Teensy 4.1 crashing when I have poor ethernet connection

[Erikvvats]

Hello,

Please note, I am not sure if I should post this at FNET library or here.

I am using this library to send API Posts to and API endpoint from a Teensy through a drone.

When the drone is far away and there is poor connection, the Teensy 4.1 will crash after a while.

Here is a code snippet for sending API POST:

void NetworkHandler::handle(const Sensor& sensorRef) {

  if (measurementCount < MAX_BUFFER_SIZE) {
    measurementBuffer[measurementCount++] = sensorRef;
  } else {
    // If the buffer is full, roll over and overwrite the oldest measurement
    for (int i = 0; i < MAX_BUFFER_SIZE - 1; i++) {
      measurementBuffer[i] = measurementBuffer[i + 1];
    }
    measurementBuffer[MAX_BUFFER_SIZE - 1] = sensorRef;
  }

  buildJSONDocument();

  for (int attempt = 0; attempt < MAX_RETRIES; attempt++) {
    if (client.connect(server, port)) {
      greenLight();
      Serial.println("Client connected");
      bool success = sendAPIPost();
      Serial.print("API post sent, free ram: "); Serial.println(freeram());
      
      if(client.connected()){
        client.flush();
      }  
      client.stop();  // Close connection after reading the response

      if (success) {
        // Successful response, reset measurementCount  , and exit loop
        measurementCount = 0; 
        break;  
      }
    }
    else {
      Serial.println("Client not connected");
      redLight();
    }

  }

jsonDocument.clear();

  jsonStr[0] = '\0';  // Clear the JSON string
}


bool NetworkHandler::sendAPIPost() {
  
  //Write API POST
  char httpRequest[2048];
  int length = snprintf(httpRequest, sizeof(httpRequest),
    "POST /api/Measurement HTTP/1.1\r\n"
    "User-Agent: python-requests/2.22.0\r\n"
    "Accept-Encoding: gzip, deflate\r\n"
    "Accept: */*\r\n"
    "Connection: keep-alive\r\n"
    "Host: %s:%d\r\n"
    "Content-Type: application/json\r\n"
    "Content-Length: %d\r\n\r\n"
    "%s",
    server, port, strlen(jsonStr), jsonStr);
  

  // Check if snprintf succeeded
  if (length < 0 || length >= sizeof(httpRequest)) {
    Serial.println("Error: HTTP request string is too large.");
    return false;
  }

  //return false;
  // Send the HTTP request headers
  
  // Split data into chunks of 64 bytes
  const int chunkSize = 64;  
  if (client.connected()){
    for (int i = 0; i < length; i += chunkSize) {
      int sizeToWrite = min(chunkSize, length - i);
      client.write((const uint8_t *)&httpRequest[i], sizeToWrite);
      delay(5);
    }
  }else {
    Serial.println("Client not connected before write.");
    return false;
  }
  
  
  //client.write((const uint8_t *)httpRequest, length);


  httpRequest[0] = '\0';  // Clear htttpRequest 

  
  // Wait for SERVER RESPONSE TIMEOUT
  unsigned long startTime = millis();
  while (!client.available()) {
    //Serial.println("Client not available");
    if (millis() - startTime > SERVER_RESPONSE_TIMEOUT) {
      client.flush();
      client.stop();
      return false; // Timeout
    }
  }

  char response[RESPONSE_BUFFER_SIZE];
  int responseIndex = 0;

  while (client.available()) {
    char c = client.read();
    // Ensure we don't exceed buffer size
    if(responseIndex < RESPONSE_BUFFER_SIZE - 1) { 
      response[responseIndex++] = c;
    }
  }
  // Null-terminate the char array
  response[responseIndex] = '\0'; 
  Serial.println(response);

  return (strstr(response, "HTTP/1.1 200 OK") != NULL);  
}

  // JSON document
  StaticJsonDocument<2048> jsonDocument;
  char jsonStr[2048];

I am not using any dynamic memory variables.

Here is a crash report:
CrashReport:
A problem occurred at (system time) 13:32:9
Code was executing from address 0x42D4
CFSR: 82
(DACCVIOL) Data Access Violation
(MMARVALID) Accessed Address: 0x4 (nullptr)
Check code at 0x42D4 - very likely a bug!
Run "addr2line -e mysketch.ino.elf 0x42D4" for filename & line number.
Temperature inside the chip was 65.78 °C
Startup CPU clock speed is 600MHz

And when I am using addr2line I get the following:
fnet_tcp.c:2367

/* Delete the repeated segment.*/
buf = cb->tcpcb_rcvchain;
cb->tcpcb_rcvchain = cb->tcpcb_rcvchain->next_chain;

/* Set the new size of the temporary buffer.*/
cb->tcpcb_count -= cb->tcpcb_rcvchain->total_length;
_fnet_netbuf_free_chain(buf);

Everything works perfect for long periods of time, <2hours when the connection is okay, however only a few minutes when the connection is poor.

I hope to hear from anybody and all help is very much appreciated.