func (c *Client) Send(ctx context.Context, messages []Message, maxWorkers int) error { sem := make(chan struct{}, maxWorkers) var wg sync.WaitGroup var resultErr error var once sync.Once for _, msg := range messages { wg.Add(1) go func(msg Message) { defer wg.Done() sem <- struct{}{} defer func() { <-sem }() body, err := json.Marshal(msg) if err != nil { once.Do(func() { resultErr = err; cancel() }) return } req, _ := http.NewRequestWithContext( ctx, http.MethodPost, c.url, bytes.NewReader(body), ) req.Header.Set("Content-Type", "application/json") resp, err := c.httpClient.Do(req) if err != nil { once.Do(func() { resultErr = err; cancel()}) return } defer resp.Body.Close() if resp.StatusCode >= 500 { once.Do(func() { resultErr = fmt.Errorf("server error") cancel()}) return } c.sentCount.Add(1) time.Sleep(time.Second) }(msg) } wg.Wait() }