Add caching to feed endpoint (#45)

In order to reduce load on Deno KV as the costs are relatively high.

lib/utils.test.ts

@@ -1,5 +1,5 @@
 import { assertEquals, assertNotEquals } from "$std/assert/mod.ts";
-import { responseJSON, responseXML } from "./utils.ts";
+import { responseJSON, responseXML, withExpiry } from "./utils.ts";
 
 Deno.test("JSON response is stringified", async () => {
   const body = { message: "Hello, World!" };
@@ -14,3 +14,41 @@ Deno.test("XML resopnse is _not_ stringified", async () => {
   assertEquals(responseBody, body);
   assertNotEquals(responseBody, JSON.stringify(body));
 });
+
+Deno.test(
+  "Response with cache control returns a response with the correct header",
+  () => {
+    const response = responseJSON({ message: "Hello, World!" }, 200);
+    const cachedResponse = withExpiry(response, 3600);
+    assertEquals(cachedResponse.headers.get("Cache-Control"), "max-age=3600");
+  },
+);
+
+Deno.test(
+  "Response with cache control returns the same body as the original",
+  async () => {
+    const body = { message: "Hello, World!" };
+    const response = responseJSON(body, 200);
+    const cachedResponse = withExpiry(response, 3600);
+    assertEquals(await cachedResponse.text(), await response.text());
+  },
+);
+
+Deno.test("Response with cache control does not modify the original", () => {
+  const response = responseJSON({ message: "Hello, World!" }, 200);
+  withExpiry(response, 3600);
+  assertEquals(response.headers.get("Cache-Control"), null);
+});
+
+Deno.test(
+  "Response with cache control returns the correct number of seconds",
+  () => {
+    const response = responseJSON({ message: "Hello, World!" }, 200);
+    const ttlInSeconds = 1234;
+    const cachedResponse = withExpiry(response, ttlInSeconds);
+    assertEquals(
+      cachedResponse.headers.get("Cache-Control"),
+      `max-age=${ttlInSeconds}`,
+    );
+  },
+);

lib/utils.ts

@@ -24,6 +24,12 @@ export function responseXML(body: string, status: Status) {
   return response(body, status, "xml");
 }
 
+export const withExpiry = <T>(response: Response, ttlInSeconds: number) => {
+  const clonedResponse = response.clone();
+  clonedResponse.headers.set("Cache-Control", `max-age=${ttlInSeconds}`);
+  return clonedResponse;
+};
+
 function response(body: string, status: number, type: "json" | "xml") {
   return new Response(body, {
     status,

routes/api/feeds/[seriesId].ts

@@ -1,18 +1,36 @@
 import { FreshContext, STATUS_CODE } from "$fresh/server.ts";
 import { caching } from "../../../lib/caching.ts";
 import { rss } from "../../../lib/rss.ts";
-import { responseJSON, responseXML } from "../../../lib/utils.ts";
+import { responseJSON, responseXML, withExpiry } from "../../../lib/utils.ts";
 
-export const handler = async (_req: Request, ctx: FreshContext): Promise<Response> => {
+const FEED_CACHE_KEY = "feeds-cache";
+
+export const handler = async (
+  request: Request,
+  ctx: FreshContext,
+): Promise<Response> => {
   const seriesId = ctx.params.seriesId;
 
+  const cache = await caches.open(FEED_CACHE_KEY);
+  const cachedResponse = await cache.match(request);
+  if (cachedResponse) {
+    console.log(`Cache hit for feed ${seriesId}`);
+    return cachedResponse;
+  }
+
   const series = await caching.getSeries({ id: seriesId });
   if (!series) {
     return responseJSON({ message: "Series not found" }, STATUS_CODE.NotFound);
   }
+
   const feed = rss.assembleFeed(series);
 
-  const xml = responseXML(feed, STATUS_CODE.OK);
+  const response = withExpiry(
+    responseXML(feed, STATUS_CODE.OK),
+    // 2 hours
+    60 * 60 * 2,
+  );
 
-  return xml;
+  await cache.put(request, response.clone());
+  return response;
 };