Why browser does not send “If-None-Match” header?

Question

I\'m trying to download (and hopefully cache) a dynamically loaded image in PHP. Here are the headers sent and received:

Request:

GET /url:resource/P         


        

Answer 1

Similar problem

I was trying to obtain Conditional GET request with If-None-Match header, having supplied proper Etag header, but to no avail in any browser I tried.

After a lot of trial I realize that browsers treat both GET and POST to the same path as a same cache candidate. Thus having GET with proper Etag was effectively canceled with immediate "POST" to the same path with Cache-Control:"no-cache, private", even though it was supplied by X-Requested-With:"XMLHttpRequest".

Hope this might be helpful to someone.