Arduino Calling HTTP POST method using SIM800L (DNS ERROR)

Using Arduino Programming Questions
1

Hi guys

I'm trying call a HTTP POST method using SIM800L and an ARDUINO MEGA

I created an endpoint in firebase

and I'm trying to send a post request to this endpoint sending a JSON

I tested it on insomnia and the endpoint is working normally

However, when I try to execute the post method using the Arduino code below, I am unsuccessful.

#define TINY_GSM_MODEM_SIM800  // Defina o modelo do modem aqui

#include <TinyGPS.h>
#include <ArduinoJson.h>
#include <TinyGsmClient.h>
String responseGSM;
String imei;
int signal = 0;
TinyGPS gps1;

String apn = "timbrasil.br";                    //APN
String apn_u = "";                     //APN-Username
String apn_p = "";                     //APN-Password
String url = "https://myEndpoint";

StaticJsonDocument<256> jsonDocument;

// Inicializa os objetos
TinyGsm modem(Serial2);

void setup() {
  Serial.begin(9600);       // Monitor Serial
  Serial1.begin(9600);      // GPS - RX:19 TX:18 - (Arduino mega2560)
  Serial2.begin(9600);      // GSM - RX:17 TX:16 - (Arduino mega2560)
  
  delay(10000);
  Serial.println("Aguardando sinal dos satélites...");

  // Inicializa o modem
  modem.restart();
  delay(10000);
  gsm_config_gprs();

  jsonDocument["imei"] = modem.getIMEI();
}

void loop() {
  bool recebido = false;
  static unsigned long delayPrint;
  
  // Módulo GPS
  while (Serial1.available()) {
    char cIn = Serial1.read();
    recebido = (gps1.encode(cIn) || recebido);
  }

  if (recebido && ((millis() - delayPrint) > 1000)) {
    delayPrint = millis();
    
    float latitude, longitude;
    unsigned long idadeInfo;

    gps1.f_get_position(&latitude, &longitude, &idadeInfo);

    if (latitude != TinyGPS::GPS_INVALID_F_ANGLE) {
      jsonDocument["latitude"] = latitude;
    }

    if (longitude != TinyGPS::GPS_INVALID_F_ANGLE) {
      jsonDocument["longitude"] = longitude;
    }

    int ano;
    byte mes, dia, hora, minuto, segundo, centesimo;
    gps1.crack_datetime(&ano, &mes, &dia, &hora, &minuto, &segundo, &centesimo, &idadeInfo);

    float altitudeGPS = gps1.f_altitude();
    if ((altitudeGPS != TinyGPS::GPS_INVALID_ALTITUDE) && (altitudeGPS != 1000000)) {
      //jsonDocument["altitude_cm"] = altitudeGPS;
    }

    float velocidade = gps1.f_speed_kmph();
    //jsonDocument["velocidade_kmph"] = velocidade;

    unsigned long sentido = gps1.course();
    //jsonDocument["sentido_grau"] = float(sentido) / 100;

    unsigned short satelites = gps1.satellites();
    unsigned long precisao = gps1.hdop();

    if (satelites != TinyGPS::GPS_INVALID_SATELLITES) {
      //jsonDocument["satelites"] = satelites;
    }

    if (precisao != TinyGPS::GPS_INVALID_HDOP) {
      //jsonDocument["precisao_cent"] = precisao;
    }

    String jsonString;
    serializeJson(jsonDocument, jsonString);
    Serial.println(modem.getSignalQuality());
    Serial.println(jsonString);

    // Envia a requisição HTTP POST
    delay(2000);
    signal = modem.getSignalQuality();
     Serial.println("qualidade do sinal:");
    Serial.println(signal);
    if(signal >= 10 && signal <= 31){
      gsm_http_post(jsonString);
    }
    
  }
}

void gsm_http_post( String postdata) {
  Serial.println(" --- Start GPRS & HTTP --- ");
  sendCommand(Serial2, "AT+SAPBR=1,1");
  sendCommand(Serial2, "AT+SAPBR=2,1");
  sendCommand(Serial2, "AT+HTTPINIT");
  sendCommand(Serial2, "AT+HTTPPARA=CID,1");
  sendCommand(Serial2, "AT+HTTPPARA=URL," + url);
  sendCommand(Serial2, "AT+HTTPPARA=CONTENT,application/x-www-form-urlencoded");
  sendCommand(Serial2, "AT+HTTPDATA=192,5000");
  sendCommand(Serial2, postdata);
  sendCommand(Serial2, "AT+HTTPACTION=1");
  sendCommand(Serial2, "AT+HTTPREAD");
  sendCommand(Serial2, "AT+HTTPTERM");
  sendCommand(Serial2, "AT+SAPBR=0,1");
}

void gsm_config_gprs() {
  Serial.println(" --- CONFIG GPRS --- ");
  sendCommand(Serial2, "AT+SAPBR=3,1,Contype,GPRS");
  sendCommand(Serial2, "AT+SAPBR=3,1,APN," + apn);
  if (apn_u != "") {
    sendCommand(Serial2, "AT+SAPBR=3,1,USER," + apn_u);
  }
  if (apn_p != "") {
    sendCommand(Serial2, "AT+SAPBR=3,1,PWD," + apn_p);
  }
}

void sendCommand(HardwareSerial &serial, String command) {
  serial.println(command);
  long wtimer = millis();
  while (wtimer + 3000 > millis()) {
    while (serial.available()) {
      Serial.write(serial.read());
    }
  }
  Serial.println();
}

String readResponse(HardwareSerial &serial) {
  String response = "";
  while (serial.available()) {
    char c = serial.read();
    response += c;
  }
  return response;
}

I tried to base myself by seeing this documentation

When executing the commands, I get a DNS ERROR

+HTTPACTION: 1,603,0

600 Not HTTP PDU
601 Network Error
602 No memory
603 DNS Error
604 Stack Busy

console with at command responses

Aguardando sinal dos satélites...
 --- CONFIG GPRS --- 

Call Ready

SMS Ready

*PSUTTZ: 2024,8,27,17,53,28,"-12",
OK


OK

19
{"imei":"867372050747224","latitude":-3.754134,"longitude":-38.51607}
qualidade do sinal:
19
 --- Start GPRS & HTTP --- 

OK


+SAPBR: 1,1,"100.115.159.171"

OK


OK


OK


OK


OK


DOWNLOAD

OK


OK


+HTTPACTION: 1,603,0


OK


OK


OK

in short

When I test the endpoint through insomnia passing the following json it works

{"imei":"867372050747224","latitude":-3.754134,"longitude":-38.51607}

the data are
stored correctly in firestore

however, in the code passing the same json it does not work

the code runs without any apparent errors but does not add any records to firebase

Would anyone have any tips to help me?

2

JSON is Content-Type: application/json, not x-www-form-urlencoded

What does the hard-coded "HTTPDATA=192,5000" mean? Usually with HTTP, the length of the JSON is included in the request.

3

This is actually something to be adjusted in my code

but I saw that the return
+HTTPACTION: 1,603,0

this means that
1 - http post
603 - DNS Error
0 - size of returned data

i.e. I am getting DNS error

Thank you for the changes you suggested

Would you also have any tips for this DNS error?