Incidente de Travamento do Event Loop

// RUIM: parse síncrono em caminho crítico
app.post("/import", express.text({ limit: "10mb" }), (req, res) => {
  const rows = JSON.parse(req.body); // bloqueia o event loop para payloads grandes
  res.json({ count: rows.length });
});
 
// MELHOR: streaming + worker ou chunking assíncrono
import { Worker } from "node:worker_threads";
 
function parseInWorker(json: string): Promise<unknown> {
  return new Promise((resolve, reject) => {
    const w = new Worker(new URL("./parse-worker.ts", import.meta.url), {
      workerData: json,
    });
    w.on("message", resolve);
    w.on("error", reject);
    w.on("exit", (code) => code !== 0 && reject(new Error(`worker exit ${code}`)));
  });
}

clinic doctor --on-port 'autocannon -c 20 -d 30 localhost:3000/health' -- node dist/main.js

import express from "express";
import { performance, monitorEventLoopDelay } from "node:perf_hooks";
 
const loopDelay = monitorEventLoopDelay({ resolution: 20 });
loopDelay.enable();
 
const app = express();
 
// Reprodução do incidente: parse síncrono de array JSON de 3MB
app.post("/webhooks/heavy", express.raw({ type: "application/json", limit: "5mb" }), (req, res) => {
  const start = performance.now();
  const payload = JSON.parse(req.body.toString("utf8"));
  const elapsed = performance.now() - start;
  res.json({ items: payload.length, parseMs: elapsed });
});
 
// Mitigação: rejeitar rotas de parse síncrono superdimensionadas; descarregar para fila
app.post("/webhooks/queued", express.raw({ type: "application/json", limit: "256kb" }), (req, res) => {
  if (req.body.length > 256 * 1024) {
    return res.status(413).json({ error: { code: "PAYLOAD_TOO_LARGE" } });
  }
  const payload = JSON.parse(req.body.toString("utf8"));
  res.status(202).json({ accepted: true, items: payload.length });
});
 
app.get("/health", (_req, res) => {
  const p99 = loopDelay.percentile(99) / 1e6; // ms
  if (p99 > 100) return res.status(503).json({ ok: false, eventLoopLagP99Ms: p99 });
  res.json({ ok: true, eventLoopLagP99Ms: p99 });
});
 
app.listen(3000);

// parse-worker.ts
import { parentPort, workerData } from "node:worker_threads";
const data = JSON.parse(workerData as string);
parentPort?.postMessage({ length: Array.isArray(data) ? data.length : 0 });

// bcrypt no caminho da requisição - limite a concorrência
import { Semaphore } from "async-mutex"; // ou um semáforo personalizado pequeno
const bcryptSlots = new Semaphore(4);