Mosquitto MQTT Client return error 10 in loop_start function call after connect call

Question

I'm writing an MQTT client which simply connects to the broker, and publishes or subscribes to a topic. Here in the program, I try to Connect to Broker and then call the loop_forever() function and is execute successfully and gets a connect acknowledgment at the client side, but instead of loop_forever(), when I called the loop_Start() for the new thread to execute all callback, it failed with the error MOSQ_ERR_NOT_SUPPORTED. Here is a code for the MQTT client for publisher and subscriber.

myMosq.h

#include <mosquittopp.h>
#include <mosquitto.h>

class myMosq : public mosqpp::mosquittopp
{
private:
    const char* host;
    const char* id;
    const char* topic;
    int         port;
    int         keepalive;

    void on_connect(int rc);
    void on_disconnect(int rc);
    void on_publish(int mid);
    void on_message(const struct mosquitto_message* message);

public:
    myMosq(const char* id, const char* _topic, const char* host, int port);
    ~myMosq();
    bool send_message(const char* _message);
};

myMosq.cpp

#include <iostream>

myMosq::myMosq(const char* _id, const char* _topic, const char* _host, int _port) : mosquittopp(_id)
{
    mosqpp::lib_init() ;        // Mandatory initialization for mosquitto library

    this->keepalive = 60;    // Basic configuration setup for myMosq class
    this->id = _id;
    this->port = _port;
    this->host = _host;
    this->topic = _topic;

    int result;
    result = connect_async(host, port, keepalive);     // non blocking connection to broker request
    if (result != MOSQ_ERR_SUCCESS)
    {
        std::cerr << "Error in connect_async" << std::endl;
    }
    result = loop_start();            // Start thread managing connection / publish/subscribe
    //result = loop_forever();            // Start thread managing connection / publish / subscribe
    if (result != MOSQ_ERR_SUCCESS)
    {
        std::cerr << "Error in loop_start: " << (mosq_err_t)result << std::endl;
    }
};

myMosq::~myMosq() 
{
    loop_stop();            // Kill the thread
    mosqpp::lib_cleanup();    // Mosquitto library cleanup
}

bool myMosq::send_message(const  char* _message)
{
    int ret = publish(NULL, this->topic, strlen(_message), _message, 1, false);
    return (ret == MOSQ_ERR_SUCCESS);
}

void myMosq::on_disconnect(int rc) 
{
    std::cout << ">> myMosq - disconnection(" << rc << ")" << std::endl;
}

void myMosq::on_connect(int rc)
{
    if (rc == 0){
        std::cout << ">> myMosq - connected with server" << std::endl;
    }
    else{
        std::cout << ">> myMosq - Impossible to connect with server(" << rc << ")" << std::endl;
    }
}

void myMosq::on_publish(int mid)
{
    std::cout << ">> myMosq - Message (" << mid << ") succeed to be published " << std::endl;
}

void myMosq::on_message(const struct mosquitto_message* message)
{
    std::cout << "Topic: " << message->topic << " Payload: " << message->payload << " Payload_Length: " << message->payloadlen << std::endl;
}

main.cpp

#include <windows.h>
#include <string>

#include "myMosq.h"

void MQTT_Subscriber(myMosq& i_client)
{
    int result = i_client.subscribe(nullptr, "logrequest", 1);
    if (result != MOSQ_ERR_SUCCESS)
    {
        std::cout << "mosquitto : subscriber error: " << mosqpp::strerror(result) << std::endl;
    }
    else
    {
        std::cout << "mosquitto : subscriber : " << result << std::endl;
    }
}

void MQTT_Publisher(myMosq& i_client)
{
    int i = 1;
    std::string message = "I am mosquitto VS pub";
    while (1)
    {
        std::string message1 = message + std::to_string(i);
        if (!i_client.send_message(message1.c_str()))
        {
            break;
        }
        Sleep(2000);
        i++;
    }
}

int main()
{
    std::cout << "In main" << std::endl;

    std::shared_ptr<myMosq> m_client = std::make_shared<myMosq>("dev3_", "logrequest", "127.0.0.1", 1883);

    //MQTT_Publisher(m_client);
    //MQTT_Subscriber(m_client);

    while (1);
    return 0;
}

I used visual studio 2022 and added all mosquito dependencies to the project. while running program with the loop_start() function I get this error: **Error in loop_start: 10**

Answer 1

The docs say loop_Start() returns "MOSQ_ERR_NOT_SUPPORTED if thread support is not available". This will be because "libmosquitto on Windows is currently compiled without thread support". This means you will need to rebuild the library with thread support (instructions).

This should no longer be necessary when version 2.1 is released.