Apply global and plugin level metric modifications before filtering (i…

…nfluxdata#5152)

internal/models/running_input.go

@@ -62,12 +62,6 @@ func (r *RunningInput) MakeMetric(metric telegraf.Metric) telegraf.Metric {
 		return nil
 	}
 
-	r.Config.Filter.Modify(metric)
-	if len(metric.FieldList()) == 0 {
-		r.metricFiltered(metric)
-		return nil
-	}
-
 	m := makemetric(
 		metric,
 		r.Config.NameOverride,
@@ -76,6 +70,12 @@ func (r *RunningInput) MakeMetric(metric telegraf.Metric) telegraf.Metric {
 		r.Config.Tags,
 		r.defaultTags)
 
+	r.Config.Filter.Modify(metric)
+	if len(metric.FieldList()) == 0 {
+		r.metricFiltered(metric)
+		return nil
+	}
+
 	r.MetricsGathered.Incr(1)
 	GlobalMetricsGathered.Incr(1)
 	return m

internal/models/running_input_test.go

@@ -7,11 +7,43 @@ import (
 	"github.com/influxdata/telegraf"
 	"github.com/influxdata/telegraf/metric"
 	"github.com/influxdata/telegraf/testutil"
-
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
+func TestMakeMetricFilterAfterApplyingGlobalTags(t *testing.T) {
+	now := time.Now()
+	ri := NewRunningInput(&testInput{}, &InputConfig{
+		Filter: Filter{
+			TagInclude: []string{"b"},
+		},
+	})
+	require.NoError(t, ri.Config.Filter.Compile())
+	ri.SetDefaultTags(map[string]string{"a": "x", "b": "y"})
+
+	m, err := metric.New("cpu",
+		map[string]string{},
+		map[string]interface{}{
+			"value": 42,
+		},
+		now)
+	require.NoError(t, err)
+
+	actual := ri.MakeMetric(m)
+
+	expected, err := metric.New("cpu",
+		map[string]string{
+			"b": "y",
+		},
+		map[string]interface{}{
+			"value": 42,
+		},
+		now)
+	require.NoError(t, err)
+
+	testutil.RequireMetricEqual(t, expected, actual)
+}
+
 func TestMakeMetricNoFields(t *testing.T) {
 	now := time.Now()
 	ri := NewRunningInput(&testInput{}, &InputConfig{