Post URLs intermittently serve ActivityPub JSON to browsers after upgrading to WordPress 7.1 (caching/content-negotiation regression)

[vincentbreton-auteur]

Quick summary

Description

Since upgrading WordPress core to version 7.1 (ActivityPub plugin was already on 9.2.2, unchanged across the update), I've had a report from a reader that clicking a post link from Mastodon led to a raw JSON response (the ActivityPub representation) instead of the normal HTML post page. Reloading/clicking the link again shortly after showed the correct HTML page.

This did not happen before the WordPress core update to 7.1, on the same hosting/caching setup and same ActivityPub plugin version.

Environment

• WordPress version: 7.1
• ActivityPub plugin version: 9.2.2
• PHP version: [si connue]
• Hosting: o2switch, using XtremCache Varnish
• Site: https://vincentbreton.fr

Steps to reproduce

Steps to reproduce

• Publish a post
• A Mastodon instance/client fetches the post URL shortly after publishing (presumably for a link preview / federation), sending an Accept header that may include both application/activity+json and text/html as a fallback
• A human visitor clicking the same URL shortly after sometimes receives the JSON response instead of HTML
• The issue resolves itself after some time (presumably once the cache entry expires or is refreshed by another HTML request)

Site owner impact

Fewer than 20% of the total website/platform users

Severity

Moderate

What other impact(s) does this issue have?

No response

If a workaround is available, please outline it here.

No response

[pfefferle]

The plugin has not changed anything in that regards. Have you added a special content negotiation handling to your caching layer?