Add layout name parser

src/restic/backend/layout.go

@@ -108,8 +108,13 @@ func hasSubdirBackendFile(fs Filesystem, dir string) (bool, error) {
 }
 
 // DetectLayout tries to find out which layout is used in a local (or sftp)
-// filesystem at the given path.
+// filesystem at the given path. If repo is nil, an instance of LocalFilesystem
+// is used.
 func DetectLayout(repo Filesystem, dir string) (Layout, error) {
+	if repo == nil {
+		repo = &LocalFilesystem{}
+	}
+
 	// key file in the "keys" dir (DefaultLayout or CloudLayout)
 	foundKeysFile, err := hasBackendFile(repo, repo.Join(dir, defaultLayoutPaths[restic.KeyFile]))
 	if err != nil {
@@ -148,3 +153,36 @@ func DetectLayout(repo Filesystem, dir string) (Layout, error) {
 
 	return nil, errors.New("auto-detecting the filesystem layout failed")
 }
+
+// ParseLayout parses the config string and returns a Layout. When layout is
+// the empty string, DetectLayout is used. If repo is nil, an instance of LocalFilesystem
+// is used.
+func ParseLayout(repo Filesystem, layout, path string) (l Layout, err error) {
+	if repo == nil {
+		repo = &LocalFilesystem{}
+	}
+
+	switch layout {
+	case "default":
+		l = &DefaultLayout{
+			Path: path,
+			Join: repo.Join,
+		}
+	case "cloud":
+		l = &CloudLayout{
+			Path: path,
+			Join: repo.Join,
+		}
+	case "s3":
+		l = &S3Layout{
+			Path: path,
+			Join: repo.Join,
+		}
+	case "":
+		return DetectLayout(repo, path)
+	default:
+		return nil, errors.Errorf("unknown backend layout string %q, may be one of default/cloud/s3", layout)
+	}
+
+	return l, nil
+}

src/restic/backend/layout_test.go

@@ -229,7 +229,8 @@ func TestDetectLayout(t *testing.T) {
 
 	var fs = &LocalFilesystem{}
 	for _, test := range tests {
-		t.Run(test.filename, func(t *testing.T) {
+		for _, fs := range []Filesystem{fs, nil} {
+			t.Run(fmt.Sprintf("%v/fs-%T", test.filename, fs), func(t *testing.T) {
 				SetupTarTestFixture(t, path, filepath.Join("testdata", test.filename))
 
 				layout, err := DetectLayout(fs, filepath.Join(path, "repo"))
@@ -249,4 +250,58 @@ func TestDetectLayout(t *testing.T) {
 				RemoveAll(t, filepath.Join(path, "repo"))
 			})
 		}
+	}
+}
+
+func TestParseLayout(t *testing.T) {
+	path, cleanup := TempDir(t)
+	defer cleanup()
+
+	var tests = []struct {
+		layoutName string
+		want       string
+	}{
+		{"default", "*backend.DefaultLayout"},
+		{"cloud", "*backend.CloudLayout"},
+		{"s3", "*backend.S3Layout"},
+		{"", "*backend.CloudLayout"},
+	}
+
+	SetupTarTestFixture(t, path, filepath.Join("testdata", "repo-layout-cloud.tar.gz"))
+
+	for _, test := range tests {
+		t.Run(test.layoutName, func(t *testing.T) {
+			layout, err := ParseLayout(nil, test.layoutName, filepath.Join(path, "repo"))
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			if layout == nil {
+				t.Fatal("wanted some layout, but detect returned nil")
+			}
+
+			layoutName := fmt.Sprintf("%T", layout)
+			if layoutName != test.want {
+				t.Fatalf("want layout %v, got %v", test.want, layoutName)
+			}
+		})
+	}
+}
+
+func TestParseLayoutInvalid(t *testing.T) {
+	path, cleanup := TempDir(t)
+	defer cleanup()
+
+	var invalidNames = []string{
+		"foo", "bar", "local",
+	}
+
+	for _, name := range invalidNames {
+		t.Run(name, func(t *testing.T) {
+			layout, err := ParseLayout(nil, name, path)
+			if err == nil {
+				t.Fatalf("expected error not found for layout name %v, layout is %v", name, layout)
+			}
+		})
+	}
 }

src/restic/backend/local/config.go

@@ -9,6 +9,7 @@ import (
 // Config holds all information needed to open a local repository.
 type Config struct {
 	Path   string
+	Layout string
 }
 
 // ParseConfig parses a local backend config.

src/restic/backend/local/local.go

@@ -24,13 +24,13 @@ var _ restic.Backend = &Local{}
 
 // Open opens the local backend as specified by config.
 func Open(cfg Config) (*Local, error) {
-	be := &Local{Config: cfg}
+	l, err := backend.ParseLayout(nil, cfg.Layout, cfg.Path)
-
+	if err != nil {
-	be.Layout = &backend.DefaultLayout{
+		return nil, err
-		Path: cfg.Path,
-		Join: filepath.Join,
 	}
 
+	be := &Local{Config: cfg, Layout: l}
+
 	// test if all necessary dirs are there
 	for _, d := range be.Paths() {
 		if _, err := fs.Stat(d); err != nil {