### Common Patterns

**1. Forward request to assets:**

```typescript
export default {
  async fetch(request: Request, env: Env): Promise<Response> {
    return env.ASSETS.fetch(request);
  },
};
```

**2. Fetch specific asset by path:**

```typescript
const response = await env.ASSETS.fetch("https://assets.local/logo.png");
```

**3. Modify request before fetching asset:**

```typescript
const url = new URL(request.url);
url.pathname = "/index.html";
return env.ASSETS.fetch(new Request(url, request));
```

**4. Transform asset response:**

```typescript
const response = await env.ASSETS.fetch(request);
const modifiedResponse = new Response(response.body, response);
modifiedResponse.headers.set("X-Custom-Header", "value");
modifiedResponse.headers.set("Cache-Control", "public, max-age=3600");
return modifiedResponse;
```

**5. Conditional asset serving:**

```typescript
export default {
  async fetch(request: Request, env: Env): Promise<Response> {
    const url = new URL(request.url);
    if (url.pathname === "/") {
      return env.ASSETS.fetch("/index.html");
    }
    return env.ASSETS.fetch(request);
  },
};
```

**6. SPA with API routes:**

Most common full-stack pattern - static SPA with backend API:

```typescript
export default {
  async fetch(request: Request, env: Env): Promise<Response> {
    const url = new URL(request.url);
    if (url.pathname.startsWith("/api/")) {
      return handleAPI(request, env);
    }
    return env.ASSETS.fetch(request);
  },
};

async function handleAPI(request: Request, env: Env): Promise<Response> {
  return new Response(JSON.stringify({ status: "ok" }), {
    headers: { "Content-Type": "application/json" },
  });
}
```

**Config:** Set `run_worker_first: ["/api/*"]` (see configuration.md:66-106)

**7. Auth gating for protected assets:**

```typescript
export default {
  async fetch(request: Request, env: Env): Promise<Response> {
    const url = new URL(request.url);
    if (url.pathname.startsWith("/admin/")) {
      const session = await validateSession(request, env);
      if (!session) {
        return Response.redirect("/login", 302);
      }
    }
    return env.ASSETS.fetch(request);
  },
};
```

**Config:** Set `run_worker_first: ["/admin/*"]`

**8. Custom headers for security:**

```typescript
export default {
  async fetch(request: Request, env: Env): Promise<Response> {
    const response = await env.ASSETS.fetch(request);
    const secureResponse = new Response(response.body, response);
    secureResponse.headers.set("X-Frame-Options", "DENY");
    secureResponse.headers.set("X-Content-Type-Options", "nosniff");
    secureResponse.headers.set("Content-Security-Policy", "default-src 'self'");
    return secureResponse;
  },
};
```

**9. A/B testing via cookies:**

```typescript
export default {
  async fetch(request: Request, env: Env): Promise<Response> {
    const cookies = request.headers.get("Cookie") || "";
    const variant = cookies.includes("variant=b") ? "b" : "a";
    const url = new URL(request.url);
    if (url.pathname === "/") {
      return env.ASSETS.fetch(`/index-${variant}.html`);
    }
    return env.ASSETS.fetch(request);
  },
};
```

**10. Locale-based routing:**

```typescript
export default {
  async fetch(request: Request, env: Env): Promise<Response> {
    const locale = request.headers.get("Accept-Language")?.split(",")[0] || "en";
    const url = new URL(request.url);
    if (url.pathname === "/") {
      return env.ASSETS.fetch(`/${locale}/index.html`);
    }
    if (!url.pathname.startsWith(`/${locale}/`)) {
      url.pathname = `/${locale}${url.pathname}`;
    }
    return env.ASSETS.fetch(url);
  },
};
```

**11. OAuth callback handling:**

```typescript
export default {
  async fetch(request: Request, env: Env): Promise<Response> {
    const url = new URL(request.url);
    if (url.pathname === "/auth/callback") {
      const code = url.searchParams.get("code");
      if (code) {
        const session = await exchangeCode(code, env);
        return new Response(null, {
          status: 302,
          headers: {
            Location: "/",
            "Set-Cookie": `session=${session}; HttpOnly; Secure; SameSite=Lax`,
          },
        });
      }
    }
    return env.ASSETS.fetch(request);
  },
};
```

**Config:** Set `run_worker_first: ["/auth/*"]`

**12. Cache control override:**

```typescript
export default {
  async fetch(request: Request, env: Env): Promise<Response> {
    const response = await env.ASSETS.fetch(request);
    const url = new URL(request.url);
    // Immutable assets (hashed filenames)
    if (/\.[a-f0-9]{8,}\.(js|css|png|jpg)$/.test(url.pathname)) {
      return new Response(response.body, {
        ...response,
        headers: {
          ...Object.fromEntries(response.headers),
          "Cache-Control": "public, max-age=31536000, immutable",
        },
      });
    }
    return response;
  },
};
```
