I'm going for the obvious one here: why even bother trying to parse this yourself? The data is within your range with the easy use of $_POST[] / $_FILES[] ..
You can still build your own class around those values instead of having your own classes try to accomplish the same data array as the php-compiler already did for you.
In order to give you a valid answer: I don't know of a way to get your php://input back, as it is probably read by the PHP compiler and therefore you are at the end of the stream ( plus: it is read-only so there is probably no way to reset the pointer to the start of the stream ).
