wp_redirect () doesn't work in nginx?

Question

I made a simple redirection plugin that works like this:

add_action('wp_head', 'myredir');
function myredir(){
    if ( is_404() ) {
        $Path=$_SERVER['REQUEST_URI'];
        wp_redirect( 'http://old.example.com'.$Path );
        exit();
    }
}

The goal is redirect 404 errors to the old domain (I need to do a manual migration from an old website and it's going to take ages)

On Apache it works fine, on Nginx it doesn't work. What can I do to fix my plugin? The Redirection plugin works fine and it looks like is using wp_redirect, so there something wrong with my code

Answer 1

It should not have worked on apache as well. wp_head is too late to make a redirect as there is already some output sent at that point and php will not send the http headers required for the redirection. You need to hook on wp_loaded or any other hook before output actually happens.