MQTT Topic Variations


I've been back to working on my HomeAssistant integration for pulling CAD data, with a focus on moving to MQTT and away from HTTP polling.

It seems there are a few potential MQTT topics where data can be published to. My CAD publishes to SMART/HILD/, but I received a report from someone with a CAD publishing to SMART/DCAD/, and it seems others have CADs publishing to SMART/IGLOO/.

The MQTT server doesn't seem to mind subscribing to multiple potential topics (so I'm currently subscribing to SMART/HILD/ and SMART/DCAD/), but I was wondering if there was a REST API endpoint or similar that could be used to discover the correct topic- it doesn't seem to be exposed through the /resource or /device endpoints.

I released v0.1.0-beta last night which has rough support for smart meter autodiscovery & MQTT streaming, but it's likely this won't work at all until I've had a chance to add better error handling.

Really appreciate any suggestions/feedback on this.

Thanks :)


  • If I subscribe to


    (obviously with my valid Glow ID) it doesn't matter whether it's HILD or DCAD or IGLOO.

  • Except that it wont auth - or at least it didn't when I tried.

  • As for knowing which topic - no sadly there is no programmatic way of knowing .

    However just ask - we will tell you and it won't change.

    It is an historical accident which can't change without affecting other users.

  • @clivee

    It worked perfectly for me just using `mosquitto_sub` so I've built that into all of my API code. Here's a simple example.

    #include <stdio.h>
    #include <stdint.h>
    #include <string.h>
    #include <unistd.h>
    #include <mosquitto.h>
    const char* usr = "";
    const char* pwd = "pwd";
    const char* dev = "DEADBEEFCAFE";
    void concb(struct mosquitto *mosq, void *obj, int rc)
      if (rc) printf("Connect rc=%d\n", rc);
    void msgcb(struct mosquitto *mosq, void *obj, const struct mosquitto_message *msg)
      printf("Topic: %s\n Payload:", msg->topic);
      printf("%.*s\n", msg->payloadlen, (char*) msg->payload);
    int main(int argc, char* argv[])
      struct mosquitto *mosq;
      int rc = 0;
      char topic[23];
      mosq = mosquitto_new(NULL, true, 0);
        mosquitto_connect_callback_set(mosq, concb);
        mosquitto_message_callback_set(mosq, msgcb);
        mosquitto_username_pw_set(mosq, usr, pwd);
        mosquitto_tls_set(mosq, NULL,  "/etc/ssl/certs",  NULL, NULL, NULL);
        mosquitto_tls_opts_set(mosq, 1, NULL, NULL);
        rc = mosquitto_connect(mosq, "", 8883, 30);
        if (rc) printf("connect, rc=%d\n", rc);
        sprintf(topic, "SMART/+/%s", dev);
        mosquitto_subscribe(mosq, NULL, topic, 0);
          rc = mosquitto_loop(mosq, -1, 1);
          if (rc)
            printf("Conn error\n");

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