/**
 * Store the current page in the cache.
 *
 * We try to store a gzipped version of the cache. This requires the
 * PHP zlib extension (http://php.net/manual/en/ref.zlib.php).
 * Presence of the extension is checked by testing for the function
 * gzencode. There are two compression algorithms: gzip and deflate.
 * The majority of all modern browsers support gzip or both of them.
 * We thus only deal with the gzip variant and unzip the cache in case
 * the browser does not accept gzip encoding.
 *
 * @see drupal_page_header
 */
function page_set_cache() {
  global $user, $base_root;

  if (!$user->uid && $_SERVER['REQUEST_METHOD'] == 'GET') {
    // This will fail in some cases, see page_get_cache() for the explanation.
    if ($data = ob_get_contents()) {
      $cache = TRUE;
      if (function_exists('gzencode')) {
        // We do not store the data in case the zlib mode is deflate.
        // This should be rarely happening.
        if (zlib_get_coding_type() == 'deflate') {
          $cache = FALSE;
        }
        else if (zlib_get_coding_type() == FALSE) {
          $data = gzencode($data, 9, FORCE_GZIP);
        }
        // The remaining case is 'gzip' which means the data is
        // already compressed and nothing left to do but to store it.
      }
      ob_end_flush();
      if ($cache && $data) {
        cache_set($base_root . request_uri(), $data, CACHE_TEMPORARY, drupal_get_headers());
      }
    }
  }
}