[feat] expose handler to allow use in custom server

Author: matths

documentation/faq/80-integrations.md

@@ -65,6 +65,34 @@ onMount(() => {
 
 Put the code to query your database in [endpoints](/docs#routing-endpoints) - don't query the database in .svelte files. You can create a `db.js` or similar that sets up a connection immediately and makes the client accessible throughout the app as a singleton. You can execute any one-time setup code in `hooks.js` and import your database helpers into any endpoint that needs them.
 
+### How use middleware?
+
+You can add middleware to `adapter-node` for production mode. In dev, you can add middleware to Vite by using a Vite plugin. For example:
+
+```js
+const myPlugin = {
+  name: 'log-request-middleware',
+  configureServer(server) {
+    server.middlewares.use((req, res, next) => {
+      console.log(`Got request ${req.url}`);
+      next();
+    })
+  }
+}
+
+/** @type {import('@sveltejs/kit').Config} */
+const config = {
+	kit: {
+		target: '#svelte',
+		vite: {
+			plugins: [ myPlugin ]
+		}
+	}
+};
+
+export default config;
+```
+
 ### Does it work with Yarn 2?
 
 Sort of. The Plug'n'Play feature, aka 'pnp', is broken (it deviates from the Node module resolution algorithm, and [doesn't yet work with native JavaScript modules](https://github.com/yarnpkg/berry/issues/638) which SvelteKit — along with an [increasing number of packages](https://blog.sindresorhus.com/get-ready-for-esm-aa53530b3f77) — uses). You can use `nodeLinker: 'node-modules'` in your [`.yarnrc.yml`](https://yarnpkg.com/configuration/yarnrc#nodeLinker) file to disable pnp, but it's probably easier to just use npm or [pnpm](https://pnpm.io/), which is similarly fast and efficient but without the compatibility headaches.

packages/adapter-node/README.md

@@ -45,6 +45,38 @@ HOST=127.0.0.1 PORT=4000 node build
 
 You can specify different environment variables if necessary using the `env` option.
 
+## Middleware
+
+The adapter exports a [Express](https://github.com/expressjs/expressjs.com) /
+[Polka](https://github.com/lukeed/polka) compatible middleware function `(req, res, next) => {}`
+as well as a reference server implementation using this with a plain node http server.
+
+But you can use your favorite server framework to combine it with other middleware and server logic.
+You can import `createHandler()`, your ready-to-use SvelteKit bundle as middleware, from `./build/handler.js`.
+
+```
+import { createHandler } from './build/handler.js';
+import express from 'express';
+
+const app = express();
+
+var myMiddleware = function (req, res, next) {
+  console.log('Hello world!');
+  next();
+};
+
+app.use(myMiddleware);
+
+app.get('/no-svelte', (req, res) => {
+  res.send('This is not Svelte!')
+});
+
+// SvelteKit
+app.get('*', createHandler());
+
+app.listen(3000)
+```
+
 ## Advanced Configuration
 
 ### esbuild

packages/adapter-node/index.js

@@ -53,7 +53,7 @@ export default function ({
 				await compress(static_directory);
 			}
 
-			utils.log.minor('Building server');
+			utils.log.minor('Building SvelteKit request handler');
 			const files = fileURLToPath(new URL('./files', import.meta.url));
 			utils.copy(files, '.svelte-kit/node');
 			writeFileSync(
@@ -66,10 +66,11 @@ export default function ({
 					port_env
 				)}] || (!path && 3000);`
 			);
+
 			/** @type {BuildOptions} */
 			const defaultOptions = {
-				entryPoints: ['.svelte-kit/node/index.js'],
-				outfile: join(out, 'index.js'),
+				entryPoints: ['.svelte-kit/node/handler.js'],
+				outfile: join(out, 'handler.js'),
 				bundle: true,
 				external: Object.keys(JSON.parse(readFileSync('package.json', 'utf8')).dependencies || {}),
 				format: 'esm',
@@ -83,6 +84,32 @@ export default function ({
 			const buildOptions = esbuildConfig ? await esbuildConfig(defaultOptions) : defaultOptions;
 			await esbuild.build(buildOptions);
 
+			utils.log.minor('Building SvelteKit reference server');
+			/** @type {BuildOptions} */
+			const defaultOptionsRefServer = {
+				entryPoints: ['.svelte-kit/node/index.js'],
+				outfile: join(out, 'index.js'),
+				bundle: true,
+				external: ['./handler.js'], // does not work, eslint does not exclude handler from target
+				format: 'esm',
+				platform: 'node',
+				target: 'node12',
+				// external exclude workaround, see https://github.com/evanw/esbuild/issues/514
+				plugins: [
+					{
+						name: 'fix-handler-exclude',
+						setup(build) {
+							// Match an import called "./handler.js" and mark it as external
+							build.onResolve({ filter: /^\.\/handler\.js$/ }, () => ({ external: true }));
+						}
+					}
+				]
+			};
+			const buildOptionsRefServer = esbuildConfig
+				? await esbuildConfig(defaultOptionsRefServer)
+				: defaultOptionsRefServer;
+			await esbuild.build(buildOptionsRefServer);
+
 			utils.log.minor('Prerendering static pages');
 			await utils.prerender({
 				dest: `${out}/prerendered`

