feat(cache): add Cache-Control middleware and update .env.example

.env.example

@@ -23,3 +23,9 @@ ANIWATCH_API_MAX_REQS=70
 
 # env to use optional redis caching functionality
 ANIWATCH_API_REDIS_CONN_URL=<rediss://default:your-secure-password@your-redis-instance-name.provider.com:6379>
+
+# Cache-Control settings for Vercel Edge Caching
+# s-maxage specifies the maximum amount of time a resource is considered fresh when served by a CDN cache
+S_MAXAGE=60
+# stale-while-revalidate specifies the amount of time a resource is served stale while a new one is fetched
+STALE_WHILE_REVALIDATE=30

src/config/cache_control_middleware.ts

@@ -0,0 +1,15 @@
+import type { MiddlewareHandler } from "hono";
+
+// Define middleware to add Cache-Control header
+const cacheControlMiddleware: MiddlewareHandler = async (c, next) => {
+  const sMaxAge = process.env.S_MAXAGE || "60";
+  const staleWhileRevalidate = process.env.STALE_WHILE_REVALIDATE || "30";
+  c.header(
+    "Cache-Control",
+    `s-maxage=${sMaxAge}, stale-while-revalidate=${staleWhileRevalidate}`
+  );
+
+  await next();
+};
+
+export default cacheControlMiddleware;

src/server.ts

@@ -5,6 +5,7 @@ import corsConfig from "./config/cors.js";
 import { ratelimit } from "./config/ratelimit.js";
 
 import { hianimeRouter } from "./routes/hianime.js";
+import cacheControlMiddleware from "./config/cache_control_middleware.js";
 
 import { Hono } from "hono";
 import { logger } from "hono/logger";
@@ -26,6 +27,7 @@ const app = new Hono<{ Variables: AniwatchAPIVariables }>();
 
 app.use(logger());
 app.use(corsConfig);
+app.use(cacheControlMiddleware);
 
 // CAUTION: For personal deployments, "refrain" from having an env
 // named "ANIWATCH_API_HOSTNAME". You may face rate limitting