Get last-modified header from response in ASP.NET

I’ve been working lately with some ASP.NET performance optimization automation HTTP modules. In one of them I needed to know if the last-modified header had been set through the Response.Cache.SetLastModified(DateTime) method. For some reason, there is no API available anywhere within the BCL to retrieve the last modified date of a response – you can only set it. Since the module wouldn’t work without a way to read the last modified date of the response, I had to use Reflector to figure out how to pull the information out using reflection. The result became a simple little method to retrieve the date