'called as a callback on the downstream.write'

def _upstream_recv(self):

    if (len(self.downstream) > 0):
        tosend = self.downstream.read()
        sent = self.sock.sendto(tosend, self.dst_addr)
        if (sent != len(tosend)):
            print ('TODO:    error:    all    was    not    sent    !    tosend:    %s    sent:    %s' % (len(tosend), sent))
