feat: remote functions cache API

.changeset/kit-cache-request-event.md

@@ -0,0 +1,9 @@
+---
+'@sveltejs/kit': minor
+'@sveltejs/adapter-node': patch
+'@sveltejs/adapter-vercel': patch
+'@sveltejs/adapter-netlify': patch
+'@sveltejs/adapter-cloudflare': patch
+---
+
+feat: add `event.cache` for responses, remote query cache/invalidation, and adapter integrations

documentation/docs/20-core-concepts/60-remote-functions.md

@@ -1167,3 +1167,94 @@ Note that some properties of `RequestEvent` are different inside remote function
 ## Redirects
 
 Inside `query`, `form` and `prerender` functions it is possible to use the [`redirect(...)`](@sveltejs-kit#redirect) function. It is *not* possible inside `command` functions, as you should avoid redirecting here. (If you absolutely have to, you can return a `{ redirect: location }` object and deal with it in the client.)
+
+## Caching
+
+By default, remote functions do not cache their results. You can change this by using the `cache` function from `getRequestEvent`, which allows you to store the result of a remote function for a certain amount of time.
+
+```ts
+/// file: src/routes/data.remote.js
+// ---cut---
+import { query, getRequestEvent } from '$app/server';
+
+export const getFastData = query(async () => {
+	const { cache } = getRequestEvent();
+
+	// cache for 100 seconds
+	cache('100s');
+
+	return { data: '...' };
+});
+```
+
+The `cache` function accepts either a string representing the time-to-live (TTL), or an object with more detailed configuration:
+
+```ts
+/// file: src/routes/data.remote.js
+import { query, getRequestEvent } from '$app/server';
+// ---cut---
+export const getFastData = query(async () => {
+	const { cache } = getRequestEvent();
+
+	cache({
+		// fresh for 1 minute
+		ttl: '1m',
+		// can serve stale up to 5 minutes
+		stale: '5m',
+		// shareable across users (CDN caching) or private to user (browser caching); default private
+		scope: 'private',
+		// used for invalidation, when not given is the URL
+		tags: ['my-data'],
+	});
+
+	// ...
+});
+```
+
+There are two variants of the cache:
+
+- **Private cache** (`scope: 'private'`): Per-user cache implemented using the browser's Cache API.
+- **Public cache** (`scope: 'public'`): Shareable across users. The implementation is platform-specific (e.g., using `CDN-Cache-Control` and `Cache-Tag` headers on Vercel/Netlify, or a runtime cache on Node).
+
+### Invalidating the cache
+
+To invalidate the cache for a specific query, you can call its `invalidate` method:
+
+```ts
+/// file: src/routes/data.remote.js
+import { query, command } from '$app/server';
+
+export const getFastData = query(async () => {
+	const { cache } = getRequestEvent();
+	cache('100s');
+	return { data: '...' };
+});
+
+export const updateData = command(async () => {
+	// invalidates getFastData;
+	// the next time someone requests it, it will be called again
+	getFastData().invalidate();
+});
+```
+
+Alternatively, if you used tags when setting up the cache, you can invalidate by tag using `cache.invalidate(...)`:
+
+```ts
+/// file: src/routes/data.remote.js
+import { query, command, getRequestEvent } from '$app/server';
+
+export const getFastData = query(async () => {
+	const { cache } = getRequestEvent();
+	cache({ ttl: '100s', tags: ['my-data'] });
+	return { data: '...' };
+});
+
+export const updateData = command(async () => {
+	const { cache } = getRequestEvent();
+	// invalidate all queries using the my-data tag;
+	// the next time someone requests a query which had that tag, it will be called again
+	cache.invalidate(['my-data']);
+});
+```
+
+> [!NOTE] tags are public since they could invalidate the private cache in the browser

packages/kit/src/core/config/index.js

@@ -101,6 +101,10 @@ function process_config(config, { cwd = process.cwd() } = {}) {
 
 	validated.kit.outDir = path.resolve(cwd, validated.kit.outDir);
 
+	if (validated.kit.cache?.path) {
+		validated.kit.cache.path = path.resolve(cwd, validated.kit.cache.path);
+	}
+
 	for (const key in validated.kit.files) {
 		if (key === 'hooks') {
 			validated.kit.files.hooks.client = path.resolve(cwd, validated.kit.files.hooks.client);

packages/kit/src/core/config/index.spec.js

@@ -60,6 +60,7 @@ const get_defaults = (prefix = '') => ({
 	extensions: ['.svelte'],
 	kit: {
 		adapter: null,
+		cache: undefined,
 		alias: {},
 		appDir: '_app',
 		csp: {

packages/kit/src/core/config/options.js

@@ -81,6 +81,14 @@ const options = object(
 				return input;
 			}),
 
+			cache: validate(undefined, (input, keypath) => {
+				if (input === undefined) return undefined;
+				return object({
+					path: string(null),
+					options: validate({}, object({}, true))
+				})(input, keypath);
+			}),
+
 			alias: validate({}, (input, keypath) => {
 				if (typeof input !== 'object') {
 					throw new Error(`${keypath} should be an object`);

