Question

I have an HTTP Handler set up which accepts a GUID parameter and returns the image from the file system.

This image will not ever change; the backend program will generate a new GUID if it does. As such, I want the image to always be cached.

Is the correct way to do this to set a status code of 304 (not modified) from the HTTP Handler?

Answer 1

I would recommend you setting proper HTTP response headers in order to indicate to the clients that the contents will not change and could be cached:

public void ProcessRequest(HttpContext context)
{
    var cache = context.Response.Cache;
    cache.SetCacheability(HttpCacheability.Public);
    cache.SetExpires(DateTime.Now.Add(CACHE_DURATION));
    cache.SetMaxAge(CACHE_DURATION);
    cache.AppendCacheExtension("must-revalidate, proxy-revalidate");

    byte[] buffer = ...
    context.Response.ContentType = "image/png";
    context.Response.OutputStream.Write(buffer, 0, buffer.Length);
}