feat: add HTTP metrics middleware for Prometheus

- Add src/middleware/metrics.js with http_requests_total, http_errors_total, etc.
- Import and use metricsMiddleware in index.js

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

index.js

@@ -5,6 +5,7 @@ import helmet from "helmet";
 import morgan from "morgan";
 import client from "prom-client";
 import { pool } from "./db.js";
+import { metricsMiddleware } from "./src/middleware/metrics.js";
 
 dotenv.config();
 const app = express();
@@ -19,6 +20,9 @@ app.use(helmet());
 app.use(morgan("tiny"));
 app.use(express.json());
 
+// Middleware de métriques HTTP (doit être avant les routes)
+app.use(metricsMiddleware);
+
 app.get("/health", (req, res) => {
   res.status(200).json({ status: "ok" });
 }); 

src/middleware/metrics.js

@@ -0,0 +1,108 @@
+import client from "prom-client";
+
+// Compteur de requêtes HTTP totales
+const httpRequestsTotal = new client.Counter({
+  name: "http_requests_total",
+  help: "Total number of HTTP requests",
+  labelNames: ["method", "route", "status_code"],
+});
+
+// Histogramme de durée des requêtes
+const httpRequestDuration = new client.Histogram({
+  name: "http_request_duration_seconds",
+  help: "Duration of HTTP requests in seconds",
+  labelNames: ["method", "route", "status_code"],
+  buckets: [0.001, 0.005, 0.015, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 1, 2, 5],
+});
+
+// Compteur de requêtes en cours
+const httpRequestsInProgress = new client.Gauge({
+  name: "http_requests_in_progress",
+  help: "Number of HTTP requests currently being processed",
+  labelNames: ["method"],
+});
+
+// Compteur d'erreurs HTTP
+const httpErrorsTotal = new client.Counter({
+  name: "http_errors_total",
+  help: "Total number of HTTP errors (4xx and 5xx)",
+  labelNames: ["method", "route", "status_code"],
+});
+
+// Taille des réponses
+const httpResponseSize = new client.Histogram({
+  name: "http_response_size_bytes",
+  help: "Size of HTTP responses in bytes",
+  labelNames: ["method", "route"],
+  buckets: [100, 500, 1000, 5000, 10000, 50000, 100000, 500000],
+});
+
+// Fonction pour normaliser les routes (éviter la cardinalité élevée)
+const normalizeRoute = (req) => {
+  // Si la route est définie par Express, l'utiliser
+  if (req.route && req.route.path) {
+    return req.baseUrl + req.route.path;
+  }
+
+  // Sinon, normaliser le path en remplaçant les IDs par des placeholders
+  let path = req.path;
+
+  // Remplacer les UUIDs
+  path = path.replace(/[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}/gi, ":id");
+
+  // Remplacer les nombres (IDs numériques)
+  path = path.replace(/\/\d+/g, "/:id");
+
+  // Remplacer les codes de ticket (format spécifique)
+  path = path.replace(/\/[A-Z0-9]{6,}/g, "/:code");
+
+  return path;
+};
+
+// Middleware de métriques
+export const metricsMiddleware = (req, res, next) => {
+  // Ignorer les endpoints de métriques et health check
+  if (req.path === "/metrics" || req.path === "/health") {
+    return next();
+  }
+
+  const startTime = Date.now();
+
+  // Incrémenter les requêtes en cours
+  httpRequestsInProgress.inc({ method: req.method });
+
+  // Capturer la fin de la réponse
+  res.on("finish", () => {
+    const duration = (Date.now() - startTime) / 1000; // En secondes
+    const route = normalizeRoute(req);
+    const statusCode = res.statusCode.toString();
+    const labels = {
+      method: req.method,
+      route: route,
+      status_code: statusCode,
+    };
+
+    // Enregistrer les métriques
+    httpRequestsTotal.inc(labels);
+    httpRequestDuration.observe(labels, duration);
+    httpRequestsInProgress.dec({ method: req.method });
+
+    // Compter les erreurs
+    if (res.statusCode >= 400) {
+      httpErrorsTotal.inc(labels);
+    }
+
+    // Taille de la réponse (si disponible)
+    const contentLength = res.get("Content-Length");
+    if (contentLength) {
+      httpResponseSize.observe(
+        { method: req.method, route: route },
+        parseInt(contentLength, 10)
+      );
+    }
+  });
+
+  next();
+};
+
+export default metricsMiddleware;