feat(adapter-netlify)!: migrate to the modern Netlify Functions API

.changeset/tender-kings-knock.md

@@ -0,0 +1,17 @@
+---
+'@sveltejs/adapter-netlify': minor
+---
+
+chore!: Migrate to the modern Netlify Functions API
+
+The Netlify adapter now generates "v2" Netlify Functions, which uses modern standards (ESM, Request,
+Response) instead of the legacy "Lambda-compatible" or "v1" format. Under the hood, this greatly
+simplifies the adapter code and improves maintainability.
+
+For more details on features this unlocks for your SvelteKit app, see
+https://developers.netlify.com/guides/migrating-to-the-modern-netlify-functions/.
+
+BREAKING CHANGES:
+
+- `platform.context` is now the [modern Netlify Functions
+  context](https://docs.netlify.com/build/functions/api/#netlify-specific-context-object)

documentation/docs/25-build-and-deploy/80-adapter-netlify.md

@@ -76,14 +76,7 @@ You may build your app using functionality provided directly by SvelteKit withou
 
 ### `_headers` and `_redirects`
 
-The [`_headers`](https://docs.netlify.com/routing/headers/#syntax-for-the-headers-file) and [`_redirects`](https://docs.netlify.com/routing/redirects/redirect-options/) files specific to Netlify can be used for static asset responses (like images) by putting them into the project root folder.
-
-### Redirect rules
-
-During compilation, redirect rules are automatically appended to your `_redirects` file. (If it doesn't exist yet, it will be created.) That means:
-
-- `[[redirects]]` in `netlify.toml` will never match as `_redirects` has a [higher priority](https://docs.netlify.com/routing/redirects/#rule-processing-order). So always put your rules in the [`_redirects` file](https://docs.netlify.com/routing/redirects/#syntax-for-the-redirects-file).
-- `_redirects` shouldn't have any custom "catch all" rules such as `/* /foobar/:splat`. Otherwise the automatically appended rule will never be applied as Netlify is only processing [the first matching rule](https://docs.netlify.com/routing/redirects/#rule-processing-order).
+The [`_headers`](https://docs.netlify.com/routing/headers/#syntax-for-the-headers-file) and [`_redirects`](https://docs.netlify.com/routing/redirects/redirect-options/) files specific to Netlify can be used for static asset responses (like images) by putting them into the project root folder. You can also use [`[[redirects]]`](https://docs.netlify.com/routing/redirects/#syntax-for-the-netlify-configuration-file) in your `netlify.toml`.
 
 ### Netlify Forms
 

packages/adapter-netlify/index.js

@@ -1,6 +1,6 @@
 /** @import { BuildOptions } from 'esbuild' */
 import { appendFileSync, existsSync, readdirSync, readFileSync, writeFileSync } from 'node:fs';
-import { dirname, join, resolve, posix } from 'node:path';
+import { join, resolve, posix } from 'node:path';
 import { fileURLToPath } from 'node:url';
 import { builtinModules } from 'node:module';
 import process from 'node:process';
@@ -241,8 +241,6 @@ async function generate_edge_functions({ builder }) {
 function generate_lambda_functions({ builder, publish, split }) {
 	builder.mkdirp('.netlify/functions-internal/.svelte-kit');
 
-	/** @type {string[]} */
-	const redirects = [];
 	builder.writeServer('.netlify/server');
 
 	const replace = {
@@ -251,9 +249,6 @@ function generate_lambda_functions({ builder, publish, split }) {
 
 	builder.copy(files, '.netlify', { replace, filter: (name) => !name.endsWith('edge.js') });
 
-	// Configuring the function to use ESM as the output format.
-	const fn_config = JSON.stringify({ config: { nodeModuleFormat: 'esm' }, version: 1 });
-
 	builder.log.minor('Generating serverless functions...');
 
 	if (split) {
@@ -302,58 +297,46 @@ function generate_lambda_functions({ builder, publish, split }) {
 				routes
 			});
 
