[exporter/dynatrace] Do not mutate the original metrics (open-telemet…

…ry#16506)

The  `Map.Sort()` call mutates the original data which can lead to subtle bugs given that the exporter marked as not mutating

.chloggen/dynatrace-no-sort.yaml

@@ -0,0 +1,11 @@
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: exporter/dynatrace
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Make sure the original metrics are not mutated
+
+# One or more tracking issues related to the change
+issues: [16506]

exporter/dynatraceexporter/internal/serialization/sum.go

@@ -16,6 +16,8 @@ package serialization // import "github.com/open-telemetry/opentelemetry-collect
 
 import (
 	"fmt"
+	"sort"
+	"strings"
 
 	dtMetric "github.com/dynatrace-oss/dynatrace-metric-utils-go/metric"
 	"github.com/dynatrace-oss/dynatrace-metric-utils-go/metric/dimensions"
@@ -149,12 +151,13 @@ func serializeCumulativeCounter(name, prefix string, dims dimensions.NormalizedD
 }
 
 func convertTotalCounterToDelta(name, prefix string, dims dimensions.NormalizedDimensionList, dp pmetric.NumberDataPoint, prevCounters *ttlmap.TTLMap) (*dtMetric.Metric, error) {
-	id := name
-
-	dp.Attributes().Sort().Range(func(k string, v pcommon.Value) bool {
-		id += fmt.Sprintf(",%s=%s", k, v.AsString())
+	attrPairs := make([]string, 0, dp.Attributes().Len())
+	dp.Attributes().Range(func(k string, v pcommon.Value) bool {
+		attrPairs = append(attrPairs, k+"="+v.AsString())
 		return true
 	})
+	sort.Strings(attrPairs)
+	id := name + strings.Join(attrPairs, ",")
 
 	prevCounter := prevCounters.Get(id)
 

exporter/dynatraceexporter/internal/serialization/sum_test.go

@@ -391,3 +391,15 @@ func Test_serializeSum(t *testing.T) {
 		})
 	})
 }
+
+func Test_convertTotalCounterToDelta_notMutating(t *testing.T) {
+	dp := pmetric.NewNumberDataPoint()
+	dp.SetIntValue(5)
+	dp.Attributes().PutStr("attr2", "val2")
+	dp.Attributes().PutStr("attr1", "val1")
+	orig := pmetric.NewNumberDataPoint()
+	dp.CopyTo(orig)
+	_, err := convertTotalCounterToDelta("m", "prefix", dimensions.NormalizedDimensionList{}, dp, ttlmap.New(1, 1))
+	assert.NoError(t, err)
+	assert.Equal(t, orig, dp) // make sure the original data point is not mutated
+}