extantion in validation file ci4 code example
Example: form validation for file type in codeigniter
if (empty($_FILES['userfile']['name']))
{
$this->form_validation->set_rules('userfile', 'Image', 'required');
}
if (empty($_FILES['userfile']['name']))
{
$this->form_validation->set_rules('userfile', 'Image', 'required');
}