backup: Try read latest manifest when available

Now that a latest manifest is written, we can use this manifest when
loading the "latest" backup.

2 files changed, 143 insertions, 6 deletions

diff --git a/internal/backup/locator.go b/internal/backup/locator.go
index 216037aea..c0ccca3b3 100644
--- a/internal/backup/locator.go
+++ b/internal/backup/locator.go
@@ -267,6 +267,8 @@ func (l PointerLocator) writeLatest(ctx context.Context, path, target string) (r
 	return nil
 }
 
+const latestManifestName = "+latest"
+
 // ManifestLocator locates backup paths based on manifest files that are
 // written to a predetermined path:
 //
@@ -297,34 +299,52 @@ func (l ManifestLocator) Commit(ctx context.Context, backup *Backup) (returnErr
 	if err := l.writeManifest(ctx, backup, backup.ID); err != nil {
 		return fmt.Errorf("manifest: commit: %w", err)
 	}
-	if err := l.writeManifest(ctx, backup, "+latest"); err != nil {
-		return fmt.Errorf("manifest: commit: %w", err)
+	if err := l.writeManifest(ctx, backup, latestManifestName); err != nil {
+		return fmt.Errorf("manifest: commit latest: %w", err)
 	}
 
 	return nil
 }
 
-// FindLatest passes through to Fallback
+// FindLatest loads the manifest called +latest. If this manifest does not
+// exist, the Fallback is used.
 func (l ManifestLocator) FindLatest(ctx context.Context, repo storage.Repository) (*Backup, error) {
-	return l.Fallback.FindLatest(ctx, repo)
+	backup, err := l.readManifest(ctx, repo, latestManifestName)
+	switch {
+	case errors.Is(err, ErrDoesntExist):
+		return l.Fallback.FindLatest(ctx, repo)
+	case err != nil:
+		return nil, fmt.Errorf("manifest: find latest: %w", err)
+	}
+
+	return backup, nil
 }
 
 // Find loads the manifest for the provided repo and backupID. If this manifest
 // does not exist, the fallback is used.
 func (l ManifestLocator) Find(ctx context.Context, repo storage.Repository, backupID string) (*Backup, error) {
-	f, err := l.Sink.GetReader(ctx, manifestPath(repo, backupID))
+	backup, err := l.readManifest(ctx, repo, backupID)
 	switch {
 	case errors.Is(err, ErrDoesntExist):
 		return l.Fallback.Find(ctx, repo, backupID)
 	case err != nil:
 		return nil, fmt.Errorf("manifest: find: %w", err)
 	}
+
+	return backup, nil
+}
+
+func (l ManifestLocator) readManifest(ctx context.Context, repo storage.Repository, backupID string) (*Backup, error) {
+	f, err := l.Sink.GetReader(ctx, manifestPath(repo, backupID))
+	if err != nil {
+		return nil, fmt.Errorf("read manifest: %w", err)
+	}
 	defer f.Close()
 
 	var backup Backup
 
 	if err := toml.NewDecoder(f).Decode(&backup); err != nil {
-		return nil, fmt.Errorf("manifest: find: %w", err)
+		return nil, fmt.Errorf("read manifest: %w", err)
 	}
 
