Server push works by sending js, css, images etc. just after responding to a request, instead of waiting for the client to receive the html, parse it and request the resources, saving a round trip. But pushing js, css, images, fonts etc. for example.com/about when those same files already got downloaded by the client when it fetched example.com a minute ago is a complete waste of bandwidth, because the client already has those files.
Keeping state server-side for each request seems expensive, and that's cannot be how it's done, since HTTP is stateless. Presumably, the client would re-request the html on subsequent visits, to see if anything's changed.
How does the HTTP2-server know what files to push?
