Cloudflare

// ❌ BAD: Throws error, retries entire batch
async queue(batch: MessageBatch): Promise<void> {
  for (const msg of batch.messages) {
    await riskyOperation(msg.body); // If this throws, entire batch retries
    msg.ack();
  }
}

// ✅ GOOD: Catch per message, handle individually
async queue(batch: MessageBatch): Promise<void> {
  for (const msg of batch.messages) {
    try {
      await riskyOperation(msg.body);
      msg.ack();
    } catch (error) {
      msg.retry({ delaySeconds: 60 });
    }
  }
}

// ❌ BAD: Skipped messages auto-retry forever
async queue(batch: MessageBatch): Promise<void> {
  for (const msg of batch.messages) {
    if (shouldProcess(msg.body)) {
      await process(msg.body);
      msg.ack();
    }
    // Missing: msg.ack() for skipped messages - they will retry!
  }
}

// ✅ GOOD: Explicitly handle all messages
async queue(batch: MessageBatch): Promise<void> {
  for (const msg of batch.messages) {
    if (shouldProcess(msg.body)) {
      await process(msg.body);
      msg.ack();
    } else {
      msg.ack(); // Explicitly ack even if not processing
    }
  }
}

async queue(batch: MessageBatch, env: Env): Promise<void> {
  for (const msg of batch.messages) {
    const processed = await env.PROCESSED_KV.get(msg.id);
    if (processed) {
      msg.ack();
      continue;
    }

    await processMessage(msg.body);
    await env.PROCESSED_KV.put(msg.id, '1', { expirationTtl: 86400 });
    msg.ack();
  }
}

// Use json for pull consumers
await env.MY_QUEUE.send(data, { contentType: 'json' });

// Use v8 only for push consumers with complex JS types
await env.MY_QUEUE.send({ date: new Date(), tags: new Set() }, { contentType: 'v8' });

async queue(batch: MessageBatch, env: Env): Promise<void> {
  for (const msg of batch.messages) {
    try {
      await processMessage(msg.body);
      msg.ack();
    } catch (error) {
      // Transient errors: retry with backoff
      if (isRetryable(error)) {
        const delay = Math.min(30 * (2 ** msg.attempts), 43200);
        msg.retry({ delaySeconds: delay });
      }
      // Permanent errors: ack to avoid infinite retries
      else {
        console.error('Permanent error, sending to DLQ:', error);
        await env.ERROR_LOG.put(msg.id, JSON.stringify({ msg: msg.body, error: String(error) }));
        msg.ack(); // Prevent further retries
      }
    }
  }
}

function isRetryable(error: unknown): boolean {
  if (error instanceof Response) {
    // Retry: rate limits, timeouts, server errors
    return error.status === 429 || error.status >= 500;
  }
  if (error instanceof Error) {
    // Don't retry: validation, auth, not found
    return !error.message.includes('validation') &&
           !error.message.includes('unauthorized') &&
           !error.message.includes('not found');
  }
  return false; // Unknown errors don't retry
}

// Dashboard/pull: use json
await env.QUEUE.send({ id: 123, name: 'test' }, { contentType: 'json' });

// Complex JS types (push only): use v8
await env.QUEUE.send({
  created: new Date(),
  tags: new Set(['a', 'b'])
}, { contentType: 'v8' });