fix: generate edge middleware to run reroute

packages/adapter-vercel/files/reroute.js

@@ -0,0 +1,67 @@
+import { reroute } from 'HOOKS';
+
+// we copy the rewrite function from `@vercel/edge` because that package can't co-exist with `@types/node`.
+// see https://github.com/sveltejs/kit/pull/9280#issuecomment-1452110035
+
+/**
+ * https://github.com/vercel/vercel/blob/4337ea0654c4ee2c91c4464540f879d43da6696f/packages/edge/src/middleware-helpers.ts#L38-L55
+ * @param {import('index.js').ExtraResponseInit | undefined} init
+ * @param {Headers} headers
+ */
+function handleMiddlewareField(init, headers) {
+	if (init?.request?.headers) {
+		if (!(init.request.headers instanceof Headers)) {
+			throw new Error('request.headers must be an instance of Headers');
+		}
+
+		const keys = [];
+		for (const [key, value] of init.request.headers) {
+			headers.set('x-middleware-request-' + key, value);
+			keys.push(key);
+		}
+
+		headers.set('x-middleware-override-headers', keys.join(','));
+	}
+}
+
+/**
+ * https://github.com/vercel/vercel/blob/4337ea0654c4ee2c91c4464540f879d43da6696f/packages/edge/src/middleware-helpers.ts#L101-L114
+ * @param {string | URL} destination
+ * @returns {Response}
+ */
+export function rewrite(destination) {
+	const headers = new Headers({});
+	headers.set('x-middleware-rewrite', String(destination));
+
+	handleMiddlewareField(undefined, headers);
+
+	return new Response(null, {
+		headers
+	});
+}
+
+/**
+ *
+ * @param {import('index.js').ExtraResponseInit=} init
+ * @returns {Response}
+ */
+export function next(init) {
+	const headers = new Headers(init?.headers ?? {});
+	headers.set('x-middleware-next', '1');
+
+	handleMiddlewareField(init, headers);
+
+	return new Response(null, {
+		...init,
+		headers
+	});
+}
+
+/**
+ * @param {Request} request
+ * @returns {Response}
+ */
+export default function middleware(request) {
+	const pathname = reroute({ url: new URL(request.url) });
+	return pathname ? rewrite(pathname) : next(request);
+}

packages/adapter-vercel/index.d.ts

@@ -157,3 +157,40 @@ export interface RequestContext {
 		 */ promise: Promise<unknown>
 	): void;
 }
+
+export interface ModifiedRequest {
+	/**
+	 * If set, overwrites the incoming headers to the origin request.
+	 *
+	 * This is useful when you want to pass data between a Middleware and a
+	 * Serverless or Edge Function.
+	 *
+	 * @example
+	 * <caption>Add a `x-user-id` header and remove the `Authorization` header</caption>
+	 *
+	 * ```ts
+	 * import { rewrite } from '@vercel/edge';
+	 * export default async function middleware(request: Request): Promise<Response> {
+	 *   const newHeaders = new Headers(request.headers);
+	 *   newHeaders.set('x-user-id', 'user_123');
+	 *   newHeaders.delete('authorization');
+	 *   return rewrite(request.url, {
+	 *     request: { headers: newHeaders }
+	 *   })
+	 * }
+	 * ```
+	 */
+	headers?: Headers;
+}
+
+export interface ExtraResponseInit extends Omit<ResponseInit, 'headers'> {
+	/**
+	 * These headers will be sent to the user response
+	 * along with the response headers from the origin.
+	 */
+	headers?: HeadersInit;
+	/**
+	 * Fields to rewrite for the upstream request.
+	 */
+	request?: ModifiedRequest;
+}

packages/adapter-vercel/index.js

@@ -220,7 +220,7 @@ const plugin = function (defaults = {}) {
 				}
 
 				const node_runtime = /nodejs([0-9]+)\.x/.exec(runtime);
-				if (runtime !== 'edge' && (!node_runtime || node_runtime[1] < 18)) {
+				if (runtime !== 'edge' && (!node_runtime || +node_runtime[1] < 18)) {
 					throw new Error(
 						`Invalid runtime '${runtime}' for route ${route.id}. Valid runtimes are 'edge' and 'nodejs18.x' or higher ` +
 							'(see the Node.js Version section in your Vercel project settings for info on the currently supported versions).'
@@ -293,6 +293,107 @@ const plugin = function (defaults = {}) {
 
 			const singular = groups.size === 1;
 
