In a custom module a, I return a JSON string that needs to be compatible with the Boost module.

My first try was using the following code:

if ((isset($_SERVER['HTTP_X_REQUESTED_WITH']) && 'XMLHttpRequest' == $_SERVER['HTTP_X_REQUESTED_WITH']) || strpos($_SERVER['REQUEST_URI'], '?json') !== FALSE) {
  header('Cache-Control: no-cache, must-revalidate');
  header('Content-type: application/json', true);
  $json = loadData();

This is obviously that this output won't be cached. Than I replaced the line with die() with the following one:

return drupal_json_output(($json));

This works, but it is not cached. I enabled the JSON output in Boost, but nothing happens.

What should I try?

Removing the two header lines does not change anything. The function drupal_json_output adds the Content-Type: application/json. But I belive that boost only accepts text/javascript. Also if I override the Content-Type again nothing will be cached.

4 Answers 4


You need to add


to the template-file, immediately prior to the exit or die statement. This will trigger the boost-module's code that stores the generated output in a cache-file. Additionally, you need to change the content-type to text/javascript.


Why do you need to cache JSON output? Anyhow, try removing header('Cache-Control: no-cache, must-revalidate'); and see what happens.

  • I tried that. No changes. I need that because drupal needs about 1.2 seconds to response and this is annoying.
    – rekire
    Apr 17, 2012 at 11:52
  • Did you tried like this: if(( isset($_SERVER['HTTP_X_REQUESTED_WITH']) && 'XMLHttpRequest' == $_SERVER['HTTP_X_REQUESTED_WITH'] ) || strpos($_SERVER['REQUEST_URI'], '?json')!==FALSE) { header('Content-type: application/json', true); $json=loadData(); return drupal_json_output(($json)); }
    – Zyy
    Apr 17, 2012 at 11:55
  • Tried to clear cache?
    – Zyy
    Apr 17, 2012 at 12:05
  • Ehm after flushing the cache boost stoped to work. Nothing is cached at the moment...
    – rekire
    Apr 17, 2012 at 12:18
  • Yep, It needs to rebuild the content. Anyhow JSON should not be cached, because you won't get real-time data. Otherwise - consider other format for content delivery.
    – Zyy
    Apr 17, 2012 at 12:25

Boost currently doesn't support application/json Content-Type. See this issue for details and patches.

  • I stopped using Boost but that makes sense, why that did not work for me.
    – rekire
    Mar 11, 2013 at 19:03

This might help others who are trying to have Boost cache JSON data.

Boost wont cache "application/json", but there are settings to cache TEXT/JAVASCRIPT AJAX request of type "text/javascript"

One problem you are going to find with : drupal_json_output() It uses : drupal_add_http_header('Content-Type', 'application/json');

So a solution you can try is this :

$data = array("hello","world");
drupal_add_http_header('Content-Type', 'text/javascript');
echo drupal_json_encode($data);

So if you have Boost "AJAX/JSON SETTINGS" enabled it should now cache the data.

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