[feat] expose handler to allow use in custom server

Author: benmccann

documentation/faq/80-integrations.md

@@ -67,7 +67,7 @@ Put the code to query your database in [endpoints](/docs#routing-endpoints) - do
 
 ### How do I use middleware?
 
-In dev, you can add middleware to Vite by using a Vite plugin. For example:
+`adapter-node` builds a middleware that use can use with your own server for production mode. In dev, you can add middleware to Vite by using a Vite plugin. For example:
 
 ```js
 const myPlugin = {

packages/adapter-node/README.md

@@ -45,6 +45,34 @@ 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 middleware `(req, res, next) => {}` that's compatible with [Express](https://github.com/expressjs/expressjs.com) / [Connect](https://github.com/senchalabs/connect) / [Polka](https://github.com/lukeed/polka). Additionally, it also exports a reference server implementation using this middleware 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 `kitMiddleware`, your ready-to-use SvelteKit bundle as middleware, from `./build/middlewares.js`.
+
+```
+import { assetsMiddleware, prerenderedMiddleware, kitMiddleware } from './build/middlewares.js';
+import polka from 'polka';
+
+const app = polka();
+
+const myMiddleware = function(req, res, next) {
+  console.log('Hello world!');
+  next();
+};
+
+app.use(myMiddleware);
+
+app.get('/no-svelte', (req, res) => {
+  res.end('This is not Svelte!')
+});
+
+app.use(assetsMiddleware, prerenderedMiddleware, kitMiddleware);
+
+app.listen(3000)
+```
+
 ## Advanced Configuration
 
 ### esbuild

packages/adapter-node/index.js

@@ -41,7 +41,7 @@ export default function ({
 				await compress(static_directory);
 			}
 
-			utils.log.minor('Building server');
+			utils.log.minor('Building SvelteKit middleware');
 			const files = fileURLToPath(new URL('./files', import.meta.url));
 			utils.copy(files, '.svelte-kit/node');
 			writeFileSync(
@@ -54,10 +54,11 @@ 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/middlewares.js'],
+				outfile: join(out, 'middlewares.js'),
 				bundle: true,
 				external: Object.keys(JSON.parse(readFileSync('package.json', 'utf8')).dependencies || {}),
 				format: 'esm',
@@ -71,6 +72,32 @@ 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: ['./middlewares.js'], // does not work, eslint does not exclude middlewares from target
+				format: 'esm',
+				platform: 'node',
+				target: 'node12',
+				// external exclude workaround, see https://github.com/evanw/esbuild/issues/514
+				plugins: [
+					{
+						name: 'fix-middlewares-exclude',
+						setup(build) {
+							// Match an import called "./middlewares.js" and mark it as external
+							build.onResolve({ filter: /^\.\/middlewares\.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/middlewares.js',
+		output: {
+			file: 'files/middlewares.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: ['./middlewares.js', './env.js', ...require('module').builtinModules]
 	},
 	{
 		input: 'src/shims.js',

packages/adapter-node/src/index.js

@@ -1,17 +1,22 @@
-// TODO hardcoding the relative location makes this brittle
-// @ts-ignore
-import { init, render } from '../output/server/app.js';
 // @ts-ignore
 import { path, host, port } from './env.js';
-import { createServer } from './server';
-
-init();
+import { assetsMiddleware, kitMiddleware, prerenderedMiddleware } from './middlewares.js';
+import compression from 'compression';
+import polka from 'polka';
 
-const instance = createServer({ render });
+const server = polka().use(
+	// https://github.com/lukeed/polka/issues/173
+	// @ts-ignore - nothing we can do about so just ignore it
+	compression({ threshold: 0 }),
+	assetsMiddleware,
+	kitMiddleware,
+	prerenderedMiddleware
+);
 
 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/kit-middleware.js

@@ -0,0 +1,40 @@
+import { getRawBody } from '@sveltejs/kit/node';
+
+/**
+ * @return {import('polka').Middleware}
+ */
+// TODO: type render function from @sveltejs/kit/adapter
+// @ts-ignore
+export function create_kit_middleware({ render }) {
+	return async (req, res) => {
+		const parsed = new URL(req.url || '', 'http://localhost');
+
+		let body;
+
+		try {
+			body = await getRawBody(req);
+		} catch (err) {
+			res.statusCode = err.status || 400;
+			return res.end(err.reason || 'Invalid request body');
+		}
+
+		const rendered = await render({
+			method: req.method,
+			headers: req.headers, // TODO: what about repeated headers, i.e. string[]
+			path: parsed.pathname,
+			query: parsed.searchParams,
+			rawBody: body
+		});
+
+		if (rendered) {
+			res.writeHead(rendered.status, rendered.headers);
+			if (rendered.body) {
+				res.write(rendered.body);
+			}
+			res.end();
+		} else {
+			res.statusCode = 404;
+			res.end('Not found');
+		}
+	};
+}

packages/adapter-node/src/middlewares.js

@@ -0,0 +1,48 @@
+// TODO hardcoding the relative location makes this brittle
+// Also, we need most of the logic in another file for testing because
+// ../output/server/app.js doesn't exist when we run the tests
+// @ts-ignore
+import { init, render } from '../output/server/app.js';
+import { create_kit_middleware } from './kit-middleware.js';
+
+import fs from 'fs';
+import { dirname, join } from 'path';
+import sirv from 'sirv';
+import { fileURLToPath } from 'url';
+
+// App is a dynamic file built from the application layer.
+
+const __dirname = dirname(fileURLToPath(import.meta.url));
+/** @type {import('polka').Middleware} */
+const noop_handler = (_req, _res, next) => next();
+const paths = {
+	assets: join(__dirname, '/assets'),
+	prerendered: join(__dirname, '/prerendered')
+};
+
+export const prerenderedMiddleware = fs.existsSync(paths.prerendered)
+	? sirv(paths.prerendered, {
+			etag: true,
+			maxAge: 0,
+			gzip: true,
+			brotli: true
+	  })
+	: noop_handler;
+
+export const assetsMiddleware = fs.existsSync(paths.assets)
+	? sirv(paths.assets, {
+			setHeaders: (res, pathname) => {
+				// @ts-expect-error - dynamically replaced with define
+				if (pathname.startsWith(/* eslint-disable-line no-undef */ APP_DIR)) {
+					res.setHeader('cache-control', 'public, max-age=31536000, immutable');
+				}
+			},
+			gzip: true,
+			brotli: true
+	  })
+	: noop_handler;
+
+export const kitMiddleware = (function () {
+	init();
+	return create_kit_middleware({ render });
+})();

packages/adapter-node/src/server.js

@@ -1,14 +1,16 @@
 import { test } from 'uvu';
-import { createServer } from '../src/server.js';
+import { createKitMiddleware } from '../src/kit-middleware.js';
 import * as assert from 'uvu/assert';
 import fetch from 'node-fetch';
+import polka from 'polka';
+import { createServer } from 'http';
 
 const { PORT = 3000 } = process.env;
 const DEFAULT_SERVER_OPTS = { render: () => {} };
 
-function startServer(opts = DEFAULT_SERVER_OPTS) {
-	const server = createServer(opts);
+async function startServer(opts = DEFAULT_SERVER_OPTS) {
 	return new Promise((fulfil, reject) => {
+		const server = polka().use(createKitMiddleware(opts));
 		server.listen(PORT, (err) => {
 			if (err) {
 				reject(err);