Using Last-Modified and If-Modified-Since on a RESTful API

Question

I've been reading a few articles regarding setting headers for Last-Modified when a response is sent from a server. I understand the purpose for it, and how to set it, etc.

I also understand the incoming If-Modified-Since header and that it's asking has anything changed since this time. I understand how to retrieve the header and convert it to a timestamp, etc.

The aspect I'm struggling to get my head around is what I compare the modified since timestamp with. My understanding is that by using last modified I don't need my API to keep retrieving masses of data if it's still the same.

So, am I supposed to make a super lightweight call to the API's cache/database and just check for the last modification to whatever dataset is being requested?

Answer 1

It's going to depend on the nature of the resource being requested, but I would think that you would want to take advantage of the web server's caching mechanism itself wherever possible. If you're using Apache, for instance, mod_cache should be the starting point for your HTTP caching needs. I'd try and avoid manually implementing a full cache header implementation because you're likely to miss something, such as inadvertently introducing security risks to your application.