prevent duplicate labels fields

core.go

@@ -121,7 +121,7 @@ func (c *core) Write(ent zapcore.Entry, fields []zapcore.Field) error {
 	c.tempLabels.mutex.Unlock()
 	lbls.mutex.RUnlock()
 
-	fields = append(fields, labelsField(c.allLabels()))
+	fields = mergeLabelFields(fields, c.allLabels())
 	fields = c.withSourceLocation(ent, fields)
 	if c.config.ServiceName != "" {
 		fields = c.withServiceContext(c.config.ServiceName, fields)

core_test.go

@@ -180,6 +180,28 @@ func TestWrite(t *testing.T) {
 	assert.NotNil(t, logs.All()[0].ContextMap()[labelsKey])
 }
 
+// ref: https://github.com/blendle/zapdriver/issues/29
+func TestWriteDuplicateLabels(t *testing.T) {
+	debugcore, logs := observer.New(zapcore.DebugLevel)
+	core := &core{
+		Core:       debugcore,
+		permLabels: newLabels(),
+		tempLabels: newLabels(),
+	}
+
+	fields := []zap.Field{
+		Labels(
+			Label("hello", "world"),
+			Label("hi", "universe"),
+		),
+	}
+
+	err := core.Write(zapcore.Entry{}, fields)
+	require.NoError(t, err)
+
+	assert.Len(t, logs.All()[0].Context, 1)
+}
+
 func TestWriteConcurrent(t *testing.T) {
 	temp := newLabels()
 	temp.store = map[string]string{"one": "1", "two": "2"}

label.go

@@ -45,6 +45,29 @@ func labelsField(l *labels) zap.Field {
 	return zap.Object(labelsKey, l)
 }
 
+func mergeLabelFields(fields []zap.Field, newLabels *labels) []zap.Field {
+	for i := range fields {
+		lbls, ok := fields[i].Interface.(*labels)
+		if !ok {
+			continue
+		}
+
+		newLabels.mutex.RLock()
+		defer newLabels.mutex.RUnlock()
+
+		lbls.mutex.Lock()
+		defer lbls.mutex.Unlock()
+
+		for k, v := range newLabels.store {
+			lbls.store[k] = v
+		}
+
+		return fields
+	}
+
+	return append(fields, labelsField(newLabels))
+}
+
 type labels struct {
 	store map[string]string
 	mutex *sync.RWMutex