explorer: add CORS for cryptographic-triangles.org (live block counter)

src/hooks.server.ts

@@ -1,10 +1,42 @@
 import type { Handle } from '@sveltejs/kit';
 
+// Allow the marketing site (cryptographic-triangles.org) to read our
+// dehydrated data endpoint so it can show a live block-height counter
+// without having to expose the wallet RPC publicly. Caddy terminates
+// TLS on blocks.cryptographic-triangles.org; the origin header below
+// is the only site that needs read access right now.
+const ALLOWED_ORIGINS = new Set([
+	'https://cryptographic-triangles.org',
+	'http://localhost',
+	'http://127.0.0.1'
+]);
+
+function corsHeadersFor(request: Request): Record<string, string> {
+	const origin = request.headers.get('origin') ?? '';
+	if (!ALLOWED_ORIGINS.has(origin)) return {};
+	return {
+		'Access-Control-Allow-Origin': origin,
+		'Access-Control-Allow-Methods': 'GET, OPTIONS',
+		'Access-Control-Allow-Headers': 'Content-Type',
+		'Access-Control-Max-Age': '600'
+	};
+}
+
 export const handle: Handle = async ({ event, resolve }) => {
+	if (event.request.method === 'OPTIONS') {
+		const headers = corsHeadersFor(event.request);
+		return new Response(null, { status: 204, headers });
+	}
+
 	const start = Date.now();
 	const response = await resolve(event);
 	const duration = Date.now() - start;
 
+	const cors = corsHeadersFor(event.request);
+	for (const [k, v] of Object.entries(cors)) {
+		response.headers.set(k, v);
+	}
+
 	console.log(`[${response.status}] ${event.request.method} ${event.url.pathname} (${duration}ms)`);
 
 	return response;