feat: add support for read in edge environments

.changeset/moody-birds-help.md

@@ -0,0 +1,6 @@
+---
+'@sveltejs/adapter-netlify': minor
+'@sveltejs/adapter-vercel': minor
+---
+
+feat: add support for `read` imported from `$app/server` in edge functions

.changeset/old-moons-lick.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/adapter-cloudflare': minor
+---
+
+feat: add support for `read` imported from `$app/server`

.changeset/weak-pillows-doubt.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': minor
+---
+
+feat: support asynchronous `read` implementations from adapters

eslint.config.js

@@ -33,6 +33,7 @@ export default [
 		},
 		ignores: [
 			'packages/adapter-cloudflare/test/apps/**/*',
+			'packages/adapter-netlify/test/apps/**/*',
 			'packages/adapter-node/rollup.config.js',
 			'packages/adapter-node/tests/smoke.spec_disabled.js',
 			'packages/adapter-static/test/apps/**/*',

package.json

@@ -37,10 +37,13 @@
 	},
 	"pnpm": {
 		"onlyBuiltDependencies": [
+			"@parcel/watcher",
 			"esbuild",
+			"netlify-cli",
 			"rolldown",
 			"sharp",
 			"svelte-preprocess",
+			"unix-dgram",
 			"workerd"
 		]
 	}

packages/adapter-cloudflare/index.js

@@ -1,13 +1,17 @@
+import { VERSION } from '@sveltejs/kit';
 import { copyFileSync, existsSync, writeFileSync } from 'node:fs';
 import path from 'node:path';
 import { fileURLToPath } from 'node:url';
 import { is_building_for_cloudflare_pages } from './utils.js';
 import { getPlatformProxy, unstable_readConfig } from 'wrangler';
 
+const name = '@sveltejs/adapter-cloudflare';
+const [kit_major, kit_minor] = VERSION.split('.');
+
 /** @type {import('./index.js').default} */
 export default function (options = {}) {
 	return {
-		name: '@sveltejs/adapter-cloudflare',
+		name,
 		async adapt(builder) {
 			if (existsSync('_routes.json')) {
 				throw new Error(
@@ -162,6 +166,18 @@ export default function (options = {}) {
 					return prerender ? emulated.prerender_platform : emulated.platform;
 				}
 			};
+		},
+		supports: {
+			read: ({ route }) => {
+				// TODO bump peer dep in next adapter major to simplify this
+				if (kit_major === '2' && kit_minor < '25') {
+					throw new Error(
+						`${name}: Cannot use \`read\` from \`$app/server\` in route \`${route.id}\` when using SvelteKit < 2.25.0`
+					);
+				}
+
+				return true;
+			}
 		}
 	};
 }

packages/adapter-cloudflare/package.json

@@ -33,14 +33,14 @@
 		"ambient.d.ts"
 	],
 	"scripts": {
-		"build": "esbuild src/worker.js --bundle --outfile=files/worker.js --external:SERVER --external:MANIFEST --format=esm",
+		"build": "esbuild src/worker.js --bundle --outfile=files/worker.js --external:SERVER --external:MANIFEST --external:cloudflare:workers --format=esm",
 		"lint": "prettier --check .",
 		"format": "pnpm lint --write",
 		"check": "tsc --skipLibCheck",
-		"prepublishOnly": "pnpm build",
 		"test:unit": "vitest run",
 		"test:e2e": "pnpm build && pnpm -r --workspace-concurrency 1 --filter=\"./test/**\" test",
-		"test": "pnpm test:unit && pnpm test:e2e"
+		"test": "pnpm test:unit && pnpm test:e2e",
+		"prepublishOnly": "pnpm build"
 	},
 	"dependencies": {
 		"@cloudflare/workers-types": "^4.20250507.0",

packages/adapter-cloudflare/src/worker.js

@@ -1,5 +1,6 @@
 import { Server } from 'SERVER';
 import { manifest, prerendered, base_path } from 'MANIFEST';
+import { env } from 'cloudflare:workers';
 import * as Cache from 'worktop/cfw.cache';
 
 const server = new Server(manifest);
@@ -9,6 +10,27 @@ const app_path = `/${manifest.appPath}`;
 const immutable = `${app_path}/immutable/`;
 const version_file = `${app_path}/version.json`;
 
