Downloading big files using FTP AT commands

[arshdeep]

Hello Team Nordic,

We are using nrf9160 DK with nrf connect SDK 1.5.0 and mfw_nrf9160_1.2.3 modem firmware .

We are currently evaluating the FTP AT command set and according to our requirement we need to download a huge file 120KB from the FTP server. Is there a way in which we can get the data in chunks, like by specifying MTU and keep storing it in buffer? We want to store this data in our second bank for doing OTA, that's why we need the data to come in parts. 

If not, can you suggest a way to do the same.

Thanks,

[Carl Richard]

Hello!

We don't have any implementation doing this at the moment, but I suggest looking into using the the REST (restart) command of FTP. This enables you to restart a download at a certain point in the data, so you can implement some sort of scheme that downloads a chunk of data, storing it in a buffer, and then restarting the download at the offset. As specified in the FTP client documentation some adjustments might have to be done for the API to work with specific servers.

Alternatively you could look into the Download Client API, which uses HTTPS/CoAP, but handles fragmentation of large files.

Best regards,
Carl Richard

[arshdeep]

Thanks Carl for the response. Both these methods suggest us to download some sought of library and use the corresponding API's but we were trying to find a way out using just the AT command set as listed here:

https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/applications/serial_lte_modem/doc/FTP_AT_commands.html

Do you know of any AT command which will allow us to achieve the same? I couldn't find a REST command in this list which seemed like a good idea in your answer.

Thanks,

[Carl Richard]

Hi again!

From what I can see the REST command isn't supported in our FTP client yet. Thus, it's not supported through the AT commands either. If this is a desired feature I suggest talking with your Nordic Regional Sales Manager(RSM), but it should be possible implement in existing FTP client library as well. 

If you are unaware of who your RSM is I'll send you a private message with his contact information.

Best regards,
Carl Richard