404 error - Plugin - Proper way to handle 404 pages?

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Working on a plugin to redirect 404 to a different page. Here's the problem. I occasionally get this in the log file:

[08-Apr-2020 14:48:45 UTC] PHP Notice:  Trying to get property of non-object in {path}/wp-includes/class-wp-query.php on line 3998
[08-Apr-2020 14:48:45 UTC] PHP Notice:  Trying to get property of non-object in {path}/wp-includes/class-wp-query.php on line 4000
[08-Apr-2020 14:48:45 UTC] PHP Notice:  Trying to get property of non-object in {path}/wp-includes/class-wp-query.php on line 4002

which is apparently related to this bug:

I've been doing this:

    add_action('template_redirect', array($this, 'My_404_Handler'));

And I've been calling is_404() in that function. From the bug report, whether it returns a true or false depends on when you call it. In my case the wp-includes/class-wp-query.php has a function get_queried_object() which can return a null value to a function is_page(). The problem, is_page() only handles object results and produces the error above when get_queried_object returns a null.

I've also looked over the server log and can't pinpoint any specific url requests that's causing this error.

I'm hoping someone has some experience with this and can tell me if changing to the code below is going to fix the problem?

    add_action('wp', array($this, 'My_404_Handler'));

I'm testing but since I don't know how to reproduce the error, I'm just taking a shot in the dark.

Thanks

edit

404 function

    public function My_Plugin_handle404() {
    if (is_404()) {
        //user set option to show the real 404
        if (get_option('Show404') == 'TRUE') {
            include(get_404_template());
        } else {
            //log the request info to the db and show a blank page with a 200 result
            $this->My_Plugin_Process_Request();
            status_header(200);
            exit;
        }
    } 
}

Working on a plugin to redirect 404 to a different page. Here's the problem. I occasionally get this in the log file:

[08-Apr-2020 14:48:45 UTC] PHP Notice:  Trying to get property of non-object in {path}/wp-includes/class-wp-query.php on line 3998
[08-Apr-2020 14:48:45 UTC] PHP Notice:  Trying to get property of non-object in {path}/wp-includes/class-wp-query.php on line 4000
[08-Apr-2020 14:48:45 UTC] PHP Notice:  Trying to get property of non-object in {path}/wp-includes/class-wp-query.php on line 4002

which is apparently related to this bug:

https://core.trac.wordpress/ticket/29660

I've been doing this:

    add_action('template_redirect', array($this, 'My_404_Handler'));

And I've been calling is_404() in that function. From the bug report, whether it returns a true or false depends on when you call it. In my case the wp-includes/class-wp-query.php has a function get_queried_object() which can return a null value to a function is_page(). The problem, is_page() only handles object results and produces the error above when get_queried_object returns a null.

I've also looked over the server log and can't pinpoint any specific url requests that's causing this error.

I'm hoping someone has some experience with this and can tell me if changing to the code below is going to fix the problem?

    add_action('wp', array($this, 'My_404_Handler'));

I'm testing but since I don't know how to reproduce the error, I'm just taking a shot in the dark.

Thanks

edit

404 function

    public function My_Plugin_handle404() {
    if (is_404()) {
        //user set option to show the real 404
        if (get_option('Show404') == 'TRUE') {
            include(get_404_template());
        } else {
            //log the request info to the db and show a blank page with a 200 result
            $this->My_Plugin_Process_Request();
            status_header(200);
            exit;
        }
    } 
}

• plugin-development
• 404-error

Share Improve this question edited Apr 8, 2020 at 18:42 uPrompt asked Apr 8, 2020 at 17:13 uPromptuPrompt 17299 bronze badges 4

• Why not use htaccess to handle 404's? Simple to do. Or you could have your plugin write to the htaccess, and let the user select the 404 page from a drop-down list of pages. – Rick Hellewell Commented Apr 8, 2020 at 18:02
• Hadn't thought of that and an idea to toy with. In the future though I want the option to redirect 404's based on the incoming request. Think honeypot. It's a research site. I want those probing the site for files or directories to find what they expect to find. – uPrompt Commented Apr 8, 2020 at 18:19
• @RickHellewell That's a very weird suggestion. What makes you think there is a .htaccess, and why should it be writable? – fuxia ♦ Commented Apr 8, 2020 at 18:23
• @fuxia I just suggested an htaccess as a way to 404, not having any details of why he needed a custom 404. And I made it a comment, rather than an answer (since my comment didn't directly access his question). And it is easy enough to have a command in a plugin to write to htaccess using the insert_with_markers() function (which is how WP does it). It is a valid way to modify htaccess - I use it in one of my plugins. – Rick Hellewell Commented Apr 8, 2020 at 20:33

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1 Answer 1

Sorted by: Reset to default 0

The proper hook to handle custom 404 content is 404_template. This happens when WordPress is trying to include the default template, but before any HTTP headers have been sent.

So you can change the template, send or overwrite HTTP headers, and all of that without any checks, because WordPress has done that for you already.

In most cases you should not redirect those requests. A redirect is a 3xx status, not a 4xx.

You might find some inspiration in my old 404 plugin.

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