What headers do I want to send together with a 304 response?

Question

When I send a 304 response. How will the browser interpret other headers which I send together with the 304?

E.g.

header(\"HTTP/1.1 304 Not Modified\");
         


        

Answer 1

This blog post helped me a lot in order to tame the "conditional get" beast.

An interesting excerpt (which partially contradicts Ben's answer) states that:

If a normal response would have included an ETag header, that header must also be included in the 304 response.

Cache headers (Expires, Cache-Control, and/or Vary), if their values might differ from those sent in a previous response.

This is in complete accordance with the RFC 2616 sec 10.3.5.

---

Below a 200 request...

HTTP/1.1 200 OK
Server: nginx/0.8.52
Date: Thu, 18 Nov 2010 16:04:38 GMT
Content-Type: image/png
Last-Modified: Thu, 15 Oct 2009 02:04:11 GMT
Expires: Thu, 31 Dec 2010 02:04:11 GMT
Cache-Control: max-age=315360000
Accept-Ranges: bytes
Content-Length: 6394
Via: 1.1 proxyIR.my.corporate.proxy.name:8080 (IronPort-WSA/6.3.3-015)
Connection: keep-alive
Proxy-Connection: keep-alive
X-Junk: xxxxxxxxxxxxxxxx

...And its optimal valid 304 counterpart.

HTTP/1.1 304 Not Modified
Server: nginx/0.8.52
Date: Thu, 18 Nov 2010 16:10:35 GMT
Expires: Thu, 31 Dec 2011 16:10:35 GMT
Cache-Control: max-age=315360000
Via: 1.1 proxyIR.my.corporate.proxy.name:8080 (IronPort-WSA/6.3.3-015)
Connection: keep-alive
Proxy-Connection: keep-alive
X-Junk: xxxxxxxxxxx

Notice that the Expires header is at most Current Date + One Year as per RFC-2616 14.21.