[exporterhelper] record metric should log the number of log records b…

…efore the data are sent to the consumers downstream (#10402)

#### Description
The sender metric within the exporterhelper should measure the number of
items coming into the sender, not what was done with the items
downstream, if the components downstream are mutable. An example of this
is provided as a unit test within this PR.

This PR also addresses nil panics that some users are experiencing. 

#### Link to tracking issue
Fixes #10033

.chloggen/exporterhelper_metric_fix.yaml

@@ -0,0 +1,20 @@
+# Use this changelog template to create an entry for release notes.
+
+# 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. otlpreceiver)
+component: exporterhelper
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: There is no guarantee that after the exporterhelper sends the plog/pmetric/ptrace data downstream that the data won't be mutated in some way. (e.g by the batch_sender) This mutation could result in the proceeding call to req.ItemsCount() to provide inaccurate information to be logged.
+
+# One or more tracking issues or pull requests related to the change
+issues: [10033]
+
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []

exporter/exporterhelper/logs.go

@@ -155,7 +155,8 @@ func newLogsExporterWithObservability(obsrep *ObsReport) requestSender {
 
 func (lewo *logsExporterWithObservability) send(ctx context.Context, req Request) error {
 	c := lewo.obsrep.StartLogsOp(ctx)
+	numLogRecords := req.ItemsCount()
 	err := lewo.nextSender.send(c, req)
-	lewo.obsrep.EndLogsOp(c, req.ItemsCount(), err)
+	lewo.obsrep.EndLogsOp(c, numLogRecords, err)
 	return err
 }

exporter/exporterhelper/logs_test.go

@@ -191,6 +191,21 @@ func TestLogsExporter_WithRecordMetrics(t *testing.T) {
 	checkRecordedMetricsForLogsExporter(t, tt, le, nil)
 }
 
+func TestLogsExporter_pLogModifiedDownStream_WithRecordMetrics(t *testing.T) {
+	tt, err := componenttest.SetupTelemetry(fakeLogsExporterName)
+	require.NoError(t, err)
+	t.Cleanup(func() { require.NoError(t, tt.Shutdown(context.Background())) })
+
+	le, err := NewLogsExporter(context.Background(), exporter.Settings{ID: fakeLogsExporterName, TelemetrySettings: tt.TelemetrySettings(), BuildInfo: component.NewDefaultBuildInfo()}, &fakeLogsExporterConfig, newPushLogsDataModifiedDownstream(nil), WithCapabilities(consumer.Capabilities{MutatesData: true}))
+	assert.NotNil(t, le)
+	assert.NoError(t, err)
+	ld := testdata.GenerateLogs(2)
+
+	assert.NoError(t, le.ConsumeLogs(context.Background(), ld))
+	assert.Equal(t, 0, ld.LogRecordCount())
+	require.NoError(t, tt.CheckExporterLogs(int64(2), 0))
+}
+
 func TestLogsRequestExporter_WithRecordMetrics(t *testing.T) {
 	tt, err := componenttest.SetupTelemetry(fakeLogsExporterName)
 	require.NoError(t, err)
@@ -359,6 +374,13 @@ func TestLogsRequestExporter_WithShutdown_ReturnError(t *testing.T) {
 	assert.Equal(t, le.Shutdown(context.Background()), want)
 }
 
+func newPushLogsDataModifiedDownstream(retError error) consumer.ConsumeLogsFunc {
+	return func(_ context.Context, log plog.Logs) error {
+		log.ResourceLogs().MoveAndAppendTo(plog.NewResourceLogsSlice())
+		return retError
+	}
+}
+
 func newPushLogsData(retError error) consumer.ConsumeLogsFunc {
 	return func(_ context.Context, _ plog.Logs) error {
 		return retError

exporter/exporterhelper/metrics.go

@@ -155,7 +155,8 @@ func newMetricsSenderWithObservability(obsrep *ObsReport) requestSender {
 
 func (mewo *metricsSenderWithObservability) send(ctx context.Context, req Request) error {
 	c := mewo.obsrep.StartMetricsOp(ctx)
+	numMetricDataPoints := req.ItemsCount()
 	err := mewo.nextSender.send(c, req)
-	mewo.obsrep.EndMetricsOp(c, req.ItemsCount(), err)
+	mewo.obsrep.EndMetricsOp(c, numMetricDataPoints, err)
 	return err
 }

exporter/exporterhelper/metrics_test.go

@@ -192,6 +192,21 @@ func TestMetricsExporter_WithRecordMetrics(t *testing.T) {
 	checkRecordedMetricsForMetricsExporter(t, tt, me, nil)
 }
 
