HTTP Request/Response class
You should take a look at Symfony's HttpFoundation component.

They've written various Request/Response objects similar to what you're attempting to do and they are extremely well done. Either I'd use them directly(save your own time). Or if this is an exploratory exercise then take a look at their code base to see how you can improve on your own solution.

It's not as sexy as writing your own objects, but it'll save you a lot of time and effort in the long run.