Middleware for static assets

[predaytor]

Currently, the middleware in Fresh (2.0.0-alpha.25) does not have access to static assets, so we cannot modify the headers:

import { App } from 'fresh';
import { State } from '~/utils.ts';

export function speculationRules(app: App<State>) {
	app.use(async (ctx) => {
		const response = await ctx.next();
		response.headers.set('Speculation-Rules', '"/speculationrules.json"');
		return response;
	});

	app.get('/speculationrules.json', async (ctx) => {
		const response = await ctx.next();
		response.headers.set('Content-Type', 'application/speculationrules+json');
		response.headers.set('Access-Control-Allow-Origin', '*');
		return response;
	});
}

Workaround:

export function speculationRules(app: App<State>) {
	// ...

	app.get('/speculationrules.json', () => {
		const rules = `
			{
				"prerender": [
					{
						"source": "document",
						"where": { "href_matches": "/*" },
						"eagerness": "moderate"
					}
				],
				"prefetch": [
					{
						"where": { "not": { "href_matches": "/*" } },
						"eagerness": "moderate"
					}
				]
			}
		`;

		return new Response(rules, {
			headers: {
				'Content-Type': 'application/speculationrules+json',
				'Access-Control-Allow-Origin': '*',
			},
		});
	});
}