Custom rewrite to fetch feed data

Question

I am trying to fetch and display data from a feed when the user goes to a specific url like /items/32 where the 32 is the actual id of the feed item that should be fetched and displayed. Notice that I am not using any custom post type for this. I am just fetching the data from an external resource based on the supplied id:

class FeedPlugin
{
  public function __construct()
  {
    add_action('init', array($this, 'addRewriteRules'));
    add_filter('query_vars', array($this, 'addQueryVars'));
    add_action('template_redirect', array($this, 'addTemplate'));
  }

  /**
   * Add query argument item_id
  **/
  public function addQueryVars(array $query_vars)
  {
    $query_vars[] = 'item_id';
    return $query_vars;
  }

  /**
   * Add a custom rewrite in the form ^/items/123/$
  **/
  public function addRewriteRules()
  {
    add_rewrite_rule(
      'items/([0-9]+)/?$',
      'index.php?pagename=items&item_id=$matches[1]',
      'top'
    );
    // This is just for testing purposes at this point.
    flush_rewrite_rules(true);
  }

  /**
   * Here we actually are fetching the data based on the id
  **/
  public function addTemplate()
  {
    global $item;
    if (get_query_var('pagename') == 'items' && 
        get_query_var('item_id')) {
        $feedUrl = 'https://example.com/api/v1/feed?id=' . get_query_var('item_id');
        $response = wp_remote_request($feedUrl);

        // For now we just assume that this works.
        $body = wp_remote_retrieve_body($response);
        $item = json_decode($body);

        // Include our custom template that renders the content from the $body variable
        // I also manage to do this by using the `template_include` filter
        include plugin_dir_path(__FILE__) . '/custom-item.php';
      }
    }
}

The above sort of works, but since I am not using a real post when visiting this route the title of the page is set to BlogName | Not found and the http status code returned when visiting this route is set to 404. I manage to solve this by using add_filter('pre_get_document_title', array($this, 'setTitle'));:

public function setTitle($title)
{
    global $item;
    if (get_query_var('pagename') == 'items') {
        return get_bloginfo('name') . ' | ' . $item->Title;
    }
    return $title;
}

and to get rid of the 404 status code I used:

global $wp_query;
$wp_query->is_404 = false;
status_header(200);

in the addTemplate() method.

Even though this seems to work it feels very messy and I wonder if there is a smoother way of doing this? Perhaps by creating some kind of fake post or similar?

Answer 1

Seems like a good candidate for add_rewrite_endpoint().

add_rewrite_endpoint( 'items', EP_ROOT, 'item_id' );

That will register the endpoint /items/<item ID> and also registers the query var item_id, and eliminates the 404 status header/title as well. But the page title would be the site name and you'd probably still want to hook to pre_get_document_title to customize the title.

And your class would be simpler:

class FeedPlugin {
    public function __construct() {
        add_action( 'init', [ $this, 'add_rewrite_endpoint' ] );
        add_action( 'template_redirect', [ $this, 'addTemplate' ] );
    }

    public function add_rewrite_endpoint() {
        add_rewrite_endpoint( 'items', EP_ROOT, 'item_id' );
    }

    public function addTemplate() {
        if ( $item_id = get_query_var( 'item_id' ) ) {
            /* your code here:
            echo 'Yay, it works! Item ID: ' . $item_id;
            exit;
            */
        }
    }
}

Don't forget to flush the rewrite rules — just visit the permalink settings page.

UPDATE

how can I specify what is valid for release_id e.g [0-9A-Z]+

So I believe you meant item_id when you said release_id?

And (at the moment) there's no "standard"/easy way to specify the preferred RegEx pattern for an endpoint added using add_rewrite_endpoint(), so if you need a custom RegEx pattern, it's actually better to use add_rewrite_rule(). :)

And here's how you can prevent the 404 error with your original code.

I believe you know it happens because you're querying a post/Page that doesn't exist (pagename=items) and I also believe you added that in the rewrite rule as an identifier for the custom feed request.

And I'm not sure if you intentionally didn't do this, but it's a very easy way to prevent the 404 error: create a Page and set its slug to items.

That may sound silly, but it actually works. (Although you'd still need to tweak the page title.) And you could just create a custom Page template (which loads/generates/renders the feed) and assign the template to that items Page, without having to hook to template_redirect.

Alternate solution without creating a Page

1. In the addRewriteRules(), just omit the pagename=items&:

   public function addRewriteRules()
   {
     add_rewrite_rule(
       'items/([0-9]+)/?$',
       'index.php?item_id=$matches[1]',
       'top'
     );
   }
   

2. In the addTemplate(), check if the matched rewrite rule is the one you added via add_rewrite_rule() above:

   public function addTemplate()
   {
     global $item, $wp;
     if ( 'items/([0-9]+)/?$' === $wp->matched_rule &&
       ( $item_id = get_query_var('item_id') ) ) {
       // your code here
     }
   }
   

But once again, you'd still need to tweak the page title which defaults to the site name.