Add _total suffix for counters reported to prometheus (#54)

Signed-off-by: Gary Brown <gary@brownuk.com>

metrics/prometheus/factory.go

@@ -126,7 +126,7 @@ func newFactory(parent *Factory, scope string, tags map[string]string) *Factory
 
 // Counter implements Counter of metrics.Factory.
 func (f *Factory) Counter(name string, tags map[string]string) metrics.Counter {
-	name = f.subScope(name)
+	name = counterNamingConvention(f.subScope(name))
 	tags = f.mergeTags(tags)
 	labelNames := f.tagNames(tags)
 	opts := prometheus.CounterOpts{
@@ -244,3 +244,10 @@ func (f *Factory) tagsAsLabelValues(labels []string, tags map[string]string) []s
 	}
 	return ret
 }
+
+func counterNamingConvention(name string) string {
+	if !strings.HasSuffix(name, "_total") {
+		name += "_total"
+	}
+	return name
+}

metrics/prometheus/factory_test.go

@@ -41,7 +41,7 @@ func TestSeparator(t *testing.T) {
 	c1.Inc(1)
 	snapshot, err := registry.Gather()
 	require.NoError(t, err)
-	m1 := findMetric(t, snapshot, "bender:rodriguez", map[string]string{"a": "b"})
+	m1 := findMetric(t, snapshot, "bender:rodriguez_total", map[string]string{"a": "b"})
 	assert.EqualValues(t, 1, m1.GetCounter().GetValue(), "%+v", m1)
 }
 
@@ -63,10 +63,10 @@ func TestCounter(t *testing.T) {
 	snapshot, err := registry.Gather()
 	require.NoError(t, err)
 
-	m1 := findMetric(t, snapshot, "bender_rodriguez", map[string]string{"a": "b", "x": "y"})
+	m1 := findMetric(t, snapshot, "bender_rodriguez_total", map[string]string{"a": "b", "x": "y"})
 	assert.EqualValues(t, 3, m1.GetCounter().GetValue(), "%+v", m1)
 
-	m2 := findMetric(t, snapshot, "bender_rodriguez", map[string]string{"a": "b", "x": "z"})
+	m2 := findMetric(t, snapshot, "bender_rodriguez_total", map[string]string{"a": "b", "x": "z"})
 	assert.EqualValues(t, 7, m2.GetCounter().GetValue(), "%+v", m2)
 }