example4.go

// run is the main logic of the service
func (s service) run(ctx context.Context, f filter) error {
    pr, pw := io.Pipe()
  
    r, err := s.ds.getData(ctx, f)
    if err != nil {
        return fmt.Errorf("querying: %v", err)
    }
  
    go writeRowsToCSV(r, pw)
    
    if err := s.up.upload(ctx, pr); err != nil {
        return fmt.Errorf("uploading: %v", err)
    }
    return nil
}

// ================csv conversion================
func writeRowsToCSV(r *rows, w io.WriteCloser) error {
    csvWriter := csv.NewWriter(w)
    defer func() {
        csvWriter.Flush()
        w.Close()
    }()
    
    for r.next() {
        // scan rows and write to csvWriter
    }
    return nil
}