The Cloudflare function that does the content negotiation for the HTML that has been compressed to Brotli 11.

[[path]].js

/**
 * Catch-all Pages Function for HTML document content negotiation.
 * Serves pre-compressed Brotli 11 .br files when client sends Accept-Encoding: br,
 * otherwise passes through to static assets (uncompressed HTML).
 * Only runs for GET and HEAD; POST /api/contact is handled by functions/api/contact.js.
 */

async function handleHtmlWithBrotli(request, env) {
	const url = new URL(request.url);
	const pathname = url.pathname;

	// Only handle HTML document requests: /, paths ending with /, or /404.html
	const isHtmlDocument = pathname === '/' || pathname.endsWith('/') || pathname === '/404.html';

	if (!isHtmlDocument) {
		return env.ASSETS.fetch(request);
	}

	const acceptsBrotli = request.headers.get('Accept-Encoding')?.includes('br') ?? false;

	if (!acceptsBrotli) {
		return env.ASSETS.fetch(request);
	}

	// Construct path to .br file: / -> /index.html.br, /blog/post/ -> /blog/post/index.html.br
	const brPath =
		pathname === '/' ? '/index.html.br' : pathname === '/404.html' ? '/404.html.br' : `${pathname}index.html.br`;

	const brUrl = new URL(brPath, url.origin);
	const brResponse = await env.ASSETS.fetch(brUrl.toString());

	if (!brResponse.ok) {
		return env.ASSETS.fetch(request);
	}

	const headers = new Headers(brResponse.headers);
	headers.set('Content-Encoding', 'br');
	headers.set('Content-Type', 'text/html; charset=UTF-8');
	headers.set('Vary', 'Accept-Encoding');
	// Prevent Cloudflare from re-compressing or modifying the response
	headers.set('Cache-Control', 'public, max-age=31536000, no-transform');

	return new Response(brResponse.body, {
		status: brResponse.status,
		headers,
		// Prevents Workers from re-compressing; required for pre-compressed Brotli
		encodeBody: 'manual',
	});
}

export const onRequestGet = async ({ request, env }) => {
	return handleHtmlWithBrotli(request, env);
};

export const onRequestHead = async ({ request, env }) => {
	return handleHtmlWithBrotli(request, env);
};