mqttc | mqtt client written in c

QOS only works if the client is SUBSCRIBEd...if you want to receive messages before you are Subscribed, you need to PUBLISH messages with the Retain flag set...and then you only get the last message that was sent. If you really need to get multiple messages, then you need to use something like AMQ, and not MQTT.

caPath is certain to be incorrect. It needs to be the Amazon root ca which you can google.

I figured out what the problem was:

I did not know that I have to attach the thing and the policy to a certificate. That seems like it was the problem, now I am getting the messages straight to my test console.

If someone runs into this issue, check out this Blog Entry which helped me fix it.

The MQTT client uses a network thread to handle a number of different aspects of the connection to the broker.

Firstly, it handles sending ping request to the broker in order to keep the connection alive. The default period for the keepalive period is 60 seconds. The connection will be dropped by the broker if it does not receive any messages in 1.5 times this value, which just happens to be 90 seconds.

Secondly, the thread handles any incoming messages that the client may have subscribed to.

Thirdly, if you try to publish a message that is bigger than the MTU of the network link, calling mqttc.publish() will only send the first packet and the loop is needed to send the rest of the payload.

There are 2 ways to run the network tasks.

1. As you have found, you can start a separate thread with the mqttc.loop_start()
2. The other option is to call mqttc.loop() within your own while loop

Your indentation is wrong, you are only adding the last record to data because data.append(d) is outside the first for-loop

Connections between clients (like your python program) and MySQL don't stay open forever when they're not in use. MySQL drops connections when its wait_timeout, or interactive_timeout, expires.

It sounds like your program works all day and sleeps all night (like the lumberjack in the Monty Python schtick). When it wakes up it has no connection to the database because MySQL closed it.

What can you do about this? In my order of preference:

1. Right before your program handles each queued item, perform a no-op operation like SELECT 1;. If that operation throws an exception, reopen the database connection. This is a good solution because it makes your application more resilient if the MySQL database server must be restarted. Sometimes cloud providers (AWS, Azure, Digital Ocean, others) have to take host machines out of service. When they do that they bounce customer virtual machines so they can start on new host machines. If you're lucky they warn you first.

2. Update your program so it closes its database connection when its queue of work becomes empty, and reopens it when it has work to do.

3. Once every so often (a minute?) do a no-op SELECT 1; as a keepalive so MySQL won't close the connection.

4. Change the wait_timeout value to something long enough. This sets it to one week.

The issue lies with understanding the msg.payload format.

While print(msg.payload) returns a legible text, msg.payload is not a string but ASCII code. After converting msg.payload from ASCII to a string, the .split function can be used. Here is the working conversion for the mqtt payload.

It is not necessary to use threads, just follow the logic of Qt: let's use signals. In the following code I show an advance of the library of an MQTT client that I am implementing that at least up to now implements what you want, in next days I will add more functionalities.

You should not put the external address into the mosquitto config file.

You should probably not even have a listen line at all as mosquitto will bind to all available IP addresses on the machine it's running with the default port (1883).

If you really must use the listen directive (e.g. in order to set up SSL) then it should be configured with the internal IP address of the machine running the broker, in this case 192.168.1.100 and with a different port number so it does not clash with the default