WP REST API and Caching Issue

[mguenter]

A follow-up to https://core.trac.wordpress.org/ticket/39861, cause I can not change the WordPress version to 5.5.3.

Hey @joehoyle and @lukecavanagh,

I just came across this ticket because I have a similar issue. We have implemented a dashboard in a WordPress submenu page. Imagine the following scenario:

1. Open the dashboard
2. JavaScript is fetching data via GET from a WP REST API endpoint
3. Click on another submenu, e.g. media library
4. Use the back button from the browser
5. Check the network log and you will see, that the WP REST API request got cached (200 OK (from disk cache))

Tested on Chrome, but I think this happens on all browsers.

How can this be fixed? Using the following header disallows the browsers to cache the response:

Cache-Control: no-cache, no-store, must-revalidate, max-age=0

Add no-store directive, see also ​https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cache-Control and ​https://www.mixmax.com/engineering/chrome-back-button-cache-no-store/

The solution? Add the no-store cache directive. It tells the browser to really not store anything at > all. So this works, and clicking the back button in Chrome will never serve up cached content: [...]

If you fix this, you need to be careful, because the directive should probably only be added on WP REST API calls.

[TimothyBlynJacobs]

Hi @mguenter,

Please add your comment to #39861 so we can keep the discussion focussed in one place. You don't need to change the version number to report the issue.

Thanks!