Log changed files after backup

internal/restic/restic.go

@@ -98,6 +98,16 @@ type Stats struct {
 	TotalBlobCount int64 `json:"total_blob_count"`
 }
 
+type DiffEntry struct {
+	Kind string
+	Path string
+}
+
+type DiffResult struct {
+	Entries []DiffEntry
+	Total   int
+}
+
 func (r *Runner) Init(ctx context.Context, repo model.Repository) error {
 	return r.run(ctx, repo, []string{"init"}, nil, nil)
 }
@@ -280,6 +290,58 @@ func (r *Runner) List(ctx context.Context, repo model.Repository, snapshot, path
 	return items, scanner.Err()
 }
 
+func (r *Runner) Diff(ctx context.Context, repo model.Repository, before, after string, limit int) (DiffResult, error) {
+	var output []byte
+	if err := r.run(ctx, repo, []string{"diff", "--metadata", before, after}, nil, &output); err != nil {
+		return DiffResult{}, err
+	}
+	return parseDiffOutput(output, limit), nil
+}
+
+func parseDiffOutput(output []byte, limit int) DiffResult {
+	if limit <= 0 {
+		limit = 50
+	}
+	result := DiffResult{}
+	scanner := bufio.NewScanner(bytes.NewReader(output))
+	scanner.Buffer(make([]byte, 0, 64*1024), 2*1024*1024)
+	for scanner.Scan() {
+		line := scanner.Text()
+		if len(line) < 2 {
+			continue
+		}
+		kind := diffKind(line[0])
+		if kind == "" {
+			continue
+		}
+		path := strings.TrimSpace(line[1:])
+		if path == "" || !strings.HasPrefix(path, "/") {
+			continue
+		}
+		result.Total++
+		if len(result.Entries) == limit {
+			copy(result.Entries, result.Entries[1:])
+			result.Entries[len(result.Entries)-1] = DiffEntry{Kind: kind, Path: path}
+			continue
+		}
+		result.Entries = append(result.Entries, DiffEntry{Kind: kind, Path: path})
+	}
+	return result
+}
+
+func diffKind(marker byte) string {
+	switch marker {
+	case '+':
+		return "new"
+	case '-':
+		return "removed"
+	case 'M':
+		return "modified"
+	default:
+		return ""
+	}
+}
+
 func (r *Runner) Restore(ctx context.Context, repo model.Repository, task model.RestoreTask, progress ProgressCallback) error {
 	args := []string{"restore", task.SnapshotID, "--target", task.Target, "--json"}
 	for _, include := range task.Includes {

internal/restic/restic_test.go

@@ -190,6 +190,49 @@ func TestRestoreReportsProgress(t *testing.T) {
 	}
 }
 
+func TestDiffReportsLastChangedPaths(t *testing.T) {
+	dir := t.TempDir()
+	argsPath := filepath.Join(dir, "args")
+	script := filepath.Join(dir, "restic")
+	body := fmt.Sprintf(`#!/bin/sh
+printf '%%s\n' "$@" > '%s'
+printf '%%s\n' 'comparing snapshot before to after:'
+printf '%%s\n' '+    /mnt/user/new.txt'
+printf '%%s\n' 'M    /mnt/user/modified-a.txt'
+printf '%%s\n' '-    /mnt/user/removed.txt'
+printf '%%s\n' 'M    /mnt/user/modified-b.txt'
+printf '%%s\n' 'Files: 1 new, 1 removed, 2 changed'
+`, argsPath)
+	if err := os.WriteFile(script, []byte(body), 0700); err != nil {
+		t.Fatal(err)
+	}
+	runner := &Runner{Binary: script, RuntimeDir: dir, Secrets: fakeSecrets{"password": "secret"}}
+	repo := model.Repository{Type: model.RepositoryLocal, Location: "/repo", PasswordRef: "password"}
+	diff, err := runner.Diff(context.Background(), repo, "before", "after", 3)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if diff.Total != 4 || len(diff.Entries) != 3 {
+		t.Fatalf("unexpected diff result: %+v", diff)
+	}
+	expected := []DiffEntry{
+		{Kind: "modified", Path: "/mnt/user/modified-a.txt"},
+		{Kind: "removed", Path: "/mnt/user/removed.txt"},
+		{Kind: "modified", Path: "/mnt/user/modified-b.txt"},
+	}
+	for index, entry := range expected {
+		if diff.Entries[index] != entry {
+			t.Fatalf("entry %d = %+v, want %+v", index, diff.Entries[index], entry)
+		}
+	}
+	args, _ := os.ReadFile(argsPath)
+	for _, expected := range []string{"diff", "--metadata", "before", "after"} {
+		if !strings.Contains(string(args), expected) {
+			t.Fatalf("arguments missing %q: %s", expected, args)
+		}
+	}
+}
+
 func TestStatsUsesRequestedRepositoryCountingMode(t *testing.T) {
 	dir := t.TempDir()
 	argsPath := filepath.Join(dir, "args")