Looking at the code I think the way to do this would be:
1. when building the content the first time parse the content to the img and css links are extracted out to a list
2. write out the list as the Link: header to a file associated with the content just add a different extension
3. modifying readfile() to read the headers file if it exists then add extra headers using the headers()
Cache Enabler is HTTP/2 focused. However, in to actually deliver assets via HTTP/2 it is still required that your origin server or CDN supports HTTP/2.
Yup I actually did this by patching cache enabler to parse the content and spit out a file that looks like the Link: header
Then I added the following to my .htaccess
<If “-f ‘%{REQUEST_FILENAME}.headers'”>
Header add Link expr=%{file:%{REQUEST_FILENAME}.headers}
</If>
Which will load up the contents of the .headers file that I generated when the cached version is created.
