MQTT - Create a messages buffer when connection to the broker is down

Code:
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eWON_cyclic_section:

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Rem --- eWON start section: Init Section

eWON_init_section:

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MsgDBPath$ = "/usr/mqttmsg_db.txt"

MaxMsgBufferFileSize% = 5000000 //max size of file used to save msg in bytes



TopicUsed$ = "/topic/flexy/data"



SETSYS INF, "LOAD"

SerNum$ = GETSYS INF, "SERNUM"



//Configure MQTT Connection parameters

MQTT "OPEN", SerNum$ , "ewonsupport.biz"

MQTT "SETPARAM", "PORT", "1883"

MQTT "SETPARAM", "KEEPALIVE", "10"

MQTT "SUBSCRIBE","/cmd/flexy",2



//Launch the MQTT process in the background

SETSYS PRG,"RESUMENEXT",1  //Continue in case of error at MQTT "CONNECT"

MQTT "CONNECT"

ErrorReturned% = GETSYS PRG,"LSTERR"

IF ErrorReturned% = 28 THEN LOGEVENT "[MQTT SCRIPT] WAN interface not yet ready" ,-1

SETSYS PRG,"RESUMENEXT",0



MsgId% = 0

Last_ConnStatus% = -1





//When receiving a message from Broker, "GOTO MqttReceiveMsg"

ONMQTT "GOTO MQTTRECEIVEMSG"  



//WAIT 3 Seconds before starting to send data

ONTIMER 1, "GOTO SENDDATA"

TSET 1,3 

END



SENDDATA:

TSET 1,0 //Stop the timer

//Read MQTT Connection Status ( 5 = Connected, other values = Not connected)

ConnStatus% = MQTT "STATUS"



IF Last_ConnStatus% <> ConnStatus% THEN

  IF ConnStatus% = 5 THEN //Connection is back online

    LOGEVENT "[MQTT SCRIPT] Flexy connected to Broker",100

    @SendSavedEvents() //Parse Saved Messages and publish them

  ELSE

    LOGEVENT "[MQTT SCRIPT] Flexy disconnected from Broker",1

  ENDIF

  Last_ConnStatus% = ConnStatus%

ENDIF



//Compute Message

MyMSG$ = STR$ MsgId% + " - Hello From Flexy " + SerNum$

IF ConnStatus% = 5 THEN //If connected --> Publish

  MQTT "PUBLISH", TopicUsed$ , MyMSG$, 2,0

  PRINT "Message published to the MQTT broker"

ELSE //If not connected --> Save message in file

  @SaveMQTTEvent(MyMSG$)

ENDIF

MsgId% = MsgId% + 1



TSET 1,5 //publish every 5 seconds

END



MQTTRECEIVEMSG:

//Executed when receiving messages from Broker

   MessageQty%=Mqtt "READ"  //Return the number of pending messages

   IF (MessageQty%>0) Then

      MsgTopic$= MQTT "MSGTOPIC"

      MsgData$ = MQTT "MSGDATA"

      LOGEVENT "[MQTT SCRIPT] Message '"+ MsgData$ + "' received on topic " +MsgTopic$,100

      GOTO MQTTRECEIVEMSG

   ENDIF

END



FUNCTION SaveMQTTEvent($Msg$)

 $filesize% = FS "size", MsgDBPath$

 IF $filesize% < MaxMsgBufferFileSize% THEN

   OPEN "file:" + MsgDBPath$ FOR BINARY APPEND AS 1

   PUT 1, $Msg$ + CHR$(10)

   CLOSE 1

   LOGEVENT "[MQTT SCRIPT] Flexy not connected - event saved" ,-1

 ELSE

   LOGEVENT "[MQTT SCRIPT] Flexy not connected - event not saved, buffer file is full" ,-1

 ENDIF

ENDFN



FUNCTION SendSavedEvents()

  $FileExist% = FS "isFile", MsgDBPath$

  IF $FileExist% = -1 THEN

    RETURN

  ENDIF

  

  $NbrMsg% = 0

  OPEN "file:" + MsgDBPath$ FOR BINARY INPUT AS 1

  $Line$ = ""

  $ReadNext:

  IF EOF 1 THEN GOTO $ReadDone

  $CHAR$ = GET 1,1

  IF $CHAR$ = CHR$(10) THEN

    MQTT "PUBLISH",TopicUsed$ , $Line$, 2,0

    $Line$ = ""

    $NbrMsg% = $NbrMsg% + 1

  ELSE

    $Line$ = $Line$ + $CHAR$

  ENDIF

  GOTO $ReadNext

  $ReadDone:

  CLOSE 1

  LOGEVENT "[MQTT SCRIPT] " + STR$ $NbrMsg% + " saved messages published",100

  ERASE MsgDBPath$

ENDFN





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