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87 lines
2.2 KiB
Markdown
87 lines
2.2 KiB
Markdown
# Gotchas & Best Practices
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## Common Errors
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### 1000: "Snippet execution failed"
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Runtime error or syntax error. Wrap code in try/catch:
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```javascript
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try { return await fetch(request); }
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catch (error) { return new Response(`Error: ${error.message}`, { status: 500 }); }
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```
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### 1100: "Exceeded execution limit"
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Code takes >5ms CPU. Simplify logic or move to Workers.
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### 1201: "Multiple origin fetches"
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Call `fetch(request)` exactly once:
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```javascript
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// ❌ Multiple origin fetches
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const r1 = await fetch(request); const r2 = await fetch(request);
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// ✅ Single fetch, reuse response
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const response = await fetch(request);
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```
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### 1202: "Subrequest limit exceeded"
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Pro: 2 subrequests, Business/Enterprise: 5. Reduce fetch calls.
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### "Cannot set property on immutable object"
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Clone before modifying:
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```javascript
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const modifiedRequest = new Request(request);
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modifiedRequest.headers.set("X-Custom", "value");
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```
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### "caches is not defined"
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Cache API NOT available in Snippets. Use Workers.
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### "Module not found"
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Snippets don't support `import`. Use inline code or Workers.
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## Best Practices
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### Performance
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- Keep code <10KB (32KB limit)
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- Optimize for 5ms CPU
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- Clone only when modifying
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- Minimize subrequests
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### Security
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- Validate all inputs
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- Use Web Crypto API for hashing
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- Sanitize headers before origin
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- Don't log secrets
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### Debugging
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```javascript
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newResponse.headers.set("X-Debug-Country", request.cf.country);
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```
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```bash
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curl -H "X-Test: true" https://example.com -v
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```
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## Available APIs
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**✅ Available:** `fetch()`, `Request`, `Response`, `Headers`, `URL`, `crypto.subtle`, `crypto.randomUUID()`, `atob()`/`btoa()`, `JSON`
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**❌ NOT Available:** `caches`, `KV`, `D1`, `R2`, `Durable Objects`, `WebSocket`, `HTMLRewriter`, `import`, Node.js APIs
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## Limits
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| Resource | Limit |
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|----------|-------|
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| Snippet size | 32KB |
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| Execution time | 5ms CPU |
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| Subrequests (Pro/Biz) | 2/5 |
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| Snippets/zone | 20 |
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## Performance Benchmarks
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| Operation | Time |
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|-----------|------|
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| Header set | <0.1ms |
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| URL parsing | <0.2ms |
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| fetch() | 1-3ms |
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| SHA-256 | 0.5-1ms |
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**Migrate to Workers when:** >5ms needed, >5 subrequests, need storage (KV/D1/R2), need npm packages, >32KB code
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