الـ Middleware ودورة حياة الـ request جُوّه Express

import express from "express";

const app = express();

app.use((req, res, next) => {
  console.log("1 أول middleware");
  next();
  console.log("5 رجعنا بعد next (الـ response خلص)");
});

app.use((req, res, next) => {
  console.log("2 تاني middleware");
  next();
});

app.get("/hello", (req, res, next) => {
  console.log("3 الـ route");
  res.json({ ok: true });
  console.log("4 بعد res.json");
});

app.listen(3000, () => console.log("http://localhost:3000"));

$ node server.js
http://localhost:3000

→ GET /hello
1 أول middleware
2 تاني middleware
3 الـ route
4 بعد res.json
5 رجعنا بعد next (الـ response خلص)
← 200 OK
{
  "ok": true
}

import express from "express";
import crypto from "node:crypto";

const app = express();

// 1) request id: كل request ليه رقم، يمشي معاه في كل الـ logs
app.use((req, res, next) => {
  req.id = req.get("X-Request-Id") ?? crypto.randomUUID().slice(0, 8);
  res.set("X-Request-Id", req.id);
  next();
});

// 2) logger: بيسجل بعد ما الـ response يخلص فعلًا
app.use((req, res, next) => {
  const start = process.hrtime.bigint();
  res.on("finish", () => {
    const ms = Number(process.hrtime.bigint() - start) / 1e6;
    console.log(`[${req.id}] ${req.method} ${req.originalUrl} ${res.statusCode} ${ms < 50 ? "<50" : Math.round(ms)}ms`);
  });
  next();
});

// 3) factory: middleware بإعدادات (closure)
function requireRole(role) {
  return (req, res, next) => {
    if (req.get("X-Role") !== role) {
      return res.status(403).json({ error: `محتاج ${role}` });
    }
    next();
  };
}

app.get("/public", (req, res) => res.json({ ok: true }));
app.get("/admin/stats", requireRole("admin"), (req, res) => res.json({ users: 1200 }));

app.get("/slow", async (req, res) => {
  await new Promise((r) => setTimeout(r, 120));
  res.json({ done: true });
});

app.listen(3000, () => console.log("http://localhost:3000"));

$ node server.js
http://localhost:3000

→ GET /public
[883cdf0a] GET /public 200 <50ms
← 200 OK
{
  "ok": true
}

→ GET /admin/stats
[21c38655] GET /admin/stats 403 <50ms
← 403 Forbidden
{
  "error": "محتاج admin"
}

→ GET /admin/stats
[ff96f48f] GET /admin/stats 200 <50ms
← 200 OK
{
  "users": 1200
}

→ GET /slow
[abc123] GET /slow 200 121ms
← 200 OK
{
  "done": true
}

import express from "express";

const app = express();

app.get("/twice", (req, res, next) => {
  res.json({ first: true });
  next(); // ❌ بعد ما الـ response اتبعت
});
app.get("/twice", (req, res) => {
  res.json({ second: true });
});

app.get("/fail", (req, res, next) => {
  next(new Error("حاجة وقعت"));
});

// error middleware: لازم 4 parameters
app.use((err, req, res, next) => {
  console.log(`[error] ${err.message}`);
  if (res.headersSent) return next(err);
  res.status(500).json({ error: err.message });
});

app.listen(3000, () => console.log("http://localhost:3000"));

$ node server.js
http://localhost:3000

→ GET /twice
[error] Cannot set headers after they are sent to the client
Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
    at ServerResponse.setHeader (node:_http_outgoing:642:11)
    at ServerResponse.header (/home/you/my-backend/node_modules/express/lib/response.js:685:10)
    at ServerResponse.send (/home/you/my-backend/node_modules/express/lib/response.js:141:14)
    at ServerResponse.json (/home/you/my-backend/node_modules/express/lib/response.js:249:15)
    at file:///home/you/my-backend/server.js:10:7
    at Layer.handleRequest (/home/you/my-backend/node_modules/router/lib/layer.js:152:17)
    at next (/home/you/my-backend/node_modules/router/lib/route.js:157:13)
    at Route.dispatch (/home/you/my-backend/node_modules/router/lib/route.js:117:3)
    at handle (/home/you/my-backend/node_modules/router/index.js:435:11)
    at Layer.handleRequest (/home/you/my-backend/node_modules/router/lib/layer.js:152:17) {
  code: 'ERR_HTTP_HEADERS_SENT'
}
← 200 OK
{
  "first": true
}

→ GET /fail
[error] حاجة وقعت
← 500 Internal Server Error
{
  "error": "حاجة وقعت"
}

import express from "express";

const app = express();
const KEYS = new Map([
  ["key-free", { plan: "free", perMinute: 2 }],
  ["key-pro", { plan: "pro", perMinute: 100 }],
]);


function apiKey(req, res, next) {
  const key = req.get("X-Api-Key");
  if (!key) return res.status(401).json({ error: "مفيش API key" });
  const client = KEYS.get(key);
  if (!client) return res.status(401).json({ error: "key غلط" });
  req.client = { key, ...client };
  next();
}

function quota() {
  const used = new Map();
  return (req, res, next) => {
    const { key, perMinute } = req.client;
    const n = (used.get(key) ?? 0) + 1;
    used.set(key, n);
    if (n > perMinute) {
      res.set("Retry-After", "60");
      return res.status(429).json({ error: "عدّيت الحد" });
    }
    res.set({ "X-RateLimit-Limit": String(perMinute), "X-RateLimit-Remaining": String(perMinute - n) });
    next();
  };
}

app.get("/health", (req, res) => res.json({ ok: true }));
app.get("/v1/me", apiKey, quota(), (req, res) => res.json({ plan: req.client.plan }));

app.listen(3000, () => console.log("http://localhost:3000"));

$ node server.js
http://localhost:3000

→ GET /health
← 200 OK
{
  "ok": true
}

→ GET /v1/me
← 401 Unauthorized
{
  "error": "مفيش API key"
}

→ GET /v1/me
← 401 Unauthorized
{
  "error": "key غلط"
}

→ GET /v1/me
← 200 OK
  connection: keep-alive
  content-length: 15
  content-type: application/json; charset=utf-8
  etag: W/"f-PSELJELPsxpZ3o3sd/j/6T8aEkQ"
  keep-alive: timeout=5
  x-powered-by: Express
  x-ratelimit-limit: 2
  x-ratelimit-remaining: 1
{
  "plan": "free"
}

→ GET /v1/me
← 200 OK
{
  "plan": "free"
}

→ GET /v1/me
← 429 Too Many Requests
  connection: keep-alive
  content-length: 31
  content-type: application/json; charset=utf-8
  etag: W/"1f-LbQaNJP3G2lT0SW+d2CzVfzMSUA"
  keep-alive: timeout=5
  retry-after: 60
  x-powered-by: Express
{
  "error": "عدّيت الحد"
}