+func TestMetricsExporter_pMetricModifiedDownStream_WithRecordMetrics(t *testing.T) {
+	tt, err := componenttest.SetupTelemetry(fakeMetricsExporterName)
+	require.NoError(t, err)
+	t.Cleanup(func() { require.NoError(t, tt.Shutdown(context.Background())) })
+
+	me, err := NewMetricsExporter(context.Background(), exporter.Settings{ID: fakeMetricsExporterName, TelemetrySettings: tt.TelemetrySettings(), BuildInfo: component.NewDefaultBuildInfo()}, &fakeMetricsExporterConfig, newPushMetricsDataModifiedDownstream(nil), WithCapabilities(consumer.Capabilities{MutatesData: true}))
+	require.NoError(t, err)
+	require.NotNil(t, me)
+	md := testdata.GenerateMetrics(2)
+
+	assert.NoError(t, me.ConsumeMetrics(context.Background(), md))
+	assert.Equal(t, 0, md.MetricCount())
+	require.NoError(t, tt.CheckExporterMetrics(int64(4), 0))
+}
+
 func TestMetricsRequestExporter_WithRecordMetrics(t *testing.T) {
 	tt, err := componenttest.SetupTelemetry(fakeMetricsExporterName)
 	require.NoError(t, err)
@@ -370,6 +385,12 @@ func newPushMetricsData(retError error) consumer.ConsumeMetricsFunc {
 		return retError
 	}
 }
+func newPushMetricsDataModifiedDownstream(retError error) consumer.ConsumeMetricsFunc {
+	return func(_ context.Context, metric pmetric.Metrics) error {
+		metric.ResourceMetrics().MoveAndAppendTo(pmetric.NewResourceMetricsSlice())
+		return retError
+	}
+}
 
 func checkRecordedMetricsForMetricsExporter(t *testing.T, tt componenttest.TestTelemetry, me exporter.Metrics, wantError error) {
 	md := testdata.GenerateMetrics(2)

exporter/exporterhelper/traces.go

@@ -155,8 +155,9 @@ func newTracesExporterWithObservability(obsrep *ObsReport) requestSender {
 
 func (tewo *tracesExporterWithObservability) send(ctx context.Context, req Request) error {
 	c := tewo.obsrep.StartTracesOp(ctx)
+	numTraceSpans := req.ItemsCount()
 	// Forward the data to the next consumer (this pusher is the next).
 	err := tewo.nextSender.send(c, req)
-	tewo.obsrep.EndTracesOp(c, req.ItemsCount(), err)
+	tewo.obsrep.EndTracesOp(c, numTraceSpans, err)
 	return err
 }

exporter/exporterhelper/traces_test.go

@@ -189,6 +189,21 @@ func TestTracesExporter_WithRecordMetrics(t *testing.T) {
 	checkRecordedMetricsForTracesExporter(t, tt, te, nil)
 }
 
+func TestTracesExporter_pLogModifiedDownStream_WithRecordMetrics(t *testing.T) {
+	tt, err := componenttest.SetupTelemetry(fakeTracesExporterName)
+	require.NoError(t, err)
+	t.Cleanup(func() { require.NoError(t, tt.Shutdown(context.Background())) })
+
+	te, err := NewTracesExporter(context.Background(), exporter.Settings{ID: fakeTracesExporterName, TelemetrySettings: tt.TelemetrySettings(), BuildInfo: component.NewDefaultBuildInfo()}, &fakeTracesExporterConfig, newTraceDataPusherModifiedDownstream(nil), WithCapabilities(consumer.Capabilities{MutatesData: true}))
+	assert.NotNil(t, te)
+	assert.NoError(t, err)
+	td := testdata.GenerateTraces(2)
+
+	assert.NoError(t, te.ConsumeTraces(context.Background(), td))
+	assert.Equal(t, 0, td.SpanCount())
+	require.NoError(t, tt.CheckExporterTraces(int64(2), 0))
+}
+
 func TestTracesRequestExporter_WithRecordMetrics(t *testing.T) {
 	tt, err := componenttest.SetupTelemetry(fakeTracesExporterName)
 	require.NoError(t, err)
@@ -372,6 +387,13 @@ func newTraceDataPusher(retError error) consumer.ConsumeTracesFunc {
 	}
 }
 
+func newTraceDataPusherModifiedDownstream(retError error) consumer.ConsumeTracesFunc {
+	return func(_ context.Context, trace ptrace.Traces) error {
+		trace.ResourceSpans().MoveAndAppendTo(ptrace.NewResourceSpansSlice())
+		return retError
+	}
+}
+
 func checkRecordedMetricsForTracesExporter(t *testing.T, tt componenttest.TestTelemetry, te exporter.Traces, wantError error) {
 	td := testdata.GenerateTraces(2)
 	const numBatches = 7