abort synchronously in SSR

Author: Rich-Harris

packages/svelte/src/index-server.js

@@ -2,7 +2,6 @@
 import { current_component } from './internal/server/context.js';
 import { noop } from './internal/shared/utils.js';
 import * as e from './internal/server/errors.js';
-import { STALE_REACTION } from '#client/constants';
 
 /** @param {() => void} fn */
 export function onDestroy(fn) {
@@ -36,20 +35,7 @@ export function unmount() {
 
 export async function tick() {}
 
-/** @type {AbortController | null} */
-let controller = null;
-
-export function getAbortSignal() {
-	if (controller === null) {
-		const c = (controller = new AbortController());
-		queueMicrotask(() => {
-			c.abort(STALE_REACTION);
-			controller = null;
-		});
-	}
-
-	return controller.signal;
-}
+export { getAbortSignal } from './internal/server/abort-signal.js';
 
 export { getAllContexts, getContext, hasContext, setContext } from './internal/server/context.js';
 

packages/svelte/src/internal/server/abort-signal.js

@@ -0,0 +1,15 @@
+import { STALE_REACTION } from '#client/constants';
+
+/** @type {AbortController | null} */
+export let controller = null;
+
+export function abort() {
+	if (controller !== null) {
+		controller.abort(STALE_REACTION);
+		controller = null;
+	}
+}
+
+export function getAbortSignal() {
+	return (controller ??= new AbortController()).signal;
+}

packages/svelte/src/internal/server/index.js

@@ -18,6 +18,7 @@ import { validate_store } from '../shared/validate.js';
 import { is_boolean_attribute, is_raw_text_element, is_void } from '../../utils.js';
 import { reset_elements } from './dev.js';
 import { Payload } from './payload.js';
+import { abort } from './abort-signal.js';
 
 // https://html.spec.whatwg.org/multipage/syntax.html#attributes-2
 // https://infra.spec.whatwg.org/#noncharacter
@@ -66,50 +67,54 @@ export let on_destroy = [];
  * @returns {RenderOutput}
  */
 export function render(component, options = {}) {
-	const payload = new Payload(options.idPrefix ? options.idPrefix + '-' : '');
+	try {
+		const payload = new Payload(options.idPrefix ? options.idPrefix + '-' : '');
 
-	const prev_on_destroy = on_destroy;
-	on_destroy = [];
-	payload.out += BLOCK_OPEN;
+		const prev_on_destroy = on_destroy;
+		on_destroy = [];
+		payload.out += BLOCK_OPEN;
 
-	let reset_reset_element;
+		let reset_reset_element;
 
-	if (DEV) {
-		// prevent parent/child element state being corrupted by a bad render
-		reset_reset_element = reset_elements();
-	}
+		if (DEV) {
+			// prevent parent/child element state being corrupted by a bad render
+			reset_reset_element = reset_elements();
+		}
 
-	if (options.context) {
-		push();
-		/** @type {Component} */ (current_component).c = options.context;
-	}
+		if (options.context) {
+			push();
+			/** @type {Component} */ (current_component).c = options.context;
+		}
 
-	// @ts-expect-error
-	component(payload, options.props ?? {}, {}, {});
+		// @ts-expect-error
+		component(payload, options.props ?? {}, {}, {});
 
-	if (options.context) {
-		pop();
-	}
+		if (options.context) {
+			pop();
+		}
 
-	if (reset_reset_element) {
-		reset_reset_element();
-	}
+		if (reset_reset_element) {
+			reset_reset_element();
+		}
 
-	payload.out += BLOCK_CLOSE;
-	for (const cleanup of on_destroy) cleanup();
-	on_destroy = prev_on_destroy;
+		payload.out += BLOCK_CLOSE;
+		for (const cleanup of on_destroy) cleanup();
+		on_destroy = prev_on_destroy;
 
-	let head = payload.head.out + payload.head.title;
+		let head = payload.head.out + payload.head.title;
 
-	for (const { hash, code } of payload.css) {
-		head += `<style id="${hash}">${code}</style>`;
-	}
+		for (const { hash, code } of payload.css) {
+			head += `<style id="${hash}">${code}</style>`;
+		}
 
-	return {
-		head,
-		html: payload.out,
-		body: payload.out
-	};
+		return {
+			head,
+			html: payload.out,
+			body: payload.out
+		};
+	} finally {
+		abort();
+	}
 }
 
 /**