@sveltejs/kit/src/core/postbuild/fallback.js

SvelteKit is the fastest way to build Svelte apps

import { readFileSync } from 'node:fs';
import { join } from 'node:path';
import { pathToFileURL } from 'node:url';
import { forked } from '../../utils/fork.js';
import * as e from '../../messages/build-errors.js';

export default forked(import.meta.url, generate_fallback);

/**
 * @param {{
 *   manifest_path: string;
 *   env: Record<string, string>
 *   out_dir: string;
 *   origin: string;
 *   assets: string;
 * }} opts
 */
async function generate_fallback({ manifest_path, env, out_dir, origin, assets }) {
	const server_root = join(out_dir, 'output');

	/** @type {import('types').ServerModule} */
	const { configure } = await import(pathToFileURL(`${server_root}/server/index.js`).href);

	/** @type {import('types').SSRManifest} */
	const manifest = (await import(pathToFileURL(manifest_path).href)).manifest;

	const { init, respond } = await configure({ building: true, manifest, env });
	await init();

	const response = await respond(new Request(origin + '/[fallback]'), {
		getClientAddress: () => {
			e.prerender_client_address();
		},
		prerendering: {
			fallback: true,
			dependencies: new Map(),
			remote_responses: new Map(),
			resolved_route_ids: new Set()
		},
		read: (file) => readFileSync(join(assets, file))
	});

	if (response.ok) {
		return await response.text();
	}

	e.prerender_fallback_failed(undefined, { stackless: true });
}