Problem with nRF-connect-SDK http_client_req() function

[royalbee]

Hi,


I open ssl socket to the server (without certificate verification),
and then use an http_client_req() call, to perform the actual http request (with additional optional headers).

That works fine for both http GET and POST requests, that have a short response from the server.

However, when the server's response is a bit larger (say 2.5KB not including response headers and cookie), I always get "Socket was closed by remote" error (-104).
I tried increasing recv_buf_len from 1KB to 8KB, but it didn't help.

When debugging http_client_req(), I see that the call to socket's recv() just returns 0 bytes, which is considered socket close by remote.
On the server logs I see that HTTP request, but no special problems appear on aws elb logs.

Performing the same request on my PC (using Postman for example), works just fine, so the problem is not on the server side (at least not with standard http/tcp settings)/

thanks in advance..

[Albrecht Markus Schellenberger]

Hello Koby,

thanks a lot for your feedback!

kobyatom said:

As I understand, the modem doesn't support receiving data larger than 2KB over SSL sockets.

Is that so?

 Yes, that is correct.

kobyatom said:

By the way, the limitation of 2KB secure socket buffer size was introduced starting from 1.1.0.
It did not exist prior to that version.

The limitation has always been there, but the release notes have been updated with this information during the release of modem firmware 1.1.0.

kobyatom said:

Is there a proven patch we can add to the modem FW to work around this limit?

No. Since this is a hardware limitation, there is no software patch available.

However, it is possible to offload the secure socket to the application core. The chapter Native TLS sockets of the Serial LTE modem application guide introduces this.

kobyatom said:

Is there a date on your road map to remove this limitation altogether?

We are continuously working on improving our products.

Regarding Rans question:

royalbee said:

Can you be more specific what you mean by "smaller responses" ?

With TLS, the modem has to receive the whole package to be able to decode it. Thus, the nRF9160 will not be able to receive a TLS package larger than 2kB. However, HTTP has a feature called content-range, where you can tell the server which part of the data you would like to receive in order to split the content into several TLS packages. But the server has to support this feature otherwise this won’t work.

You can have a look at how this is implemented in our download_client library.

I hope my answers could clarify the situation.

Best regards,

Markus

[kobyatom]

Thank you for your reply Markus.

Some more questions:

Looking at the paragraph on Native TLS Sockets, it states that HTTP Client is not supported.

Does that mean that HTTPS GET and POST not be supported if I use TLS Sockets?

Regarding "We are continuously working on improving our products.", and since it will require a HW change to support TLS fragments > 2KB, is there a known plan to update the nRF9160 HW in that respect?

Regarding "content-range", will it also work when sending data > 2KB?

Kind regards,

Koby