feat: Respect abort signals during serverside fetch optimization

packages/kit/src/runtime/server/fetch.js

@@ -145,10 +145,7 @@ export function create_fetch({ event, options, manifest, state, get_cookie_heade
 					);
 				}
 
-				const response = await respond(request, options, manifest, {
-					...state,
-					depth: state.depth + 1
-				});
+				const response = await internal_fetch(request, options, manifest, state);
 
 				const set_cookie = response.headers.get('set-cookie');
 				if (set_cookie) {
@@ -195,3 +192,43 @@ function normalize_fetch_input(info, init, url) {
 
 	return new Request(typeof info === 'string' ? new URL(info, url) : info, init);
 }
+
+/**
+ * @param {Request} request
+ * @param {import('types').SSROptions} options
+ * @param {import('@sveltejs/kit').SSRManifest} manifest
+ * @param {import('types').SSRState} state
+ * @returns {Promise<Response>}
+ */
+async function internal_fetch(request, options, manifest, state) {
+	if (request.signal) {
+		if (request.signal.aborted) {
+			throw new DOMException('The operation was aborted.', 'AbortError');
+		}
+
+		let remove_abort_listener = () => {};
+		/** @type {Promise<never>} */
+		const abort_promise = new Promise((_, reject) => {
+			const on_abort = () => {
+				reject(new DOMException('The operation was aborted.', 'AbortError'));
+			};
+			request.signal.addEventListener('abort', on_abort, { once: true });
+			remove_abort_listener = () => request.signal.removeEventListener('abort', on_abort);
+		});
+
+		const result = await Promise.race([
+			respond(request, options, manifest, {
+				...state,
+				depth: state.depth + 1
+			}),
+			abort_promise
+		]);
+		remove_abort_listener();
+		return result;
+	} else {
+		return await respond(request, options, manifest, {
+			...state,
+			depth: state.depth + 1
+		});
+	}
+}

packages/kit/test/apps/basics/src/routes/load/fetch-abort-signal/+page.server.js

@@ -0,0 +1,31 @@
+export async function load({ fetch }) {
+	const aborted_controller = new AbortController();
+	aborted_controller.abort();
+
+	let aborted_immediately = false;
+	try {
+		await fetch('/load/fetch-abort-signal/data', { signal: aborted_controller.signal });
+	} catch (error) {
+		if (error.name === 'AbortError') {
+			aborted_immediately = true;
+		}
+	}
+
+	let aborted_during_request = false;
+	try {
+		await fetch('/load/fetch-abort-signal/slow', { signal: AbortSignal.timeout(100) });
+	} catch (error) {
+		if (error.name === 'AbortError') {
+			aborted_during_request = true;
+		}
+	}
+
+	const successful_response = await fetch('/load/fetch-abort-signal/data');
+	const successful_data = await successful_response.json();
+
+	return {
+		aborted_immediately,
+		aborted_during_request,
+		successful_data
+	};
+}

packages/kit/test/apps/basics/src/routes/load/fetch-abort-signal/+page.svelte

@@ -0,0 +1,10 @@
+<script>
+	export let data;
+</script>
+
+<div>
+	<h1>AbortSignal Test Results</h1>
+	<p class="aborted-immediately">Aborted immediately: {data.aborted_immediately}</p>
+	<p class="aborted-during-request">Aborted during request: {data.aborted_during_request}</p>
+	<p class="successful-data">Successful data: {JSON.stringify(data.successful_data)}</p>
+</div>

packages/kit/test/apps/basics/src/routes/load/fetch-abort-signal/data/+server.js

@@ -0,0 +1,5 @@
+import { json } from '@sveltejs/kit';
+
+export async function GET() {
+	return json({ message: 'success', timestamp: Date.now() });
+}

packages/kit/test/apps/basics/src/routes/load/fetch-abort-signal/slow/+server.js

@@ -0,0 +1,3 @@
+export function GET() {
+	return new Promise(() => {});
+}

packages/kit/test/apps/basics/test/test.js

@@ -569,6 +569,14 @@
 
 		expect(await page.textContent('h1')).toBe('404');
 	});
+
+	test('AbortSignal works with internal fetch optimization', async ({ page }) => {
+		await page.goto('/load/fetch-abort-signal');
+
+		expect(await page.textContent('.aborted-immediately')).toBe('Aborted immediately: true');
+		expect(await page.textContent('.aborted-during-request')).toBe('Aborted during request: true');
+		expect(await page.textContent('.successful-data')).toContain('"message":"success"');
+	});
 });
 
 test.describe('Nested layouts', () => {