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I want to use hiveMQ public broker in my project that's the same broker as what available in PubSubClient esp8266 examples but when I change WiFi SSID and password in example and upload it I got this output:

Connecting to <SSID NAME>
........
WiFi connected
IP address: 
192.168.1.14
Attempting MQTT connection...failed, rc=-2 try again in 5 seconds
Attempting MQTT connection...failed, rc=-2 try again in 5 seconds
Attempting MQTT connection...failed, rc=-4 try again in 5 seconds
Attempting MQTT connection...failed, rc=-4 try again in 5 seconds
Attempting MQTT connection...failed, rc=-4 try again in 5 seconds
Attempting MQTT connection...

I tried this with pubsub client v2.8/v2.6/v2.4 and esp32 latest version and esp8266 latest version and 2.3

in response to the comment as I said my code is esp8266_basic example in the PubSub client examples and here is my code:

#include <ESP8266WiFi.h>
#include <PubSubClient.h>

// Update these with values suitable for your network.

const char* ssid = "<SSID>";
const char* password = "<PASS>";
const char* mqtt_server = "broker.mqtt-dashboard.com"; //tested with broker.mqttdashboard.com

WiFiClient espClient;
PubSubClient client(espClient);
long lastMsg = 0;
char msg[50];
int value = 0;

void setup() {
  pinMode(BUILTIN_LED, OUTPUT);     // Initialize the BUILTIN_LED pin as an output
  Serial.begin(115200);
  setup_wifi();
  client.setServer(mqtt_server, 1883); //8000 and 1883 tested
  client.setCallback(callback);
}

void 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());
}

void callback(char* topic, byte* payload, unsigned int length) {
  Serial.print("Message arrived [");
  Serial.print(topic);
  Serial.print("] ");
  for (int i = 0; i < length; i++) {
    Serial.print((char)payload[i]);
  }
  Serial.println();

  // Switch on the LED if an 1 was received as first character
  if ((char)payload[0] == '1') {
    digitalWrite(BUILTIN_LED, LOW);   // Turn the LED on (Note that LOW is the voltage level
    // but actually the LED is on; this is because
    // it is acive low on the ESP-01)
  } else {
    digitalWrite(BUILTIN_LED, HIGH);  // Turn the LED off by making the voltage HIGH
  }

}

void reconnect() {
  // Loop until we're reconnected
  while (!client.connected()) {
    Serial.print("Attempting MQTT connection...");
    // Attempt to connect
    if (client.connect("ESP8266Client")) {
      Serial.println("connected");
      // Once connected, publish an announcement...
      client.publish("outTopic", "hello world");
      // ... and resubscribe
      client.subscribe("inTopic");
    } else {
      Serial.print("failed, rc=");
      Serial.print(client.state());
      Serial.println(" try again in 5 seconds");
      // Wait 5 seconds before retrying
      delay(5000);
    }
  }
}
void loop() {

  if (!client.connected()) {
    reconnect();
  }
  client.loop();

  long now = millis();
  if (now - lastMsg > 2000) {
    lastMsg = now;
    ++value;
    snprintf (msg, 75, "hello world #%ld", value);
    Serial.print("Publish message: ");
    Serial.println(msg);
    client.publish("outTopic", msg);
  }
}

on esp32 I remove pinMode(BUILTIN_LED, OUTPUT); // Initialize the BUILTIN_LED pin as an output and

  if ((char)payload[0] == '1') {
    digitalWrite(BUILTIN_LED, LOW);   // Turn the LED on (Note that LOW is the voltage level
    // but actually the LED is on; this is because
    // it is acive low on the ESP-01)
  } else {
    digitalWrite(BUILTIN_LED, HIGH);  // Turn the LED off by making the voltage HIGH
  }

sections and includes

and sometimes output is like this:

Attempting MQTT connection...connected
Attempting MQTT connection...connected
Attempting MQTT connection...failed, rc=-4 try again in 5 seconds
Attempting MQTT connection...connected
Attempting MQTT connection...connected
Attempting MQTT connection...connected
Attempting MQTT connection...failed, rc=-4 try again in 5 seconds
Attempting MQTT connection...connected
Attempting MQTT connection...connected
Attempting MQTT connection...failed, rc=-4 try again in 5 seconds
Attempting MQTT connection...failed, rc=-4 try again in 5 seconds
Attempting MQTT connection...connected
Attempting MQTT connection...connected
Attempting MQTT connection...connected
Attempting MQTT connection...connected
Attempting MQTT connection...connected
Attempting MQTT connection...connected
Attempting MQTT connection...connected
Attempting MQTT connection...connected
Attempting MQTT connection...failed, rc=-4 try again in 5 seconds
Attempting MQTT connection...failed, rc=-4 try again in 5 seconds
Attempting MQTT connection...connected
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  • Obviously there is a problem but beyond that who knows? All you have said is that this is an ESP8266 and you get getting an MQTT connection error. Please add some additional details. – jwh20 Jan 1 at 11:37
  • 1
    It is not at all clear what you are asking. Does your code make a succesfull MQTT connection, does it not connect, does it connect sometimes or does it disconnect sometimes? Does it work when it's connected? Why did you remove the pinMode() on the ESP32. BTW why do you use the deprecated BUILTIN_LED instead of LED_BUILTIN ? – StarCat Jan 1 at 15:18
  • @StarCat thanks for commenting, about removing pinMode, I do it because I just need to test it for MQTT and BUILTIN_LED makes a compiler error that says that's not declared and that's about LED and not important for connection and absolutely board doesn't connect to the broker (some times in my tests on another version of Arduino IDE on an older system I got connection successful message but nothing published or subscribed) – radinParsaei Jan 1 at 16:29
  • rc=-4 means MQTT_CONNECTION_TIMEOUT, rc=-2 means MQTT_CONNECT_FAILED, given that you are accessing a public-facing MQTT web service site, the chances are you would need to connect it with username and password in addition to the ClinetID, so you might need to change client.connect("ESP8266Client") to (mqttClient.connect(clientID,mqttUserName,mqttPass)). – hcheung Jan 2 at 1:59
2

I found this video as a problem solver, This may help you. All MQTT Errors explained very well and Suggester Different troubleshooting techniques https://youtu.be/CbodTTk-D18

1
  • Thanks a lot for your answer But as I mentioned that issue was made because I live in a country with network censorship. When I changed my network provider everything worked fine. Finally after a week the first network provider I tested with fixed that issue and now everything works – radinParsaei Jun 22 at 18:26
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all things are OK and the problem is about my network I think there blocked MQTT (cause I couldn't connect any broker and not just hiveMQ) or other related things cause also my notebook doesn't connect I changed my network provider and the problem fixed

if you ran into the same issue, check other stuff and finally check with a computer in your network (don't use things like http://www.hivemq.com/demos/websocket-client/)

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