feat: expose metrics from expvar (#52)

* feat: expose metrics from expvar

* adding tests for metrics

* small changes after PR

pkg/admin/handlers/admin_entities.go

@@ -18,6 +18,7 @@
 package handlers
 
 import (
+	"expvar"
 	"net/http"
 	"os"
 
@@ -107,3 +108,8 @@ func (a Admin) AppInfoHeader(next http.Handler) http.Handler {
 	}
 	return http.HandlerFunc(fn)
 }
+
+// Metrics returns expvar info
+func (a Admin) Metrics(w http.ResponseWriter, r *http.Request) {
+	expvar.Handler().ServeHTTP(w, r)
+}

pkg/admin/handlers/admin_entities_test.go

@@ -18,6 +18,7 @@
 package handlers
 
 import (
+	"encoding/json"
 	"net/http"
 	"net/http/httptest"
 	"testing"
@@ -157,3 +158,25 @@ func TestAppInfoHeaderHandler(t *testing.T) {
 	assert.Equal(t, res.Header["Author"], []string{"2"})
 	assert.Equal(t, res.Header["App-Name"], []string{"3"})
 }
+
+func TestMetrics(t *testing.T) {
+
+	req, _ := http.NewRequest("GET", "/metrics", nil)
+
+	rr := httptest.NewRecorder()
+	a := NewAdmin("1", "2", "3", nil)
+	http.HandlerFunc(a.Metrics).ServeHTTP(rr, req)
+
+	assert.Equal(t, http.StatusOK, rr.Code, "Status code differs")
+
+	var expVarMap JSON
+	err := json.Unmarshal(rr.Body.Bytes(), &expVarMap)
+	assert.Nil(t, err)
+
+	memStatsMap, ok := expVarMap["memstats"]
+	assert.True(t, ok)
+
+	assert.Contains(t, memStatsMap, "Alloc")
+	assert.Contains(t, memStatsMap, "BySize")
+	assert.Contains(t, memStatsMap, "BuckHashSys")
+}

pkg/admin/router.go

@@ -38,6 +38,7 @@ func NewRouter(srvcs []handlers.HealthChecker) *chi.Mux {
 
 	r.Get("/health", optlyAdmin.Health)
 	r.Get("/info", optlyAdmin.AppInfo)
+	r.Get("/metrics", optlyAdmin.Metrics)
 
 	return r
 }