workers-runtime-apis

# Cloudflare Workers Runtime APIs

Master the Workers runtime APIs: Fetch, Streams, Crypto, Cache, WebSockets, and text encoding.

## Quick Reference

| API | Purpose | Common Use |
|-----|---------|------------|
| **Fetch** | HTTP requests | External APIs, proxying |
| **Streams** | Data streaming | Large files, real-time |
| **Crypto** | Cryptography | Hashing, signing, encryption |
| **Cache** | Response caching | Performance optimization |
| **WebSockets** | Real-time connections | Chat, live updates |
| **Encoding** | Text encoding | UTF-8, Base64 |

## Quick Start: Fetch API

```typescript
export default {
  async fetch(request: Request, env: Env): Promise<Response> {
    // Basic fetch
    const response = await fetch('https://api.example.com/data');

    // With options
    const postResponse = await fetch('https://api.example.com/users', {
      method: 'POST',
      headers: {
        'Content-Type': 'application/json',
        'Authorization': `Bearer ${env.API_KEY}`,
      },
      body: JSON.stringify({ name: 'John' }),
    });

    // Clone for multiple reads
    const clone = response.clone();
    const json = await response.json();
    const text = await clone.text();

    return Response.json(json);
  }
};
```

## Critical Rules

1. **Always set timeouts for external requests** - Workers have a 30s limit, external APIs can hang
2. **Clone responses before reading body** - Body can only be read once
3. **Use streaming for large payloads** - Don't buffer entire response in memory
4. **Cache external API responses** - Reduce latency and API costs
5. **Handle Crypto operations in try/catch** - Invalid inputs throw errors
6. **WebSocket hibernation for cost** - Use Durable Objects with hibernation

## Top 10 Errors Prevented

| Error | Symptom | Prevention |
|-------|---------|------------|
| Body already read | `TypeError: Body has already been consumed` | Clone response before reading |
| Fetch timeout | Request hangs, worker times out | Use `AbortCont