ESP32无法连接HiveMQ MQTT Broker问题求助

问题背景 #

主从架构项目，主控节点从ESP8266切换为ESP32后，无法连接HiveMQ Broker，串口返回连接失败错误码rc=-2，但WiFi连接正常。

代码片段 #

#include "DHT.h"
#include <BluetoothSerial.h>
#include <WiFi.h>
#include <WiFiClientSecure.h>
#include <PubSubClient.h>

#define DHTPIN 4
#define DHTTYPE DHT11

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

// MQTT
const char *MQTT_SERVER = "x.s2.eu.hivemq.cloud";
const int MQTT_PORT = 8883;  // Use an integer for MQTT port
const char *MQTT_USERNAME = "x";
const char *MQTT_PASSWORD = "x";
const char *MQTT_CLIENT_ID = "esp32_master";

DHT dht(DHTPIN, DHTTYPE);
BluetoothSerial SerialBT;
WiFiClientSecure espClient;
PubSubClient client(espClient);
char sensorData[50];

/****** root certificate *********/
static const char *root_ca PROGMEM = R"EOF(
-----BEGIN CERTIFICATE-----
MIIFazCCA1OgAwIBAgIRAIIQz7DSQONZRGPgu2OCiwAwDQYJKoZIhvcNAQELBQAw
TzELMAkGA1UEBhMCVVMxKTAnBgNVBAoTIEludGVybmV0IFNlY3VyaXR5IFJlc2Vh
cmNoIEdyb3VwMRUwEwYDVQQDEwxJU1JHIFJvb3QgWDEwHhcNMTUwNjA0MTEwNDM4
WhcNMzUwNjA0MTEwNDM4WjBPMQswCQYDVQQGEwJVUzEpMCcGA1UEChMgSW50ZXJu
ZXQgU2VjdXJpdHkgUmVzZWFyY2ggR3JvdXAxFTATBgNVBAMTDElTUkcgUm9vdCBY
MTCCAiIwDQYJKoZIhvcNAQEBBQADggIPADCCAgoCggIBAK3oJHP0FDfzm54rVygc
h77ct984kIxuPOZXoHj3dcKi/vVqbvYATyjb3miGbESTtrFj/RQSa78f0uoxmyF+
0TM8ukj13Xnfs7j/EvEhmkvBioZxaUpmZmyPfjxwv60pIgbz5MDmgK7iS4+3mX6U
A5/TR5d8mUgjU+g4rk8Kb4Mu0UlXjIB0ttov0DiNewNwIRt18jA8+o+u3dpjq+sW
T8KOEUt+zwvo/7V3LvSye0rgTBIlDHCNAymg4VMk7BPZ7hm/ELNKjD+Jo2FR3qyH
B5T0Y3HsLuJvW5iB4YlcNHlsdu87kGJ55tukmi8mxdAQ4Q7e2RCOFvu396j3x+UC
B5iPNgiV5+I3lg02dZ77DnKxHZu8A/lJBdiB3QW0KtZB6awBdpUKD9jf1b0SHzUv
KBds0pjBqAlkd25HN7rOrFleaJ1/ctaJxQZBKT5ZPt0m9STJEadao0xAH0ahmbWn
OlFuhjuefXKnEgV4We0+UXgVCwOPjdAvBbI+e0ocS3MFEvzG6uBQE3xDk3SzynTn
jh8BCNAw1FtxNrQHusEwMFxIt4I7mKZ9YIqioymCzLq9gwQbooMDQaHWBfEbwrbw
qHyGO0aoSCqI3Haadr8faqU9GY/rOPNk3sgrDQoo//fb4hVC1CLQJ13hef4Y53CI
rU7m2Ys6xt0nUW7/vGT1M0NPAgMBAAGjQjBAMA4GA1UdDwEB/wQEAwIBBjAPBgNV
HRMBAf8EBTADAQH/MB0GA1UdDgQWBBR5tFnme7bl5AFzgAiIyBpY9umbbjANBgkq
hkiG9w0BAQsFAAOCAgEAVR9YqbyyqFDQDLHYGmkgJykIrGF1XIpu+ILlaS/V9lZL
ubhzEFnTIZd+50xx+7LSYK05qAvqFyFWhfFQDlnrzuBZ6brJFe+GnY+EgPbk6ZGQ
3BebYhtF8GaV0nxvwuo77x/Py9auJ/GpsMiu/X1+mvoiBOv/2X/qkSsisRcOj/KK
NFtY2PwByVS5uCbMiogziUwthDyC3+6WVwW6LLv3xLfHTjuCvjHIInNzktHCgKQ5
ORAzI4JMPJ+GslWYHb4phowim57iaztXOoJwTdwJx4nLCgdNbOhdjsnvzqvHu7Ur
TkXWStAmzOVyyghqpZXjFaH3pO3JLF+l+/+sKAIuvtd7u+Nxe5AW0wdeRlN8NwdC
jNPElpzVmbUq4JUagEiuTDkHzsxHpFKVK7q4+63SM1N95R1NbdWhscdCb+ZAJzVc
boyi3B43njTOQ5yOf+1CceWxG1bQVs5ZufpsMljq4Ui0/1lvh+wjChP4kqKOJ2qxq
4RgqsahDYVvTH9w7jXbyLeiNdd8XM2w9U/t7y0Ff/9yi0GE44Za4rF2LN9d11TPA
mRGunUHBcnWEvgJBQl9nJEiU0Zsnvgc/ubhPgXRR4Xq37Z0j4r7g1SgEEzwxA57d
emyPxgcYxn/eR44/KJ4EBs+lVDR3veyJm+kXQ99b21/+jh5Xos1AnX5iItreGCc=
-----END CERTIFICATE-----
)EOF";

void setup() {
  Serial.begin(9600);
  SerialBT.begin("ESP32_Master");
  Serial.println(F("Master has started!"));
  dht.begin();

  if (!connectToWiFi()) {
    // If WiFi connection fails, you might want to handle it accordingly.
    // For simplicity, I'm setting up MQTT only when WiFi is successfully connected.
    espClient.setCACert(root_ca);
    client.setServer(MQTT_SERVER, MQTT_PORT);
  }
}

void loop() {
  if (!client.connected() && WiFi.status() == WL_CONNECTED) reconnect(); // check if client is connected
  handleData();

