Cloudflare Workers Runtime APIs

async function fetchWithTimeout(url: string, timeout: number = 5000): Promise<Response> {
  const controller = new AbortController();
  const timeoutId = setTimeout(() => controller.abort(), timeout);

  try {
    const response = await fetch(url, { signal: controller.signal });
    return response;
  } finally {
    clearTimeout(timeoutId);
  }
}

async function fetchWithRetry(
  url: string,
  options: RequestInit = {},
  retries: number = 3
): Promise<Response> {
  for (let i = 0; i < retries; i++) {
    try {
      const response = await fetch(url, options);
      if (response.ok) return response;

      // Retry on 5xx errors
      if (response.status >= 500 && i < retries - 1) {
        await new Promise(r => setTimeout(r, Math.pow(2, i) * 1000));
        continue;
      }

      return response;
    } catch (error) {
      if (i === retries - 1) throw error;
      await new Promise(r => setTimeout(r, Math.pow(2, i) * 1000));
    }
  }
  throw new Error('Max retries exceeded');
}

function createUppercaseStream(): TransformStream<string, string> {
  return new TransformStream({
    transform(chunk, controller) {
      controller.enqueue(chunk.toUpperCase());
    }
  });
}

// Usage
const response = await fetch('https://example.com/text');
const transformed = response.body!
  .pipeThrough(new TextDecoderStream())
  .pipeThrough(createUppercaseStream())
  .pipeThrough(new TextEncoderStream());

return new Response(transformed);

async function streamLargeFile(url: string): Promise<Response> {
  const response = await fetch(url);

  // Stream directly without buffering
  return new Response(response.body, {
    headers: {
      'Content-Type': response.headers.get('Content-Type') || 'application/octet-stream',
    },
  });
}

async function sha256(data: string): Promise<string> {
  const encoder = new TextEncoder();
  const dataBuffer = encoder.encode(data);
  const hashBuffer = await crypto.subtle.digest('SHA-256', dataBuffer);
  const hashArray = Array.from(new Uint8Array(hashBuffer));
  return hashArray.map(b => b.toString(16).padStart(2, '0')).join('');
}

async function signHMAC(key: string, data: string): Promise<string> {
  const encoder = new TextEncoder();
  const keyData = encoder.encode(key);
  const dataBuffer = encoder.encode(data);

  const cryptoKey = await crypto.subtle.importKey(
    'raw',
    keyData,
    { name: 'HMAC', hash: 'SHA-256' },
    false,
    ['sign']
  );

  const signature = await crypto.subtle.sign('HMAC', cryptoKey, dataBuffer);
  return btoa(String.fromCharCode(...new Uint8Array(signature)));
}

export default {
  async fetch(request: Request, env: Env, ctx: ExecutionContext): Promise<Response> {
    const cache = caches.default;
    const cacheKey = new Request(request.url, { method: 'GET' });

    // Check cache
    let response = await cache.match(cacheKey);
    if (response) {
      return response;
    }

    // Fetch and cache
    response = await fetch(request);
    response = new Response(response.body, response);
    response.headers.set('Cache-Control', 'public, max-age=3600');

    // Store in cache (don't await)
    ctx.waitUntil(cache.put(cacheKey, response.clone()));

    return response;
  }
};

// Durable Object with WebSocket hibernation
export class WebSocketRoom {
  state: DurableObjectState;

  constructor(state: DurableObjectState) {
    this.state = state;
  }

  async fetch(request: Request): Promise<Response> {
    const upgradeHeader = request.headers.get('Upgrade');
    if (upgradeHeader !== 'websocket') {
      return new Response('Expected websocket', { status: 426 });
    }

    const pair = new WebSocketPair();
    const [client, server] = Object.values(pair);

    // Accept with hibernation
    this.state.acceptWebSocket(server);

    return new Response(null, { status: 101, webSocket: client });
  }

  async webSocketMessage(ws: WebSocket, message: string | ArrayBuffer) {
    // Handle incoming message
    const data = typeof message === 'string' ? message : new TextDecoder().decode(message);

    // Broadcast to all connected clients
    for (const client of this.state.getWebSockets()) {
      client.send(data);
    }
  }

  async webSocketClose(ws: WebSocket, code: number, reason: string) {
    ws.close(code, reason);
  }
}