add resetcounter methods

Author: n-oden

README.md

@@ -14,13 +14,15 @@ This package is intended as a way to publish metrics for applications that are _
 
 ## 🚨 Upgrading
 
-Between v0.5.0 and v0.6.0, the behavior of the `IncrCounter` method changed: previously it would create a `GAUGE` [metric kind](https://cloud.google.com/monitoring/api/v3/kinds-and-types), but from v0.6.0 forward it will create a `CUMULATIVE` metric kind.  (See https://github.com/google/go-metrics-stackdriver/issues/18 for a discussion.)
+Between v0.5.0 and v0.6.0, the behavior of the `IncrCounter()` method changed: previously it would create a `GAUGE` [metric kind](https://cloud.google.com/monitoring/api/v3/kinds-and-types), but from v0.6.0 forward it will create a `CUMULATIVE` metric kind.  (See https://github.com/google/go-metrics-stackdriver/issues/18 for a discussion.)
 
-However, once a [MetricDescriptor](https://cloud.google.com/logging/docs/reference/v2/rest/v2/projects.metrics#MetricDescriptor) has been created in Google Cloud Monitoring, its `metricKind` field cannot be changed.  So if you have any _existing_ `GAUGE` metrics that were created by `IncrCounter`, you will see errors in your logs when the v0.6.0 client attempts to update them and fails.  Your options for handling this are:
+However, once a [MetricDescriptor](https://cloud.google.com/logging/docs/reference/v2/rest/v2/projects.metrics#MetricDescriptor) has been created in Google Cloud Monitoring, its `metricKind` field cannot be changed.  So if you have any _existing_ `GAUGE` metrics that were created by `IncrCounter()`, you will see errors in your logs when the v0.6.0 client attempts to update them and fails.  Your options for handling this are:
 
 1. Change the name of the metric you are passing to `IncrCounter` (creating a new metricDescriptor with a different name), or:
 2. Delete the existing metricDescriptor using the [delete API](https://cloud.google.com/monitoring/api/ref_v3/rest/v3/projects.metricDescriptors/delete) and let go-metrics re-create it as a `CUMULATIVE` metric
 
+Additionally, v0.6.0 adds `ResetCounter()` and `ResetCounterWithLabels()` methods: calling these methods resets the counter value to zero.
+
 ## Details
 
 [stackdriver.NewSink](https://godoc.org/github.com/google/go-metrics-stackdriver#NewSink)'s return value satisfies the go-metrics library's [MetricSink](https://godoc.org/github.com/armon/go-metrics#MetricSink) interface. When providing a `stackdriver.Sink` to libraries and applications instrumented against `MetricSink`, the metrics will be aggregated within this library and written to stackdriver as [Generic Task](https://cloud.google.com/monitoring/api/resources#tag_generic_task) timeseries metrics.

stackdriver.go

@@ -562,6 +562,34 @@ func (s *Sink) IncrCounterWithLabels(key []string, val float32, labels []metrics
 	}
 }
 
+// ResetCounter resets a counter to zero
+func (s *Sink) ResetCounter(key []string) {
+	s.ResetCounterWithLabels(key, nil)
+}
+
+// ResetCounterWithLabels resets a counter to zero
+func (s *Sink) ResetCounterWithLabels(key []string, labels []metrics.Label) {
+	n := newSeries(key, labels)
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	initVal := float64(0)
+	startTime := time.Now().Add(time.Millisecond * -1)
+	c, ok := s.counters[n.hash]
+	if ok {
+		// counter exists, reset to 0 and reset startTime
+		c.value = initVal
+		c.startTime = startTime
+	} else {
+		// counter did not exist, init at 0 value
+		s.counters[n.hash] = &counter{
+			name:      n,
+			value:     initVal,
+			startTime: startTime,
+		}
+	}
+}
+
 // AddSample adds a sample to a histogram metric.
 func (s *Sink) AddSample(key []string, val float32) {
 	s.AddSampleWithLabels(key, val, nil)

stackdriver_test.go

@@ -458,6 +458,81 @@ func TestSample(t *testing.T) {
 				}
 			},
 		},
+		{
+			name: "reset counter",
+			collect: func() {
+				ss.IncrCounter([]string{"foo", "bar"}, 1.0)
+				ss.IncrCounter([]string{"foo", "bar"}, 1.0)
+				ss.ResetCounter([]string{"foo", "bar"})
+			},
+			createFn: func(t *testing.T) func(context.Context, *monitoringpb.CreateTimeSeriesRequest) (*emptypb.Empty, error) {
+				return func(_ context.Context, req *monitoringpb.CreateTimeSeriesRequest) (*emptypb.Empty, error) {
+					want := &monitoringpb.CreateTimeSeriesRequest{
+						Name: "projects/foo",
+						TimeSeries: []*monitoringpb.TimeSeries{
+							{
+								Metric: &metricpb.Metric{
+									Type: "custom.googleapis.com/go-metrics/foo_bar_counter",
+								},
+								MetricKind: metricpb.MetricDescriptor_CUMULATIVE,
+								Points: []*monitoringpb.Point{
+									{
+										Value: &monitoringpb.TypedValue{
+											Value: &monitoringpb.TypedValue_DoubleValue{
+												DoubleValue: 0.0,
+											},
+										},
+									},
+								},
+							},
+						},
+					}
+					if diff := diffCreateMsg(want, req); diff != "" {
+						t.Errorf("unexpected CreateTimeSeriesRequest (-want +got):\n%s", diff)
+					}
+					return &emptypb.Empty{}, nil
+				}
+			},
+		},
+		{
+			name: "reset counter with label",
+			collect: func() {
+				ss.IncrCounterWithLabels([]string{"foo", "bar"}, 1.0, []metrics.Label{{Name: "env", Value: "dev"}})
+				ss.IncrCounterWithLabels([]string{"foo", "bar"}, 1.0, []metrics.Label{{Name: "env", Value: "dev"}})
+				ss.ResetCounterWithLabels([]string{"foo", "bar"}, []metrics.Label{{Name: "env", Value: "dev"}})
+			},
+			createFn: func(t *testing.T) func(context.Context, *monitoringpb.CreateTimeSeriesRequest) (*emptypb.Empty, error) {
+				return func(_ context.Context, req *monitoringpb.CreateTimeSeriesRequest) (*emptypb.Empty, error) {
+					want := &monitoringpb.CreateTimeSeriesRequest{
+						Name: "projects/foo",
+						TimeSeries: []*monitoringpb.TimeSeries{
+							{
+								Metric: &metricpb.Metric{
+									Type: "custom.googleapis.com/go-metrics/foo_bar_counter",
+									Labels: map[string]string{
+										"env": "dev",
+									},
+								},
+								MetricKind: metricpb.MetricDescriptor_CUMULATIVE,
+								Points: []*monitoringpb.Point{
+									{
+										Value: &monitoringpb.TypedValue{
+											Value: &monitoringpb.TypedValue_DoubleValue{
+												DoubleValue: 0.0,
+											},
+										},
+									},
+								},
+							},
+						},
+					}
+					if diff := diffCreateMsg(want, req); diff != "" {
+						t.Errorf("unexpected CreateTimeSeriesRequest (-want +got):\n%s", diff)
+					}
+					return &emptypb.Empty{}, nil
+				}
+			},
+		},
 		{
 			name: "gauge",
 			collect: func() {