How to know when to send a 304 Not Modified response

Question

I\'m writing a resource handling method where I control access to various files, and I\'d like to be able to make use of the browser\'s cache. My question is two-fold:

Answer 1

A 304 Not Modified response can result from a GET or HEAD request with either an If-Modified-Since ("IMS") or an If-Not-Match ("INM") header.

In order to decide what to do when you receive these headers, imagine that you are handling the GET request without these conditional headers. Determine what the values of your ETag and Last-Modified headers would be in that response and use them to make the decision. Hopefully you have built your system such that determining this is less costly than constructing the complete response.

If there is an INM and the value of that header is the same as the value you would place in the ETag, then respond with 304.

If there is an IMS and the date value in that header is later than the one you would place in the Last-Modified, then respond with 304.

Else, proceed as though the request did not contain those headers.

For a least-effort approach to part 2 of your question, figure out which of the (Expires, ETag, and Last-Modified) headers you can easily and correctly produce in your Web application.

For suggested reading material:

http://www.w3.org/Protocols/rfc2616/rfc2616.html

http://www.mnot.net/cache_docs/