Implement counter

Author: Kynson

src/counter.ts

@@ -0,0 +1,35 @@
+import { DurableObject } from 'cloudflare:workers';
+
+class InvalidState extends Error {
+	constructor(message: string) {
+		super(message);
+
+		this.name = 'InvalidState';
+	}
+}
+
+export default class Counter extends DurableObject {
+	private isDestroyed = false;
+
+	async increment() {
+		if (this.isDestroyed) {
+			throw new InvalidState('cannot increment counter as it is pending to be destroyed');
+		}
+
+		// ctx is defined by the super class
+		let value: number = (await this.ctx.storage.get('value')) ?? 0;
+
+		value++;
+		await this.ctx.storage.put('value', value);
+
+		return value;
+	}
+
+	/**
+	 * Clears data stored in transactional storage, the object will be evicted when it is idle for a while
+	 */
+	async destroy() {
+		await this.ctx.storage.delete('value');
+		this.isDestroyed = true;
+	}
+}

src/index.ts

@@ -0,0 +1,90 @@
+import Counter from './counter';
+
+function generateJSONResponse(
+  body: Record<string, unknown>,
+  status = 200,
+  additionalHeaders: Record<string, unknown> = {}
+) {
+  return new Response(JSON.stringify(body), {
+    status,
+    headers: {
+      'Content-Type': 'application/json',
+      ...additionalHeaders,
+    },
+  });
+}
+
+function getCounterObjectStub(
+  pathname: string,
+  counterNamespace: DurableObjectNamespace<Counter>
+) {
+  const counterID: DurableObjectId = counterNamespace.idFromName(pathname);
+  return counterNamespace.get(counterID);
+}
+
+async function handleGetRequest(
+  pathname: string,
+  counterNamespace: DurableObjectNamespace<Counter>
+) {
+  const counterObjectStub = getCounterObjectStub(pathname, counterNamespace);
+  const newValue = await counterObjectStub.increment();
+
+  return generateJSONResponse({ newValue });
+}
+
+async function handleDeleteRequest(
+  pathname: string,
+  counterNamespace: DurableObjectNamespace<Counter>
+) {
+  const counterObjectStub = getCounterObjectStub(pathname, counterNamespace);
+  await counterObjectStub.destroy();
+
+  return generateJSONResponse({
+    message: 'The counter is scheduled to be destroyed.',
+  });
+}
+
+async function handleRequest(
+  pathname: string,
+  method: string,
+  counterNamespace: DurableObjectNamespace<Counter>
+) {
+  switch (method) {
+    case 'GET':
+      return await handleGetRequest(pathname, counterNamespace);
+    case 'DELETE':
+      return await handleDeleteRequest(pathname, counterNamespace);
+    default:
+      return generateJSONResponse(
+        { message: 'The method used in this request is not supported.' },
+        405,
+        {
+          Allow: 'GET, DELETE',
+        }
+      );
+  }
+}
+
+export default {
+  async fetch(request, env): Promise<Response> {
+    const counterNamespace = env.COUNTER as DurableObjectNamespace<Counter>;
+
+    const { url, method } = request;
+    const { pathname } = new URL(url);
+
+    try {
+      return await handleRequest(pathname, method, counterNamespace);
+    } catch (error) {
+      if (error instanceof Error && error.message.startsWith('InvalidState')) {
+        return generateJSONResponse({ message: error.message }, 400);
+      }
+
+      return generateJSONResponse(
+        { message: 'Unknown internal server error occured.' },
+        500
+      );
+    }
+  },
+} satisfies ExportedHandler<Env>;
+
+export { Counter };