+/**
+ * We don't know the origin until we receive a request, but
+ * that's guaranteed to happen before we call `read`
+ * @type {string}
+ */
+let origin;
+
+const initialized = server.init({
+	// @ts-expect-error env contains environment variables and bindings
+	env,
+	read: async (file) => {
+		const response = await /** @type {{ ASSETS: { fetch: typeof fetch } }} */ (env).ASSETS.fetch(
+			`${origin}/${file}`
+		);
+		if (!response.ok) {
+			throw new Error(`Failed to fetch ${file}: ${response.status} ${response.statusText}`);
+		}
+		return response.body;
+	}
+});
+
 export default {
 	/**
 	 * @param {Request} req
@@ -17,10 +39,10 @@ export default {
 	 * @returns {Promise<Response>}
 	 */
 	async fetch(req, env, ctx) {
-		await server.init({
-			// @ts-expect-error env contains environment variables and bindings
-			env
-		});
+		if (!origin) {
+			origin = new URL(req.url).origin;
+			await initialized;
+		}
 
 		// skip cache if "cache-control: no-cache" in request
 		let pragma = req.headers.get('cache-control') || '';

packages/adapter-cloudflare/test/apps/workers/src/routes/read/+server.js

@@ -0,0 +1,6 @@
+import { read } from '$app/server';
+import file from './file.txt?url';
+
+export function GET() {
+	return read(file);
+}

packages/adapter-cloudflare/test/apps/workers/src/routes/read/file.txt

@@ -0,0 +1 @@
+Hello! This file is read by `read` from `$app/server`.

packages/adapter-cloudflare/test/apps/workers/test/test.js

@@ -1,5 +1,10 @@
+import fs from 'node:fs';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
 import { expect, test } from '@playwright/test';
 
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
+
 test('worker', async ({ page }) => {
 	await page.goto('/');
 	await expect(page.locator('h1')).toContainText('Sum: 3');
@@ -9,3 +14,9 @@ test('ctx', async ({ request }) => {
 	const res = await request.get('/ctx');
 	expect(await res.text()).toBe('ctx works');
 });
+
+test('read from $app/server works', async ({ request }) => {
+	const content = fs.readFileSync(path.resolve(__dirname, '../src/routes/read/file.txt'), 'utf-8');
+	const response = await request.get('/read');
+	expect(await response.text()).toBe(content);
+});

packages/adapter-netlify/index.js

@@ -5,6 +5,9 @@ import { builtinModules } from 'node:module';
 import process from 'node:process';
 import esbuild from 'esbuild';
 import toml from '@iarna/toml';
+import { VERSION } from '@sveltejs/kit';
+
+const [kit_major, kit_minor] = VERSION.split('.');
 
 /**
  * @typedef {{
@@ -13,26 +16,6 @@ import toml from '@iarna/toml';
  * } & toml.JsonMap} NetlifyConfig
  */
 
-/**
- * TODO(serhalp) Replace this custom type with an import from `@netlify/edge-functions`,
- * once that type is fixed to include `excludedPath` and `function`.
- * @typedef {{
- *	 functions: Array<
- *		 | {
- *				 function: string;
- *				 path: string;
- *				 excludedPath?: string | string[];
- *		   }
- *		 | {
- *				 function: string;
- *				 pattern: string;
- *				 excludedPattern?: string | string[];
- *		   }
- *	 >;
- *	 version: 1;
- *	 }} HandlerManifest
- */
-
 const name = '@sveltejs/adapter-netlify';
 const files = fileURLToPath(new URL('./files', import.meta.url).href);
 
@@ -114,11 +97,11 @@ export default function ({ split = false, edge = edge_set_in_env_var } = {}) {
 		},
 
 		supports: {
-			// reading from the filesystem only works in serverless functions
 			read: ({ route }) => {
-				if (edge) {
+				// TODO bump peer dep in next adapter major to simplify this
+				if (edge && kit_major === '2' && kit_minor < '25') {
 					throw new Error(
-						`${name}: Cannot use \`read\` from \`$app/server\` in route \`${route.id}\` when using edge functions`
+						`${name}: Cannot use \`read\` from \`$app/server\` in route \`${route.id}\` when using edge functions and SvelteKit < 2.25.0`
 					);
 				}
 
@@ -161,7 +144,7 @@ async function generate_edge_functions({ builder }) {
 	const path = '/*';
 	// We only need to specify paths without the trailing slash because
 	// Netlify will handle the optional trailing slash for us
-	const excludedPath = [
+	const excluded = [
 		// Contains static files
 		`/${builder.getAppPath()}/*`,
 		...builder.prerendered.paths,
@@ -179,13 +162,13 @@ async function generate_edge_functions({ builder }) {
 		'/.netlify/*'
 	];
 
-	/** @type {HandlerManifest} */
+	/** @type {import('@netlify/edge-functions').Manifest} */
 	const edge_manifest = {
 		functions: [
 			{
 				function: 'render',
 				path,
-				excludedPath
+				excludedPath: /** @type {`/${string}`[]} */ (excluded)
 			}
 		],
 		version: 1
@@ -232,7 +215,7 @@ function generate_lambda_functions({ builder, publish, split }) {
 		'0SERVER': './server/index.js' // digit prefix prevents CJS build from using this as a variable name, which would also get replaced
 	};
 
