Merge pull request #1991 from restic/debug-1978

scanner: Use context only for cancellation

changelog/unreleased/issue-1978

@@ -0,0 +1,12 @@
+Bugfix: Do not return an error when the scanner is faster than backup
+
+When restic makes a backup, there's a background task called "scanner" which
+collects information on how many files and directories are to be saved, in
+order to display progress information to the user. When the backup finishes
+faster than the scanner, it is aborted because the result is not needed any
+more. This logic contained a bug, where quitting the scanner process was
+treated as an error, and caused restic to print an unhelpful error message
+("context canceled").
+
+https://github.com/restic/restic/issues/1978
+https://github.com/restic/restic/pull/1991

internal/archiver/scanner.go

@@ -52,20 +52,17 @@ func (s *Scanner) Scan(ctx context.Context, targets []string) error {
 		}
 
 		if ctx.Err() != nil {
-			return ctx.Err()
+			return nil
 		}
 	}
 
-	if ctx.Err() != nil {
-		return ctx.Err()
-	}
 	s.Result("", stats)
 	return nil
 }
 
 func (s *Scanner) scan(ctx context.Context, stats ScanStats, target string) (ScanStats, error) {
 	if ctx.Err() != nil {
-		return stats, ctx.Err()
+		return stats, nil
 	}
 
 	// exclude files by path before running stat to reduce number of lstat calls
@@ -89,10 +86,6 @@ func (s *Scanner) scan(ctx context.Context, stats ScanStats, target string) (Sca
 		stats.Files++
 		stats.Bytes += uint64(fi.Size())
 	case fi.Mode().IsDir():
-		if ctx.Err() != nil {
-			return stats, ctx.Err()
-		}
-
 		names, err := readdirnames(s.FS, target)
 		if err != nil {
 			return stats, s.Error(target, fi, err)
@@ -109,9 +102,6 @@ func (s *Scanner) scan(ctx context.Context, stats ScanStats, target string) (Sca
 		stats.Others++
 	}
 
-	if ctx.Err() != nil {
-		return stats, ctx.Err()
-	}
 	s.Result(target, stats)
 	return stats, nil
 }

internal/archiver/scanner_test.go

@@ -289,7 +289,7 @@ func TestScannerCancel(t *testing.T) {
 		"other": TestFile{Content: "other"},
 	}
 
-	result := ScanStats{Files: 2, Bytes: 6}
+	result := ScanStats{Files: 2, Dirs: 1, Bytes: 6}
 
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
@@ -319,12 +319,8 @@ func TestScannerCancel(t *testing.T) {
 	}
 
 	err = sc.Scan(ctx, []string{"."})
-	if err == nil {
-		t.Errorf("did not find expected error")
-	}
-
-	if err != context.Canceled {
-		t.Errorf("unexpected error found, want %v, got %v", context.Canceled, err)
+	if err != nil {
+		t.Errorf("unexpected error %v found", err)
 	}
 
 	if lastStats != result {