incompatible remaining_length in connect

[willee]

Hi,
In CONNECT Packet fixed header, The Remaining Length is encoded using a variable length encoding scheme which uses a single byte for values up to 127. Larger values are handled as follows. The least significant seven bits of each byte encode the data, and the most significant bit is used to indicate that there are following bytes in the representation. Thus each byte encodes 128 values and a "continuation bit". The maximum number of bytes in the Remaining Length field is four.

Size of Remaining Length
#Byte x From=>To
#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)

In connect, Remaining Length feild is only msg[1],only one  bytes, which is incompatible Remaining Length larger than 127 bytes

Willee Gong

[willee]

Hi,
One workaroud:

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)

Willee Gong

[pfalcon]

Duplicate of #163