feat: Add local, fs-based fetch during prerender

Author: rschristian

demo/public/local-fetch-test.txt

@@ -0,0 +1 @@
+Local fetch works

demo/src/components/LocalFetch.tsx

@@ -0,0 +1,32 @@
+import { useState } from "preact/hooks";
+
+const cache = new Map();
+
+async function load(url: string) {
+	const res = await fetch(url);
+	return await res.text();
+}
+
+function useFetch(url: string) {
+	const [_, update] = useState({});
+
+	let data = cache.get(url);
+	if (!data) {
+		data = load(url);
+		cache.set(url, data);
+		data.then(
+			(res: string) => update((data.res = res)),
+			(err: Error) => update((data.err = err)),
+		);
+	}
+
+	if (data.res) return data.res;
+	if (data.err) throw data.err;
+	throw data;
+}
+
+export function LocalFetch() {
+	const data = useFetch("/local-fetch-test.txt");
+
+	return <p>{data.trimEnd()}</p>;
+}

demo/src/pages/Home/index.tsx

@@ -1,4 +1,5 @@
 import { ReactComponent } from "../../components/Compat";
+import { LocalFetch } from "../../components/LocalFetch";
 
 import preactLogo from "../../assets/preact.svg";
 import "./style.css";
@@ -11,6 +12,7 @@ export function Home() {
 			</a>
 			<h1>Get Started building Vite-powered Preact Apps </h1>
 			<ReactComponent />
+			<LocalFetch />
 			<section>
 				<Resource
 					title="Learn Preact"

src/prerender.ts

@@ -149,6 +149,25 @@ export function PrerenderPlugin({
 			// @ts-ignore
 			globalThis.self = globalThis;
 
+			// Local, fs-based fetch implementation for prerendering
+			const nodeFetch = globalThis.fetch;
+			// @ts-ignore
+			globalThis.fetch = async (url: string, opts: RequestInit | undefined) => {
+				if (/^\//.test(url)) {
+					const text = () =>
+						fs.readFile(
+							`${path.join(
+								viteConfig.root,
+								viteConfig.build.outDir,
+							)}/${url.replace(/^\//, "")}`,
+							"utf-8",
+						);
+					return { text, json: () => text().then(JSON.parse) };
+				}
+
+				return nodeFetch(url, opts);
+			};
+
 			// Grab the generated HTML file, which we'll use as a template:
 			const tpl = (bundle["index.html"] as OutputAsset).source as string;
 			let htmlDoc = parse(tpl);