def connect(self, clean_session=True):
    print("MQTTClient connect start")
    self.sock = socket.socket()
    self.sock.connect(self.addr)
    if self.ssl:
        import ussl
        self.sock = ussl.wrap_socket(self.sock, **self.ssl_params)
    msg = bytearray(b"\x10") 
    remaining_length = 10 + 2 + len(self.client_id)
    ConnectFlags = clean_session << 1
    if self.user is not None:
        remaining_length += 2 + len(self.user) + 2 + len(self.pswd)
        ConnectFlags |= 0xC0
    if self.lw_topic:
        remaining_length += 2 + len(self.lw_topic) + 2 + len(self.lw_msg)
        ConnectFlags |= 0x4 | (self.lw_qos & 0x1) << 3 | (self.lw_qos & 0x2) << 3
        ConnectFlags |= self.lw_retain << 5
    offset = 1
    #1:0(0x00)=>127(0x7F);
    #2:128(0x80,0x01)=>16383(0xFF,0x7F
    #3:16384(0x80,0x80,0x01)=>2097151(0xFF,0xFF,0x7F)
    #4:2097152(0x80,0x80,0x80,0x01)=>268435455(0xFF,0xFF,0xFF,0x7F)
    assert remaining_length < 268435455
    while True:
        byte = remaining_length % 128
        remaining_length = remaining_length // 128
        if remaining_length > 0:
            byte = byte | 0x80
        msg.extend(struct.pack("!B", byte))
        print('MQTTClient connect msg[',offset,']:',hex(byte))
        if remaining_length == 0:
            break
        offset=offset+1
    msg.extend(b"\0\x04MQTT\x04")
    msg.extend(struct.pack("!B", ConnectFlags))
    if self.keepalive:
        assert self.keepalive < 65536
        msg.extend(struct.pack("!B", self.keepalive >> 8))
        msg.extend(struct.pack("!B", self.keepalive & 0x00FF))

    self.sock.write(msg)