Server push also isn’t required to reap most of the benefits. In the places where I’ve tried it I’ve not seen any benefit over link preload headers + HTTP2 without push. Many CDNs that support HTTP2 haven’t bothered to support server push at all, I suspect due to the limited advantages compared to the extra complexity.

Pretty sure server push is being deprecated - current implementation is 'only half a feature', as clients lack the ability to tell the server what's already in cache.

In theory the client can cancel the response for a resource it's already got but by the time the response bytes reach the client it's really too late

Yeah and if the client volunteers the list of all it has in cache it would result in some massive requests and a kind of quasi-cookie.

I always found this feature interesting but weird.

Random thought. But isn't this a potential use for a bloom filter?

Yes bloom filters were a potential for Cache Digests, original prototype for Cache Digests used Golomb coded set as memory representation is smaller than Bloom filter

https://github.com/h2o/h2o/issues/421

But then Cache Digests moved onto Cuckoo Filters - https://github.com/httpwg/http-extensions/pull/413

Your webapp needs to start the push, browsers will interrupt it if they find the resource is already in cache after it has parsed the HTML.