Why doesn't sending headers work?

Question

PHP

In the application class, I call the controller
following response->send () - sending headers.
send():

public function send(){
    
    $status = isset($this->http_messages[$this->http_status])? $this->http_messages[$this->http_status] : $this->http_status;
    
    if(!headers_sent()){
      if(isset($_SERVER['SERVER_PROTOCOL'])){
        header($_SERVER['SERVER_PROTOCOL']. ' ' .$status, true);
      }
      else{
        header('HTTP/1.1 '.$status, true);
      }
    }
  }

Status is always 200
I set cookies or do a redirect, then I do response->send, that is,
in the application class it looks like this:

App::start(){
$controller->action() - тут отправляются заголовки( установка кук и т.д)
$response->send();
}

if you remove response->send(), then everything works fine, why?

Answer 1

You have if(!headers_sent()) there ...
Apparently, some headers are sent earlier.