This function will publish a message to a MQTT server.
The function will not block the MQTT interface while waiting for confirmation when using QoS 1 or 2.
The message will only be sent if connected to the MQTT server.
If the connection is lost before the function returns, the message will be sent when the connection is re-established, unless mqttPendingClear is called.
Input:
handle : INT
The handle to the MQTT connection.
topic : STRING
The topic of the message.
qos : SINT (0..2)
The QoS to publish the message with.
retained : BOOL
If TRUE the server should retain a copy of the message, if FALSE the message is not retained.
Retained messages will be transmitted to new subscribers of the topic by the server.
data : PTR
Address to the buffer with the contents of the message.
size : INT
The number of bytes to send.
Please note that the maximum size of the message depends on the architecture of the device:
oX32 architecture: 1024 bytes, oNX32 architecture: 4096 bytes. oNX32L architecture: 16384 bytes.
Returns: INT
0
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- Message was sent.
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1
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- Invalid handle.
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2
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- Not connected to the MQTT server.
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3
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- Invalid parameter.
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4
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- A publish is already in progress.
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5
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- Message transmission interrupted due to connection loss. The message will be transmitted again when connection is reestablished.
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Declaration:
FUNCTION mqttPublish : INT;
VAR_INPUT
handle : INT;
topic : STRING;
qos : SINT;
retained : BOOL;
data : PTR;
size : INT;
END_VAR;
Example:
INCLUDE rtcu.inc
VAR
mqtt : INT;
text : STRING;
topic : STRING;
time : TON;
temp : DINT;
rc : INT;
buf : ARRAY [1..15] OF SINT;
END_VAR;
PROGRAM example;
DebugMsg(message := "Initialize GPRS...");
gsmPower(power := ON);
gprsOpen();
WHILE NOT gprsConnected() DO
DebugMsg(message := "Waiting for cellular connection...");
Sleep(delay := 2500);
END_WHILE;
DebugMsg(message := "Initialize MQTT...");
text := strFormat(format := "RTCU_\4", v4 := boardSerialNumber());
topic := strFormat(format := "RTCU/\4/temperature", v4 := boardSerialNumber());
mqtt := mqttOpen(ip := "test.mosquitto.org", port := 1883, clientid := text);
DebugFmt(message := "MQTT handle= \1", v1 := mqtt);
IF NOT mqttConnected(handle := mqtt) THEN
rc := mqttStatus(handle := mqtt);
DebugFmt(message := "Connection failed, Status=\1", v1 := rc);
END_IF;
time(trig := OFF, pt := 60000);
BEGIN
time(trig := ON);
IF time.q THEN
temp := boardTemperature();
text := dintToStr(v := temp / 100) + "." + dintToStr(v := abs(v := temp MOD 100));
strToMemory(dst := ADDR(buf), str := text, len := strLen(str := text));
rc := mqttPublish(
handle := mqtt,
topic := topic,
qos := 1,
retained := FALSE,
data := ADDR(buf),
size := strLen(str := text)
);
DebugFmt(message := "Published= \1", v1 := rc);
time(trig := OFF);
END_IF;
END;
END_PROGRAM;
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