ETag + conditional GET for read-heavy endpoints

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                  import type { RequestHandler } from 'express';
import crypto from 'node:crypto';

export function weakEtag(value: string) {
  const hash = crypto.createHash('sha1').update(value).digest('hex');
  return `W/"${hash}"`;
}

export const conditionalGet: RequestHandler = (req, res, next) => {
  res.locals._ifNoneMatch = req.header('if-none-match');
  next();
};

For read-heavy endpoints, clients often fetch the same resource repeatedly (profile data, settings, a snip page) even when it hasn’t changed. ETags let the client send If-None-Match and the server respond with 304 Not Modified, saving bandwidth and CPU. The important detail is that your ETag must change when the representation changes; I usually derive it from an updated_at timestamp + id, or a real content hash if needed. I also set Cache-Control appropriately so intermediaries behave. This is a simple, standards-based performance win that works without introducing complex caching infrastructure.

Mateo Rodriguez

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ETag + conditional GET for read-heavy endpoints

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