avoid the need for set_nonce dance

Author: Rich-Harris

packages/kit/src/runtime/server/page/data_serializer.js

@@ -18,13 +18,9 @@ import {
 export function server_data_serializer(event, event_state, options) {
 	let promise_id = 1;
 
-	const { iterator, add } = create_async_iterator();
+	const iterator = create_async_iterator();
 	const global = get_global_name(options);
 
-	/** @type {(nonce: string) => void} */
-	let set_nonce;
-	const nonce = /** @type {Promise<string>} */ new Promise((r) => (set_nonce = r));
-
 	/** @param {any} thing */
 	function replacer(thing) {
 		if (typeof thing?.then === 'function') {
@@ -56,11 +52,11 @@ export function server_data_serializer(event, event_state, options) {
 							str = devalue.uneval([, error], replacer);
 						}
 
-						return `<script${await nonce}>${global}.resolve(${id}, ${str.includes('app.decode') ? `(app) => ${str}` : `() => ${str}`})</script>\n`;
+						return `${global}.resolve(${id}, ${str.includes('app.decode') ? `(app) => ${str}` : `() => ${str}`})`;
 					}
 				);
 
-			add(promise);
+			iterator.add(promise);
 
 			return `${global}.defer(${id})`;
 		} else {
@@ -96,15 +92,13 @@ export function server_data_serializer(event, event_state, options) {
 		},
 
 		get_data(csp) {
-			set_nonce(csp.script_needs_nonce ? ` nonce="${csp.nonce}"` : '');
+			const open = `<script${csp.script_needs_nonce ? ` nonce="${csp.nonce}"` : ''}>`;
+			const close = `</script>\n`;
+
 			return {
 				data: `[${strings.join(',')}]`,
-				chunks: promise_id > 1 ? iterator : null
+				chunks: promise_id > 1 ? iterator.iterate((str) => open + str + close) : null
 			};
-		},
-
-		discard() {
-			set_nonce('');
 		}
 	};
 }
@@ -120,7 +114,7 @@ export function server_data_serializer(event, event_state, options) {
 export function server_data_serializer_json(event, event_state, options) {
 	let promise_id = 1;
 
-	const { iterator, add } = create_async_iterator();
+	const iterator = create_async_iterator();
 
 	const reducers = {
 		...Object.fromEntries(
@@ -166,7 +160,7 @@ export function server_data_serializer_json(event, event_state, options) {
 					}
 				);
 
-			add(promise);
+			iterator.add(promise);
 
 			return id;
 		}
@@ -201,7 +195,7 @@ export function server_data_serializer_json(event, event_state, options) {
 		get_data() {
 			return {
 				data: `{"type":"data","nodes":[${strings.join(',')}]}\n`,
-				chunks: promise_id > 1 ? iterator : null
+				chunks: promise_id > 1 ? iterator.iterate() : null
 			};
 		}
 	};

packages/kit/src/runtime/server/page/index.js

@@ -281,9 +281,6 @@ export async function render_page(
 							const layouts = compact(branch.slice(0, j + 1));
 							const nodes = new PageNodes(layouts.map((layout) => layout.node));
 
-							// prevent memory leak by resolving the `nonce` promise of the unused data_serializer
-							data_serializer.discard();
-
 							return await render_response({
 								event,
 								event_state,

packages/kit/src/runtime/server/page/types.d.ts

@@ -45,7 +45,6 @@ export interface Cookie {
 export type ServerDataSerializer = {
 	add_node(i: number, node: ServerDataNode | null): void;
 	get_data(csp: Csp): { data: string; chunks: AsyncIterable<string> | null };
-	discard(): void;
 };
 
 export type ServerDataSerializerJson = {

packages/kit/src/utils/streaming.js

@@ -16,9 +16,10 @@ function defer() {
 
 /**
  * Create an async iterator and a function to push values into it
+ * @template T
  * @returns {{
- *   iterator: AsyncIterable<any>;
- *   add: (promise: Promise<any>) => void;
+ *   iterate: (transform?: (input: T) => T) => AsyncIterable<T>;
+ *   add: (promise: Promise<T>) => void;
  * }}
  */
 export function create_async_iterator() {
@@ -27,16 +28,23 @@ export function create_async_iterator() {
 	const deferred = [defer()];
 
 	return {
-		iterator: {
-			[Symbol.asyncIterator]() {
-				return {
-					next: async () => {
-						const next = await deferred[0].promise;
-						if (!next.done) deferred.shift();
-						return next;
-					}
-				};
-			}
+		iterate: (transform = (x) => x) => {
+			return {
+				[Symbol.asyncIterator]() {
+					return {
+						next: async () => {
+							const next = await deferred[0].promise;
+
+							if (!next.done) {
+								deferred.shift();
+								return { value: transform(next.value), done: false };
+							}
+
+							return next;
+						}
+					};
+				}
+			};
 		},
 		add: (promise) => {
 			count += 1;

packages/kit/src/utils/streaming.spec.js

@@ -2,15 +2,15 @@ import { expect, test } from 'vitest';
 import { create_async_iterator } from './streaming.js';
 
 test('works with fast consecutive promise resolutions', async () => {
-	const { iterator, add } = create_async_iterator();
+	const { iterate, add } = create_async_iterator();
 
 	add(Promise.resolve(1));
 	add(Promise.resolve(2));
 
 	const actual = [];
-	for await (const value of iterator) {
+	for await (const value of iterate((n) => n * 10)) {
 		actual.push(value);
 	}
 
-	expect(actual).toEqual([1, 2]);
+	expect(actual).toEqual([10, 20]);
 });