  // Reading temperature or humidity takes about 250 milliseconds!
  // Sensor readings may also be up to 2 seconds 'old' (it's a very slow sensor)
  int h = dht.readHumidity();
  int t = dht.readTemperature();

  // Check if any reads failed and exit early (to try again).
  if (isnan(h) || isnan(t)) {
    Serial.println(F("Failed to read from DHT sensor!"));
    return;
  }

  String sensorData = "{\"id\":\"0\",\"temperature\":" + String(t) + ",\"humidity\":" + String(h) + "}\n";
  Serial.println(sensorData);

  // Send sensor data to MQTT
  if (client.connected()) {
    client.publish("suhu", sensorData.c_str());
    Serial.println("Data sent to MQTT broker");
  }

  // You can use the sensorData array for other purposes beyond printing
  // For example, you might want to store it in a database, etc.

  delay(10000);  // Adjust the delay according to your requirements
}

void handleData() {
  if (SerialBT.available()) {
    // Read data from slave via Bluetooth
    String data = SerialBT.readStringUntil('\n');

    // Send data to MQTT
    if (client.connected()) {
      client.publish("suhu", data.c_str());
      Serial.println("Data sent to MQTT broker");
    }
  }
}

bool connectToWiFi() {
  Serial.println("Connecting to WiFi");
  WiFi.begin(ssid, password);

  int attempts = 0;
  while (WiFi.status() != WL_CONNECTED && attempts < 10) {
    delay(1000);
    Serial.println(F("Connecting to WiFi..."));
    attempts++;
  }

  if (WiFi.status() == WL_CONNECTED) {
    Serial.println("Connected to WiFi");
    return true;
  } else {
    Serial.println("Failed to connect to WiFi");
    return false;
  }
}

void reconnect() {
  // Loop until we're reconnected
  while (!client.connected()) {
    Serial.print("Attempting MQTT connection...");
    String clientId = "ESP32_Master";
    clientId += String(random(0xffff), HEX);
    // Attempt to connect
    if (client.connect(clientId.c_str(), MQTT_USERNAME, MQTT_PASSWORD)) {
      Serial.println("connected");

      // client.subscribe("led_state");   // subscribe the topics here

    } else {
      Serial.print("failed, rc=");
      Serial.print(client.state());
      Serial.println(" try again in 5 seconds");   // Wait 5 seconds before retrying
      delay(5000);
    }
  }
}

串口输出 #

Connecting to WiFi...
Connecting to WiFi...
Connecting to WiFi...
Connected to WiFi
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=-2 try again in 5 seconds
Attempting MQTT connection...failed, rc=-2 try again in 5 seconds

解决方案 #

1. 修正Setup函数逻辑错误 #

当前代码中if (!connectToWiFi())的逻辑完全颠倒，只有WiFi连接失败时才初始化MQTT参数，这是核心问题。修改为WiFi连接成功后再初始化：

void setup() {
  Serial.begin(9600);
  SerialBT.begin("ESP32_Master");
  Serial.println(F("Master has started!"));
  dht.begin();

  if (connectToWiFi()) {
    // WiFi连接成功后初始化MQTT
    espClient.setCACert(root_ca);
    client.setServer(MQTT_SERVER, MQTT_PORT);
    client.setTimeout(10000); // 增加连接超时时间
  } else {
    Serial.println("WiFi连接失败，无法初始化MQTT");
  }
}

2. 关闭ESP32 WiFi休眠模式 #

ESP32默认的WiFi省电模式可能导致连接不稳定，在WiFi连接函数中添加关闭休眠的代码：

bool connectToWiFi() {
  Serial.println("Connecting to WiFi");
  WiFi.begin(ssid, password);
  WiFi.setSleep(false); // 禁用WiFi休眠

  int attempts = 0;
  while (WiFi.status() != WL_CONNECTED && attempts < 10) {
    delay(1000);
    Serial.println(F("Connecting to WiFi..."));
    attempts++;
  }

  if (WiFi.status() == WL_CONNECTED) {
    Serial.println("Connected to WiFi");
    return true;
  } else {
    Serial.println("Failed to connect to WiFi");
    return false;
  }
}

3. 验证根CA证书有效性 #

HiveMQ Cloud使用Let's Encrypt证书，根证书可能更新。建议通过浏览器访问你的HiveMQ服务器地址（x.s2.eu.hivemq.cloud），查看证书链并导出最新的根CA证书替换现有代码中的证书内容。

4. 确认MQTT参数正确性 #

• 检查用户名、密码是否与HiveMQ控制台配置一致
• 确保HiveMQ ACL规则允许该客户端ID连接
• 确认服务器地址和端口（8883）无误

内容的提问来源于stack exchange，提问作者eXtazzy