feat: keep a rolling backup of the last 10 config versions

internal/config/jsonstore.go

@@ -7,12 +7,17 @@ import (
 	"os"
 	"path/filepath"
 	"sync"
+	"time"
 
 	v1 "github.com/garethgeorge/backrest/gen/go/v1"
 	"github.com/natefinch/atomic"
 	"google.golang.org/protobuf/encoding/protojson"
 )
 
+var (
+	configKeepVersions = 10
+)
+
 type JsonFileStore struct {
 	Path string
 	mu   sync.Mutex
@@ -49,17 +54,22 @@ func (f *JsonFileStore) Update(config *v1.Config) error {
 		Multiline: true,
 	}.Marshal(config)
 	if err != nil {
-		return fmt.Errorf("failed to marshal config: %w", err)
+		return fmt.Errorf("marshal config: %w", err)
 	}
 
 	err = os.MkdirAll(filepath.Dir(f.Path), 0755)
 	if err != nil {
-		return fmt.Errorf("failed to create config directory: %w", err)
+		return fmt.Errorf("create config directory: %w", err)
+	}
+
+	// backup the old config file
+	if err := f.makeBackup(); err != nil {
+		return fmt.Errorf("backup config file: %w", err)
 	}
 
 	err = atomic.WriteFile(f.Path, bytes.NewReader(data))
 	if err != nil {
-		return fmt.Errorf("failed to write config file: %w", err)
+		return fmt.Errorf("write config file: %w", err)
 	}
 
 	// only the user running backrest should be able to read the config.
@@ -69,3 +79,37 @@ func (f *JsonFileStore) Update(config *v1.Config) error {
 
 	return nil
 }
+
+func (f *JsonFileStore) makeBackup() error {
+	curConfig, err := os.ReadFile(f.Path)
+	if err != nil {
+		if errors.Is(err, os.ErrNotExist) {
+			return nil
+		}
+		return err
+	}
+
+	// backup the current config file
+	backupName := fmt.Sprintf("%s.bak.%s", f.Path, time.Now().Format("2006-01-02-15-04-05"))
+	if err := atomic.WriteFile(backupName, bytes.NewBuffer(curConfig)); err != nil {
+		return err
+	}
+	if err := os.Chmod(backupName, 0600); err != nil {
+		return err
+	}
+
+	// only keep the last 10 versions
+	files, err := filepath.Glob(f.Path + ".bak.*")
+	if err != nil {
+		return err
+	}
+	if len(files) > configKeepVersions {
+		for _, file := range files[:len(files)-configKeepVersions] {
+			if err := os.Remove(file); err != nil {
+				return err
+			}
+		}
+	}
+
+	return nil
+}