-			const fn = `import { init } from '../serverless.js';\n\nexport const handler = init(${manifest});\n`;
+			const fn = `import { init } from '../serverless.js';\n\nexport default init(${manifest});\n\nexport const config = {\n\tpath: "${pattern}",\n\tpreferStatic: true\n};\n`;
 
 			writeFileSync(`.netlify/functions-internal/${name}.mjs`, fn);
-			writeFileSync(`.netlify/functions-internal/${name}.json`, fn_config);
 			if (builder.hasServerInstrumentationFile?.()) {
 				builder.instrument?.({
 					entrypoint: `.netlify/functions-internal/${name}.mjs`,
 					instrumentation: '.netlify/server/instrumentation.server.js',
 					start: `.netlify/functions-start/${name}.start.mjs`,
 					module: {
-						exports: ['handler']
+						exports: ['default']
 					}
 				});
 			}
-
-			const redirect = `/.netlify/functions/${name} 200`;
-			redirects.push(`${pattern} ${redirect}`);
-			redirects.push(`${pattern === '/' ? '' : pattern}/__data.json ${redirect}`);
 		}
 	} else {
 		const manifest = builder.generateManifest({
 			relativePath: '../server'
 		});
 
-		const fn = `import { init } from '../serverless.js';\n\nexport const handler = init(${manifest});\n`;
+		const fn = `import { init } from '../serverless.js';\n\nexport default init(${manifest});\n\nexport const config = {\n\tpath: "/*",\n\tpreferStatic: true\n};\n`;
 
-		writeFileSync(`.netlify/functions-internal/${FUNCTION_PREFIX}render.json`, fn_config);
 		writeFileSync(`.netlify/functions-internal/${FUNCTION_PREFIX}render.mjs`, fn);
 		if (builder.hasServerInstrumentationFile?.()) {
 			builder.instrument?.({
 				entrypoint: `.netlify/functions-internal/${FUNCTION_PREFIX}render.mjs`,
 				instrumentation: '.netlify/server/instrumentation.server.js',
 				start: `.netlify/functions-start/${FUNCTION_PREFIX}render.start.mjs`,
 				module: {
-					exports: ['handler']
+					exports: ['default']
 				}
 			});
 		}
-
-		redirects.push(`* /.netlify/functions/${FUNCTION_PREFIX}render 200`);
 	}
 
-	// this should happen at the end, after builder.writeClient(...),
-	// so that generated redirects are appended to custom redirects
-	// rather than replaced by them
-	builder.log.minor('Writing redirects...');
-	const redirects_file = join(publish, '_redirects');
+	// Copy user's custom _redirects file if it exists
 	if (existsSync('_redirects')) {
+		builder.log.minor('Copying user redirects...');
+		const redirects_file = join(publish, '_redirects');
 		builder.copy('_redirects', redirects_file);
 	}
-	builder.mkdirp(dirname(redirects_file));
-	appendFileSync(redirects_file, `\n\n${redirects.join('\n')}`);
 }
 
 function get_netlify_config() {
@@ -378,11 +361,6 @@ function get_publish_directory(netlify_config, builder) {
 			return;
 		}
 
-		if (netlify_config.redirects) {
-			throw new Error(
-				"Redirects are not supported in netlify.toml. Use _redirects instead. For more details consult the readme's troubleshooting section."
-			);
-		}
 		if (resolve(netlify_config.build.publish) === process.cwd()) {
 			throw new Error(
 				'The publish directory cannot be set to the site root. Please change it to another value such as "build" in netlify.toml.'

packages/adapter-netlify/package.json

@@ -44,8 +44,7 @@
 	},
 	"dependencies": {
 		"@iarna/toml": "^2.2.5",
-		"esbuild": "^0.25.4",
-		"set-cookie-parser": "^2.6.0"
+		"esbuild": "^0.25.4"
 	},
 	"devDependencies": {
 		"@netlify/dev": "catalog:",
@@ -59,7 +58,6 @@
 		"@sveltejs/kit": "workspace:^",
 		"@sveltejs/vite-plugin-svelte": "catalog:",
 		"@types/node": "catalog:",
-		"@types/set-cookie-parser": "catalog:",
 		"rollup": "^4.14.2",
 		"typescript": "^5.3.3",
 		"vitest": "catalog:"

packages/adapter-netlify/src/serverless.js

@@ -1,12 +1,11 @@
 import './shims';
 import { Server } from '0SERVER';
-import { split_headers } from './headers.js';
 import { createReadableStream } from '@sveltejs/kit/node';
 import process from 'node:process';
 
