Expose the Gatherer and use new registry over prometheus default registry

counter_test.go

@@ -0,0 +1,61 @@
+package metrics
+
+import (
+	"testing"
+
+	dto "github.com/prometheus/client_model/go"
+)
+
+func TestCounter(t *testing.T) {
+	expected := struct {
+		Name  string
+		Help  string
+		Type  dto.MetricType
+		Value float64
+	}{
+		"test_counter_counter_total",
+		"count all the things",
+		dto.MetricType_COUNTER,
+		5,
+	}
+
+	ns := NewNamespace("test", "counter", nil)
+
+	c := ns.NewCounter("counter", "count all the things")
+	c.Inc(5)
+
+	Register(ns)
+	defer Deregister(ns)
+
+	mfs, err := Gather()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if len(mfs) != 1 {
+		t.Fatalf("expected one metric family but got %d", len(mfs))
+	}
+
+	family := mfs[0]
+	if *family.Name != expected.Name {
+		t.Fatalf("expected name `%s` but got `%s`", expected.Name, *family.Name)
+	}
+
+	if *family.Help != expected.Help {
+		t.Fatalf("expected help `%s` but got `%s`", expected.Help, *family.Help)
+	}
+
+	if *family.Type != expected.Type {
+		t.Fatalf("expected type `%d` but got `%d`", expected.Type, *family.Type)
+	}
+
+	if len(family.Metric) != 1 {
+		t.Fatalf("expected one metric but got %d", len(family.Metric))
+	}
+
+	metric := family.Metric[0]
+	value := metric.GetCounter().GetValue()
+	if value != expected.Value {
+		t.Fatalf("expected counter value %f but got %f", expected.Value, value)
+	}
+}

gather.go

@@ -0,0 +1,17 @@
+package metrics
+
+import (
+	"github.com/prometheus/client_golang/prometheus"
+	dto "github.com/prometheus/client_model/go"
+)
+
+// Gatherer returns the metric gatherer
+func Gatherer() prometheus.Gatherer {
+	return registry
+}
+
+// Gather calls the gatherer to return all the metric families of
+// every metric in the registry.
+func Gather() ([]*dto.MetricFamily, error) {
+	return Gatherer().Gather()
+}

handler.go

@@ -3,11 +3,11 @@ package metrics
 import (
 	"net/http"
 
-	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
 )
 
 // Handler returns the global http.Handler that provides the prometheus
 // metrics format on GET requests
 func Handler() http.Handler {
-	return prometheus.Handler()
+	return promhttp.HandlerFor(Gatherer(), promhttp.HandlerOpts{})
 }

register.go

@@ -1,15 +1,13 @@
 package metrics
 
-import "github.com/prometheus/client_golang/prometheus"
-
 // Register adds all the metrics in the provided namespace to the global
 // metrics registry
 func Register(n *Namespace) {
-	prometheus.MustRegister(n)
+	registry.MustRegister(n)
 }
 
 // Deregister removes all the metrics in the provided namespace from the
 // global metrics registry
 func Deregister(n *Namespace) {
-	prometheus.Unregister(n)
+	registry.Unregister(n)
 }

registry.go

@@ -0,0 +1,7 @@
+package metrics
+
+import "github.com/prometheus/client_golang/prometheus"
+
+var (
+	registry = prometheus.NewRegistry()
+)