Returns the actual size of a chunk (as opposed to the entire size field, which may include some flags).

def get_size(self):
        """
        Returns the actual size of a chunk (as opposed to the entire size field, which may include some flags).
        """
        raise NotImplementedError("%s not implemented for %s" % (self.get_size.__func__.__name__,
                                                                 self.__class__.__name__))