1# Snippets Patterns
2 
3## Security Headers
4 
5```javascript
6export default {
7  async fetch(request) {
8    const response = await fetch(request);
9    const newResponse = new Response(response.body, response);
10    newResponse.headers.set("X-Frame-Options", "DENY");
11    newResponse.headers.set("X-Content-Type-Options", "nosniff");
12    newResponse.headers.delete("X-Powered-By");
13    return newResponse;
14  }
15}
16```
17 
18**Rule:** `true` (all requests)
19 
20## Geo-Based Routing
21 
22```javascript
23export default {
24  async fetch(request) {
25    const country = request.cf.country;
26    if (["GB", "DE", "FR"].includes(country)) {
27      const url = new URL(request.url);
28      url.hostname = url.hostname.replace(".com", ".eu");
29      return Response.redirect(url.toString(), 302);
30    }
31    return fetch(request);
32  }
33}
34```
35 
36## A/B Testing
37 
38```javascript
39export default {
40  async fetch(request) {
41    const cookies = request.headers.get("Cookie") || "";
42    let variant = cookies.match(/ab_test=([AB])/)?.[1] || (Math.random() < 0.5 ? "A" : "B");
43    
44    const req = new Request(request);
45    req.headers.set("X-Variant", variant);
46    const response = await fetch(req);
47    
48    if (!cookies.includes("ab_test=")) {
49      const newResponse = new Response(response.body, response);
50      newResponse.headers.append("Set-Cookie", `ab_test=${variant}; Path=/; Secure`);
51      return newResponse;
52    }
53    return response;
54  }
55}
56```
57 
58## Bot Detection
59 
60```javascript
61export default {
62  async fetch(request) {
63    const botScore = request.cf.botManagement?.score;
64    if (botScore && botScore < 30) return new Response("Denied", { status: 403 });
65    return fetch(request);
66  }
67}
68```
69 
70**Requires:** Bot Management plan
71 
72## API Auth Header Injection
73 
74```javascript
75export default {
76  async fetch(request) {
77    if (new URL(request.url).pathname.startsWith("/api/")) {
78      const req = new Request(request);
79      req.headers.set("X-Internal-Auth", "secret_token");
80      req.headers.delete("Authorization");
81      return fetch(req);
82    }
83    return fetch(request);
84  }
85}
86```
87 
88## CORS Headers
89 
90```javascript
91export default {
92  async fetch(request) {
93    if (request.method === "OPTIONS") {
94      return new Response(null, {
95        status: 204,
96        headers: {
97          "Access-Control-Allow-Origin": "*",
98          "Access-Control-Allow-Methods": "GET, POST, PUT, DELETE",
99          "Access-Control-Allow-Headers": "Content-Type, Authorization"
100        }
101      });
102    }
103    const response = await fetch(request);
104    const newResponse = new Response(response.body, response);
105    newResponse.headers.set("Access-Control-Allow-Origin", "*");
106    return newResponse;
107  }
108}
109```
110 
111## Maintenance Mode
112 
113```javascript
114export default {
115  async fetch(request) {
116    if (request.headers.get("X-Bypass-Token") === "admin") return fetch(request);
117    return new Response("<h1>Maintenance</h1>", {
118      status: 503,
119      headers: { "Content-Type": "text/html", "Retry-After": "3600" }
120    });
121  }
122}
123```
124 
125## Pattern Selection
126 
127| Pattern | Complexity | Use Case |
128|---------|-----------|----------|
129| Security Headers | Low | All sites |
130| Geo-Routing | Low | Regional content |
131| A/B Testing | Medium | Experiments |
132| Bot Detection | Medium | Requires Bot Management |
133| API Auth | Low | Backend protection |
134| CORS | Low | API endpoints |
135| Maintenance | Low | Deployments |
136