Devacademy L4_e2. mqtt_connect error -12 when connecting to HiveMq serverless cluster.

RE: Devacademy L4_e2. mqtt_connect error -12 when connecting to HiveMq serverless cluster.

andychess — Fri, 27 Jun 2025 20:04:41 GMT

And finally, I have the answer. I eventually found this link : https://github.com/zephyrproject-rtos/zephyr/issues/73089 with this comment revealing the cause of the problem.

There are multiple ways to assign the username and password and most will compile, but fail at runtime. The final solution for me was to declare the mqtt_utf structs as static in main.c and then pass them as pointers to client_init. It then took several attempts to find a working solution to assigning the values to the structs. The final version looks like this:

int client_init(struct mqtt_client* client, struct mqtt_utf8* uname, struct mqtt_utf8* pass)

{

int err;

/* Initializes the client instance. */

mqtt_client_init(client);

/* Resolves the configured hostname and initializes the MQTT broker structure */

err = broker_init();

if (err) {

LOG_ERR("Failed to initialise broker connection");

return err;

}

uname->utf8 = (uint8_t*)"xxxxxxxxxx";

uname->size = (uint32_t)strlen(uname->utf8);

pass->utf8 = (uint8_t*)"xxxxxxxxxx";

pass->size = (uint32_t)strlen(pass->utf8);

/* MQTT client configuration */

client->broker = &broker;

client->evt_cb = mqtt_evt_handler;

client->client_id.utf8 = client_id_get();

client->client_id.size = strlen(client->client_id.utf8);

client->password = pass;

client->user_name = uname;

client->protocol_version = MQTT_VERSION_3_1_1;

This issue has cost me three production days and the fix is is incredibly flakey. I would be grateful if a more elegant and robust method of implementing the username and password fields could be found in a future release.

In the meantime, I hope this post helps someone struggling with the same problem.

RE: Devacademy L4_e2. mqtt_connect error -12 when connecting to HiveMq serverless cluster.

andychess — Fri, 27 Jun 2025 09:27:47 GMT

I just took another look this morning and see now that the password first and then the username appear to be becoming corrupted with the first line of the mqtt_mutex_lock call at line 268 of mqtt.c. I ran the debugger several times and got consistent results. If this is correct, the mqtt_client struct is corrupted prior to entering client_connect.

Please could someone confirm if this is in fact the case?

RE: Devacademy L4_e2. mqtt_connect error -12 when connecting to HiveMq serverless cluster.

andychess — Thu, 26 Jun 2025 08:43:04 GMT

I started to debug mqtt_connect this morning and have found that the -12 seems to be coming from connect_request_encode line 832 which is pack_utf8_str(client->username, buf).

The few other posts I have read seem also to be related to problems with the username / password structures.

Any thoughts?

RE: Devacademy L4_e2. mqtt_connect error -12 when connecting to HiveMq serverless cluster.

andychess — Wed, 25 Jun 2025 18:13:01 GMT

Hi Susheel,

Thanks for the quick response.

This is the output with the settings as above.

*** Using Zephyr OS v4.0.99-77f865b8f8d0 ***
[00:00:00.365,753] <inf> Lesson4_Exercise2: Initializing modem library
[00:00:00.710,418] <inf> Lesson4_Exercise2: match

[00:00:00.710,449] <inf> Lesson4_Exercise2: Connecting to LTE network
[00:00:01.919,677] <inf> Lesson4_Exercise2: RRC mode: Connected
[00:00:06.263,183] <inf> Lesson4_Exercise2: Network registration status: Connected - roaming
[00:00:06.263,275] <inf> Lesson4_Exercise2: Connected to LTE network
[00:00:06.486,022] <inf> Lesson4_Exercise2: IPv4 Address found 46.137.47.218
[00:00:06.486,541] <inf> Lesson4_Exercise2: client_id = nrf-359404230139975
[00:00:06.486,572] <inf> Lesson4_Exercise2: TLS enabled
[00:00:08.184,326] <err> Lesson4_Exercise2: Error in mqtt_connect: -12
[00:00:08.184,356] <inf> Lesson4_Exercise2: Reconnecting in 60 seconds...
[00:00:13.665,435] <inf> Lesson4_Exercise2: RRC mode: Idle
[00:01:08.292,297] <inf> Lesson4_Exercise2: RRC mode: Connected
[00:01:10.078,338] <err> Lesson4_Exercise2: Error in mqtt_connect: -12
[00:01:10.078,369] <inf> Lesson4_Exercise2: Reconnecting in 60 seconds...
[00:01:15.674,865] <inf> Lesson4_Exercise2: RRC mode: Idle

The two lines regarding the MBEDTLS_HEAP caused build errors due to dependencies. I haven't come across these settings before, can you give me a link to the relevant documentation.

As I'm new to working with cellular (hence why I'm doing the course), can you give me some tips on how best to debug the TLS handshake. Presumably, this is the source of the problem(?)

RE: Devacademy L4_e2. mqtt_connect error -12 when connecting to HiveMq serverless cluster.

Susheel Nuguru — Wed, 25 Jun 2025 11:25:34 GMT

-12 error is due to insufficient memory and not any access with username or password.

Make sure you have given enough memory for all the contexts that need heap memory in your prj.conf something like below. Use this as template and start to reconfigure things up and down in mem size. You might have to do some trial and error if you do not indend to do proper debugging to see where you get this error. If would be helpful to give us full serial log here so that I can attempt to get a hint of the context of the error.

