Fix carbon2 serializer not falling through to field separate when carbon2_format field is unset (#8201)

plugins/outputs/sumologic/sumologic_test.go

@@ -245,20 +245,6 @@ func TestContentType(t *testing.T) {
 			},
 			expectedBody: []byte("metric=cpu field=value  42 0\n"),
 		},
-		{
-			name: "carbon2 (data format unset) is supported and falls back to include field in metric name",
-			plugin: func() *SumoLogic {
-				s := Default()
-				s.headers = map[string]string{
-					contentTypeHeader: carbon2ContentType,
-				}
-				sr, err := carbon2.NewSerializer(string(carbon2.Carbon2FormatFieldEmpty))
-				require.NoError(t, err)
-				s.SetSerializer(sr)
-				return s
-			},
-			expectedBody: []byte("metric=cpu_value  42 0\n"),
-		},
 		{
 			name: "carbon2 (data format = metric includes field) is supported",
 			plugin: func() *SumoLogic {

plugins/serializers/carbon2/carbon2.go

@@ -12,13 +12,13 @@ import (
 type format string
 
 const (
-	Carbon2FormatFieldEmpty          = format("")
+	carbon2FormatFieldEmpty          = format("")
 	Carbon2FormatFieldSeparate       = format("field_separate")
 	Carbon2FormatMetricIncludesField = format("metric_includes_field")
 )
 
 var formats = map[format]struct{}{
-	Carbon2FormatFieldEmpty:          {},
+	carbon2FormatFieldEmpty:          {},
 	Carbon2FormatFieldSeparate:       {},
 	Carbon2FormatMetricIncludesField: {},
 }
@@ -29,10 +29,16 @@ type Serializer struct {
 
 func NewSerializer(metricsFormat string) (*Serializer, error) {
 	var f = format(metricsFormat)
+
 	if _, ok := formats[f]; !ok {
 		return nil, fmt.Errorf("unknown carbon2 format: %s", f)
 	}
 
+	// When unset, default to field separate.
+	if f == carbon2FormatFieldEmpty {
+		f = Carbon2FormatFieldSeparate
+	}
+
 	return &Serializer{
 		metricsFormat: f,
 	}, nil
@@ -60,8 +66,6 @@ func (s *Serializer) createObject(metric telegraf.Metric) []byte {
 		}
 
 		switch metricsFormat {
-		// Field separate is the default when no format specified.
-		case Carbon2FormatFieldEmpty:
 		case Carbon2FormatFieldSeparate:
 			m.WriteString(serializeMetricFieldSeparate(
 				metric.Name(), fieldName,
@@ -101,7 +105,7 @@ func (s *Serializer) getMetricsFormat() format {
 }
 
 func (s *Serializer) IsMetricsFormatUnset() bool {
-	return s.metricsFormat == Carbon2FormatFieldEmpty
+	return s.metricsFormat == carbon2FormatFieldEmpty
 }
 
 func serializeMetricFieldSeparate(name, fieldName string) string {