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Handle incoming request cancellation in Workers with Request.signal

May 22, 2025, 01:00 AM

Workers

In Cloudflare Workers, you can now attach an event listener to Request objects, using the signal property ↗. This allows you to perform tasks when the request to your Worker is canceled by the client. To use this feature, you must set the enable_request_signal compatibility flag.

You can use a listener to perform cleanup tasks or write to logs before your Worker's invocation ends. For example, if you run the Worker below, and then abort the request from the client, a log will be written:

JavaScript

index.js

export default {
  async fetch(request, env, ctx) {
    // This sets up an event listener that will be called if the client disconnects from your
    // worker.
    request.signal.addEventListener("abort", () => {
      console.log("The request was aborted!");
    });

    const { readable, writable } = new IdentityTransformStream();
    sendPing(writable);
    return new Response(readable, {
      headers: { "Content-Type": "text/plain" },
    });
  },
};

async function sendPing(writable) {
  const writer = writable.getWriter();
  const enc = new TextEncoder();

  for (;;) {
    // Send 'ping' every second to keep the connection alive
    await writer.write(enc.encode("ping\r\n"));
    await scheduler.wait(1000);
  }
}

TypeScript

index.ts

export default {
  async fetch(request, env, ctx): Promise<Response> {
    // This sets up an event listener that will be called if the client disconnects from your
    // worker.
    request.signal.addEventListener('abort', () => {
      console.log('The request was aborted!');
    });

    const { readable, writable } = new IdentityTransformStream();
    sendPing(writable);
    return new Response(readable, { headers: { 'Content-Type': 'text/plain' } });
  },
} satisfies ExportedHandler<Env>;

async function sendPing(writable: WritableStream): Promise<void> {
  const writer = writable.getWriter();
  const enc = new TextEncoder();

  for (;;) {
    // Send 'ping' every second to keep the connection alive
    await writer.write(enc.encode('ping\r\n'));
    await scheduler.wait(1000);
  }
}

For more information see the Request documentation.