Ignore staleness markers (#300)

* ignore staleness markers

* handle stale NaN if they are integers

* handle stale sum+count NaNs in histograms

go.mod

@@ -11,6 +11,7 @@ require (
 	github.com/golang/protobuf v1.5.2
 	github.com/google/go-cmp v0.5.6
 	github.com/jstemmer/go-junit-report v0.9.1
+	github.com/prometheus/prometheus v2.5.0+incompatible
 	go.opencensus.io v0.23.0
 	golang.org/x/lint v0.0.0-20210508222113-6edffad5e616
 	golang.org/x/net v0.0.0-20210503060351-7fd8e65b6420

go.sum

@@ -176,6 +176,8 @@ github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINE
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/prometheus/client_model v0.0.0-20190812154241-14fe0d1b01d4/go.mod h1:xMI15A0UPsDsEKsMN9yxemIoYk6Tm2C1GtYGdfGttqA=
+github.com/prometheus/prometheus v2.5.0+incompatible h1:7QPitgO2kOFG8ecuRn9O/4L9+10He72rVRJvMXrE9Hg=
+github.com/prometheus/prometheus v2.5.0+incompatible/go.mod h1:oAIUtOny2rjMX0OWN5vPR5/q/twIROJvdqnQKDdil/s=
 github.com/rogpeppe/fastuuid v1.2.0/go.mod h1:jVj6XXZzXRy/MSR5jhDC/2q6DgLz+nrA6LYCDYWNEvQ=
 github.com/rogpeppe/go-internal v1.3.0/go.mod h1:M8bDsm7K2OlrFYOpmOWEs/qY81heoFRclV5y23lUDJ4=
 github.com/spaolacci/murmur3 v0.0.0-20180118202830-f09979ecbc72/go.mod h1:JwIasOWyU6f++ZhiEuf87xNszmSA2myDM2Kzu9HwQUA=

metrics_proto.go

@@ -23,6 +23,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"math"
 	"path"
 	"strings"
 
@@ -32,6 +33,7 @@ import (
 	metricspb "github.com/census-instrumentation/opencensus-proto/gen-go/metrics/v1"
 	resourcepb "github.com/census-instrumentation/opencensus-proto/gen-go/resource/v1"
 	timestamppb "github.com/golang/protobuf/ptypes/timestamp"
+	promvalue "github.com/prometheus/prometheus/pkg/value"
 	distributionpb "google.golang.org/genproto/googleapis/api/distribution"
 	labelpb "google.golang.org/genproto/googleapis/api/label"
 	googlemetricpb "google.golang.org/genproto/googleapis/api/metric"
@@ -481,13 +483,20 @@ func protoToMetricPoint(value interface{}) (*monitoringpb.TypedValue, error) {
 		return nil, fmt.Errorf("protoToMetricPoint: unknown Data type: %T", value)
 
 	case *metricspb.Point_Int64Value:
+		// drop handle stale NaNs that were cast to integers
+		if isStaleInt64(v.Int64Value) {
+			return nil, nil
+		}
 		return &monitoringpb.TypedValue{
 			Value: &monitoringpb.TypedValue_Int64Value{
 				Int64Value: v.Int64Value,
 			},
 		}, nil
 
 	case *metricspb.Point_DoubleValue:
+		if promvalue.IsStaleNaN(v.DoubleValue) {
+			return nil, nil
+		}
 		return &monitoringpb.TypedValue{
 			Value: &monitoringpb.TypedValue_DoubleValue{
 				DoubleValue: v.DoubleValue,
@@ -498,6 +507,9 @@ func protoToMetricPoint(value interface{}) (*monitoringpb.TypedValue, error) {
 		dv := v.DistributionValue
 		var mv *monitoringpb.TypedValue_DistributionValue
 		if dv != nil {
+			if isStaleInt64(dv.Count) || promvalue.IsStaleNaN(dv.Sum) {
+				return nil, nil
+			}
 			var mean float64
 			if dv.Count > 0 {
 				mean = float64(dv.Sum) / float64(dv.Count)
@@ -534,6 +546,10 @@ func protoToMetricPoint(value interface{}) (*monitoringpb.TypedValue, error) {
 	}
 }
 
+func isStaleInt64(v int64) bool {
+	return v == int64(math.Float64frombits(promvalue.StaleNaN))
+}
+
 func bucketCounts(buckets []*metricspb.DistributionValue_Bucket) []int64 {
 	bucketCounts := make([]int64, len(buckets))
 	for i, bucket := range buckets {