Admin-ajax responds with 0 due to empty $_REQUEST

Question

I'm banging my head against updating an existing client site with lazy-loading content. At the moment the issue seems to be in the admin-ajax.php file, where the script dies prematurely on

if ( empty( $_REQUEST['action'] ) )
  die( '0' );

The error in console: GET http://www.example.com/wp-admin/admin-ajax.php?lang=en&action=example_frontpage_feed&page=0&next_time=0 net::ERR_EMPTY_RESPONSE

Everything works just fine on localhost. If I go straight to the url on browser, there's a flash of 'This page isn't working' screen but then it shows the right content. Also, if I change that piece on admin-ajax.php to anything else like die(1), the lazy-loader works just fin. That seems to me like a fix that might introduce some maintenance issues later, though.

Here's the ajax request:

fetchingFeed = true;
$.ajax({
  // url got from php doing basically this:
  // Example['ajax_url'] = admin_url( 'admin-ajax.php?lang=' . constant('ICL_LANGUAGE_CODE') )
  url: Example.ajax_url,
  dataType: 'json',
  type: 'get',
  data: { action: 'example_frontpage_feed', page: feedPage, next_time: feedNextTime },
  success: function(response) {
    if(response.success) {
      renderFeedPosts(response.posts);
      feedPage = response.nextPage;
      feedNextTime = response.nextTime;
    } else {
      if(response.error) {
        handleFeedLoadError(response.error);
      }
    }

    fetchingFeed = false;
  },
  error: function() {
    handleFeedLoadError();
    fetchingFeed = false;
  }
})

And here's the action

function example_frontpage_feed_ajax() {
  require_once 'inc/fetch-feed.php';

  $fetch_page = isset($_GET['page']) ? intval($_GET['page']) : 0;
  $fetch_next_time = isset($_GET['next_time']) ? $_GET['next_time'] : null;

  header('Access-Control-Allow-Origin: https://www.example.com');

  example_feed_content($fetch_page, $fetch_next_time);
}

add_action('wp_ajax_nopriv_example_frontpage_feed', 'example_frontpage_feed_ajax');
add_action('wp_ajax_example_frontpage_feed', 'example_frontpage_feed_ajax');

EDIT: The function example_feed_content basically gets posts and calls wp_send_json(blah blah)

Answer 1

In end of Ajax function you need to die() function

function example_frontpage_feed_ajax() {
  require_once 'inc/fetch-feed.php';

  $fetch_page = isset($_GET['page']) ? intval($_GET['page']) : 0;
  $fetch_next_time = isset($_GET['next_time']) ? $_GET['next_time'] : null;

  header('Access-Control-Allow-Origin: https://www.example.com');

  example_feed_content($fetch_page, $fetch_next_time);

  die(); // This is important in ajax
}

add_action('wp_ajax_nopriv_example_frontpage_feed', 'example_frontpage_feed_ajax');
add_action('wp_ajax_example_frontpage_feed', 'example_frontpage_feed_ajax');