-	builder.copy(`${files}/esm`, '.netlify', { replace });
+	builder.copy(files, '.netlify', { replace });
 
 	// Configuring the function to use ESM as the output format.
 	const fn_config = JSON.stringify({ config: { nodeModuleFormat: 'esm' }, version: 1 });

packages/adapter-netlify/package.json

@@ -32,12 +32,14 @@
 		"index.d.ts"
 	],
 	"scripts": {
-		"dev": "node -e \"fs.rmSync('files', { force: true, recursive: true })\" && rollup -cw",
-		"build": "node -e \"fs.rmSync('files', { force: true, recursive: true })\" && rollup -c && node -e \"fs.cpSync('src/edge.js', 'files/edge.js')\"",
-		"test": "vitest run",
+		"dev": "rollup -cw",
+		"build": "rollup -c",
 		"check": "tsc",
 		"lint": "prettier --check .",
 		"format": "pnpm lint --write",
+		"test": "pnpm test:unit && pnpm test:integration",
+		"test:unit": "vitest run",
+		"test:integration": "pnpm build && pnpm -r --workspace-concurrency 1 --filter=\"./test/**\" test",
 		"prepublishOnly": "pnpm build"
 	},
 	"dependencies": {
@@ -46,6 +48,7 @@
 		"set-cookie-parser": "^2.6.0"
 	},
 	"devDependencies": {
+		"@netlify/edge-functions": "^2.15.1",
 		"@netlify/functions": "^4.0.0",
 		"@rollup/plugin-commonjs": "^28.0.1",
 		"@rollup/plugin-json": "^6.1.0",

packages/adapter-netlify/rollup.config.js

@@ -1,20 +1,39 @@
 import { nodeResolve } from '@rollup/plugin-node-resolve';
 import commonjs from '@rollup/plugin-commonjs';
 import json from '@rollup/plugin-json';
+import { rmSync } from 'node:fs';
+
+/**
+ * @param {string} filepath
+ * @returns {import('rollup').Plugin}
+ */
+function clearOutput(filepath) {
+	return {
+		name: 'clear-output',
+		buildStart: {
+			order: 'pre',
+			sequential: true,
+			handler() {
+				rmSync(filepath, { recursive: true, force: true });
+			}
+		}
+	};
+}
 
 /** @type {import('rollup').RollupOptions} */
 const config = {
 	input: {
 		serverless: 'src/serverless.js',
-		shims: 'src/shims.js'
+		shims: 'src/shims.js',
+		edge: 'src/edge.js'
 	},
 	output: {
-		dir: 'files/esm',
+		dir: 'files',
 		format: 'esm'
 	},
 	// @ts-ignore https://github.com/rollup/plugins/issues/1329
-	plugins: [nodeResolve({ preferBuiltins: true }), commonjs(), json()],
-	external: (id) => id === '0SERVER' || id.startsWith('node:'),
+	plugins: [clearOutput('files'), nodeResolve({ preferBuiltins: true }), commonjs(), json()],
+	external: (id) => id === '0SERVER' || id === 'MANIFEST' || id.startsWith('node:'),
 	preserveEntrySignatures: 'exports-only'
 };
 

packages/adapter-netlify/src/edge.js

@@ -3,18 +3,32 @@ import { manifest } from 'MANIFEST';
 
 const server = new Server(manifest);
 
+/**
+ * We don't know the origin until we receive a request, but
+ * that's guaranteed to happen before we call `read`
+ * @type {string}
+ */
+let origin;
+
 const initialized = server.init({
 	// @ts-ignore
-	env: Deno.env.toObject()
+	env: Deno.env.toObject(),
+	read: async (file) => {
+		const response = await fetch(`${origin}/${file}`);
+		if (!response.ok) {
+			throw new Error(`Failed to fetch ${file}: ${response.status} ${response.statusText}`);
+		}
+		return response.body;
+	}
 });
 
-/**
- * @param { Request } request
- * @param { any } context
- * @returns { Promise<Response> }
- */
+/** @type {import('@netlify/edge-functions').EdgeFunction} */
 export default async function handler(request, context) {
-	await initialized;
+	if (!origin) {
+		origin = new URL(request.url).origin;
+		await initialized;
+	}
+
 	return server.respond(request, {
 		platform: { context },
 		getClientAddress() {

packages/adapter-netlify/test/apps/basic/.gitignore

@@ -0,0 +1,6 @@
+.DS_Store
+node_modules
+/.svelte-kit
+/.netlify
+/build
+deno.lock

packages/adapter-netlify/test/apps/basic/netlify.toml

@@ -0,0 +1,2 @@
+[dev]
+  publish = "build"