How does Drupal avoid saving message information in the page cache?

Code of the page_get_cache function:

 

function page_get_cache($status_only = FALSE) {  static $status = FALSE;  global $user, $base_root;  if ($status_only) {    return $status;  }  $cache = NULL;  if (!$user->uid && $_SERVER[‘REQUEST_METHOD‘] == ‘GET‘ && count(drupal_set_message()) == 0 && $_SERVER[‘SERVER_SOFTWARE‘] !== ‘PHP CLI‘) {    $cache = cache_get($base_root . request_uri(), ‘cache_page‘);    if (empty($cache)) {      ob_start();      $status = TRUE;    }  }  return $cache;}

It can be seen that the cache is obtained only when the message is 0.

 

Let's take a look at the page_set_cache function, which stores the cache

 1 function page_set_cache() { 2   global $user, $base_root; 3  4   if (!$user->uid && $_SERVER[‘REQUEST_METHOD‘] == ‘GET‘ && page_get_cache(TRUE)) { 5     // This will fail in some cases, see page_get_cache() for the explanation. 6     if ($data = ob_get_contents()) { 7       if (variable_get(‘page_compression‘, TRUE) && extension_loaded(‘zlib‘)) { 8         $data = gzencode($data, 9, FORCE_GZIP); 9       }10       ob_end_flush();11       cache_set($base_root . request_uri(), $data, ‘cache_page‘, CACHE_TEMPORARY, drupal_get_headers());12     }13   }14 }

There is a line of code page_get_cache (true) to determine whether the cache can be found. If it cannot be found, return true, and then the page will be cached. When drupal_set_message () is not empty, page_get_cache (true) always returns false. It can be seen that Drupal judges whether there is a message when obtaining the page cache and setting the page cache, the cache is set or the cache is obtained only when the message is empty.