`SenMLBasePack::toJson`, change `dest` type from stream to byte array

Hi there. I have a suggestion to make. Since it is specifically about this library, I didn't want to put it in the KPN forum. First, I will explain my project setup and then the problem I am facing.

my project details

I am working with Sodaq One / To send and receive data using Lora communication, I am using Sodaq_RN2483 library as suggested in learn.sodaq. I can send and receive raw payloads, hex format via these functions:

uint8_t Sodaq_RN2483::sendReqAck(uint8_t port, const uint8_t* payload, uint8_t size, uint8_t maxRetries){...}
uint16_t Sodaq_RN2483::receive(uint8_t* buffer, uint16_t size, uint16_t payloadStartPosition){...}

using thingML

Next, I tried using the thingsML library and send instructions using this format. I started with a simple example based on getting started and check the result on serialUSB.

#include <thingsml.h>
#include "Arduino.h"

#define debugSerial SERIAL_PORT_MONITOR

SenMLPack device;

SenMLDoubleRecord temperature(THINGSML_TEMPERATURE, SENML_UNIT_DEGREES_CELSIUS);

void setup() {
    while ((!SerialUSB) && (millis() < 10000)){
    // Wait 10 seconds for the Serial Monitor
    }
    debugSerial.begin(57600);
    device.add(temperature);
    delay(1000);
    debugSerial.println("start");
}

void loop(){
    int val = 23;
    temperature.set(val);

    device.toJson(debugSerial,SENML_RAW);        //print to screen
    device.toJson(debugSerial,SENML_HEX);        //print to screen

    delay(60000);
}

Which results in:

start
[{"i_":-24,"v":23.0}]5B7B22695F223A2D32342C2276223A32332E307D5D

The problem

Next, I try to send this data using the functionSodaq_RN2483::sendReqAck. The changes I made in the code above is as follow:

    int val = 23, BUFF_SIZE = 1024;  
    char buff[BUFF_SIZE];

    temperature.set(val);

    BUFF_SIZE = device.toJson(buff,BUFF_SIZE ,SENML_HEX);        //print to screen

Finally, using sendReqAck(1,(uint8_t*)buff, BUFF_SIZE,3) will send completely different data than the buff value. Since it is a stream, the data within the buff is not HEX format. Instead of sending 5B7B (the first two bytes), it would send 35423742.

The question/suggestion

So I thought changing the format would be more helpful. That is if the KPN decoder does not take care of it.

P.S.

For the sake of clarity and being brief, I left out the other parts of my code. I will share them if it's necessary.

kpn-iot / thingsml-c-library