 	backup.ID = backupID
diff --git a/internal/backup/locator_test.go b/internal/backup/locator_test.go
index cca9ee8e8..1d6010554 100644
--- a/internal/backup/locator_test.go
+++ b/internal/backup/locator_test.go
@@ -610,3 +610,120 @@ custom_hooks_path = 'path/to/002.custom_hooks.tar'
 		})
 	}
 }
+
+func TestManifestLocator_FindLatest(t *testing.T) {
+	t.Parallel()
+
+	for _, tc := range []struct {
+		desc           string
+		repo           storage.Repository
+		setup          func(t *testing.T, ctx context.Context, backupPath string)
+		expectedBackup *Backup
+	}{
+		{
+			desc: "finds manifest",
+			repo: &gitalypb.Repository{
+				StorageName:  "default",
+				RelativePath: "vanity/repo.git",
+			},
+			setup: func(t *testing.T, ctx context.Context, backupPath string) {
+				testhelper.WriteFiles(t, backupPath, map[string]any{
+					"vanity/repo/LATEST":        "abc123",
+					"vanity/repo/abc123/LATEST": "002",
+					"manifests/default/vanity/repo.git/+latest.toml": `object_format = 'sha1'
+
+[[steps]]
+bundle_path = 'manifest-path/to/001.bundle'
+ref_path = 'manifest-path/to/001.refs'
+custom_hooks_path = 'manifest-path/to/001.custom_hooks.tar'
+
+[[steps]]
+bundle_path = 'manifest-path/to/002.bundle'
+ref_path = 'manifest-path/to/002.refs'
+previous_ref_path = 'manifest-path/to/001.refs'
+custom_hooks_path = 'manifest-path/to/002.custom_hooks.tar'
+`,
+				})
+			},
+			expectedBackup: &Backup{
+				ID: "+latest",
+				Repository: &gitalypb.Repository{
+					StorageName:  "default",
+					RelativePath: "vanity/repo.git",
+				},
+				ObjectFormat: "sha1",
+				Steps: []Step{
+					{
+						BundlePath:      "manifest-path/to/001.bundle",
+						RefPath:         "manifest-path/to/001.refs",
+						CustomHooksPath: "manifest-path/to/001.custom_hooks.tar",
+					},
+					{
+						BundlePath:      "manifest-path/to/002.bundle",
+						RefPath:         "manifest-path/to/002.refs",
+						PreviousRefPath: "manifest-path/to/001.refs",
+						CustomHooksPath: "manifest-path/to/002.custom_hooks.tar",
+					},
+				},
+			},
+		},
+		{
+			desc: "fallback",
+			repo: &gitalypb.Repository{
+				StorageName:  "default",
+				RelativePath: "vanity/repo.git",
+			},
+			setup: func(t *testing.T, ctx context.Context, backupPath string) {
+				testhelper.WriteFiles(t, backupPath, map[string]any{
+					"vanity/repo/LATEST":        "abc123",
+					"vanity/repo/abc123/LATEST": "002",
+				})
+			},
+			expectedBackup: &Backup{
+				ID: "abc123",
+				Repository: &gitalypb.Repository{
+					StorageName:  "default",
+					RelativePath: "vanity/repo.git",
+				},
+				ObjectFormat: "sha1",
+				Steps: []Step{
+					{
+						BundlePath:      "vanity/repo/abc123/001.bundle",
+						RefPath:         "vanity/repo/abc123/001.refs",
+						CustomHooksPath: "vanity/repo/abc123/001.custom_hooks.tar",
+					},
+					{
+						BundlePath:      "vanity/repo/abc123/002.bundle",
+						RefPath:         "vanity/repo/abc123/002.refs",
+						PreviousRefPath: "vanity/repo/abc123/001.refs",
+						CustomHooksPath: "vanity/repo/abc123/002.custom_hooks.tar",
+					},
+				},
+			},
+		},
+	} {
+		tc := tc
+		t.Run(tc.desc, func(t *testing.T) {
+			t.Parallel()
+
+			ctx := testhelper.Context(t)
+			backupPath := testhelper.TempDir(t)
+
+			tc.setup(t, ctx, backupPath)
+
+			sink := NewFilesystemSink(backupPath)
+			var l Locator = PointerLocator{
+				Sink: sink,
+			}
+			l = ManifestLocator{
+				Sink:     sink,
+				Fallback: l,
+			}
+
+			backup, err := l.FindLatest(ctx, tc.repo)
+			require.NoError(t, err)
+
+			require.Equal(t, tc.expectedBackup, backup)
+		})
+	}
+}