HTTP server: Request timeouts
A handler that depends on a slow upstream can hold a connection open forever. A per-request deadline turns that into a fast 504 instead. This example aborts the handler's work when a deadline passes or when the client disconnects, whichever comes first.
const DEADLINE_MS = 1000;Simulated upstream work that honors aborts. Real code would pass the signal to fetch, a database driver, or another cancellable API.
function doWork(ms: number, signal: AbortSignal): Promise<Response> {
return new Promise((resolve, reject) => {
if (signal.aborted) return reject(signal.reason);
const timer = setTimeout(
() => resolve(new Response("Work finished\n")),
ms,
);
signal.addEventListener("abort", () => {
clearTimeout(timer);
reject(signal.reason);
}, { once: true });
});
}
Deno.serve(async (req) => {
const url = new URL(req.url);/slow takes longer than the deadline, anything else finishes quickly.
const workMs = url.pathname === "/slow" ? 3000 : 10;One controller, two reasons to abort: the deadline timer fires, or the client goes away (req.signal). Passing the combined signal into the work means an impatient client also cancels upstream calls instead of leaving them running.
const controller = new AbortController();
const deadline = setTimeout(() => {
controller.abort(new DOMException("Deadline exceeded", "TimeoutError"));
}, DEADLINE_MS);
req.signal.addEventListener(
"abort",
() => controller.abort(req.signal.reason),
{ once: true },
);
try {
return await doWork(workMs, controller.signal);
} catch (err) {
if (err instanceof DOMException && err.name === "TimeoutError") {
return new Response("Gateway timeout\n", { status: 504 });
}
throw err;
} finally {Always clear the timer. A leaked timer keeps the event loop busy and trips the timer sanitizer when the handler runs under Deno.test.
clearTimeout(deadline);
}
});AbortSignal.any([AbortSignal.timeout(DEADLINE_MS), req.signal]) builds the same combined signal in one line. The explicit timer used above has one advantage: it can be cleared as soon as the work completes. The fast path finishes well inside the deadline: curl -i http://localhost:8000/fast HTTP/1.1 200 OK content-type: text/plain;charset=UTF-8 content-length: 14 date: Thu, 11 Jun 2026 18:55:21 GMT Work finished The slow path is cut off after about one second: curl -i http://localhost:8000/slow HTTP/1.1 504 Gateway Timeout content-type: text/plain;charset=UTF-8 content-length: 16 date: Thu, 11 Jun 2026 18:55:22 GMT Gateway timeout
Run this example locally using the Deno CLI:
deno run -N https://docs.deno.com/examples/scripts/http_server_request_timeouts.ts