WP Graphql Stale-While-Revalidate Caching With Redis Object Cache

wp-graphql-swr-cache.php

<?php

function get_request_hash($query, $vars)
{
  return md5($query . json_encode($vars));
}

function should_cache($query, $op, $vars)
{
  global $wp_object_cache;

  if (!method_exists($wp_object_cache, 'redis_instance')) {
    return false;
  }
  if (in_array($op, ['ProductsQuery', 'MenuQuery'])) {
    return true;
  }

  return false;
}
add_action(
  'do_graphql_request',
  function ($query, $op, $vars, $params) {
    global $wp_object_cache;
    
    if (!should_cache($query, $op, $vars)) {
      return;
    }

    $key = get_request_hash($query, $vars);

    $redis = $wp_object_cache->redis_instance();
    $data = $redis->get($key);
    
    if ($data) {
      $data_age = time() - $redis->get($key . '_time');
      header('Content-Type: application/json');
      header('Access-Control-Allow-Origin: *');
      if ($data_age >= 120) {
        header('x-tw-cache-status: stale');
        define('TW_CACHE_STATUS', 'stale');
      } else {
        header('x-tw-cache-status: hit');
      }
      echo $data;
      if (is_callable('fastcgi_finish_request')) {
        // Response is sent, so finish the request.
        fastcgi_finish_request();
      }
      if ($data_age <= 120) {
        // Cache is fresh, less than 120 seconds old. No updating is necessary, so end the process
        die();
      }
    } else {
      header('x-tw-cache-status: miss');
    }
  },
  10,
  4
);

add_action(
  'graphql_return_response',
  function ($res, $unfiltered_res, $schema, $op, $query, $vars, $obj) {
    global $wp_object_cache;
    if (!should_cache($query, $op, $vars)) {
      return;
    }

    $key = get_request_hash($query, $vars);
    $redis = $wp_object_cache->redis_instance();
    $redis->set($key, wp_json_encode($res->toArray()));
    $redis->set($key . '_time', time());
    if (TW_CACHE_STATUS == 'stale') {
      // Stale response was already sent, so after updating cache, end the process
      die();
    }
  },
  10,
  7
);