doc(cloudflare): custom worker (#129)

Author: vicb

pages/cloudflare/howtos/_meta.json

@@ -3,5 +3,6 @@
   "stripeAPI": "Stripe API",
   "dev-deploy": "Develop and Deploy",
   "env-vars": "Enviroment Variables",
-  "image": "Image Optimization"
+  "image": "Image Optimization",
+  "custom-worker": "Custom Worker"
 }

pages/cloudflare/howtos/custom-worker.mdx

@@ -0,0 +1,43 @@
+## Custom Worker
+
+The worker generated by the Cloudflare adapter only exports [a fetch handler](https://developers.cloudflare.com/workers/runtime-apis/handlers/fetch/).
+
+Sometimes your application needs to expose another type of handler (i.e. [a scheduled handler](https://developers.cloudflare.com/workers/runtime-apis/handlers/scheduled/)) or export a [Durable Object](https://developers.cloudflare.com/durable-objects/api/base/). This can be achieved by creating a custom worker.
+
+The custom worker re-uses the generated fetch handler.
+
+### Create your custom worker Worker
+
+The following custom worker re-uses the generated fetch handler and adds a scheduled handler:
+
+```ts
+// custom-worker.ts
+
+// @ts-ignore `.open-next/worker.ts` is generated at build time
+import { default as handler } from "./.open-next/worker.js";
+
+export default {
+  fetch: handler.fetch,
+
+  async scheduled(event) {
+    // ...
+  },
+} satisfies ExportedHandler<CloudflareEnv>;
+
+// The re-export is only required if your app uses the DO Queue and DO Tag Cache
+// See https://opennext.js.org/cloudflare/caching for details
+// @ts-ignore `.open-next/worker.ts` is generated at build time
+export { DOQueueHandler, DOShardedTagCache } from "./.open-next/worker.js";
+```
+
+See [an example in the adapter repository](https://github.com/opennextjs/opennextjs-cloudflare/blob/main/examples/playground14/worker.ts).
+
+### Update the entry point in your wrangler configuration
+
+```diff
+// wrangler.jsonc
+{
+-  "main": "./.open-next/worker.js"
++  "main": "./path/to/custom-worker.ts",
+}
+```