Gotchas

// ❌ WRONG - fire and forget
export default {
  async tail(events) {
    fetch(endpoint, { body: JSON.stringify(events) });
  }
};

// ❌ WRONG - blocking await
export default {
  async tail(events, env, ctx) {
    await fetch(endpoint, { body: JSON.stringify(events) });
  }
};

// ✅ CORRECT
export default {
  async tail(events, env, ctx) {
    ctx.waitUntil(
      (async () => {
        await fetch(endpoint, { body: JSON.stringify(events) });
        await processMore();
      })()
    );
  }
};

// ❌ WRONG
if (event.outcome === 500) { /* never matches */ }

// ✅ CORRECT
if (event.outcome === 'exception') { /* script threw */ }
if (event.event?.response?.status === 500) { /* HTTP 500 */ }

// ❌ WRONG: const date = new Date(event.eventTimestamp * 1000);
// ✅ CORRECT: const date = new Date(event.eventTimestamp);

import type { TraceItem } from '@cloudflare/workers-types';
export default {
  async tail(events: TraceItem[], env, ctx) { /* ... */ }
};

export default {
  async tail(events, env, ctx) {
    if (Math.random() > 0.1) return;  // 10% sample
    ctx.waitUntil(sendToEndpoint(events));
  }
};

const safePayload = events.map(e => ({
  ...e,
  logs: e.logs.map(log => ({
    ...log,
    message: log.message.map(m => {
      try { return JSON.parse(JSON.stringify(m)); }
      catch { return String(m); }
    })
  }))
}));

ctx.waitUntil((async () => {
  try {
    await fetch(env.ENDPOINT, { body: JSON.stringify(events) });
  } catch (error) {
    console.error("Tail error:", error);
    await env.FALLBACK_KV.put(`failed:${Date.now()}`, JSON.stringify(events));
  }
})());

cd tail-worker && wrangler deploy
cd ../producer && wrangler deploy

export default {
  async fetch(request) {
    if (request.url.includes('/test')) {
      console.log('Test log');
      throw new Error('Test error');
    }
    return new Response('OK');
  }
};