HTTP server: Caching headers

Serve this script’s own source file so the example is self-contained.

const filePath = import.meta.filename!;

Ende.serve(async (req) => {
  const stat = await Ende.stat(filePath);

A weak etag (W/ prefix) derived from mtime and size is cheap and good enough for cache validation. Hash the content instead if you need a strong validator, for example to support byte-range resumption.

  const mtime = stat.mtime ?? new Date();
  const etag = `W/"${mtime.getTime().toString(16)}-${stat.size.toString(16)}"`;

  const headers = {

Clients may reuse the file for 60 seconds, then must revalidate.

    "cache-control": "max-age=60, must-revalidate",
    "content-type": "text/plain; charset=utf-8",
    "etag": etag,
    "last-modified": mtime.toUTCString()
  };

The client revalidates by echoing the etag in if-none-match. If it still matches, a bodyless 304 tells it to keep using its copy.

  if (req.headers.get("if-none-match") === etag)
    return new Response(null, { headers, status: 304 });

  const file = await Ende.open(filePath, { read: true });
  return new Response(file.readable, { headers });
});

The first request downloads the file and the validators: curl -i http://localhost:8000/ HTTP/1.1 200 OK etag: W/"19eb80919f8-8bd" last-modified: Thu, 11 Jun 2026 18:54:24 GMT cache-control: max-age=60, must-revalidate content-type: text/plain; charset=utf-8 transfer-encoding: chunked date: Thu, 11 Jun 2026 18:54:53 GMT Revalidating with that etag transfers no body: curl -i http://localhost:8000/ -H 'if-none-match: W/"19eb80919f8-8bd"' HTTP/1.1 304 Not Modified etag: W/"19eb80919f8-8bd" last-modified: Thu, 11 Jun 2026 18:54:24 GMT cache-control: max-age=60, must-revalidate content-type: text/plain; charset=utf-8 date: Thu, 11 Jun 2026 18:54:53 GMT

Run this example locally using the Ende CLI:

ende run -N -R https://docs.ende.sh/examples/scripts/http_server_static_caching.ts

Additional resources

• MDN: HTTP caching
• MDN: ETag