You can find the values that were used by the MQTTSubscribe and MQTTPublish nodes to process the MQTT message. You can also use fields in the local environment to dynamically alter the behavior of the MQTTPublish node.
These fields are available in the following message tree structures:
LocalEnvironment fields
When you use the
MQTTSubscribe node, it stores information that you can access in the LocalEnvironment.MQTT.Input message tree. The fields in this structure are described in the following table.
Table 1. List of elements in the LocalEnvironment.MQTT.Input
subtree
| Element Name |
Element Data Type |
Description |
| Duplicate |
CHARACTER |
Whether the message is a duplicate of a previous
message. Set to TRUE or FALSE. |
| Retained |
CHARACTER |
Whether the message is a retained message. Set
to TRUE or FALSE.
Retained is set to TRUE if the message
was kept by the server and is now being sent when the client first
connects to the server. |
| Topic |
CHARACTER |
The name of the MQTT topic the received message
was published to. |
| QualityOfService |
CHARACTER |
Quality of service of the received message.
Set to 0 (at most once), 1 (at
least once), or 2 (exactly once). |
This structure is populated with each message written to the Out terminal of the
MQTTSubscribe node.
LocalEnvironment.Destination fields
When you use the
MQTTPublish node, you can override certain properties with elements in the LocalEnvironment.Destination.MQTT.Output message tree. The fields in this structure are described in the following table.
Table 2. List of elements in the LocalEnvironment.Destination.MQTT.Output
subtree
| Element Name |
Element Data Type |
Description |
| retained |
CHARACTER |
Whether the message is a retained message. Set
to TRUE or FALSE.
The default is FALSE. Set to TRUE if
the message for a topic must be held by the MQTT server after delivery
to all currently connected clients, and then delivered to new clients
when they connect to that topic. Each retained message for a topic
replaces the previous retained message for that topic. In this way,
devices can receive the most recent retained message immediately on
connecting to a topic. |
| TopicName |
CHARACTER |
The name of the MQTT topic the message will
be published to. |
| qos |
CHARACTER |
Quality of service of the published message.
Set to 0 (at most once), 1 (at
least once), or 2 (exactly once). |
| URL |
CHARACTER |
The URL that is used to connect to the MQTT server. The URL includes the
protocol, the host name, and the port. For
example:tcp://myMQTTserver.com:1883
or, if the connection is
encrypted:ssl://myMQTTserver.com:8883
If set, the value of the URL property
takes precedence over the values of the following MQTT message flow node properties:
|
LocalEnvironment.WrittenDestination fields
When you use the
MQTTPublish node, it stores information that you can access in the LocalEnvironment.WrittenDestination.MQTT message tree. The fields in this structure are described in the following table.
Table 3. List of elements in the LocalEnvironment.WrittenDestination.MQTT
subtree
| Element Name |
Element Data Type |
Description |
| ClientId |
CHARACTER |
The unique name of the client. |
| DeliveryToken.isComplete |
BOOLEAN |
Whether the message was successfully published
to the MQTT topic. Set to TRUE or FALSE. |
This structure is populated with each message written to the Out terminal of the
MQTTPublish node.