One of the hot features that came with HTTP/2 was PUSH frames. The main idea is
that if the server can predict what requests a client might want to make, the
server can preemptively send request/response pairs to the client and warm its
cache.
This is a feature Ive been very interested in for a long time. I feel that it
can be incredibly useful for APIs to invalidate & warm caches, remove the need
for compound requests (which I feel is a hack, although sometimes a
necessary one).
To help advance this idea, Ive worked on a Internet Draft to let API
clients tell the server what resources they would like to have pushed, I built
a Node.js framework with first-class, deeply integrated Push support, and
added support for Prefer-Push to Ketting.
Unfortunately HTTP/2 push always felt like feature that wasnt quite there yet.
Its usefulness was stunted due to Cache-Digest for HTTP/2 being killed
off, and no browser APIs to hook into push events.
The Chrome team has considered removing Push support since at least 2018. The
main reason being that they hadnt really seen the performance benefit for
pushing static assets. At the time, I tried to defend the feature for
the API use-case.
Yesterday, the Chrome team announced to remove the feature from their
HTTP/2 and HTTP/3 protocol implementations.
Im a little sad that it never got to its full potential, but with this step,
I no longer think its worthwhile to invest in this feature. So Im ceasing
my work on Prefer-Push, and will also remove support from the next major
Ketting version.
On a positive note, I spent a lot of time thinking and working on this, but
it is sometimes nice to just be able to close a chapter, rather than to wait
and let it sizzle out. Its not an ideal conclusion, but its a conclusion
nonetheless.
Lacking server-driver push, were back to many small HTTP request, or compound
requests. This means you either have the N+1 problem, or (in the case of
compound requests) poor integration with HTTP caches. More on this here.
If youre going the compound request route, there is a draft of a similar
header as Prefer-Push; Prefer: transclude, which Ketting also
supports.
A feature that I hoped would work well in the future with Server Push was
server-initiated cache invalidation. We never quite got that. To work around
this, we use Websockets and will keep doing this for the forseeable future.
To reduce general latency of fetching many things, the 103 Early Hints
can help, although this is not supported yet in Chrome, and this is also
only really useful for speeding up delivery of assets like images, css and
Javascript as theres no way to hook into 1xx responses programmatically in
a browser.