Use ETag or Last-Modified to utilize 304 Not Modified until ESI fragment has expired then send a 200

[Rob Olmos]

I believe this may be more of a feature request because I'm unable to 
find anything in regards to this but basically I would like to utilize 
"304 Not Modified" responses until an ESI fragment has expired and then 
send a "200 OK" with the full document and updated ESI fragment.

Right now I have a parent document that has a couple ESI fragments 
within it. Essentially I would like to set a cache header, such as an 
ETag, on the parent document so that client browsers can utilize 
If-None-Match or If-Modified-Since and receive "304 Not Modified" 
instead of a 200 with the whole document thus saving bandwidth.

Is there a way to check within the VCL parent document request that an 
ESI fragment has expired?

I'm thinking that would allow me to update the Etag or Last-Modified 
headers of the parent document. However, it would also need to update 
the parent document cached object with these new values as well and 
Varnish would need to be aware of that so it doesn't send a 304 but 
instead a 200.

Thanks

-- 
Rob Olmos
EnderTech