sw.js

function registerWasmHTTPListener(
	wasm,
	{ base, cacheName, passthrough, args = [] } = {},
) {
	let path = new URL(registration.scope).pathname;
	if (base && base !== "")
		path = `${trimEnd(path, "/")}/${trimStart(base, "/")}`;

	const handlerPromise = new Promise((setHandler) => {
		self.wasmhttp = {
			path,
			setHandler,
		};
	});

	const go = new Go();
	go.argv = [wasm, ...args];
	const source = cacheName
		? caches
				.open(cacheName)
				.then((cache) => cache.match(wasm))
				.then((response) => response ?? fetch(wasm))
		: caches.match(wasm).then((response) => response ?? fetch(wasm));
	WebAssembly.instantiateStreaming(source, go.importObject).then(
		({ instance }) => go.run(instance),
	);

	addEventListener("fetch", (e) => {
		if (passthrough?.(e.request)) {
			e.respondWith(fetch(e.request));
			return;
		}

		const { pathname } = new URL(e.request.url);
		if (!pathname.startsWith(path)) return;

		e.respondWith(handlerPromise.then((handler) => handler(e.request)));
	});
}

function trimStart(s, c) {
	let r = s;
	while (r.startsWith(c)) r = r.slice(c.length);
	return r;
}

function trimEnd(s, c) {
	let r = s;
	while (r.endsWith(c)) r = r.slice(0, -c.length);
	return r;
}