Addresses review comments

Creates a package for metrics where handlers are moved

internal/api/handlers.go

@@ -8,15 +8,12 @@ import (
 	"net/http"
 	"strconv"
 	"strings"
-
-	"github.com/prometheus/client_golang/prometheus"
-	"github.com/prometheus/client_golang/prometheus/collectors"
-	"github.com/prometheus/client_golang/prometheus/promhttp"
 )
 
 // NewGoCertRouter takes in an environment struct, passes it along to any handlers that will need
-// access to it, then builds and returns it for a server to consume
-func NewGoCertRouter(env *Environment) http.Handler {
+// access to it, and takes an http.Handler that will be used to handle metrics.
+// then builds and returns it for a server to consume
+func NewGoCertRouter(env *Environment, metricsHandler http.Handler) http.Handler {
 	router := http.NewServeMux()
 	router.HandleFunc("GET /certificate_requests", GetCertificateRequests(env))
 	router.HandleFunc("POST /certificate_requests", PostCertificateRequest(env))
@@ -26,15 +23,15 @@ func NewGoCertRouter(env *Environment) http.Handler {
 	router.HandleFunc("POST /certificate_requests/{id}/certificate/reject", RejectCertificate(env))
 	router.HandleFunc("DELETE /certificate_requests/{id}/certificate", DeleteCertificate(env))
 
-	v1 := http.NewServeMux()
-	v1.HandleFunc("GET /status", HealthCheck)
-	v1.Handle("/api/v1/", http.StripPrefix("/api/v1", router))
-	reg := prometheus.NewRegistry()
-	reg.MustRegister(collectors.NewGoCollector())
-	prometheusHandler := promhttp.HandlerFor(reg, promhttp.HandlerOpts{})
-	v1.Handle("/api/v1/metrics", prometheusHandler)
+	monitoringMux := http.NewServeMux()
+	monitoringMux.HandleFunc("/status", HealthCheck)
+	monitoringMux.Handle("/metrics", metricsHandler)
+
+	api := http.NewServeMux()
+	api.Handle("/api/v1/", http.StripPrefix("/api/v1", router))
+	api.Handle("/", monitoringMux)
 
-	return logging(v1)
+	return logging(api)
 }
 
 // the health check endpoint simply returns a http.StatusOK

internal/api/handlers_test.go

@@ -10,6 +10,7 @@ import (
 
 	server "github.com/canonical/gocert/internal/api"
 	"github.com/canonical/gocert/internal/certdb"
+	metrics "github.com/canonical/gocert/internal/metrics"
 )
 
 const (
@@ -107,7 +108,8 @@ func TestGoCertRouter(t *testing.T) {
 	}
 	env := &server.Environment{}
 	env.DB = testdb
-	ts := httptest.NewTLSServer(server.NewGoCertRouter(env))
+	metricsHandler := metrics.NewPrometheusHandler()
+	ts := httptest.NewTLSServer(server.NewGoCertRouter(env, metricsHandler))
 	defer ts.Close()
 
 	client := ts.Client()
@@ -323,7 +325,7 @@ func TestGoCertRouter(t *testing.T) {
 		{
 			desc:     "metrics endpoint success",
 			method:   "GET",
-			path:     "/api/v1/metrics",
+			path:     "/metrics",
 			data:     "",
 			response: "go_goroutines",
 			status:   http.StatusOK,
@@ -345,7 +347,7 @@ func TestGoCertRouter(t *testing.T) {
 				t.Fatal(err)
 			}
 			switch path := tC.path; path {
-			case "/api/v1/metrics":
+			case "/metrics":
 				if res.StatusCode != tC.status || !strings.Contains(string(resBody), tC.response) {
 					t.Errorf("expected response did not match.\nExpected vs Received status code: %d vs %d\nExpected vs Received body: \n%s\nvs\n%s\n", tC.status, res.StatusCode, tC.response, string(resBody))
 				}

internal/api/server.go

@@ -11,6 +11,7 @@ import (
 	"time"
 
 	"github.com/canonical/gocert/internal/certdb"
+	metrics "github.com/canonical/gocert/internal/metrics"
 	"gopkg.in/yaml.v3"
 )
 
@@ -85,7 +86,8 @@ func NewServer(configFile string) (*http.Server, error) {
 
 	env := &Environment{}
 	env.DB = db
-	router := NewGoCertRouter(env)
+	metricsHandler := metrics.NewPrometheusHandler()
+	router := NewGoCertRouter(env, metricsHandler)
 
 	s := &http.Server{
 		Addr: fmt.Sprintf(":%d", config.Port),

internal/metrics/metrics.go

@@ -0,0 +1,32 @@
+package metrics
+
+import (
+	"net/http"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/collectors"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+)
+
+type MetricsHandler interface {
+	http.Handler
+}
+
+// PrometheusHandler implements the MetricsHandler interface.
+type PrometheusHandler struct {
+	registry *prometheus.Registry
+}
+
+// Returns a new PrometheusHandler.
+func NewPrometheusHandler() MetricsHandler {
+	registry := prometheus.NewRegistry()
+	registry.MustRegister(collectors.NewGoCollector())
+	return &PrometheusHandler{
+		registry: registry,
+	}
+}
+
+// ServeHTTP implements the http.Handler interface, allowing the PrometheusHandler to handle HTTP requests.
+func (p *PrometheusHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	promhttp.HandlerFor(p.registry, promhttp.HandlerOpts{}).ServeHTTP(w, r)
+}

internal/metrics/metrics_test.go

@@ -0,0 +1,33 @@
+package metrics_test
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	metrics "github.com/canonical/gocert/internal/metrics"
+)
+
+// TestPrometheusHandler tests that the Prometheus metrics handler responds correctly to an HTTP request.
+func TestPrometheusHandler(t *testing.T) {
+	handler := metrics.NewPrometheusHandler()
+
+	request, err := http.NewRequest("GET", "/", nil)
+	if err != nil {
+		t.Fatalf("could not create request: %v", err)
+	}
+
+	recorder := httptest.NewRecorder()
+	handler.ServeHTTP(recorder, request)
+
+	if status := recorder.Code; status != http.StatusOK {
+		t.Errorf("handler returned wrong status code: got %v want %v", status, http.StatusOK)
+	}
+	if recorder.Body.String() == "" {
+		t.Errorf("handler returned an empty body")
+	}
+	if !strings.Contains(recorder.Body.String(), "go_goroutines") {
+		t.Errorf("handler returned an empty body")
+	}
+}