CONFIG_MAIN_STACK_SIZE=8192 
CONFIG_HEAP_MEM_POOL_SIZE=16384 
CONFIG_MBEDTLS_HEAP=y
CONFIG_MBEDTLS_HEAP_SIZE=16384

#slim down Zephyr net-buffers if still hitting RAM limits
CONFIG_NET_BUF_RX_COUNT=5
CONFIG_NET_BUF_TX_COUNT=5

RE: Devacademy L4_e2. mqtt_connect error -12 when connecting to HiveMq serverless cluster.

andychess — Wed, 25 Jun 2025 07:54:51 GMT

I forgot to mention that I am using the isrgrootx1.pem and the certificate.h is:

#define CA_CERTIFICATE \
"-----BEGIN CERTIFICATE-----\n"\
"MIIFazCCA1OgAwIBAgIRAIIQz7DSQONZRGPgu2OCiwAwDQYJKoZIhvcNAQELBQAw\n"\
"TzELMAkGA1UEBhMCVVMxKTAnBgNVBAoTIEludGVybmV0IFNlY3VyaXR5IFJlc2Vh\n"\
"cmNoIEdyb3VwMRUwEwYDVQQDEwxJU1JHIFJvb3QgWDEwHhcNMTUwNjA0MTEwNDM4\n"\
"WhcNMzUwNjA0MTEwNDM4WjBPMQswCQYDVQQGEwJVUzEpMCcGA1UEChMgSW50ZXJu\n"\
"ZXQgU2VjdXJpdHkgUmVzZWFyY2ggR3JvdXAxFTATBgNVBAMTDElTUkcgUm9vdCBY\n"\
"MTCCAiIwDQYJKoZIhvcNAQEBBQADggIPADCCAgoCggIBAK3oJHP0FDfzm54rVygc\n"\
"h77ct984kIxuPOZXoHj3dcKi/vVqbvYATyjb3miGbESTtrFj/RQSa78f0uoxmyF+\n"\
"0TM8ukj13Xnfs7j/EvEhmkvBioZxaUpmZmyPfjxwv60pIgbz5MDmgK7iS4+3mX6U\n"\
"A5/TR5d8mUgjU+g4rk8Kb4Mu0UlXjIB0ttov0DiNewNwIRt18jA8+o+u3dpjq+sW\n"\
"T8KOEUt+zwvo/7V3LvSye0rgTBIlDHCNAymg4VMk7BPZ7hm/ELNKjD+Jo2FR3qyH\n"\
"B5T0Y3HsLuJvW5iB4YlcNHlsdu87kGJ55tukmi8mxdAQ4Q7e2RCOFvu396j3x+UC\n"\
"B5iPNgiV5+I3lg02dZ77DnKxHZu8A/lJBdiB3QW0KtZB6awBdpUKD9jf1b0SHzUv\n"\
"KBds0pjBqAlkd25HN7rOrFleaJ1/ctaJxQZBKT5ZPt0m9STJEadao0xAH0ahmbWn\n"\
"OlFuhjuefXKnEgV4We0+UXgVCwOPjdAvBbI+e0ocS3MFEvzG6uBQE3xDk3SzynTn\n"\
"jh8BCNAw1FtxNrQHusEwMFxIt4I7mKZ9YIqioymCzLq9gwQbooMDQaHWBfEbwrbw\n"\
"qHyGO0aoSCqI3Haadr8faqU9GY/rOPNk3sgrDQoo//fb4hVC1CLQJ13hef4Y53CI\n"\
"rU7m2Ys6xt0nUW7/vGT1M0NPAgMBAAGjQjBAMA4GA1UdDwEB/wQEAwIBBjAPBgNV\n"\
"HRMBAf8EBTADAQH/MB0GA1UdDgQWBBR5tFnme7bl5AFzgAiIyBpY9umbbjANBgkq\n"\
"hkiG9w0BAQsFAAOCAgEAVR9YqbyyqFDQDLHYGmkgJykIrGF1XIpu+ILlaS/V9lZL\n"\
"ubhzEFnTIZd+50xx+7LSYK05qAvqFyFWhfFQDlnrzuBZ6brJFe+GnY+EgPbk6ZGQ\n"\
"3BebYhtF8GaV0nxvwuo77x/Py9auJ/GpsMiu/X1+mvoiBOv/2X/qkSsisRcOj/KK\n"\
"NFtY2PwByVS5uCbMiogziUwthDyC3+6WVwW6LLv3xLfHTjuCvjHIInNzktHCgKQ5\n"\
"ORAzI4JMPJ+GslWYHb4phowim57iaztXOoJwTdwJx4nLCgdNbOhdjsnvzqvHu7Ur\n"\
"TkXWStAmzOVyyghqpZXjFaH3pO3JLF+l+/+sKAIuvtd7u+Nxe5AW0wdeRlN8NwdC\n"\
"jNPElpzVmbUq4JUagEiuTDkHzsxHpFKVK7q4+63SM1N95R1NbdWhscdCb+ZAJzVc\n"\
"oyi3B43njTOQ5yOf+1CceWxG1bQVs5ZufpsMljq4Ui0/1lvh+wjChP4kqKOJ2qxq\n"\
"4RgqsahDYVvTH9w7jXbyLeiNdd8XM2w9U/t7y0Ff/9yi0GE44Za4rF2LN9d11TPA\n"\
"mRGunUHBcnWEvgJBQl9nJEiU0Zsnvgc/ubhPgXRR4Xq37Z0j4r7g1SgEEzwxA57d\n"\
"emyPxgcYxn/eR44/KJ4EBs+lVDR3veyJm+kXQ99b21/+jh5Xos1AnX5iItreGCc=\n"\
"-----END CERTIFICATE-----"