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

You should send a 304 if the client has explicitly stated that it may already have the page in its cache. This is called a conditional GET, which should include the if-modified-since header in the request.

Basically, this request header contains a date from which the client claims to have a cached copy. You should check if content has changed after this date and send a 304 if it hasn't.

See http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.25 for the related section in the RFC.