Should HTTP 304 Not Modified-responses contain cache-control headers?

Question

I\'ve tried to understand this, and searched SO for similar questions, but I still don\'t have a 100% understanding on how this is supposed to work.

I get this respo

Answer 1

If I understand correctly then the browser is in fact caching for 120 seconds and your server is responding 304 Not Modified to subsequent If-Modified-Since requests. This "IMS" request occurs when the end-user accesses the same URL. At that time the browser can send an If-Modified-Since request. The browser wants to know if it is displaying stale content. This seems normal.

Upon receiving this request your server should reply 200 OK, 304 Not Modified (or a 4XX, if necessary).

I do not believe you should set your server to send a Cache-Control header with the 304 response for two reasons:
1. You do not want any intermediary caches to cache that 304 response (there is a possibility that they could)
2. The 120 second TTL will not be refreshed by the 304 response. The browser will retain the object for 120 seconds from the 200 OK response. After 120 seconds the browser should send a GET request, not an If-Modified-Since, so your server will respond with the bytes of the file and not just a 304 response.

Note that the browser will not request the file again automatically after 120 seconds unless the end-user specifically requests it via a page load or directly inputting the URL into their address bar (or unless you have a custom application that controls that functionality somehow).

Edited the first paragraph to read a bit better(hopefully)