Bypassing Cache with HTTP Headers

/*
  * Set $regex_path_patterns accordingly.
  *
  * We don't set this variable for you, so you must define it
  * yourself per your specific use case before the following conditional.
  *
  * For example, to exclude pages in the /news/ and /about/ path from cache, set:
  *
  *   $regex_path_patterns = array(
  *     '#^/news/?#',
  *     '#^/about/?#',
  *   );
  */

$regex_path_patterns = array(
  '#^/news/?#',
  '#^/about/?#',
);

// Loop through the patterns.
foreach ($regex_path_patterns as $regex_path_pattern) {
  if (preg_match($regex_path_pattern, $_SERVER['REQUEST_URI'])) {
    drupal_page_is_cacheable(FALSE);
    $conf['page_cache_maximum_age'] = 0;

    // No need to continue the loop once there's a match.
    break;
  }
}

/*
  * Set $regex_path_patterns accordingly.
  *
  * We don't set this variable for you, so you must define it
  * yourself per your specific use case before the following conditional.
  *
  * For example, to exclude pages in the /news/ and /about/ path from cache, set:
  *
  *   $regex_path_patterns = array(
  *     '#^/news/?#',
  *     '#^/about/?#',
  *   );
  */

$regex_path_patterns = array(
  '#^/news/?#',
  '#^/about/?#',
);

// Loop through the patterns.
foreach ($regex_path_patterns as $regex_path_pattern) {
  if (preg_match($regex_path_pattern, $_SERVER['REQUEST_URI'])) {
    add_action( 'send_headers', 'add_header_nocache', 15 );

    // No need to continue the loop once there's a match.
    break;
  }
}
function add_header_nocache() {
      header( 'Cache-Control: no-cache, must-revalidate, max-age=0' );
}


/* For WP REST API specific paths, we use a different approach by using the rest_post_dispatch filter */

// wp-json paths or any custom endpoints
$regex_json_path_patterns = array(
  '#^/wp-json/wp/v2?#',
  '#^/wp-json/?#'
);

foreach ($regex_json_path_patterns as $regex_json_path_pattern) {
  if (preg_match($regex_json_path_pattern, $_SERVER['REQUEST_URI'])) {
      // re-use the rest_post_dispatch filter in the Pantheon page cache plugin
      add_filter( 'rest_post_dispatch', 'filter_rest_post_dispatch_send_cache_control', 12 );
      break;
  }
}

// Re-define the send_header value with any custom Cache-Control header
function filter_rest_post_dispatch_send_cache_control( $response ) {
    $response->header( 'Cache-Control', 'no-cache, must-revalidate, max-age=0' );
    return $response;
}