PUBREC

Assured Publish Received (part 1)

This message is the response from the receiving end to a PUBLISH message of QoS 2. It is the second message of the QoS 2 protocol flow. 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 QoS2 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 (5)
DUP flag
QoS level
RETAIN
 
0
1
0
1
 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 PUBREC message.
 

DUP flag

The DUP flag is not used for the PUBREC message.
 

RETAIN flag

The RETAIN flag is not used for the PUBREC 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 PUBREC 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 PUBREC message, the recipient should send a PUBREL message to the sender with the same Message Identifier. For more discussion on actions to be performed, see the Protocol Flow section.
 

Discussion

ASC on DUP flag
The protocol flows for QoS2 do not require the use of the DUP flag, so it has been dropped.
ASC on naming
This is the message formerly known as PUBACK1
ASC on message mnemonics
PUBACK1, 2 and 3 are rather boring names for these messags. Can we think of more meaningful names?
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Last Modified: 19-Oct-99