Add layout auto detection

src/restic/backend/layout.go

@@ -1,7 +1,13 @@
 package backend
 
 import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"regexp"
 	"restic"
+	"restic/errors"
+	"restic/fs"
 )
 
 // Layout computes paths for file name storage.
@@ -10,3 +16,135 @@ type Layout interface {
 	Dirname(restic.Handle) string
 	Paths() []string
 }
+
+// Filesystem is the abstraction of a file system used for a backend.
+type Filesystem interface {
+	Join(...string) string
+	ReadDir(string) ([]os.FileInfo, error)
+}
+
+// ensure statically that *LocalFilesystem implements Filesystem.
+var _ Filesystem = &LocalFilesystem{}
+
+// LocalFilesystem implements Filesystem in a local path.
+type LocalFilesystem struct {
+}
+
+// ReadDir returns all entries of a directory.
+func (l *LocalFilesystem) ReadDir(dir string) ([]os.FileInfo, error) {
+	f, err := fs.Open(dir)
+	if err != nil {
+		return nil, err
+	}
+
+	entries, err := f.Readdir(-1)
+	if err != nil {
+		return nil, err
+	}
+
+	err = f.Close()
+	if err != nil {
+		return nil, err
+	}
+
+	return entries, nil
+}
+
+// Join combines several path components to one.
+func (l *LocalFilesystem) Join(paths ...string) string {
+	return filepath.Join(paths...)
+}
+
+var backendFilenameLength = len(restic.ID{}) * 2
+var backendFilename = regexp.MustCompile(fmt.Sprintf("^[a-fA-F0-9]{%d}$", backendFilenameLength))
+
+func hasBackendFile(fs Filesystem, dir string) (bool, error) {
+	entries, err := fs.ReadDir(dir)
+	if err != nil && os.IsNotExist(errors.Cause(err)) {
+		return false, nil
+	}
+
+	if err != nil {
+		return false, errors.Wrap(err, "ReadDir")
+	}
+
+	for _, e := range entries {
+		if backendFilename.MatchString(e.Name()) {
+			return true, nil
+		}
+	}
+
+	return false, nil
+}
+
+var dataSubdirName = regexp.MustCompile("^[a-fA-F0-9]{2}$")
+
+func hasSubdirBackendFile(fs Filesystem, dir string) (bool, error) {
+	entries, err := fs.ReadDir(dir)
+	if err != nil && os.IsNotExist(errors.Cause(err)) {
+		return false, nil
+	}
+
+	if err != nil {
+		return false, errors.Wrap(err, "ReadDir")
+	}
+
+	for _, subdir := range entries {
+		if !dataSubdirName.MatchString(subdir.Name()) {
+			continue
+		}
+
+		present, err := hasBackendFile(fs, fs.Join(dir, subdir.Name()))
+		if err != nil {
+			return false, err
+		}
+
+		if present {
+			return true, nil
+		}
+	}
+
+	return false, nil
+}
+
+// DetectLayout tries to find out which layout is used in a local (or sftp)
+// filesystem at the given path.
+func DetectLayout(repo Filesystem, dir string) (Layout, error) {
+	// key file in the "keys" dir (DefaultLayout or CloudLayout)
+	foundKeysFile, err := hasBackendFile(repo, repo.Join(dir, defaultLayoutPaths[restic.KeyFile]))
+	if err != nil {
+		return nil, err
+	}
+
+	// key file in the "key" dir (S3Layout)
+	foundKeyFile, err := hasBackendFile(repo, repo.Join(dir, s3LayoutPaths[restic.KeyFile]))
+	if err != nil {
+		return nil, err
+	}
+
+	// data file in "data" directory (S3Layout or CloudLayout)
+	foundDataFile, err := hasBackendFile(repo, repo.Join(dir, s3LayoutPaths[restic.DataFile]))
+	if err != nil {
+		return nil, err
+	}
+
+	// data file in subdir of "data" directory (DefaultLayout)
+	foundDataSubdirFile, err := hasSubdirBackendFile(repo, repo.Join(dir, s3LayoutPaths[restic.DataFile]))
+	if err != nil {
+		return nil, err
+	}
+
+	if foundKeysFile && foundDataFile && !foundKeyFile && !foundDataSubdirFile {
+		return &CloudLayout{}, nil
+	}
+
+	if foundKeysFile && foundDataSubdirFile && !foundKeyFile && !foundDataFile {
+		return &DefaultLayout{}, nil
+	}
+
+	if foundKeyFile && foundDataFile && !foundKeysFile && !foundDataSubdirFile {
+		return &S3Layout{}, nil
+	}
+
+	return nil, errors.New("auto-detecting the filesystem layout failed")
+}

src/restic/backend/layout_test.go

@@ -5,13 +5,13 @@ import (
 	"path/filepath"
 	"reflect"
 	"restic"
-	"restic/test"
+	. "restic/test"
 	"sort"
 	"testing"
 )
 
 func TestDefaultLayout(t *testing.T) {
-	path, cleanup := test.TempDir(t)
+	path, cleanup := TempDir(t)
 	defer cleanup()
 
 	var tests = []struct {
@@ -79,7 +79,7 @@ func TestDefaultLayout(t *testing.T) {
 }
 
 func TestCloudLayout(t *testing.T) {
-	path, cleanup := test.TempDir(t)
+	path, cleanup := TempDir(t)
 	defer cleanup()
 
 	var tests = []struct {
@@ -147,7 +147,7 @@ func TestCloudLayout(t *testing.T) {
 }
 
 func TestS3Layout(t *testing.T) {
-	path, cleanup := test.TempDir(t)
+	path, cleanup := TempDir(t)
 	defer cleanup()
 
 	var tests = []struct {
@@ -213,3 +213,40 @@ func TestS3Layout(t *testing.T) {
 		})
 	}
 }
+
+func TestDetectLayout(t *testing.T) {
+	path, cleanup := TempDir(t)
+	defer cleanup()
+
+	var tests = []struct {
+		filename string
+		want     string
+	}{
+		{"repo-layout-local.tar.gz", "*backend.DefaultLayout"},
+		{"repo-layout-cloud.tar.gz", "*backend.CloudLayout"},
+		{"repo-layout-s3-old.tar.gz", "*backend.S3Layout"},
+	}
+
+	var fs = &LocalFilesystem{}
+	for _, test := range tests {
+		t.Run(test.filename, func(t *testing.T) {
+			SetupTarTestFixture(t, path, filepath.Join("testdata", test.filename))
+
+			layout, err := DetectLayout(fs, 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)
+			}
+
+			RemoveAll(t, filepath.Join(path, "repo"))
+		})
+	}
+}