packages/kit/src/core/sync/write_server.js

@@ -46,6 +46,11 @@ export const options = {
 	env_private_prefix: '${config.kit.env.privatePrefix}',
 	hash_routing: ${s(config.kit.router.type === 'hash')},
 	hooks: null, // added lazily, via \`get_hooks\`
+	kit_cache_config: ${s({
+		path: config.kit.cache?.path,
+		options: config.kit.cache?.options ?? {}
+	})},
+	kit_cache_handler: null,
 	preload_strategy: ${s(config.kit.output.preloadStrategy)},
 	root,
 	service_worker: ${has_service_worker},

packages/kit/src/exports/internal/server.js

@@ -20,3 +20,6 @@ export {
 	get_request_store,
 	try_get_request_store
 } from './event.js';
+
+export { SVELTEKIT_CACHE_CONTROL_INVALIDATE_HEADER } from '../../runtime/shared.js';
+export { with_runtime_cache, RuntimeCacheStore } from '../../runtime/server/runtime-cache.js';

packages/kit/src/exports/public.d.ts

@@ -328,12 +328,61 @@ export interface Emulator {
 	platform?(details: { config: any; prerender: PrerenderOption }): MaybePromise<App.Platform>;
 }
 
+/**
+ * Options for [`event.cache`](https://svelte.dev/docs/kit/@sveltejs-kit#RequestEvent)
+ */
+export interface CacheOptions {
+	ttl: string | number;
+	stale?: string | number;
+	/** @default 'private' */
+	scope?: 'public' | 'private';
+	tags?: string[];
+	/** @default false */
+	refresh?: boolean;
+}
+
+/**
+ * Normalized cache directive passed to custom `kit.cache` handlers.
+ */
+export interface KitCacheDirective {
+	scope: 'public' | 'private';
+	maxAgeSeconds: number;
+	staleSeconds?: number;
+	tags: string[];
+	refresh: boolean;
+}
+
+/**
+ * Custom cache integration (e.g. platform purge hooks). Export `create` or `default` from `kit.cache.path`.
+ */
+export interface KitCacheHandler {
+	setHeaders?(
+		headers: Headers,
+		directive: KitCacheDirective,
+		ctx: { remote_id?: string | null }
+	): MaybePromise<void>;
+	invalidate?(tags: string[]): MaybePromise<void>;
+}
+
+export interface RequestCache {
+	(arg: CacheOptions | string): void;
+	invalidate(tags: string[]): void;
+}
+
 export interface KitConfig {
 	/**
 	 * Your [adapter](https://svelte.dev/docs/kit/adapters) is run when executing `vite build`. It determines how the output is converted for different platforms.
 	 * @default undefined
 	 */
 	adapter?: Adapter;
+	/**
+	 * Optional module that implements [`KitCacheHandler`](https://svelte.dev/docs/kit/@sveltejs-kit#KitCacheHandler) via a `create` or default export function.
+	 */
+	cache?: {
+		/** Absolute or project-relative path resolved from your app root */
+		path?: string;
+		options?: Record<string, unknown>;
+	};
 	/**
 	 * An object containing zero or more aliases used to replace values in `import` statements. These aliases are automatically passed to Vite and TypeScript.
 	 *
@@ -1554,6 +1603,12 @@ export interface RequestEvent<
 	 */
 	isSubRequest: boolean;
 
+	/**
+	 * Configure HTTP caching for this response. `public` uses shared caches (CDN / `Cache-Control`);
+	 * `private` applies only to remote query responses stored via the browser Cache API.
+	 */
+	cache: RequestCache;
+
 	/**
 	 * Access to spans for tracing. If tracing is not enabled, these spans will do nothing.
 	 * @since 2.31.0
@@ -2178,6 +2233,10 @@ export type RemoteQuery<T> = RemoteResource<T> & {
 	 * This prevents SvelteKit needing to refresh all queries on the page in a second server round-trip.
 	 */
 	refresh(): Promise<void>;
+	/**
+	 * Queue cache invalidation for this query (public or private, depending on how it was cached).
+	 */
+	invalidate(): void;
 	/**
 	 * Temporarily override a query's value during a [single-flight mutation](https://svelte.dev/docs/kit/remote-functions#Single-flight-mutations) to provide optimistic updates.
 	 *
@@ -2210,7 +2269,7 @@ export type RemotePrerenderFunction<Input, Output> = (
 ) => RemoteResource<Output>;
 
