ability to share default registry

example/main.go

@@ -24,6 +24,7 @@ import (
 	"time"
 
 	"contrib.go.opencensus.io/exporter/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
 	"go.opencensus.io/stats"
 	"go.opencensus.io/stats/view"
 )
@@ -78,6 +79,6 @@ func main() {
 
 	addr := ":9999"
 	log.Printf("Serving at %s", addr)
-	http.Handle("/metrics", exporter)
+	http.Handle("/metrics", promhttp.Handler())
 	log.Fatal(http.ListenAndServe(addr, nil))
 }

prometheus.go

@@ -23,6 +23,7 @@ import (
 	"sync"
 
 	"context"
+
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
 	"go.opencensus.io/metric/metricdata"
@@ -44,6 +45,8 @@ type Exporter struct {
 type Options struct {
 	Namespace   string
 	Registry    *prometheus.Registry
+	Registerer  prometheus.Registerer
+	Gatherer    prometheus.Gatherer
 	OnError     func(err error)
 	ConstLabels prometheus.Labels // ConstLabels will be set as labels on all views.
 }
@@ -53,12 +56,19 @@ func NewExporter(o Options) (*Exporter, error) {
 	if o.Registry == nil {
 		o.Registry = prometheus.NewRegistry()
 	}
-	collector := newCollector(o, o.Registry)
+	if o.Registerer == nil {
+		o.Registerer = o.Registry
+	}
+	if o.Gatherer == nil {
+		o.Gatherer = o.Registry
+	}
+
+	collector := newCollector(o, o.Registerer)
 	e := &Exporter{
 		opts:    o,
-		g:       o.Registry,
+		g:       o.Gatherer,
 		c:       collector,
-		handler: promhttp.HandlerFor(o.Registry, promhttp.HandlerOpts{}),
+		handler: promhttp.HandlerFor(o.Gatherer, promhttp.HandlerOpts{}),
 	}
 	collector.ensureRegisteredOnce()
 
@@ -112,7 +122,7 @@ type collector struct {
 	registerOnce sync.Once
 
 	// reg helps collector register views dynamically.
-	reg *prometheus.Registry
+	reg prometheus.Registerer
 
 	// reader reads metrics from all registered producers.
 	reader *metricexport.Reader
@@ -132,7 +142,7 @@ func (c *collector) Collect(ch chan<- prometheus.Metric) {
 	c.reader.ReadAndExport(me)
 }
 
-func newCollector(opts Options, registrar *prometheus.Registry) *collector {
+func newCollector(opts Options, registrar prometheus.Registerer) *collector {
 	return &collector{
 		reg:    registrar,
 		opts:   opts,

prometheus_test.go

@@ -28,6 +28,7 @@ import (
 	"go.opencensus.io/tag"
 
 	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
 )
 
 type mSlice []*stats.Int64Measure
@@ -448,3 +449,88 @@ tests_foo{key_1="issue659",key_2="",key_3="issue659",key_4="",key_5="issue659"}
 		t.Fatalf("output differed from expected output: %s want: %s", output, want)
 	}
 }
+
+func TestShareDefaultRegistry(t *testing.T) {
+	_, err := NewExporter(Options{
+		Registerer: prometheus.DefaultRegisterer,
+		Gatherer:   prometheus.DefaultGatherer,
+	})
+	if err != nil {
+		t.Fatalf("failed to create prometheus exporter: %v", err)
+	}
+	m := stats.Int64("tests/foo", "foo", stats.UnitDimensionless)
+	v := &view.View{
+		Name:        m.Name(),
+		Description: m.Description(),
+		Measure:     m,
+		Aggregation: view.Count(),
+	}
+	if err := view.Register(v); err != nil {
+		t.Fatalf("failed to create views: %v", err)
+	}
+	defer view.Unregister(v)
+	view.SetReportingPeriod(time.Millisecond)
+
+	stats.Record(context.Background(), m.M(1))
+
+	// counter, prometheus way
+	c := prometheus.NewCounter(prometheus.CounterOpts{Name: "prom_counter", Help: "Prometheus Counter"})
+	prometheus.MustRegister(c)
+
+	c.Add(1)
+
+	// Use prometheus handler
+	srv := httptest.NewServer(promhttp.Handler())
+	defer srv.Close()
+
+	var i int
+	var output string
+	for {
+		time.Sleep(10 * time.Millisecond)
+		if i == 1000 {
+			t.Fatal("no output at /metrics (10s wait)")
+		}
+		i++
+
+		resp, err := http.Get(srv.URL)
+		if err != nil {
+			t.Fatalf("failed to get /metrics: %v", err)
+		}
+
+		body, err := ioutil.ReadAll(resp.Body)
+		if err != nil {
+			t.Fatalf("failed to read body: %v", err)
+		}
+		resp.Body.Close()
+
+		output = string(body)
+		if output != "" {
+			break
+		}
+	}
+
+	if strings.Contains(output, "collected before with the same name and label values") {
+		t.Fatal("metric name and labels being duplicated but must be unique")
+	}
+
+	if strings.Contains(output, "error(s) occurred") {
+		t.Fatal("error reported by prometheus registry")
+	}
+
+	wantOc := `# HELP tests_foo foo
+# TYPE tests_foo counter
+tests_foo 1
+`
+	if !strings.Contains(output, wantOc) {
+		t.Errorf("output does not contain opencensus counter. Output: %s want: %s", output, wantOc)
+	}
+
+	wantP := `# HELP prom_counter Prometheus Counter
+# TYPE prom_counter counter
+prom_counter 1
+`
+	if !strings.Contains(output, wantP) {
+		t.Errorf("output does not contain opencensus counter. Output: %s want: %s", output, wantP)
+	}
+
+}