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How would you implement a global request timeout middleware in Express to prevent a slow request from hanging indefinitely?

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Answer

A timeout middleware starts a timer when a request begins, and if the response hasn't been sent by the time the timer fires, it sends a timeout response (like 503 or 504) and marks the request as timed out so any later attempt by the actual handler to still respond is safely ignored -- this protects against a slow downstream dependency (a hung database query, an unresponsive third-party API) tying up server resources indefinitely.

function requestTimeout(ms) {
  return (req, res, next) => {
    const timer = setTimeout(() => {
      if (!res.headersSent) res.status(503).json({ error: 'Request timed out' });
    }, ms);
    res.on('finish', () => clearTimeout(timer));
    next();
  };
}

app.use(requestTimeout(10000));

Real-world example An API wraps every route with a 10-second global timeout middleware, ensuring that if a specific downstream service call hangs indefinitely due to a network issue, the affected request still returns a clear timeout error to the client rather than hanging forever and slowly exhausting server resources.

Common follow-ups: What happens to the underlying operation (like a database query) that was still in progress when the timeout fires -- does it get cancelled, or does it keep running in the background?;How would you set different timeout durations for different routes based on their expected typical response time?

Performance Optimization & Profiling;Error Handling