feat: add request id middleware for api responses

backend/app.js

@@ -2,8 +2,10 @@ const express = require("express");
 const cors = require("cors");
 const path = require("path");
 const User = require("./models/user.model");
+const requestIdMiddleware = require("./middleware/request-id");
 
 const app = express();
+app.use(requestIdMiddleware);
 app.use(express.json());
 
 // Serve static files from public directory

backend/middleware/request-id.js

@@ -0,0 +1,37 @@
+const crypto = require("crypto");
+
+function generateRequestId() {
+  if (typeof crypto.randomUUID === "function") {
+    return crypto.randomUUID();
+  }
+  return crypto.randomBytes(16).toString("hex");
+}
+
+function isPlainObject(value) {
+  return (
+    value !== null &&
+    typeof value === "object" &&
+    !Array.isArray(value) &&
+    Object.prototype.toString.call(value) === "[object Object]"
+  );
+}
+
+function requestIdMiddleware(req, res, next) {
+  const requestId = generateRequestId();
+
+  req.request_id = requestId;
+  res.locals.request_id = requestId;
+  res.setHeader("X-Request-Id", requestId);
+
+  const originalJson = res.json.bind(res);
+  res.json = (payload) => {
+    if (isPlainObject(payload) && payload.request_id === undefined) {
+      return originalJson({ ...payload, request_id: requestId });
+    }
+    return originalJson(payload);
+  };
+
+  next();
+}
+
+module.exports = requestIdMiddleware;