char message[600];  // Buffer to hold the message

void setup() {
  Serial.begin(115200);
  while (!Serial);
  Serial.setTimeout(500);

  Serial.println("Type a message (end with Enter):");
}

void loop() {

  // Serial.print("x ");
  delay(10);

}

void serialEvent() {
  uint16_t bytesRead;
  do {
    bytesRead = Serial.readBytesUntil('\n', message, sizeof(message) - 1);
  } while(bytesRead == 0 || (message[0] == '<' && bytesRead == 1));
  
  if (message[bytesRead - 1] == '<') {
    bytesRead-- ;
  }

  message[bytesRead] = 0;  // Null-terminate the string
  Serial.println();
  Serial.print(bytesRead);
  Serial.print(" bytes message: ");
  Serial.print(message);
  Serial.println("«");
}