fix metrics

serve/calc.go

@@ -10,10 +10,22 @@ import (
 var errTimeout = errors.New(`Operation timedout`)
 
 func (m *MathHandler) calculate(f formula, b []byte) ([]byte, error) {
+	f.metrics.accesses.Inc()
+	timer := prometheus.NewTimer(f.metrics.calcTime)
+	defer timer.ObserveDuration()
+
+	var res []byte
+	var err error
 	if f.opt.Immutable() {
-		return m.calculateImmutable(f, b)
+		res, err = m.calculateImmutable(f, b)
+	} else {
+		res, err = m.calculatemutable(f, b)
+
+	}
+	if err != nil {
+		f.metrics.errors.Inc()
 	}
-	return m.calculatemutable(f, b)
+	return res, err
 }
 
 func (m *MathHandler) calculateImmutable(f formula, b []byte) ([]byte, error) {

serve/http.go

@@ -40,16 +40,12 @@ func (m *MathHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	}
 
 	if f, ok := m.formulas[path.Clean(r.URL.Path)]; ok {
-		f.metrics.accesses.Inc()
-
 		result, err := m.calculate(f, b)
 		if err == errTimeout {
-			f.metrics.errors.Inc()
 			httpError(w, err.Error(), http.StatusRequestTimeout)
 			return
 		}
 		if err != nil {
-			f.metrics.errors.Inc()
 			httpError(w, err.Error(), http.StatusInternalServerError)
 			return
 		}

serve/http_test.go

@@ -26,6 +26,7 @@ func TestMathHandler_ServeHTTP_app_err(t *testing.T) {
 		t.Error("Expected error", resp.StatusCode)
 	}
 }
+
 func TestMathHandler_ServeHTTP_timeout(t *testing.T) {
 	m := MathHandler{timeout: time.Nanosecond}
 	m.formulas = make(map[string]formula)

serve/metrics.go

@@ -10,6 +10,7 @@ type metrics struct {
 	errors      prometheus.Counter
 	cacheMisses prometheus.Counter
 	cacheSize   prometheus.Gauge
+	cacheTime   prometheus.Histogram
 	calcTime    prometheus.Histogram
 }
 
@@ -26,6 +27,10 @@ func register(name string) *metrics {
 	cacheSize := promauto.NewGauge(prometheus.GaugeOpts{
 		Name: name + "_cache_size",
 	})
+	cacheTime := promauto.NewHistogram(prometheus.HistogramOpts{
+		Name:    name + "_cache_time",
+		Buckets: prometheus.ExponentialBuckets(0.5e-3, 2, 14),
+	})
 	calcTime := promauto.NewHistogram(prometheus.HistogramOpts{
 		Name:    name + "_calculation_time",
 		Buckets: prometheus.ExponentialBuckets(0.5e-3, 2, 14),
@@ -36,6 +41,7 @@ func register(name string) *metrics {
 		errors:      errors,
 		cacheMisses: cacheMisses,
 		cacheSize:   cacheSize,
+		cacheTime:   cacheTime,
 		calcTime:    calcTime,
 	}
 }