我一直在尝试通过 MQTT 将我的 ESP32 板连接到我的笔记本电脑。我已经在我的笔记本电脑上安装了 Mosquitto MQTT 代理，但我每次都无法连接我的 ESP32。这是我用来检查 MQTT 连接的测试代码。

#include <WiFi.h>
#include <PubSubClient.h>
const char* ssid = "......";              //WiFi Name
const char* password = "......";      //WiFi Password
const char* server= "xxx.xxx.xx.xx";    //RPi or Machine IP on which the broker is

WiFiClient espClient;
PubSubClient client(espClient);

int setup_WiFi(){
  delay(10);
  // We start by connecting to a WiFi network
  Serial.println();
  Serial.print("Connecting to ");
  Serial.println(ssid);

  WiFi.begin(ssid, password);

  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  Serial.println("");
  Serial.println("WiFi connected");
  Serial.println("IP address: ");
  Serial.println(WiFi.localIP());
  Serial.print("Attempting MQTT connection...");
  client.connect("esp32");      
  if (client.connect("esp32")){                 
      Serial.println("connected");
    }
    else {
      Serial.print("failed, rc=");
      Serial.println(client.state());
    }
    return 0;
}

int reconnect() {
  unsigned long startAttemptTime = millis();
  while (!client.connected())  
    {
    Serial.println("Attempting MQTT connection...");
    // Attempt to connect
    if (client.connect("esp32")){
      Serial.println("connected");
    } 
    else {
      Serial.print("failed, rc=");
      Serial.println(client.state());
      Serial.println(" try again in 5 seconds");
      // Wait 5 seconds before retrying
      delay(5000);
    }
  }
  return 0;
}

int send_mqtt(){
  setup_WiFi();
  char sss[15]="Hello World";
   if (!client.connected()){
    reconnect();
  } 
  client.publish("esp32/test", sss);    //send message
  WiFi.disconnect(true);
  Serial.println("Sent");
  return 0;
}
void setup() {
  Serial.begin(115200);
  client.setServer(server, 1883);   //mqtt server details
  setup_WiFi();
  reconnect();
    }

void loop() {
  send_mqtt();
  delay(10000);     //Wait 10 secs before next transmission
}

但每次我得到错误

失败，rc=-2

在过去的两个月左右的时间里，我一直在尝试做同样的事情，但没有成功。同时，我广泛搜索了互联网，看看我做错了什么。我确保两个设备都在同一个局域网上。