Sending a char array using RF24Network on Arduino

Question

I am trying to use the RF24Network library to create a sensor network in which the root node connects to an MQTT broker using the PubSubCient library.

I have done a basic test which relays the MQTT topic and message payload from MQTT to one other node in the network, it does this by using sprintf to create a delimited string of the current millis() time on the root node, the topic and message which is stored in a car array of size 200 (as the size of the RF payload must be predefined), I can see from serial output that this is being done correctly.

However from the serial output of the receiving node I find that only the first 24 characters of the string are being received and I am out of ideas as to why this is the case.

Code for sending node:

void ByteToChar(byte* bytes, char* chars, unsigned int count){
    for(unsigned int i = 0; i < count; i++)
         chars[i] = (char)bytes[i];
    chars[count] = '\0';
}

void callback(char* topic, byte* message, unsigned int length) {
  Serial.println("Sending...");

  char buf[length + 1];
  ByteToChar(message, buf, length);

  char payload[200];
  sprintf(payload, "%lu:%s:%s", millis(), topic, buf);

  Serial.println(payload);
  Serial.println(sizeof(payload));

  RF24NetworkHeader header(other_node);
  bool ok = network.write(header, payload, sizeof(payload));
  if (ok)
    Serial.println("ok.");
  else
    Serial.println("failed.");

  free(payload);
}

And receiving node:

while ( network.available() )
  {
    RF24NetworkHeader header;
    char payload[200];
    memset(payload, 0, 200);
    network.read(header, &payload, sizeof(payload));

    Serial.println(payload);
    Serial.println(sizeof(payload));
    free(payload);
  }

It's not impossible that I have just overlooked something very simple. Any help is greatly appreciated.

Edit: This would probably be helpful, this is the data I am sending from the root node: 4203:in_3:hello world again

and this is what I get: 4203:in_3:hello world ag

Answer 1

Looking into the source of size_t RF24Network::read

bufsize = min(maxlen,frame_size-sizeof(RF24NetworkHeader));

That are at most 24 bytes.

Answer 2

I have tried payloads larger than 24 bytes, it works. Somehow, the lib supports a FRAGMENTATION feature. 72-byte payload works on UNO, but not bigger.

https://tmrh20.github.io/RF24Network/AdvancedConfig.html