 /**
- * The return value of a remote `query` function. See [Remote functions](https://svelte.dev/docs/kit/remote-functions#query) for full documentation.
+ * The return value of a remote `query` function (client stub or shared typing). See [Remote functions](https://svelte.dev/docs/kit/remote-functions#query) for full documentation.
  */
 export type RemoteQueryFunction<Input, Output> = (
 	arg: undefined extends Input ? Input | void : Input

packages/kit/src/exports/vite/dev/index.js

@@ -19,6 +19,7 @@ import { is_chrome_devtools_request, not_found } from '../utils.js';
 import { SCHEME } from '../../../utils/url.js';
 import { check_feature } from '../../../utils/features.js';
 import { escape_html } from '../../../utils/escape.js';
+import { with_runtime_cache } from '../../../runtime/server/runtime-cache.js';
 
 const cwd = process.cwd();
 // vite-specifc queries that we should skip handling for css urls
@@ -546,24 +547,28 @@ export async function dev(vite, vite_config, svelte_config, get_remotes) {
 					return;
 				}
 
-				const rendered = await server.respond(request, {
-					getClientAddress: () => {
-						const { remoteAddress } = req.socket;
-						if (remoteAddress) return remoteAddress;
-						throw new Error('Could not determine clientAddress');
-					},
-					read: (file) => {
-						if (file in manifest._.server_assets) {
-							return fs.readFileSync(from_fs(file));
-						}
+				const rendered = await with_runtime_cache(
+					request,
+					{
+						getClientAddress: () => {
+							const { remoteAddress } = req.socket;
+							if (remoteAddress) return remoteAddress;
+							throw new Error('Could not determine clientAddress');
+						},
+						read: (file) => {
+							if (file in manifest._.server_assets) {
+								return fs.readFileSync(from_fs(file));
+							}
 
-						return fs.readFileSync(path.join(svelte_config.kit.files.assets, file));
+							return fs.readFileSync(path.join(svelte_config.kit.files.assets, file));
+						},
+						before_handle: (event, config, prerender) => {
+							async_local_storage.enterWith({ event, config, prerender });
+						},
+						emulator
 					},
-					before_handle: (event, config, prerender) => {
-						async_local_storage.enterWith({ event, config, prerender });
-					},
-					emulator
-				});
+					server
+				);
 
 				if (rendered.status === 404) {
 					// @ts-expect-error

packages/kit/src/exports/vite/preview/index.js

@@ -5,6 +5,7 @@ import { lookup } from 'mrmime';
 import sirv from 'sirv';
 import { loadEnv, normalizePath } from 'vite';
 import { createReadableStream, getRequest, setResponse } from '../../../exports/node/index.js';
+import { with_runtime_cache } from '../../../runtime/server/runtime-cache.js';
 import { installPolyfills } from '../../../exports/node/polyfills.js';
 import { SVELTE_KIT_ASSETS } from '../../../constants.js';
 import { is_chrome_devtools_request, not_found } from '../utils.js';
@@ -203,9 +204,9 @@ export async function preview(vite, vite_config, svelte_config) {
 				request: req
 			});
 
-			await setResponse(
-				res,
-				await server.respond(request, {
+			const rendered = await with_runtime_cache(
+				request,
+				{
 					getClientAddress: () => {
 						const { remoteAddress } = req.socket;
 						if (remoteAddress) return remoteAddress;
@@ -219,8 +220,10 @@ export async function preview(vite, vite_config, svelte_config) {
 						return fs.readFileSync(join(svelte_config.kit.files.assets, file));
 					},
 					emulator
-				})
+				},
+				server
 			);
+			await setResponse(res, rendered);
 		});
 	};
 }

packages/kit/src/runtime/app/server/remote/command.js

@@ -4,6 +4,7 @@
 import { get_request_store } from '@sveltejs/kit/internal/server';
 import { create_validator, run_remote_function } from './shared.js';
 import { MUTATIVE_METHODS } from '../../../../constants.js';
+import { create_invalidate_cache } from '../../../server/cache.js';
 
 /**
  * Creates a remote command. When called from the browser, the function will be invoked on the server via a `fetch` call.
@@ -80,7 +81,14 @@ export function command(validate_or_fn, maybe_fn) {
 		state.remote.refreshes ??= {};
 
 		const promise = Promise.resolve(
-			run_remote_function(event, state, true, () => validate(arg), fn)
+			run_remote_function(
+				event,
+				state,
+				true,
+				create_invalidate_cache(state),
+				() => validate(arg),
+				fn
+			)
 		);
 
 		// @ts-expect-error

packages/kit/src/runtime/app/server/remote/form.js

@@ -13,6 +13,7 @@ import {
 } from '../../../form-utils.js';
 import { get_cache, run_remote_function } from './shared.js';
 import { ValidationError } from '@sveltejs/kit/internal';
+import { create_invalidate_cache } from '../../../server/cache.js';
 
 /**
  * Creates a form object that can be spread onto a `<form>` element.
@@ -123,6 +124,7 @@ export function form(validate_or_fn, maybe_fn) {
 				output.submission = true;
 
 				const { event, state } = get_request_store();
+
 				const validated = await schema?.['~standard'].validate(data);
 
 				if (meta.validate_only) {
@@ -145,6 +147,7 @@ export function form(validate_or_fn, maybe_fn) {
 							event,
 							state,
 							true,
+							create_invalidate_cache(state),
 							() => data,
 							(data) => (!maybe_fn ? fn() : fn(data, issue))
 						);