cannot publish data to my local mqtt server - mqtt

Question

Please i wish somebody could help me with this. I've been struggling into it since a couple of weeks, i am so new to that.
I want to send data from ESP32 SIM800L to a mqtt broker.
The mqtt server is running on my local machine and the ESP32 SIM800 can perfectly connect to APN.
I saw many tutorials doing it with WIFI connection but not GPRS(what i am using).
I finally find this: tinyGSM and this :arduino mqtt mongodb
And i adapted it as follows, but still getting connection failed:
// Your GPRS credentials (leave empty, if not needed)
const char apn[] = "internet.tn"; // APN (example: internet.vodafone.pt) use https://wiki.apnchanger.org
const char gprsUser[] = ""; // GPRS User
const char gprsPass[] = ""; // GPRS Password
// SIM card PIN (leave empty, if not defined)
const char simPIN[] = "";
uint32_t lastReconnectAttempt = 0;
// TTGO T-Call pins
#define MODEM_RST 5
#define MODEM_PWKEY 4
#define MODEM_POWER_ON 23
#define MODEM_TX 27
#define MODEM_RX 26
#define I2C_SDA 21
#define I2C_SCL 22
// Set serial for debug console (to Serial Monitor, default speed 115200)
#define SerialMon Serial
// Set serial for AT commands (to SIM800 module)
#define SerialAT Serial1
// Configure TinyGSM library
#define TINY_GSM_MODEM_SIM800 // Modem is SIM800
#define TINY_GSM_RX_BUFFER 1024 // Set RX buffer to 1Kb
#include <Wire.h>
#include <TinyGsmClient.h>
#include <PubSubClient.h>
#ifdef DUMP_AT_COMMANDS
#include <StreamDebugger.h>
StreamDebugger debugger(SerialAT, SerialMon);
TinyGsm modem(debugger);
#else
TinyGsm modem(SerialAT);
#endif
// I2C for SIM800 (to keep it running when powered from battery)
TwoWire I2CPower = TwoWire(0);
const char* broker = "localhost";
const char* topicInit = "GsmClientTest/init";
// Function prototypes
void subscribeReceive(char* topic, byte* payload, unsigned int length);
// TinyGSM Client for Internet connection
// gsm and MQTT related objects
TinyGsmClient client(modem);
PubSubClient mqtt(client);
long mqtttimer = 0; // Timer for counting 5 seconds and retrying mqtt connection
byte mqtttarea = 1;
#define uS_TO_S_FACTOR 1000000 /* Conversion factor for micro seconds to seconds */
#define TIME_TO_SLEEP 3600 /* Time ESP32 will go to sleep (in seconds) 3600 seconds = 1 hour */
void mqttCallback(char* topic, byte* payload, unsigned int len) {
SerialMon.print("Message arrived [");
SerialMon.print(topic);
SerialMon.print("]: ");
SerialMon.write(payload, len);
SerialMon.println();}
boolean mqttConnect() {
SerialMon.print("Connecting to ");
SerialMon.print(broker);
// Connect to MQTT Broker
boolean status = mqtt.connect("GsmClientTest");
// Or, if you want to authenticate MQTT:
//boolean status = mqtt.connect("GsmClientName", "mqtt_user", "mqtt_pass");
if (status == false) {
SerialMon.println(" fail");
return false;
}
SerialMon.println(" success");
mqtt.publish(topicInit, "GsmClientTest started");
// mqtt.subscribe(topicLed);
return mqtt.connected();}
void setup() {
SerialMon.begin(9600);
// Start I2C communication
I2CPower.begin(I2C_SDA, I2C_SCL, 400000);
// Set modem reset, enable, power pins
pinMode(MODEM_PWKEY, OUTPUT);
pinMode(MODEM_RST, OUTPUT);
pinMode(MODEM_POWER_ON, OUTPUT);
digitalWrite(MODEM_PWKEY, LOW);
digitalWrite(MODEM_RST, HIGH);
digitalWrite(MODEM_POWER_ON, HIGH);
// Set GSM module baud rate and UART pins
SerialAT.begin(9600, SERIAL_8N1, MODEM_RX, MODEM_TX);
delay(3000);
// Restart SIM800 module, it takes quite some time
// To skip it, call init() instead of restart()
SerialMon.println("Initializing modem...");
modem.restart();
// use modem.init() if you don't need the complete restart
// Unlock your SIM card with a PIN if needed
if (strlen(simPIN) && modem.getSimStatus() != 3 ) {
modem.simUnlock(simPIN);
}
SerialMon.print("Connecting to APN: ");
SerialMon.print(apn);
if (!modem.gprsConnect(apn, gprsUser, gprsPass)) {
SerialMon.println(" fail");
}
else {
SerialMon.println(" OK");
}
// MQTT Broker setup
mqtt.setServer(broker, 1883);
mqtt.setCallback(mqttCallback);
esp_sleep_enable_timer_wakeup(TIME_TO_SLEEP * uS_TO_S_FACTOR);
}
void loop() {
// This is needed at the top of the loop!
if (!mqtt.connected()) {
SerialMon.println("=== MQTT NOT CONNECTED ===");
// Reconnect every 10 seconds
uint32_t t = millis();
if (t - lastReconnectAttempt > 10000L) {
lastReconnectAttempt = t;
if (mqttConnect()) {
lastReconnectAttempt = 0;
}
}
delay(100);
return;
}
mqtt.publish(topicInit, "Hello");
mqtt.loop();
}

Answer 1

You set the broker's name to localhost:
const char* broker = "localhost";
localhost and the IP address 127.0.0.1 mean "the host that this code is running on". When you're typing commands on the computer running the broker, localhost will mean that computer. There's no way it will work on the ESP32.
You need to name or IP address of the computer running the broker. How you find that will depend on the operating system you're running.
If that computer is on your local network it's probably using a private IP address like 10.0.1.x or 192.168.1.x. If that's the case you'll need to either use port forwarding in your router to forward packets to it (and then you'll use your router's IP address and not your broker's).
If you're using your router's IP address, that can change without warning, so you'll need to use something like Dynamic DNS to keep up to date with its current IP address.
You'll likely be better off running the broker outside of your network on a cloud-based virtual server or by using one of the several commercial MQTT services out there. Most of them have a free tier which will allow a reasonable amount of traffic per month.
Regardless, localhost will never work here. You need the real, public IP address or name of your broker.