Download from Azure fails with error code -122

[Thomas van Doornmalen]

Hi,

I want to download FOTA-updates with HTTPS from a function app running on Azure. I am not using IoT hub or MQTT. I'm using modem firmware 2.0.4 in combination with version 2.7.0 of the nRF Connect SDK. I have provisioned the required root certificate, and the download is performed via the download_client.

When a download is attempted, a connection is established, but downloading fails with error code -122 when `recv` is called for the first time. My understanding is that this is due to the secure buffer in the modem (2kB) being exhausted due to Azure sending too much data. I have enabled `CONFIG_DOWNLOAD_CLIENT_HTTP_FRAG_SIZE_1024, but this leads to the same result. Is there a way to resolve this? The other questions I've found all refer to IoT hub and MQTT.

[Simon D-M]

Hi,

Sorry, I don't have much information to work with here... Can you maybe share some code snippets that allow me to have a better look at your implementation.

Here is the documentation for the "Download Client" library (link). Did you call "download_client_set_host()" and "modem_key_mgmt_write()" as asked here?

Moreover, the application must provision the TLS credentials and pass the security tag to the library when using HTTPS and calling the download_client_set_host() function. To provision a TLS certificate to the modem, use modem_key_mgmt_write() and other Modem key management APIs.

Also, I am wondering why you are not using the Azure FOTA library (link)? I believe it should handle most of your issue by itself.

Best regards,

Simon

[Thomas van Doornmalen]

Our download starts via `fota_download_util_download_start(uri, type, sec_tag, our_fota_download_callback)`, I cannot share the implementation of the callback here, but can confirm `download_client_set_host` is called. The certificate has been provisioned, otherwise connecting fails.

We are not using the FOTA library because it requires using Azure IoT Hub:

Prerequisites

• A Device Update account and instance configured with an IoT hub.

[Simon D-M]

Hi,

We usually prefer having public tickets, but I can make this ticket private if that allows you to send some code snippets (just confirm that you want it, and I'll switch its visibility).

Because right now, I don't have much to work with... It would be much easier with some more information (graphs, UMLs, code snippets, ...).

Best regards,

Simon

[Thomas van Doornmalen]

I've managed to figure it out, the key information was in the documentation of the download client:

The library requires the host server to provide a Content-Range field in the HTTP GET header when using HTTPS.

The error I received (-122) was confusing to me because I incorrectly attributed it to the size of the certificates. After implementing support for the Range and Content-Range in our download endpoint, the download succeeded.