function wnet_get_transient_remote_json($transientname, $url, $interval=1800) {
  // those are the same arguments as 'set_transient()'

  $stalecachename = 'stalecache_' . $transientname;
  // we generate a consistent name for the backup data

     if ( false === ( $json = get_transient($transientname) ) ) {
       $response = wp_remote_get($url);
       // get the remote data as before, but this time...

       if (is_wp_error($response) || ! isset($response['body']) || 200 != $response['response']['code']) {
       // check to see all of the ways that the data request could return an error.

         $json = get_option($stalecachename);
         // one of our checks failed, so we get the stale cache data from WP Options and store in the $json variable.

       } else {
         $json =  $response['body'];
         // no errors!  we store the remote data in the $json variable.

         if (! get_option($stalecachename)) {
           add_option($stalecachename, $json, '', 'no');
           // Store the data in the $json variable in the options table as a backup.
           // We _could_ have just used update_option(), but by using add_option() with 'no' in the third arg
           // we keep the option from being 'autoloaded' into memory and reducing memory usage.
         } else {
           update_option($stalecachename, $json);
           // update_option() preserves the 'autoload' setting of a previously created option.
         }
       }

       set_transient($transientname, $json, $interval );
       // Regardless of whether we got the data from the remote site or our local backup, we store that data in the transient.
       // We won't try to regenerate that data until the transient expires.

    }
    return $json;
    // on general principle return the data we are storing in case we'd like to do something with it.
  }
}