connect_packet elements could be unified. about async_mqtt HOT 1 CLOSED

redboltz commented on June 2, 2024

connect_packet elements could be unified.

from async_mqtt.

Comments (1)

redboltz commented on June 2, 2024

@anarthal

Connect Packet contains the following fields:

https://docs.oasis-open.org/mqtt/mqtt/v5.0/os/mqtt-v5.0-os.html#_Toc3901033

Field	Bytes	Note	async_mqtt member variable
FixedHeader	1		fixed_header_
RemainingLength	1-4	variable	remaining_length_buf_
ProtocolName	6	0x00,0x04,'M','Q','T','T'	protocol_name_and_level_
ProtocolVersion(Protocol Level in v3.1.1)	1	value is 5	protocol_name_and_level_
ConnectFlags	1		connect_flags_
KeepAlive	2		keep_alive_buf_

Subsequent packets are of variable length and/or optional. That makes memory gaps.

That is in common v3.1.1 and v5.

protocol_name_and_level_ already been unified. Because they are just checked on create but never access later.

The possible unification candidates are connect_flags_ and keep_alive_buf. They are fixed size.

So if I unified them, The member woud be as follows:

Field	Bytes	Note	async_mqtt member variable
FixedHeader	1		fixed_header_
RemainingLength	1-4	variable	remaining_length_buf_
ProtocolName	6	0x00,0x04,'M','Q','T','T'	pn_pl_cf_ka_
ProtocolVersion(Protocol Level in v3.1.1)	1	value is 5	pn_pl_cf_ka_
ConnectFlags	1		pn_pl_cf_ka_
KeepAlive	2		pn_pl_cf_ka_

However, ConnectFlags are modified and referred in the packet member function frequently.
I can do it introducing reference or iteratoror index. But it would become a little complecated.

CONNECT packet is send only at the beggining of the session. So performance requirement is comparatively low. (I am not sure the unification could impact the performance)

Finally, I decided to remain the current code.

from async_mqtt.

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