Add cloudflare cache (#4412)

Author: johnwalshuk

.changeset/pretty-carpets-scream.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/adapter-cloudflare': patch
+---
+
+Add cloudflare cache to store responses with a cache header.

packages/adapter-cloudflare/files/worker.js

@@ -50,12 +50,34 @@ export default {
 
 		// dynamically-generated pages
 		try {
-			return await server.respond(req, {
-				platform: { env, context },
-				getClientAddress() {
-					return req.headers.get('cf-connecting-ip');
+			// @ts-expect-error - `default` exists only in the cloudflare workers environment
+			const cache = caches.default;
+			let response = await cache.match(req);
+
+			if (!response) {
+				response = await server.respond(req, {
+					platform: { env, context },
+					getClientAddress() {
+						return req.headers.get('cf-connecting-ip');
+					}
+				});
+
+				// Use waitUntil so you can return the response without blocking on
+				// writing to cache
+				try {
+					// If cookies are being set, ensure we dont cache the page.
+					if (response.headers.has('Set-Cookie')) {
+						response = new Response(response.body, response);
+						response.headers.append('Cache-Control', 'private=Set-Cookie');
+					}
+
+					context.waitUntil(cache.put(req, response.clone()));
+				} catch {
+					// noop
 				}
-			});
+			}
+
+			return response;
 		} catch (e) {
 			return new Response('Error rendering route: ' + (e.message || e.toString()), { status: 500 });
 		}