Example

Procedure

1. Initialize a client.
   For more information, see Step 1: Initialize a client.
2. Configure required features.
   For more information, see Step 2: Configure required features.
3. Establish a connection.
   For more information, see Step 3: Establish a connection.
4. Optional:If you want to send a broadcast message to all devices under a product, the devices must call the aiot_mqtt_sub operation to subscribe to the specified topic.
   • Sample code

         {
             char *sub_topic = "/broadcast/a18wP******/test";
     
             res = aiot_mqtt_sub(mqtt_handle, sub_topic, NULL, 1, NULL);
             if (res < 0) {
                 printf("aiot_mqtt_sub failed, res: -0x%04X\n", -res);
                 return -1;
             }
         }

   • Parameters:

     Parameter	Example	Description
     sub_topic	/broadcast/a18wP******/test	The topic to which the broadcast message is sent. Format: /broadcast/${productKey}/custom field. a1oGs****** indicates the ProductKey of the device. test indicates a custom field. For more information about topics, see What is a topic?.

5. Receive the broadcast message.
   1. After the device is connected to IoT Platform, you can call the PubBroadcast operation to send a broadcast message.
      Notice

      We recommend that you send a maximum of one broadcast message per minute to prevent throttling.

      For more information, see Broadcast messages.

   2. The device calls the aiot_mqtt_recv operation to receive the message. Then, the callback is called to perform the required operations.
      In this example, the callback is demo_mqtt_default_recv_handler.
   3. Define the callback to process the broadcast message.
      Check whether the message is a broadcast message based on the topic format.

      • If you need to send the broadcast message to all online devices under a product, the devices do not need to subscribe to a broadcast topic first. After each device receives the message, you can check whether the message is a broadcast message based on the topic format. The format of a broadcast topic is /sys/${productKey}/${deviceName}/broadcast/request/${MessageId}.
      • If you need to send the broadcast message to all devices that subscribe to a custom topic, the devices must subscribe to the topic first. The format of a custom broadcast topic is /broadcast/${productKey}/custom field.

      You can specify the processing logic of the callback based on your business needs. In this example, the broadcast message is printed.

      void demo_mqtt_default_recv_handler(void *handle, const aiot_mqtt_recv_t *packet, void *userdata)
      {
          switch (packet->type) {
              ...
              ...
              case AIOT_MQTTRECV_PUB: {
                  printf("pub, qos: %d, topic: %.*s\n", packet->data.pub.qos, packet->data.pub.topic_len, packet->data.pub.topic);
                  printf("pub, payload: %.*s\n", packet->data.pub.payload_len, packet->data.pub.payload);
                  /* TODO: Print the broadcast message */           
              }
              break;
      
              ...
              ...       
      
              default: {
      
              }
          }
      }

6. End the connection.
   For more information, see Step 8: Disconnect the device from IoT Platform.
7. Exit the program.
   For more information, see Step 9: Exit the program.