Using JSONBufferWriter to append to an array inside buffer after initial write

[ozzie]

I have a program that I am planning to implement publishing of json data with, but I have encountered a use case that I can’t find well documented, or just may not be possible.

Problem description

My use case looks something like this

int publishBufferLen = 678;
// make a buffer on the heap to store our sensor readings until we are ready to publish
char *publishBuffer = new char[publishBufferLen];
memset(publishBuffer, 0, publishBufferLen);

// add a reading to the buffer if there is room, else publish readings
void addReadingToBuffer(float value)
{
    if (sizeof(publishBuffer) == 0) // if the buffer is empty
    {
        JSONBufferWriter writer(testJsonBuffer, jsonBufferLen);
        writer.beginObject();
        writer.name("d").beginArray();
            writer.value(value);
        writer.endArray();
        writer.endObject();
    }
    else if (sizeof(publishBuffer) + sizeof(String(value)) < publishBufferLen) // append to the array
    {
        /**
            This is where I would like to append to the array,
            previously the data structure was defined as:
            
            {
                "d": [ ]
            }

            I would like to append a reading to the json buffer 

            {
                "d": [ 123.123 ]
            }

            Like so
        */
    }
    else // the data wont fit in the buffer, publish what we have and create a new one
    {
        publish("test", publishBuffer, PRIVATE);
        delete[] publishBuffer;
        publishBuffer = new char[publishBufferLen];
        addReadingToBuffer(value);
    }
}

void loop()
{
    delay(5000);
    addReadingToBuffer(sensor.getReading());
}

Question

If possible, how can I use the JSONBufferWriter object to append this data to publishBuffer in this way?

[ozzie]

The solution to the problem ended up being this:

Declare the json writer on the heap, and do not close the array until you are finished writing objects in it.