def delete(self, doc):
        if doc.id is None:
            raise DatabaseException('Document does not have id')
        if doc.sid is None:
            try:
                rs = self.db.docs.remove({'id': doc.id}, safe=True)
                assert rs['n'] == 1
            except Exception as e:
                raise DatabaseException(e)
            return None
        doc.data = None
        return self.update(doc)
async def echo_client_streams(reader, writer):
    sock = writer.get_extra_info('socket')
    try:
        sock.setsockopt(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1)
    except (OSError, NameError):
        pass
    if PRINT:
        print('Connection from', sock.getpeername())
    while True:
        data = await reader.read(1000000)
        if not data:
            break
        writer.write(data)
    if PRINT:
        print('Connection closed')
    writer.close()