How to connect to MQTT broker using Arduino UNO and ESP-01 WiFi module?

[szaboanna01]

I would like to use ESP-01 module and Arduino UNO in order to connect to a WiFi network and connect to a public MQTT broker. However, my code does not work.

#include <SoftwareSerial.h>
#include <WiFiEsp.h>
#include <WiFiEspClient.h>
#include <PubSubClient.h>  // The MQTT library

SoftwareSerial espSerial =  SoftwareSerial(2,3);

const char* ssid = "xxx";              
const char* password = "xxx";  

// Public MQTT broker
const char* mqtt_server = "broker.hivemq.com";
const int mqtt_port =1883;
const int websocket_port=8000;

WiFiEspClient espClient;
PubSubClient client(espClient);

void setup() {
  Serial.begin(9600);
  espSerial.begin(9600);  
  espSerial.setTimeout(50);
  connectToWiFiNetwork();
  
  //connect to MQTT server
  client.setServer(mqtt_server, mqtt_port);
  //client.setCallback(callback);

  randomSeed(micros());
  String clientId = "xxx-";   // Create a random client ID
  clientId += String(random(0xffff), HEX);
  if (client.connect(clientId.c_str())) {
    Serial.println("connected");
  } 
  else {
    Serial.print("\nfailed, rc=");
    Serial.println(client.state());
   }
}

void connectToWiFiNetwork(){
    Serial.println("Connecting to "+String(ssid));
    while (espSerial.available()) espSerial.read();
    espSerial.println("AT+GMR");       // print firmware info
    waitForResponse("OK",1000);
    espSerial.println("AT+CWMODE=1");  // configure as client
    waitForResponse("OK",2000);
    espSerial.print("AT+CWJAP=\"");    // connect to your WiFi network
    espSerial.print(ssid);
    espSerial.print("\",\"");
    espSerial.print(password);
    espSerial.println("\"");
    waitForResponse("OK",10000);
}

boolean waitForResponse(String target1,  int timeout){
    String data="";
    char a;
    unsigned long startTime = millis();
    boolean rValue=false;
    while (millis() - startTime < timeout) {
        while(espSerial.available() > 0) {
            a = espSerial.read();
            /*if (debug)*/ Serial.print(a);
            if(a == '\0') continue;
            data += a;
        }
        if (data.indexOf(target1) != -1) {
            rValue=true;
            break;
        } 
    }
    return rValue;
}

ESP-01 connects to WiFi correctly, however when it reaches the point when it has to connect to MQTT broker, the Serial monitor just give me some stupid characters. What should I do? Could you recommend a solution for it?

[Juraj]

you didn't initialize the WiFiEsp library.
let the library handle the AT commands.