 /**
  * @param {import('@sveltejs/kit').SSRManifest} manifest
- * @returns {import('@netlify/functions').Handler}
+ * @returns {(request: Request, context: import('@netlify/functions').Context) => Promise<Response>}
  */
 export function init(manifest) {
 	const server = new Server(manifest);
@@ -17,77 +16,17 @@ export function init(manifest) {
 		read: (file) => createReadableStream(`.netlify/server/${file}`)
 	});
 
-	return async (event, context) => {
+	return async (request, context) => {
 		if (init_promise !== null) {
 			await init_promise;
 			init_promise = null;
 		}
 
-		const response = await server.respond(to_request(event), {
+		return server.respond(request, {
 			platform: { context },
 			getClientAddress() {
-				return /** @type {string} */ (event.headers['x-nf-client-connection-ip']);
+				return context.ip;
 			}
 		});
-
-		const partial_response = {
-			statusCode: response.status,
-			...split_headers(response.headers)
-		};
-
-		if (!is_text(response.headers.get('content-type'))) {
-			// Function responses should be strings (or undefined), and responses with binary
-			// content should be base64 encoded and set isBase64Encoded to true.
-			// https://github.com/netlify/functions/blob/main/src/function/response.ts
-			return {
-				...partial_response,
-				isBase64Encoded: true,
-				body: Buffer.from(await response.arrayBuffer()).toString('base64')
-			};
-		}
-
-		return {
-			...partial_response,
-			body: await response.text()
-		};
-	};
-}
-
-/**
- * @param {import('@netlify/functions').HandlerEvent} event
- * @returns {Request}
- */
-function to_request({ httpMethod, headers, rawUrl, body, isBase64Encoded }) {
-	/** @type {RequestInit} */
-	const init = {
-		method: httpMethod,
-		headers: new Headers(/** @type {Record<string, string>} */ (headers))
 	};
-
-	if (httpMethod !== 'GET' && httpMethod !== 'HEAD') {
-		const encoding = isBase64Encoded ? 'base64' : 'utf-8';
-		init.body = typeof body === 'string' ? Buffer.from(body, encoding) : body;
-	}
-
-	return new Request(rawUrl, init);
-}
-
-const text_types = new Set([
-	'application/xml',
-	'application/json',
-	'application/x-www-form-urlencoded',
-	'multipart/form-data'
-]);
-
-/**
- * Decides how the body should be parsed based on its mime type
- *
- * @param {string | undefined | null} content_type The `content-type` header of a request/response.
- * @returns {boolean}
- */
-function is_text(content_type) {
-	if (!content_type) return true; // defaults to json
-	const type = content_type.split(';')[0].toLowerCase(); // get the mime type
-
-	return type.startsWith('text/') || type.endsWith('+xml') || text_types.has(type);
 }

packages/adapter-netlify/test/apps/basic/netlify/functions/render.mjs

@@ -1,39 +1,6 @@
-// This is a temporary workaround to be compatible with Netlify's new dev server
-// TODO: remove this once we overhaul the Netlify adapter to use Netlify's new serverless function format https://docs.netlify.com/build/functions/get-started/?data-tab=TypeScript#write-a-function
-
-import { handler } from '../../.netlify/functions-internal/sveltekit-render.mjs';
-
-/**
- * @param {Request} request
- * @param {import('@netlify/functions').HandlerContext} context
- */
-export default async function (request, context) {
-	const [rawUrl, rawQuery] = request.url.split('?');
-	/** @type {import('@netlify/functions').HandlerEvent} */
-	const event = {
-		rawUrl,
-		rawQuery: rawQuery || '',
-		headers: Object.fromEntries(request.headers),
-		httpMethod: request.method,
-		isBase64Encoded: false,
-		path: new URL(request.url).pathname,
-		queryStringParameters: Object.fromEntries(new URL(request.url).searchParams),
-		body: request.body && (await request.text()),
-		multiValueHeaders: {},
-		multiValueQueryStringParameters: null
-	};
-	const result = await handler(event, context);
-	if (result) {
-		return new Response(result.body, {
-			status: result.statusCode,
-			// @ts-ignore
-			headers: result.headers
-		});
-	}
-
-	return new Response('Not Found', { status: 404 });
-}
+export { default } from '../../.netlify/functions-internal/sveltekit-render.mjs';
 
 export const config = {
-	path: '/*'
+	path: '/*',
+	preferStatic: true
 };