added non-blocking write to channel and tests

internal/monitor/metadata.go

@@ -30,12 +30,16 @@ func (m *Metadata) Save(file string) error {
 	return os.WriteFile(file, contents, 0o600)
 }
 
+var errEmptyMetadata = fmt.Errorf("metadata file is empty")
+
 func (m *Metadata) Load(file string) error {
 	contents, err := os.ReadFile(file)
 	if err != nil {
 		return fmt.Errorf("reading file: %w", err)
 	}
-
+	if len(contents) == 0 {
+		return errEmptyMetadata
+	}
 	if err := json.Unmarshal(contents, m); err != nil {
 		return fmt.Errorf("file: %v content: %v parsing json: %w", file, string(contents), err)
 	}
@@ -48,7 +52,7 @@ func watchForMetadataChanges(ctx context.Context, log logrus.FieldLogger, metada
 	if err != nil {
 		return nil, fmt.Errorf("setting up new watcher: %w", err)
 	}
-	updates := make(chan Metadata, 10)
+	updates := make(chan Metadata, 1)
 
 	if err := watcher.Add(filepath.Dir(metadataFilePath)); err != nil {
 		return nil, fmt.Errorf("adding watch: %w", err)
@@ -61,7 +65,11 @@ func watchForMetadataChanges(ctx context.Context, log logrus.FieldLogger, metada
 				log.Warnf("loading metadata failed: %v", err)
 			}
 		} else {
-			updates <- metadata
+			select {
+			case updates <- metadata:
+			default:
+				log.Warnf("metadata update skipped, channel full")
+			}
 		}
 	}
 

internal/monitor/metatada_test.go

@@ -73,15 +73,20 @@ func Test_monitor_waitForMetadata(t *testing.T) {
 	time.Sleep(time.Second * 1)
 
 	// create the file, expect the event to arrive at updates channel
-	meta := Metadata{
-		ClusterID: uuid.New().String(),
-		LastStart: 123,
+	var meta Metadata
+	maxI := int64(124)
+	for i := int64(0); i <= maxI; i++ {
+		meta = Metadata{
+			ClusterID: uuid.New().String(),
+			LastStart: i,
+		}
+		require.NoError(t, meta.Save(syncFile))
 	}
-	require.NoError(t, meta.Save(syncFile))
 
 	metadata, ok := <-updates
 	require.True(t, ok)
-	require.Equal(t, int64(123), metadata.LastStart)
+	require.True(t, maxI >= metadata.LastStart, "expected last start to be %d, got %d", maxI, metadata.LastStart)
+	require.True(t, metadata.LastStart != 0, "expected last start to be non-zero, got %d", metadata.LastStart)
 
 	cancel()