Payload
The Payload portion of a PUBLISH message contains strictly application-specific
data. No assumptions are made about the nature or content of this data,
and this portion of the message should be treated as a BLOB.
As a specific point, if the application wishes to apply any compression
to the Payload data, then it is the responsibility of the application
to define appriate flag fields in the Payload to convey the compression
details. No provision is made in the Fixed or Variable Header portions
of the message for application-specific flags.
Several message types make use of the Payload portion of the message
for carrying information relevant to that message. These messages are listed
below. See the appropriate section for more details.
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CONNECT
The Payload section of the CONNECT message contains either one or three
UTF-encoded strings.
The first uniquely identifies the client to the broker.
The second and third are only present if the Will Flag is set
in the Connect Flags byte. The second is the "Will Topic", and the third
is the "Will Message". See the CONNECT section
for discussion of these terms.
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SUBSCRIBE
The Payload of a SUBSCRIBE message contains a list of Topic Names which
the client wishes to subscribe to, and the Quality of Service at which
it wishes to subscribe to each of these Topics.
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SUBACK
The Payload of a SUBACK message contains a list of "granted" Quality
of Service levels. Each of these is the QoS at which the broker's
administrators have permitted the client to subscribe to a particular Topic
Name. The order of granted QoS levels in the list is the same as the Topic
Name list in the corresponding SUBSCRIBE message.
Discussion
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Last Modified: 22-Oct-99