pkg/monitor: fix linter errors

pkg/monitor/monitor.go

@@ -355,10 +355,12 @@ func (m *Manager) AssignPID(key string, pid int) error {
 	if err != nil {
 		return fmt.Errorf("failed to open tasks file for key %s: %w", key, err)
 	}
-	defer f.Close()
-
 	data := []byte(strconv.Itoa(pid) + "\n")
 	if _, err := f.Write(data); err != nil {
+		f.Close() //nolint:errcheck // report the write error
+		return fmt.Errorf("failed to write pid %d for key %s: %w", pid, key, err)
+	}
+	if err := f.Close(); err != nil {
 		return fmt.Errorf("failed to write pid %d for key %s: %w", pid, key, err)
 	}
 	log().Info("assigned PID to mon_group", "key", key, "pid", pid)
@@ -411,7 +413,7 @@ func pidInTasksFile(path string, pid int) (bool, error) {
 		}
 		return false, fmt.Errorf("failed to open tasks file %s: %w", path, err)
 	}
-	defer f.Close()
+	defer f.Close() //nolint:errcheck // read-only
 
 	target := strconv.Itoa(pid)
 	sc := bufio.NewScanner(f)

pkg/monitor/monitor_test.go

@@ -927,7 +927,8 @@ func TestRemove_ConcurrentEnsureGroup(t *testing.T) {
 
 		var wg sync.WaitGroup
 		wg.Go(func() {
-			mgr.Remove("pod-uid-1")
+			// Racing with EnsureGroup, we're not interested in the error but the state (checked later)
+			_ = mgr.Remove("pod-uid-1")
 		})
 		var ensureErr error
 		wg.Go(func() {
@@ -969,10 +970,11 @@ func TestRemove_ConcurrentReadCounters(t *testing.T) {
 	go func() {
 		defer close(done)
 		for i := 0; i < 100; i++ {
-			mgr.ReadCounters("pod-uid-1")
+			// Racing with Remove below so errors are expected, we only assert on no panic/data race
+			_, _ = mgr.ReadCounters("pod-uid-1")
 		}
 	}()
 	// Give the reader goroutine a head start, then remove.
-	mgr.Remove("pod-uid-1")
+	_ = mgr.Remove("pod-uid-1")
 	<-done
 }

pkg/monitor/validate.go

@@ -104,7 +104,7 @@ func isHex(s string) bool {
 		return false
 	}
 	for _, c := range s {
-		if !((c >= '0' && c <= '9') || (c >= 'a' && c <= 'f') || (c >= 'A' && c <= 'F')) {
+		if (c < '0' || c > '9') && (c < 'a' || c > 'f') && (c < 'A' || c > 'F') {
 			return false
 		}
 	}