#include <WiFi.h>
#include <PubSubClient.h>
// Wi-Fi Credentials
const char* ssid = "Wokwi-GUEST";
const char* password = "";
// MQTT Broker Settings
const char* mqtt_server = "mqtt.eclipseprojects.io"; // Example public broker
const char* mqtt_topic = "esp32/test/topic36"; // Topic to subscribe to
WiFiClient espClient;
PubSubClient client(espClient);
// Function to connect to Wi-Fi
void connectWiFi() {
 // Serial.println("Connecting to WiFi...");
 WiFi.begin(ssid, password);
 while (WiFi.status() != WL_CONNECTED) {
 delay(1000);
 Serial.println("Connecting to WiFi...");
 }
 Serial.println("WiFi Connected");
}
// Function to connect to the MQTT broker
void connectMQTT() {
 while (!client.connected()) {
 Serial.println("Attempting MQTT connection...");
 // Create a unique client ID
 String clientId = "ESP32Client-" + String(random(0xffff), HEX);
 if (client.connect(clientId.c_str())) {
 Serial.println("Connected to MQTT broker");
 // Subscribe to the topic
 client.subscribe(mqtt_topic);
 } else {
 Serial.print("Failed to connect, state: ");
 Serial.println(client.state());
 delay(5000); // Retry after 5 seconds
 }
 }
}
// MQTT Callback to handle incoming messages
void callback(char* topic, byte* payload, unsigned int length) {
 String message = "";
 for (int i = 0; i < length; i++) {
 message += (char)payload[i];
 }
 Serial.print("Received message: ");
 Serial.println(message);
}
void setup() {
 Serial.begin(115200); // Initialize Serial Monitor
 connectWiFi(); // Connect to Wi-Fi
 client.setServer(mqtt_server, 1883); // Set MQTT broker address and port
 client.setCallback(callback); // Set the callback function to handle messages
 connectMQTT(); // Ensure MQTT connection is established
}
void loop() {
 if (!client.connected()) {
 connectMQTT(); // Reconnect if the connection is lost
 }
 client.loop(); // Keep the connection alive and listen for messages
 delay(100); // Small delay for stability
}