Add migration to compress all data

internal/migrations/compress_repo_v2.go

@@ -0,0 +1,102 @@
+package migrations
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/restic/restic/internal/repository"
+	"github.com/restic/restic/internal/restic"
+)
+
+func init() {
+	register(&CompressRepoV2{})
+}
+
+type CompressRepoV2 struct{}
+
+func (*CompressRepoV2) Name() string {
+	return "compress_all_data"
+}
+
+func (*CompressRepoV2) Desc() string {
+	return "compress all data in the repo"
+}
+
+func (*CompressRepoV2) Check(ctx context.Context, repo restic.Repository) (bool, error) {
+	// only do very fast checks on the version here, we don't want the list of
+	// available migrations to take long to load
+	if repo.Config().Version < 2 {
+		return false, nil
+	}
+
+	return true, nil
+}
+
+// Apply requires that the repository must be already locked exclusively, this
+// is done by the caller, so we can just go ahead, rewrite the packs as they
+// are, remove the packs and rebuild the index.
+func (*CompressRepoV2) Apply(ctx context.Context, repo restic.Repository) error {
+	ctx, cancel := context.WithCancel(ctx)
+	defer cancel()
+
+	err := repo.LoadIndex(ctx)
+	if err != nil {
+		return fmt.Errorf("index load failed: %w", err)
+	}
+
+	packsWithUncompressedData := restic.NewIDSet()
+	keepBlobs := restic.NewBlobSet()
+
+	for blob := range repo.Index().Each(ctx) {
+		keepBlobs.Insert(blob.BlobHandle)
+
+		if blob.UncompressedLength != 0 {
+			// blob is already compressed, ignore
+			continue
+
+		}
+
+		// remember pack ID
+		packsWithUncompressedData.Insert(blob.PackID)
+	}
+
+	if len(packsWithUncompressedData) == 0 {
+		// nothing to do
+		return nil
+	}
+
+	// don't upload new indexes until we're done
+	repo.(*repository.Repository).DisableAutoIndexUpdate()
+	obsoletePacks, err := repository.Repack(ctx, repo, repo, packsWithUncompressedData, keepBlobs, nil)
+	if err != nil {
+		return fmt.Errorf("repack failed: %w", err)
+	}
+
+	if len(obsoletePacks) != len(packsWithUncompressedData) {
+		return fmt.Errorf("Repack() return other packs, %d != %d", len(obsoletePacks), len(packsWithUncompressedData))
+	}
+
+	// build new index
+	idx := repo.Index().(*repository.MasterIndex)
+	obsoleteIndexes, err := idx.Save(ctx, repo, obsoletePacks, nil, nil)
+	if err != nil {
+		return fmt.Errorf("saving new index failed: %w", err)
+	}
+
+	// remove data
+	for id := range obsoleteIndexes {
+		err = repo.Backend().Remove(ctx, restic.Handle{Name: id.String(), Type: restic.IndexFile})
+		if err != nil {
+			return fmt.Errorf("remove file failed: %w", err)
+		}
+	}
+
+	for id := range obsoletePacks {
+		err = repo.Backend().Remove(ctx, restic.Handle{Name: id.String(), Type: restic.PackFile})
+		if err != nil {
+			return fmt.Errorf("remove file failed: %w", err)
+		}
+	}
+
+	return nil
+}