MQTT buffer size not working after 7500 bytes (IDFGH-14541)

[juanpgg-git]

Answers checklist.

• I have read the documentation ESP-IDF Programming Guide and the issue is not addressed there.
• I have updated my IDF branch (master or release) to the latest version and checked that the issue is present there.
• I have searched the issue tracker for a similar issue and not found a similar issue.

General issue report

I'm working with an ESP32 in Platformio using the Arduino framework and the ESP-IDF MQTT (mqtt_client.h) implementation.
platform = espressif32 @ 6.9.0 (which uses ESP-IDF 4.4.7)

The broker is AWS IoT Core. So far I've been able to do the provisioning process and send data back and forth without problem.

The problem is I need to be able to receive 15kB in the payload, but if I set the buffer size greater than 7500 bytes, the client is not able to connect.

Error is:
Other event id: 0 E (18401) esp-tls-mbedtls: mbedtls_ssl_handshake returned -0x2880 E (18402) esp-tls: Failed to open new connection E (18403) TRANSPORT_BASE: Failed to open a new connection E (18409) MQTT_CLIENT: Error transport connect MQTT_EVENT_ERROR MQTT_EVENT_DISCONNECTED

I also tried increasing the MQTT task size, but that didn't work.

This is the specific code:
esp_mqtt_client_config_t aws_mqtt_cfg = { .event_handle = mqtt_event_handler, .uri = "xxxxxxxxxxxx", .port = SERVER_PORT, .client_id = "xxxxxxxx", //.task_stack = 12000, .buffer_size = 7500, .cert_pem = AWS_CERT_CA, .client_cert_pem = AWS_CERT_CA_new, .client_key_pem = AWS_CERT_PRIVATE_new, };

I checked the heap size before connecting and there's around 80kB free to use, so that shouldn't be the problem. I also tried looking for the max mqtt buffer size but found no rule about it.

Thanks a lot in advance