stale-while-revalidate.mjs

import http from "node:http";
import { request, Agent, interceptors, setGlobalDispatcher } from "undici";

// Interceptors to add response caching, DNS caching and retrying to the dispatcher
const { cache, dns, retry } = interceptors;

const defaultDispatcher = new Agent({
  connections: 100, // Limit concurrent kept-alive connections to not run out of resources
  headersTimeout: 10_000, // 10 seconds; set as appropriate for the remote servers you plan to connect to
  bodyTimeout: 10_000,
}).compose(
  cache(),
  dns(),
  retry()
);

setGlobalDispatcher(defaultDispatcher); // Add these interceptors to all `fetch` and Undici `request` calls

async function run(n) {
  console.log(`Runnig ${n} request sequentially`);

  for (let i = 0; i <= n; i++) {
    // const query = { _: new Date().toISOString(), i };
    const query = { i };
    const res = await request({
      origin: "http://localhost:8080",
      path: `?i=${i % 10}`,
      // query,
      headers: {
        "Content-Tupe": "application/json",
        UserAgent: "UndiciExample/1.0.0",
      },
    });
    const text = await res.body.text();
  }
};

const N = 1000;
const bigChunk = new Array(N)
  .fill(0)
  .map((i) => new Array(N).fill(0).map(() => Math.random()));
const bigJSON = JSON.stringify(bigChunk, null, 2);

const server = new http.Server((req, res) => {
  res
    .writeHead(200, {
      "Content-Type": "application/json",
      // memory will start leaking after this time
      // "Cache-Control": `public, max-age=${String(1)}`,
      "Cache-Control": `"public, max-age=1, stale-while-revalidate=1"`,
    })
    .end(bigJSON);
})
server.listen("8080");

const sleep = (t) => new Promise((resolve) => setTimeout(resolve, t));
const logMemory = () => {
  global.gc?.();

  console.log(
    Object.fromEntries(
      Object.entries(process.memoryUsage()).map(([k, v]) => [
        k,
        v / 1024 / 1024,
      ])
    )
  );
}

global.logMemory = logMemory;
global.run = run;

logMemory();

await run(100);
logMemory();

await run(100);
logMemory();

console.log("Sleeping for 2s to trigger GC");
await sleep(2000);
logMemory();

console.log("^ see how much `external` & `arrayBuffers` increased with each run?");
// server.close();

stdout.log

{
  rss: 107.09375,
  heapTotal: 72.96875,
  heapUsed: 37.90514373779297,
  external: 3.2410106658935547,
  arrayBuffers: 0.1122894287109375
}
Runnig 100 request sequentially
{
  rss: 2600.625,
  heapTotal: 2205.65625,
  heapUsed: 2170.1848220825195,
  external: 281.41249084472656,
  arrayBuffers: 231.66439628601074
}
Runnig 100 request sequentially
{
  rss: 2736.78125,
  heapTotal: 2044.453125,
  heapUsed: 2008.7924270629883,
  external: 512.9489650726318,
  arrayBuffers: 486.3542881011963
}
Sleeping for 2s to trigger GC
{
  rss: 2737.296875,
  heapTotal: 75.09375,
  heapUsed: 40.322914123535156,
  external: 466.6343173980713,
  arrayBuffers: 463.193058013916
}
^ see how much `external` & `arrayBuffers` increased with each run?