Add a copy of the input metric when adding to aggregator (#5266)

internal/models/running_aggregator.go

@@ -109,11 +109,12 @@ func (r *RunningAggregator) metricDropped(metric telegraf.Metric) {
 // Add a metric to the aggregator and return true if the original metric
 // should be dropped.
 func (r *RunningAggregator) Add(metric telegraf.Metric) bool {
-
 	if ok := r.Config.Filter.Select(metric); !ok {
 		return false
 	}
 
+	metric = metric.Copy()
+
 	r.Config.Filter.Modify(metric)
 	if len(metric.FieldList()) == 0 {
 		return r.Config.DropOriginal

internal/models/running_aggregator_test.go

@@ -7,7 +7,6 @@ import (
 
 	"github.com/influxdata/telegraf"
 	"github.com/influxdata/telegraf/testutil"
-
 	"github.com/stretchr/testify/require"
 )
 
@@ -152,6 +151,32 @@ func TestAddDropOriginal(t *testing.T) {
 	require.False(t, ra.Add(m2))
 }
 
+func TestAddDoesNotModifyMetric(t *testing.T) {
+	ra := NewRunningAggregator(&TestAggregator{}, &AggregatorConfig{
+		Name: "TestRunningAggregator",
+		Filter: Filter{
+			FieldPass: []string{"a"},
+		},
+		DropOriginal: true,
+	})
+	require.NoError(t, ra.Config.Filter.Compile())
+
+	now := time.Now()
+
+	m := testutil.MustMetric(
+		"cpu",
+		map[string]string{},
+		map[string]interface{}{
+			"a": int64(42),
+			"b": int64(42),
+		},
+		now)
+	expected := m.Copy()
+	ra.Add(m)
+
+	testutil.RequireMetricEqual(t, expected, m)
+}
+
 type TestAggregator struct {
 	sum int64
 }