MQTTPublish
Publish to MQTT
NOTE: See MQTT for more information on the use of MQTT in Campbell Scientific data loggers.
Syntax
Result = MQTTPublish( TopicString, Payload, QoS, Retain )
Example
'Declare Variables
Public Counter
Public Result
Public Flag As Boolean
Public Payload As String = "TestString"
'Main Program
BeginProg
Scan (1,Sec,0,0)
If Flag Then
Counter +=1
'MQTTPublish(TopicString,Payload,QoS,Retain)
Result = MQTTPublish ("TestTopic",Payload,0,0)
Flag = false
EndIf
NextScan
EndProg
Remarks
The MQTTPublish function must be called from within a Scan. If a publish QoS of 1 is used, this function will wait on a response or timeout before continuing to run CRBasic.
MQTT topic structure
The topic structure is user defined. This instruction does not inherit the base topic from the MQTTBaseTopic datalogger setting.
Return Value (Result)
The function returns 0 if the MQTTPublish is successful. It will return an error if the MQTTPublish fails. The return value can be stored in an array.
The following error codes are possible:
| Error Code | Description |
|---|---|
| 0 | No error |
| -1 | No MQTT connection |
| -2 | No Topic |
| -3 | Wildcard in topic string. |
| -4 | Bad Data Table payload pointer |
| -5 | Bad memory pointer (system error) |
| -101 | No new data to publish in table |
Parameters
TopicString
A string that defines the payload. Format conforms to MQTT v3.1.1.
PayLoad
The payload for the publish function. This is a user-formatted message of type string. The payload parameter can accept elements from a string array.
NOTE: The maximum MQTT packet size is 4800 bytes.
QoS
Publish Quality of Service. Supports levels 0 and 1 per MQTT v3.1.1. Level 2 is not supported.
Retain
Broker retains value. Not supported by Amazon Web Services; must be 0.