Cannot modify header information - headers already sent (wp_redirect in functions.php)

Question

I already consulted this post and this post but did not see a solution.

I need to redirect a page based on its $post->post_type and from what little I know, I can get this information inside the template_redirect hook.

So I have code below inside functions.php (of astra-child theme):

add_action('template_redirect', 'redir_sorteio'); 

function redir_sorteio() {
    global $post;
    if ($post->post_type == 'sorteio') 
        wp_redirect('/edicao/?id=' . $post->ID);
}

And it works perfectly.

But for some reason, errors have appeared within the log, like:

[18-May-2018 01:11:22 UTC] PHP Warning:  Cannot modify header information - headers already sent by (output started at /home/rogeriod/public_html/wordpress/sortemania/wp-content/themes/astra-child/functions.php:32) in /home/rogeriod/public_html/wordpress/sortemania/wp-includes/functions.php on line 1311

Where line 32 of functions.php (above) is the wp_redirect('/edicao/?id=' . $post->ID) and line 1311 of wordpress functions.php is the header command inside do_robotsfunction:

function do_robots() {
    header( 'Content-Type: text/plain; charset=utf-8' );

How can I find out what causes this and resolve it, since wp_redirect is working and no error appears directly to the user?

Answer 1

Try replacing wp_redirect with wp_safe_redirect and if you have php closing tag "?>" at end of files, remove them, at least you can check the header.php for php closing tag.

Answer 2

Actually the answers to change to wp_safe_redirect and put exit(); at the end, partially resolved the problem and it is a solution that only works inside the template_redirect, because in other places the problem persists.

This became a nightmare and I realized that it is also the nightmare of many, until I was able to find in a post an efficient, albeit unorthodox, solution: javascript.

So, after several attempts and errors, I got a stable code like this:

add_action('template_redirect', 'redireciona_sorteio'); 

function redireciona_sorteio() {
    global $post;
    if (isset($post->post_type)) {
        if ($post->post_type == 'sorteio') {
            if (!$post->ID) {
                echo '<script> location.replace("/"); </script>';
            }
            else {
                wp_safe_redirect('/edicao/?id=' . $post->ID);
                exit();
            }
        }
    }
}