PUBACK
Publish Acknowledgement
This message is the response from the receiving end to a PUBLISH
message of QoS 1. See the Protocol
Flow section for more details. In the case of a PUBLISH being sent
by a publishing client, this would be from the broker. It is also the response
from a subscriber upon receiving a PUBLISH message of QoS1 from the broker.
Fixed Header
See the Fixed Header section for more information,
| bit |
7
|
6
|
5
|
4
|
3
|
2
|
1
|
0
|
| byte 1 |
Message Type (4)
|
DUP flag
|
QoS level
|
RETAIN
|
| |
0
|
1
|
0
|
0
|
x
|
x
|
x
|
x
|
| byte 2 |
Remaining Length (2)
|
|
|
0
|
0
|
0
|
0
|
0
|
0
|
1
|
0
|
QoS level
The QoS level is not used for the PUBACK message.
DUP flag
The DUP flag is not used for the PUBACK message.
RETAIN flag
The RETAIN flag is not used for the PUBACK message
Remaining Length
The Remaining Length is the length of the Variable Header (2 bytes)
This may be a multi-byte field. See the Fixed
Header section for more details.
Variable Header
The Variable Header portion of the PUBACK message contains the Message
Identifier of the PUBLISH message that is being
acknowledged.
See the Variable Header section for
more information.
| bit |
7
|
6
|
5
|
4
|
3
|
2
|
1
|
0
|
| byte 1 |
Message Identifier MSB
|
| byte 2 |
Message Identifier LSB
|
Payload
NONE
Actions
Upon receipt of a PUBACK message, the client can discard the original message,
as it has now been received and logged by the broker. For more discussion
on actions to be performed, see the Protocol Flow
section.
Discussion
-
ASC on DUP flag
-
The protocol flows for QoS1 do not require the use of the DUP flag, so
it has been dropped.
-
AN on Payload
-
At this point in time I do not envisage the need for any payload contents
in the PUBACK response from the broker. If there is any information that
needs to be conveyed from the Argo broker within the PUBACK message then
it should be defined here.
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Last Modified: 19-Oct-99