This patch handles the case where the caller has specified the size
argument. When size is unspecified, it should be handled as if size was
infinite. By the formula from your patch, this should be

 recv_size = min(self.max_readsize, max(self._rbufsize, left))
  (== min(self.max_readsize, inf) == self.max_readsize)

and not the current code:
            if self._rbufsize <= 1:
                recv_size = self.default_bufsize
            else:
                recv_size = self._rbufsize
            while True:
                data = self._sock.recv(recv_size)

BTW,  I still think this max_readsize limit should be handled somewhere
deeper in the code. at least maybe in the _socketobject class.