Returning 404 for all non existant UnifiedPush requests (where up=1) will follow UnifiedPush spec and Webpush spec and probably avoid many issues :)

RFC 8030 (Webpush)

A push service MAY expire a subscription at any time. If there are
outstanding requests to an expired push message subscription resource
(Section 6) from a user agent or to an expired receipt subscription
resource (Section 6.3) from an application server, this MUST be
signaled by returning a 404 (Not Found) status code.

UnifiedPush

404

The endpoint does not exist and SHOULD NOT be used anymore. Implementing this is OPTIONAL for both the application server and push server.

From the discussion in chat:
Maybe returning 404 after some time (12h ?) for the same reasons we chose to do so for matrix ?

@karmanyaahm @p1gp1g I am inclined to close this, since nobody has complained. The 5xx rates are still high, but I have just learned to live with it ... Thoughts?

If no one's having noticable problems, it ought to be fine. Still kinda weird it hasn't normalized down though :/

EDITED by @binwiederhier: Removed image containing lots of 507 errors to UP topics. The UP topics are secrets, so I removed the picture.

It keeps happening and increasing.

@Lastorder-DC please censor the picture. Unified Push topics are secrets.

Edit: I took the liberty of removing the image for you.

This is happening because your server is pushing messages to topics that do not have any subscribers. They are dead topics.

The alternative to returning 507 would be to let them through, but then you'd get rate limited and banned within a matter of minutes. So you can either live with the errors, or manually purge the topics from Mastodon.

I am also ok with pull requests to handle it specifically for Mastodon if there are suggestions.

@binwiederhier Forgot that. Sorry! (Actually I have sensored them but accidently choose non-sensored version...)

We're seeing a buildup of push messages to ntfy.sh, presumably to UP. Returning a 4XX code so that the queue is deleted would help a lot, since we're continually getting IP banned by the sheer volume of requests backed up.

Also relevant: mastodon/mastodon#26078

I've talked with @karmanyaahm about this issue, and the consensus seems to be that, 12h after deletion, nfty should be returning 410s for a given subscription.

Actually, the .Stale() function will give a better approximation of when to expire.