LastValue should export as gauge metric kind (#17)

* Fix the bug for the situation when the aggregation type is LastValue. The metric kind should be gauge instead of cummulative

* Fix the format

* Fix the minor bugs for that second and nanos conflicts in the newGaugePoints

* Duplicate the Point create part instead of the whole TimeSeries. Remove the useless input argument in the newGaugePoint method

* Modify the format of stats.go

Author: peiqinzhao

stats.go

@@ -242,6 +242,8 @@ func (e *statsExporter) createMeasure(ctx context.Context, vd *view.Data) error
 	metricType := namespacedViewName(viewName)
 	var valueType metricpb.MetricDescriptor_ValueType
 	unit := m.Unit()
+	// Default metric Kind
+	metricKind := metricpb.MetricDescriptor_CUMULATIVE
 
 	switch agg.Type {
 	case view.AggTypeCount:
@@ -259,6 +261,7 @@ func (e *statsExporter) createMeasure(ctx context.Context, vd *view.Data) error
 	case view.AggTypeDistribution:
 		valueType = metricpb.MetricDescriptor_DISTRIBUTION
 	case view.AggTypeLastValue:
+		metricKind = metricpb.MetricDescriptor_GAUGE
 		switch m.(type) {
 		case *stats.Int64Measure:
 			valueType = metricpb.MetricDescriptor_INT64
@@ -269,7 +272,6 @@ func (e *statsExporter) createMeasure(ctx context.Context, vd *view.Data) error
 		return fmt.Errorf("unsupported aggregation type: %s", agg.Type.String())
 	}
 
-	metricKind := metricpb.MetricDescriptor_CUMULATIVE
 	displayNamePrefix := defaultDisplayNamePrefix
 	if e.o.MetricPrefix != "" {
 		displayNamePrefix = e.o.MetricPrefix
@@ -297,6 +299,15 @@ func (e *statsExporter) createMeasure(ctx context.Context, vd *view.Data) error
 }
 
 func newPoint(v *view.View, row *view.Row, start, end time.Time) *monitoringpb.Point {
+	switch v.Aggregation.Type {
+	case view.AggTypeLastValue:
+		return newGaugePoint(v, row, end)
+	default:
+		return newCumulativePoint(v, row, start, end)
+	}
+}
+
+func newCumulativePoint(v *view.View, row *view.Row, start, end time.Time) *monitoringpb.Point {
 	return &monitoringpb.Point{
 		Interval: &monitoringpb.TimeInterval{
 			StartTime: &timestamp.Timestamp{
@@ -312,6 +323,20 @@ func newPoint(v *view.View, row *view.Row, start, end time.Time) *monitoringpb.P
 	}
 }
 
+func newGaugePoint(v *view.View, row *view.Row, end time.Time) *monitoringpb.Point {
+	gaugeTime := &timestamp.Timestamp{
+		Seconds: end.Unix(),
+		Nanos:   int32(end.Nanosecond()),
+	}
+	return &monitoringpb.Point{
+		Interval: &monitoringpb.TimeInterval{
+			StartTime: gaugeTime,
+			EndTime:   gaugeTime,
+		},
+		Value: newTypedValue(v, row),
+	}
+}
+
 func newTypedValue(vd *view.View, r *view.Row) *monitoringpb.TypedValue {
 	switch v := r.Data.(type) {
 	case *view.CountData:

stats_test.go

@@ -85,6 +85,15 @@ func TestExporter_makeReq(t *testing.T) {
 		Measure:     m,
 		Aggregation: view.Count(),
 	}
+
+	lastValueView := &view.View{
+		Name:        "lasttestview",
+		Description: "desc",
+		TagKeys:     []tag.Key{key},
+		Measure:     m,
+		Aggregation: view.LastValue(),
+	}
+
 	distView := &view.View{
 		Name:        "distview",
 		Description: "desc",
@@ -247,13 +256,13 @@ func TestExporter_makeReq(t *testing.T) {
 		{
 			name:   "last value agg",
 			projID: "proj-id",
-			vd:     newTestViewData(v, start, end, &last1, &last2),
+			vd:     newTestViewData(lastValueView, start, end, &last1, &last2),
 			want: []*monitoringpb.CreateTimeSeriesRequest{{
 				Name: monitoring.MetricProjectPath("proj-id"),
 				TimeSeries: []*monitoringpb.TimeSeries{
 					{
 						Metric: &metricpb.Metric{
-							Type: "custom.googleapis.com/opencensus/testview",
+							Type: "custom.googleapis.com/opencensus/lasttestview",
 							Labels: map[string]string{
 								"test_key":        "test-value-1",
 								opencensusTaskKey: taskValue,
@@ -266,7 +275,7 @@ func TestExporter_makeReq(t *testing.T) {
 							{
 								Interval: &monitoringpb.TimeInterval{
 									StartTime: &timestamp.Timestamp{
-										Seconds: start.Unix(),
+										Seconds: end.Unix(),
 										Nanos:   int32(start.Nanosecond()),
 									},
 									EndTime: &timestamp.Timestamp{
@@ -282,7 +291,7 @@ func TestExporter_makeReq(t *testing.T) {
 					},
 					{
 						Metric: &metricpb.Metric{
-							Type: "custom.googleapis.com/opencensus/testview",
+							Type: "custom.googleapis.com/opencensus/lasttestview",
 							Labels: map[string]string{
 								"test_key":        "test-value-2",
 								opencensusTaskKey: taskValue,
@@ -295,7 +304,7 @@ func TestExporter_makeReq(t *testing.T) {
 							{
 								Interval: &monitoringpb.TimeInterval{
 									StartTime: &timestamp.Timestamp{
-										Seconds: start.Unix(),
+										Seconds: end.Unix(),
 										Nanos:   int32(start.Nanosecond()),
 									},
 									EndTime: &timestamp.Timestamp{