metrics: Add http_requests metric

router.go

@@ -5,6 +5,7 @@ import (
 	"log"
 	"net/http"
 	"runtime/debug"
+	"strconv"
 	"time"
 
 	"gitea.hashru.nl/dsprenkels/rushlink/internal/db"
@@ -37,6 +38,37 @@ func recoveryMiddleware(next http.Handler) http.Handler {
 	})
 }
 
+type statusResponseWriter struct {
+	Inner      http.ResponseWriter
+	StatusCode int
+}
+
+func (w *statusResponseWriter) Header() http.Header {
+	return w.Inner.Header()
+}
+
+func (w *statusResponseWriter) Write(buf []byte) (int, error) {
+	if w.StatusCode == 0 {
+		w.WriteHeader(http.StatusOK)
+	}
+	return w.Inner.Write(buf)
+}
+
+func (w *statusResponseWriter) WriteHeader(statusCode int) {
+	w.StatusCode = statusCode
+	w.Inner.WriteHeader(statusCode)
+}
+
+func metricsMiddleware(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		srw := statusResponseWriter{Inner: w}
+		next.ServeHTTP(&srw, r)
+		status := strconv.Itoa(srw.StatusCode)
+		metricRequestsTotalCounter.WithLabelValues(status, r.Method).Inc()
+	})
+}
+
+// StartMainServer starts the main http server listening on addr.
 func StartMainServer(addr string, db *db.Database, fs *db.FileStore) {
 	rl := rushlink{
 		db: db,
@@ -46,6 +78,7 @@ func StartMainServer(addr string, db *db.Database, fs *db.FileStore) {
 	// Initialize Gorilla router
 	router := mux.NewRouter()
 	router.Use(recoveryMiddleware)
+	router.Use(metricsMiddleware)
 	router.HandleFunc("/", rl.indexGetHandler).Methods("GET")
 	router.HandleFunc("/", rl.newPasteHandler).Methods("POST")
 	router.HandleFunc("/{key:[A-Za-z0-9-_]{4,}}", rl.viewPasteHandler).Methods("GET")