packages/adapter-node/rollup.config.js

@@ -3,6 +3,16 @@ import commonjs from '@rollup/plugin-commonjs';
 import json from '@rollup/plugin-json';
 
 export default [
+	{
+		input: 'src/handler.js',
+		output: {
+			file: 'files/handler.js',
+			format: 'esm',
+			sourcemap: true
+		},
+		plugins: [nodeResolve(), commonjs(), json()],
+		external: ['../output/server/app.js', ...require('module').builtinModules]
+	},
 	{
 		input: 'src/index.js',
 		output: {
@@ -11,7 +21,7 @@ export default [
 			sourcemap: true
 		},
 		plugins: [nodeResolve(), commonjs(), json()],
-		external: ['../output/server/app.js', './env.js', ...require('module').builtinModules]
+		external: ['./handler.js', './env.js', ...require('module').builtinModules]
 	},
 	{
 		input: 'src/shims.js',

packages/adapter-node/src/handler.js

@@ -0,0 +1,8 @@
+// TODO hardcoding the relative location makes this brittle
+import { init, render } from '../output/server/app.js'; // eslint-disable-line import/no-unresolved
+import { createPolkaHandler } from './polka-handler.js';
+
+export function createHandler() {
+	init();
+	return createPolkaHandler({ render });
+}

packages/adapter-node/src/index.js

@@ -1,15 +1,11 @@
-// TODO hardcoding the relative location makes this brittle
-import { init, render } from '../output/server/app.js'; // eslint-disable-line import/no-unresolved
 import { path, host, port } from './env.js'; // eslint-disable-line import/no-unresolved
-import { createServer } from './server';
-
-init();
-
-const instance = createServer({ render });
+import { createHandler } from './handler.js';
+import { createServer } from 'http';
 
+const server = createServer(createHandler());
 const listenOpts = { path, host, port };
-instance.listen(listenOpts, () => {
+server.listen(listenOpts, () => {
 	console.log(`Listening on ${path ? path : host + ':' + port}`);
 });
 
-export { instance };
+export { server };

packages/adapter-node/src/server.js renamed to packages/adapter-node/src/polka-handler.js

@@ -15,7 +15,7 @@ const paths = {
 	prerendered: join(__dirname, '/prerendered')
 };
 
-export function createServer({ render }) {
+export function createPolkaHandler({ render }) {
 	const prerendered_handler = fs.existsSync(paths.prerendered)
 		? sirv(paths.prerendered, {
 				etag: true,
@@ -38,7 +38,7 @@ export function createServer({ render }) {
 		  })
 		: noop_handler;
 
-	const server = polka().use(
+	const polka_instance = polka().use(
 		compression({ threshold: 0 }),
 		assets_handler,
 		prerendered_handler,
@@ -73,5 +73,5 @@ export function createServer({ render }) {
 		}
 	);
 
-	return server;
+	return polka_instance.handler;
 }

packages/adapter-node/tests/smoke.js

@@ -1,14 +1,17 @@
 import { test } from 'uvu';
-import { createServer } from '../src/server.js';
+import { createPolkaHandler } from '../src/polka-handler.js';
 import * as assert from 'uvu/assert';
 import fetch from 'node-fetch';
+import { createServer } from 'http';
 
 const { PORT = 3000 } = process.env;
 const DEFAULT_SERVER_OPTS = { render: () => {} };
 
 function startServer(opts = DEFAULT_SERVER_OPTS) {
-	const server = createServer(opts);
+	const handler = createPolkaHandler(opts);
+
 	return new Promise((fulfil, reject) => {
+		const server = createServer(handler);
 		server.listen(PORT, (err) => {
 			if (err) {
 				reject(err);
@@ -21,14 +24,14 @@ function startServer(opts = DEFAULT_SERVER_OPTS) {
 test('starts a server', async () => {
 	const server = await startServer();
 	assert.ok('server started');
-	server.server.close();
+	server.close();
 });
 
 test('serves a 404', async () => {
 	const server = await startServer();
 	const res = await fetch(`http://localhost:${PORT}/nothing`);
 	assert.equal(res.status, 404);
-	server.server.close();
+	server.close();
 });
 
 test('responses with the rendered status code', async () => {
@@ -43,7 +46,7 @@ test('responses with the rendered status code', async () => {
 	});
 	const res = await fetch(`http://localhost:${PORT}/wow`);
 	assert.equal(res.status, 203);
-	server.server.close();
+	server.close();
 });
 
 test('passes through umlaut as encoded path', async () => {