very long and high speed message publish

[rvxfahim]

I am receiving multiple CAN bus message every 20ms which is decoded and arranged as a JSON message and sent to the publishing task using FreeRTOS queue. the message is 500 bytes long. I am confused how should I set the setspinTimeout (can't understand what it even does by looking at the code comments in the header files) and how often should i call spinOnce.

#include <ros.h>
#include <std_msgs/String.h>

ros::NodeHandle nh;
std_msgs::String str_msg;
ros::Publisher chatter("CAN_Data", &str_msg);

void messageSenderTask(void *pvParameters)
{
  // ... [initialization and other code]

  while (true)
  {
    char message[JSON_BUFFER_SIZE];
    if (xQueueReceive(messageQueue, message, (TickType_t)0))
    {
      if (nh.connected())
      {
        str_msg.data = message;
        chatter.publish(&str_msg);
      }
    }

    vTaskDelayUntil(&xLastWakeTime, pdMS_TO_TICKS(10));
  }
}

void setup()
{
  // ... [initialization and other setup code]

  nh.getHardware()->setConnection(server, serverPort);
  nh.initNode();
  nh.advertise(chatter);
  nh.setSpinTimeout(50);

  // ... [creation of other tasks]
}

void loop()
{
  nh.spinOnce();
  taskYIELD();
}

some questions:
does calling publish return immediately and does it write all the 500 bytes to the rosserial server node in one publish call ? Can i call publish multiple times in a subroutine without calling spinOnce or does each publish call needs spinOnce call ?
looking for advice on any modifications to this code for this purpose.
EDIT:
board is OLIMEX ESP32 EVB working with Ethernet connection