the indexes have for the pack file
+		for b := range repo.Index().ListPacks(wgCtx, ids) {
+			blobs := b.Blobs
+			if len(blobs) == 0 {
+				printer.E("no blobs found for pack %v", b.PackID)
+				bar.Add(1)
+				continue
+			}
+
+			err := repo.LoadBlobsFromPack(wgCtx, b.PackID, blobs, func(blob restic.BlobHandle, buf []byte, err error) error {
+				if err != nil {
+					// Fallback path
+					buf, err = repo.LoadBlob(wgCtx, blob.Type, blob.ID, nil)
+					if err != nil {
+						printer.E("failed to load blob %v: %v", blob.ID, err)
+						return nil
+					}
+				}
+				id, _, _, err := repo.SaveBlob(wgCtx, blob.Type, buf, restic.ID{}, true)
+				if !id.Equal(blob.ID) {
+					panic("pack id mismatch during upload")
+				}
+				return err
+			})
+			if err != nil {
+				return err
+			}
+			bar.Add(1)
+		}
+		return repo.Flush(wgCtx)
+	})
+
+	err := wg.Wait()
+	bar.Done()
+	if err != nil {
+		return err
+	}
+
+	// remove salvaged packs from index
+	printer.P("rebuilding index")
+
+	bar = printer.NewCounter("packs processed")
+	err = repo.Index().Save(ctx, repo, ids, nil, restic.MasterIndexSaveOpts{
+		SaveProgress: bar,
+		DeleteProgress: func() *progress.Counter {
+			return printer.NewCounter("old indexes deleted")
+		},
+		DeleteReport: func(id restic.ID, err error) {
+			printer.VV("removed index %v", id.String())
+		},
+	})
+
+	if err != nil {
+		return err
+	}
+
+	// cleanup
+	printer.P("removing salvaged pack files")
+	// if we fail to delete the damaged pack files, then prune will remove them later on
+	bar = printer.NewCounter("files deleted")
+	_ = restic.ParallelRemove(ctx, repo, ids, restic.PackFile, nil, bar)
+	bar.Done()
+
+	return nil
+}