How to abort `Deno.serve` via request

Question

How to abort Deno.serve via request right after the respective response was sent?

My current workaround is a 1s sleep before aborting the AbortController. I've tried queueMicrotask, but it seems like the response is not sent via the main thread.

Here is my workaround:

//example.ts
//deno run --allow-net=127.0.0.1 example.ts

const port = 3000;
const hostname = "127.0.0.1";
const ac = new AbortController();
const signal = ac.signal;

let isShuttingDown = false;
const server = Deno.serve(
  { port, hostname, signal },
  (req: Request, _info: Deno.ServeHandlerInfo) => {
    if (isShuttingDown) {
      return new Response("Server is shutting down!", { status: 503 });
    }
    const url = new URL(req.url);
    if (
      url.pathname === "/shutdown"
    ) {
      isShuttingDown = true;
      // queueMicrotask(()=>{ //does not run after response is sent
      //   ac.abort();
      // });
      setTimeout(() => {
        ac.abort();
      }, 1000); //give client time to receive response
      return new Response(null, { status: 202 });
    }
    return new Response("hello");
  },
);
await server.finished;
console.log("server stopped");

Is there a better way than waiting with a long enough timeout?

Answer 1

In Deno v1.38, an unstable method shtudown was added to the class Deno.HttpServer to facilitate graceful shutdown.

shutdown(): Promise<void>

Gracefully close the server. No more new connections will be accepted, while pending requests will be allowed to finish.

I haven't yet reviewed the source code implementation (so maybe I'm missing something) but using it inside a server handler function currently still appears to require a delay. Perhaps the implementation prevents any new responses from being sent immediately after invocation — the documentation does not make this clear.

In short, you can gracefully shutdown the server in your request handler callback function just before returning the response, like this:

function handler() {
  queueMicrotask(httpServer.shutdown);
  return new Response(/* … */);
}

Here's a complete reproducible example:

server.ts:

/// <reference lib="deno.unstable" />

function delay(ms: number): Promise<void> {
  return new Promise((res) => setTimeout(res, ms));
}

function createPlainTextResponse(
  text: string,
  init: ResponseInit = {},
): Response {
  const { headers: headersInit, ...rest } = init;
  const headers = new Headers(headersInit);
  headers.set("Content-Type", "text/plain; charset=utf-8");
  return new Response(text, { ...rest, headers });
}

function handleNotFound(): Response {
  return createPlainTextResponse("Not Found", { status: 404 });
}

const routeHandlers: Record<string, Deno.ServeHandler> = {
  "/hello": () => createPlainTextResponse("Hello world"),
  "/shutdown": () => {
    queueMicrotask(httpServer.shutdown);
    return createPlainTextResponse("Server is shutting down", { status: 202 });
  },
};

const handleRequest: Deno.ServeHandler = (request, info) => {
  const url = new URL(request.url);
  const handler = routeHandlers[url.pathname] ?? handleNotFound;
  return handler(request, info);
};

function printStartupMessage({ hostname, port, secure }: {
  hostname: string;
  port: number;
  secure?: boolean;
}): void {
  if (!hostname || hostname === "0.0.0.0") hostname = "localhost";
  const address =
    new URL(`http${secure ? "s" : ""}://${hostname}:${port}/`).href;
  console.log(`Listening at ${address}`);
  console.log("Use ctrl+c to stop");
}

async function logInfoAndSendTestRequests(
  opts: Parameters<NonNullable<Deno.ServeOptions["onListen"]>>[0],
): Promise<void> {
  printStartupMessage(opts);
  const origin = `http://${opts.hostname}:${opts.port}`;

  console.log("Client started");

  for (const pathname of ["/hello", "/oops", "/shutdown", "/hello"]) {
    try {
      await delay(250);
      const response = await fetch(`${origin}${pathname}`);
      const text = await response.text();
      console.log(pathname, response.status, text);
    } catch (cause) {
      console.error("Caught client exception:", cause);
    }
  }

  console.log("Client stopped");
}

const opts = {
  hostname: "localhost",
  onListen: logInfoAndSendTestRequests,
  port: 3000,
} satisfies Deno.ServeOptions;

const httpServer = Deno.serve(opts, handleRequest);
await httpServer.finished;
console.log("Server stopped");

Terminal:

% deno --version
deno 1.38.3 (release, aarch64-apple-darwin)
v8 12.0.267.1
typescript 5.2.2

% deno run --unstable --allow-net=localhost:3000 server.ts
Listening at http://localhost:3000/
Use ctrl+c to stop
Client started
/hello 200 Hello world
/oops 404 Not Found
Server stopped
/shutdown 202 Server is shutting down
Caught client exception: TypeError: error sending request for url (http://localhost:3000/hello): error trying to connect: tcp connect error: Connection refused (os error 61)
    at async mainFetch (ext:deno_fetch/26_fetch.js:277:12)
    at async fetch (ext:deno_fetch/26_fetch.js:504:7)
    at async Object.logInfoAndSendTestRequests [as onListen] (file:///Users/deno/so-77547677/server.ts:58:24)
Client stopped

% echo $?
0