Add basic abortsignal example (#992)

Showing how to apply timeouts to fetch requests

Author: connyay

Cargo.lock

@@ -0,0 +1,14 @@
+[package]
+name = "abort-signal-on-workers"
+version = "0.1.0"
+edition = "2021"
+
+[package.metadata.release]
+release = false
+
+[lib]
+crate-type = ["cdylib"]
+
+[dependencies]
+worker.workspace = true
+futures-util = { workspace = true, features = ["async-await"] }

examples/abort-signal/Cargo.toml

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+# AbortSignal example
+
+Cancel in-flight fetch requests using `AbortController` and `AbortSignal` in a Rust Cloudflare Worker.
+
+## Routes
+
+| Route | Description |
+|---|---|
+| `GET /abort?url=<url>` | Fetches the URL and immediately aborts. Always returns an abort error. |
+| `GET /timeout?url=<url>&timeout=<ms>` | Fetches the URL with a timeout (default 2000ms). Cancels the request if the server doesn't respond in time. |
+
+## Local slow server
+
+A slow Node server is included for testing timeouts locally:
+
+```sh
+node slow-server.mjs              # port 3000, 5s delay
+node slow-server.mjs 9000 10      # port 9000, 10s delay
+```
+
+The server has two endpoints:
+- `GET /` returns a response after the default delay
+- `GET /delay/:ms` returns a response after `:ms` milliseconds
+
+## Testing
+
+1. Start the slow server on a port (e.g. 3000):
+   ```sh
+   node slow-server.mjs 3000
+   ```
+
+2. Start the Worker (in the `abort-signal` example directory):
+   ```sh
+   npx wrangler dev
+   ```
+
+3. Test immediate abort:
+   ```sh
+   curl "http://localhost:8787/abort?url=http://localhost:3000"
+   # → "Aborted: ..."
+   ```
+
+4. Test timeout (500ms timeout against a 5s delayed server):
+   ```sh
+   curl "http://localhost:8787/timeout?url=http://localhost:3000&timeout=500"
+   # → "Request timed out after 500ms"
+   ```
+
+5. Test timeout where the server responds in time (using `/delay/100` for 100ms):
+   ```sh
+   curl "http://localhost:8787/timeout?url=http://localhost:3000/delay/100&timeout=2000"
+   # → "Got response: {\"delayed_ms\":100,\"message\":\"slow response\"}"
+   ```

examples/abort-signal/README.md

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+// A minimal HTTP server that responds after a configurable delay.
+// Used to test AbortSignal timeouts against a real slow endpoint.
+//
+// Usage:
+//   node slow-server.mjs            # default 5s delay on port 3000
+//   node slow-server.mjs 9000 10    # port 9000, 10s delay
+//
+// Endpoints:
+//   GET /           → responds after <delay> seconds
+//   GET /delay/:ms  → responds after :ms milliseconds
+
+import { createServer } from "node:http";
+
+const PORT = parseInt(process.argv[2] || "3000", 10);
+const DEFAULT_DELAY_S = parseInt(process.argv[3] || "5", 10);
+
+const server = createServer((req, res) => {
+  const url = new URL(req.url, `http://localhost:${PORT}`);
+  const match = url.pathname.match(/^\/delay\/(\d+)$/);
+  const delayMs = match
+    ? parseInt(match[1], 10)
+    : DEFAULT_DELAY_S * 1000;
+
+  console.log(`${req.method} ${url.pathname} → will respond in ${delayMs}ms`);
+
+  const timer = setTimeout(() => {
+    res.writeHead(200, { "Content-Type": "application/json" });
+    res.end(JSON.stringify({ delayed_ms: delayMs, message: "slow response" }));
+  }, delayMs);
+
+  req.on("close", () => clearTimeout(timer));
+});
+
+server.listen(PORT, () => {
+  console.log(`Slow server listening on http://localhost:${PORT}`);
+  console.log(`Default delay: ${DEFAULT_DELAY_S}s`);
+});

examples/abort-signal/slow-server.mjs

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+use std::time::Duration;
+
+use futures_util::future::Either;
+use worker::{
+    event, AbortController, AbortSignal, Context, Delay, Env, Fetch, Request, Response, Result,
+    RouteContext, Router,
+};
+
+fn get_target_url(req: &Request) -> Result<String> {
+    req.url()?
+        .query_pairs()
+        .find(|(k, _)| k == "url")
+        .map(|(_, v)| v.into_owned())
+        .ok_or_else(|| worker::Error::RustError("Missing 'url' query param".into()))
+}
+
+async fn abort_immediate(req: Request, _ctx: RouteContext<()>) -> Result<Response> {
+    let target = get_target_url(&req)?;
+
+    let signal = AbortSignal::abort();
+    let fetch = Fetch::Url(target.parse()?);
+
+    match fetch.send_with_signal(&signal).await {
+        Ok(mut resp) => {
+            let text = resp.text().await?;
+            Response::ok(format!("Unexpected success: {text}"))
+        }
+        Err(e) => Response::ok(format!("Aborted: {e}")),
+    }
+}
+
+async fn abort_timeout(req: Request, _ctx: RouteContext<()>) -> Result<Response> {
+    let target = get_target_url(&req)?;
+
+    let timeout_ms: u64 = req
+        .url()?
+        .query_pairs()
+        .find(|(k, _)| k == "timeout")
+        .and_then(|(_, v)| v.parse().ok())
+        .unwrap_or(2000);
+
+    let url = target.parse()?;
+    let controller = AbortController::default();
+    let signal = controller.signal();
+
+    let fetch_fut = async {
+        let mut resp = Fetch::Url(url).send_with_signal(&signal).await?;
+        let text = resp.text().await?;
+        Ok::<_, worker::Error>(text)
+    };
+
+    let timeout_fut = async {
+        Delay::from(Duration::from_millis(timeout_ms)).await;
+        controller.abort();
+    };
+
+    futures_util::pin_mut!(fetch_fut);
+    futures_util::pin_mut!(timeout_fut);
+
+    match futures_util::future::select(timeout_fut, fetch_fut).await {
+        Either::Left((_timed_out, _cancelled)) => {
+            Response::ok(format!("Request timed out after {timeout_ms}ms"))
+        }
+        Either::Right((Ok(body), _)) => Response::ok(format!("Got response: {body}")),
+        Either::Right((Err(e), _)) => Response::ok(format!("Fetch error: {e}")),
+    }
+}
+
+#[event(fetch)]
+pub async fn main(req: Request, env: Env, _ctx: Context) -> Result<Response> {
+    Router::new()
+        .get_async("/abort", abort_immediate)
+        .get_async("/timeout", abort_timeout)
+        .run(req, env)
+        .await
+}

examples/abort-signal/src/lib.rs

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+name = "abort-signal-on-workers"
+main = "build/worker/shim.mjs"
+compatibility_date = "2026-04-28"
+
+[build]
+command = "cargo install \"worker-build@^0.8\" && worker-build --release"