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I created a hiveMQ cluster in the HiveMq cloud and created a username and password.

From Paho C library I created MQTTClient_connectOptions and put my username and password as parameters:

#define ADDRESS     "myURL:8883"  // broker address for use in local machine 
#define CLIENTID    "myclientID"
#define TOPIC  "testtopic"
#define TIMEOUT     10000L   // ms
#define USERNAME "myUsername"
#define PASSWORD "myPassword" 

int main(int argc, char* argv[])
{
    /* MQTT Client initialization */ 
    MQTTClient client;
    MQTTClient_connectOptions conn_opts = MQTTClient_connectOptions_initializer;
    MQTTClient_message pubmsg = MQTTClient_message_initializer;
    MQTTClient_deliveryToken token;

    int rc; //status code received from broker
    rc = MQTTClient_create(&client, ADDRESS, CLIENTID,
                            MQTTCLIENT_PERSISTENCE_NONE, NULL);
    printf("Client create reason code: %d\n", rc);
    conn_opts.keepAliveInterval = 20;
    conn_opts.cleansession = 1;
    conn_opts.username = USERNAME;
    conn_opts.password = PASSWORD;
    

    MQTTClient_setCallbacks(client, NULL, connlost, msgarrvd, delivered);

    // checks whether the connection is successful or not
    if ((rc = MQTTClient_connect(client, &conn_opts)) != MQTTCLIENT_SUCCESS)
    {
        printf("Failed to connect, return code %d\n", (MQTTClient_connect(client, &conn_opts)));
        exit(-1);
    }

    MQTTClient_message msg = MQTTClient_message_initializer;
    
    /*
        sending data
        pass sensor data to this function for publishing
    */
    rc = publish_message(client, TOPIC, msg, &token, "4561237891", "23.6", "170.3", "524.08");

    // Disconnect
    int timeout = 100;  //second
    MQTTClient_disconnect(client, timeout);
    MQTTClient_destroy(&client);

    return rc;
}

the MQTTClient_connect cannot connect to the broker and return -1:

Failed to connect, return code -1

I tried connecting with MQTT CLI, it was successful, I published and subscribed to a topic and transferred a msg. So my authentication is wrong.

How to correctly connect with simple authentication with the Paho C library?

Shahriar.M
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  • Is `MQTTClient_create` returning `MQTTCLIENT_SUCCESS` (0)? – Brits Mar 10 '21 at 07:38
  • @Brits yes, it prints: `Client create reason code: 0` – Shahriar.M Mar 10 '21 at 07:52
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    Sorry - thought you were getting -1 back but... Change `printf("Failed to connect, return code %d\n"...` to output the value of `rc` (currently you are calling `MQTTClient_connect` a second time which masks the true error). – Brits Mar 10 '21 at 07:55
  • Does `ADDRESS` include a protocol rather than just a host:port? – hardillb Mar 10 '21 at 07:55
  • @Brits: right, I changed it but it still prints : `Failed to connect, return code -1` – Shahriar.M Mar 10 '21 at 08:00
  • @hardillb: no, just url:port, here it is with a little change: `5xxxxxxxxxxxxxxxxxxxxxxxxx7bcac5.env-1.hivemq.cloud:8883` – Shahriar.M Mar 10 '21 at 08:02

2 Answers2

2

The ADDRESS should be URI not just a host:port combination.

So you need to include tcp:// or ssl:// before the host:port

e.g. ssl://5xxxxxxxxxxxxxxxxxxxxxxxxx7bcac5.env-1.hivemq.cloud:8883

From the Paho C client doc:

Parameters

  • handle -- A pointer to an MQTTClient handle. The handle is populated with a valid client reference following a successful return from this function.
  • serverURI -- A null-terminated string specifying the server to which the client will connect. It takes the form protocol://host:port. Currently, protocol must be tcp or ssl. For host, you can specify either an IP address or a host name. For instance, to connect to a server running on the local machines with the default MQTT port, specify tcp://localhost:1883.
hardillb
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2

As @hardillb already wrote, you need to connect to HiveMQ Cloud with TLS.

You do that by connecting to ssl://<your-address>:<your-port> and enabling it for the client by addding MQTTClient_SSLOptions to your MQTTClient_connectOptions.

MQTTClient_SSLOptions ssl_opts = MQTTClient_SSLOptions_initializer;
ssl_opts.enableServerCertAuth = 0;
conn_opts.ssl = &ssl_opts;

Source: https://www.hivemq.com/blog/mqtt-client-library-pahocclient/

You need the variants with the s (e.g. paho-mqtt3cs) to support SSL/TLS.

This is also used in the source of the command line tools: https://github.com/eclipse/paho.mqtt.c/blob/master/src/samples/paho_cs_pub.c

The github README also shows how to build it (if required): https://github.com/eclipse/paho.mqtt.c/blob/master/README.md

Schäbo
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