+			const hooks_filename = builder.config.kit.files.hooks.universal.split('/').at(-1);
+			const hooks_output_path = `${builder.getServerDirectory()}/chunks/${hooks_filename}.js`;
+
+			if (!singular && hooks_output_path) {
+				/**
+				 * @param {string} name
+				 * @param {import('.').EdgeConfig} config
+				 */
+				async function generate_middleware(name, config) {
+					const tmp = builder.getBuildDirectory(`vercel-tmp/${name}`);
+					const relativePath = path.posix.relative(tmp, hooks_output_path);
+
+					builder.copy(`${files}/${name}.js`, `${tmp}/${name}.js`, {
+						replace: {
+							HOOKS: relativePath
+						}
+					});
+
+					try {
+						const result = await esbuild.build({
+							entryPoints: [`${tmp}/${name}.js`],
+							outfile: `${dirs.functions}/${name}.func/index.js`,
+							target: 'es2020', // TODO verify what the edge runtime supports
+							bundle: true,
+							platform: 'browser',
+							format: 'esm',
+							external: [
+								...compatible_node_modules,
+								...compatible_node_modules.map((id) => `node:${id}`),
+								...(config.external || [])
+							],
+							sourcemap: 'linked',
+							banner: { js: 'globalThis.global = globalThis;' },
+							loader: {
+								'.wasm': 'copy'
+							}
+						});
+
+						if (result.warnings.length > 0) {
+							const formatted = await esbuild.formatMessages(result.warnings, {
+								kind: 'warning',
+								color: true
+							});
+
+							console.error(formatted.join('\n'));
+						}
+					} catch (error) {
+						for (const e of error.errors) {
+							for (const node of e.notes) {
+								const match =
+									/The package "(.+)" wasn't found on the file system but is built into node/.exec(
+										node.text
+									);
+
+								if (match) {
+									node.text = `Cannot use "${match[1]}" when deploying to Vercel Edge Functions.`;
+								}
+							}
+						}
+
+						const formatted = await esbuild.formatMessages(error.errors, {
+							kind: 'error',
+							color: true
+						});
+
+						console.error(formatted.join('\n'));
+
+						throw new Error(
+							`Bundling with esbuild failed with ${error.errors.length} ${
+								error.errors.length === 1 ? 'error' : 'errors'
+							}`
+						);
+					}
+
+					write(
+						`${dirs.functions}/${name}.func/.vc-config.json`,
+						JSON.stringify(
+							{
+								runtime: 'edge',
+								regions: config.regions,
+								entrypoint: 'index.js',
+								framework: {
+									slug: 'sveltekit',
+									version: VERSION
+								}
+							},
+							null,
+							'\t'
+						)
+					);
+				}
+
+				static_config.routes.push({
+					src: '/.*',
+					middlewarePath: 'reroute',
+					continue: true
+				});
+
+				await generate_middleware('reroute', { external: defaults?.external });
+			}
+
 			for (const group of groups.values()) {
 				const generate_function =
 					group.config.runtime === 'edge' ? generate_edge_function : generate_serverless_function;

packages/adapter-vercel/internal.d.ts

@@ -6,3 +6,8 @@ declare module 'MANIFEST' {
 	import { SSRManifest } from '@sveltejs/kit';
 	export const manifest: SSRManifest;
 }
+
+declare module 'HOOKS' {
+	import { Reroute } from '@sveltejs/kit';
+	export const reroute: Reroute;
+}