Well that sucks. Caddy has supported HTTP/2 push for a very long time (except for a few months after v2 was released since it was a total rewrite). https://caddyserver.com/docs/caddyfile/directives/push
I guess I'll have to go back to putting all the images base64 encoded into the html :-(
Instead of pushing the images just set headers for the images above the fold:
Link: </img/1.jpg>; rel=preload; as=image
The advantage to this method is that the browser can look up the images in its cache first and avoid transferring unnecessary data.
The downside is that it will take at least one round trip for the browser to request them. So if your HTML is short and quick to generate the connection might go idle before your receive these requests.
Link: </img/1.jpg>; rel=preload; as=image; nopush
I wonder if the proxies would consider some sort of hybrid mode where they proactively fetch the link header and cache it (if it isn't already cached) but don't push it to the client. I can't find any indication that this has been implemented or considered anywhere. Of course if your edge was much closer to the user the the origin it wouldn't have much benefit. But it would still be nice.