如何在 C++ 中使用 libmosquitto 和 SSL/TLS 连接到 mqtt 代理答案

【问题标题】：How to connect to mqtt broker using libmosquitto and SSL/TLS in C++如何在 C++ 中使用 libmosquitto 和 SSL/TLS 连接到 mqtt 代理
【发布时间】：2019-03-18 18:10:46
【问题描述】：

我正在尝试订阅使用 SSL/TLS 对客户端进行身份验证的 mqtt 代理。我使用libmosquitto 来做到这一点。

我运行此代码来执行订阅

#include <csignal>
#include <iostream>
#include <sys/types.h>
#include <unistd.h>

#include <mosquitto.h>

#define WITH_AUTHENTICATION

#define MQTT_HOST       "exmaple.com"
#define MQTT_PORT       8883
#define TARGET_USER     "use"
#define TARGET_PW       "password"
#define TARGET_TOPIC    "/example-topic"
#define CERTIFICATE     "/home/luca/TRIALS/tryMqttS/cert.pem"

using namespace std;

static int run  = 1;




void signalHandler (int s) {
    run = 0;
}




void messageCallback (struct mosquitto *mosq, void *obj, const struct mosquitto_message *message) {
    bool match  = 0;
    cout << "got message  " << (char *) message->payload << "  from topic  " << message->topic << endl;
}




int main(int argc, char *argv[])
{
    uint8_t reconnect       = true;
    string clientID         = "mosquitto_client_" + to_string (getpid());
    struct mosquitto *mosq  = nullptr;
    int resCode             = 0;

    signal (SIGINT, signalHandler);
    signal (SIGTERM, signalHandler);

    mosquitto_lib_init ();

    mosq    = mosquitto_new (clientID.c_str(), true, 0);

    if(mosq){
        mosquitto_message_callback_set (mosq, messageCallback);

#ifdef WITH_AUTHENTICATION
        cout << "Pw set result:             " << mosquitto_strerror (mosquitto_username_pw_set  (mosq, TARGET_USER, TARGET_PW)) << endl;
        cout << "Tls insecure set result:   " << mosquitto_strerror (mosquitto_tls_insecure_set (mosq, false)) << endl;
        cout << "Tls opts set result:       " << mosquitto_strerror (mosquitto_tls_opts_set     (mosq, 1, NULL, NULL)) << endl;
        cout << "Tls set result:            " << mosquitto_strerror (mosquitto_tls_set (mosq, CERTIFICATE, nullptr, nullptr, nullptr, /*pw_cb * */ nullptr)) << endl;
#endif


        cout << "Connection result:         " << mosquitto_strerror (mosquitto_connect (mosq, MQTT_HOST, MQTT_PORT, 60)) << endl;
        cout << "Subscription result:       " << mosquitto_strerror (mosquitto_subscribe (mosq, NULL, TARGET_TOPIC, 0)) << endl;


        while (run) {
            resCode = mosquitto_loop (mosq, 20, 1);
            if (resCode) {
                cout << "ERROR:  " << mosquitto_strerror (resCode) << "  (" << resCode << ")\n";
                sleep(1);
                mosquitto_reconnect (mosq);
            }
        }

        mosquitto_destroy (mosq);
    }

    mosquitto_lib_cleanup ();

    return 0;
}

但输出每次都是一样的：

Connection result:    0
Subscription result:  0
ERROR:  The connection was lost.  (7)
ERROR:  The connection was lost.  (7)
ERROR:  The connection was lost.  (7)
ERROR:  The connection was lost.  (7)
ERROR:  The connection was lost.  (7)
ERROR:  The connection was lost.  (7)
ERROR:  The connection was lost.  (7)
ERROR:  The connection was lost.  (7)
ERROR:  The connection was lost.  (7)
ERROR:  The connection was lost.  (7)
ERROR:  The connection was lost.  (7)

使用外部工具（例如mqttfx）并使用相同的身份验证凭据，订阅很好，我可以接收主题上发布的消息。

如何正确执行订阅？是否缺少一些设置？

【问题讨论】：

当您尝试连接时代理日志会显示什么内容？
很遗憾，我无法访问运行代理的机器
您的代码显示为localhost，那么您为什么无权访问代理日志？
是的，但是我写不出真实的IP地址
好吧，然后使用example.com 之类的东西，因为localhost 具有非常具体的含义（它与任何外部设备的行为都不同），并暗示了一堆在这里不是这样的东西。

标签： c++ ssl mqtt libmosquitto

【解决方案1】：

订阅MQTT Broker需要在您指定的主机和端口上运行。在您的代码中，您使用exmaple.com（我认为您的意思是example.com）作为MQTT Broker 主机。此主机上没有运行Broker。所以连接不上。使用test.mosquitto.org 托管公开可用的MQTT Broker。

或者您可以在您的计算机上的端口8883 上运行您自己的MQTT Broker。然后你可以使用localhost进行连接

【讨论】：