MQTT: Failing to detect broker disconnect

Hi Henry,

Can you try the mqtt example from the SDK and see if that works?

Regards,
Gigi Joseph.

Dear Gigi,

Is the MQTT client from the example working stable? I did try this in the beginning but found that the socket was closed remotely due to the client timing out (read from the MQTT server logs).

Is the SDK MQTT sample also based on the Paho client?

Thanks
Henry

Dear Gigi,

I just ran the MQTT SDK example and received the following output:

Version: Client LIB 1.0.3, Common LIB 1.1.1.
C: FH-B1 0x10 to net 17, Sent (45 Bytes) [@ 15]
C: Rcvd msg Fix-Hdr (Byte1) 0x20 from net 17 [@ 15]
C: Cleaning session for net 17
C: Msg w/ ID 0x0000, processing status: Good

Success: conn to Broker no. 1
 C: FH-B1 0x82 to net 17, Sent (79 Bytes) [@ 15]
C: Rcvd msg Fix-Hdr (Byte1) 0x90 from net 17 [@ 15]
C: Msg w/ ID 0x0001, processing status: Good
Client subscribed on following topics:
/cc3200/ToggleLEDCmdL1
/cc3200/ToggleLEDCmdL2
/cc3200/ToggleLEDCmdL3
C: FH-B1 0xc0 to net 17, Sent (2 Bytes) [@ 40]
C: Rcvd msg Fix-Hdr (Byte1) 0x30 from net 17 [@ 40]

Publish Message Received
Topic: /cc3200/ToggleLEDCmdL1 [Qos: 0]
Data is: test
C: Msg w/ ID 0x0000, processing status: Good
C: Rcvd msg Fix-Hdr (Byte1) 0xd0 from net 17 [@ 40]
C: Msg w/ ID 0x0000, processing status: Good
C: Net 17, Raw Error -1, Time Out: N
C: RX closing Net 17 [-1]
C: Cleaning session for net 17
C: Net 17 now closed

I send one "test" message to the subscribed topic "ToggleLEDCmdL1" and it arrived as one can see. Afterwards I remotely disconnected the CC3200 Client from the broker.

The MQTT SDK example does recognize the connection loss (see last 4 lines). But how can I act upon those messages? Are they thrown from the library?

Again, the Socket Event Handler does not get triggered. Where do these "C: [..]" messages actually come from? I could not find them in the source of the example.

Thanks for your help!

Henry

Quick add-on:

I did a dirty work-around for identifying the connection loss by changing the UART_PRINT debug output to a different function "mqtt_msg_handler":

/* library configuration */
SlMqttClientLibCfg_t Mqtt_Client={
    1882,
    TASK_PRIORITY,
    30,
    false,
    (long(*)(const char *, ...))mqtt_msg_handler
};

And the this function simply does a string compare:

void mqtt_msg_handler(const char *msg) {

	const char *find = "C: Net";
	if (strncmp(msg, find, sizeof(find)) == 0) {

		UART_PRINT("Connection loss detected.");
	}
}

I guess this is not meant to be the way this should be done, so please could someone tell me what would be the proper way to handle connection losses?

Thanks

Henry

Hi Henry,

The TCP socket recv returns 0 if the connection is closed from the remote side.

Socket recv may also return the -ve value indicating the various errors with the exception of -11 (SL_EAGAIN) in case of non blocking socket notifying application to try again.

Regards,
Ankur

Dear Ankur,

That is very helpful input, thanks.

In regards to my approach of catching the debug messages of the TI MQTT example, is this the correct way to do it (see my recent posts)?

Henry

Hi Henry,

Handling of disconnection from the server depends upon the application and use case. In the SDK example application exit upon disconnection. You can very well modify the example to attempt reconnection with the server.

MQTT library call the registered callback (sl_MqttDisconnect() in sdk example) upon detecting a disconnection.

Regards,
Ankur

Dear Ankur,

I have just double checked with the MQTT example from the SDK but the sl_MqttDisconnect() is not called when the socket is broken (e.g. broker gets unavailable).

Am I doing something wrong?

Thanks
Henry

Hi ,

This is SDK 1.1.0 known issue, you may patch the solution from this site:

This

Rebuild mqtt lib and your example

And please also note that do not call sl_ExtLib_MqttClientCtxDelete in sl_MqttDisconnect to avoid 

system hang.

Henry,

As suggested by Johnson please incorporate the changes mentioned on the known issue wiki (processors.wiki.ti.com/.../CC32xx_Summary_of_Known_Issues) and let us know the results.

Johnson,

Thanks for the response.

Regards,
Ankur

Hi Henry,

I am closing this thread, if you are still seeing this issue please open a new thread and add a link to this one for reference.

Regards,
Ankur