How to detect that the peer closed a TCP socket

RE: How to detect that the peer closed a TCP socket

NelsonGoncalves — Mon, 04 Oct 2021 13:42:31 GMT

Hello Markus,

Updating the modem firmware to version 1.3.0 fixed the issue.

And looking at the Wireshark traces, the modem is also properly closing the TCP session devzone.nordicsemi.com/.../tcl_5F00_close_5F00_mfw_5F00_1.3.0.pcapng

RE: How to detect that the peer closed a TCP socket

Albrecht Markus Schellenberger — Wed, 29 Sep 2021 17:12:38 GMT

Hello again,

could you update your modem firmware to version 1.3.0 and check if that makes any difference? I got the feedback from our development team that during their tests with mfw 1.3.0, poll sets event NRF_POLLHUB successfully .

Regards,

Markus

RE: How to detect that the peer closed a TCP socket

Albrecht Markus Schellenberger — Wed, 29 Sep 2021 08:31:51 GMT

Hello Nelson,

Just a quick update: currently, we do not have the test setup to reproduce the issue you are facing, but our development team is looking into it as we speak. I will hopefully be able to provide you with some more updates soon.

Regards,

Markus

RE: How to detect that the peer closed a TCP socket

Albrecht Markus Schellenberger — Fri, 17 Sep 2021 12:13:00 GMT

Hello Nelson,

[quote user="NelsonGoncalves"]In the attached Wireshark file, my PC (the client) has IP address 192.168.178.29 and the nRF9160 module (the server) has IP address 178.50.73.204. The Wireshark tracing test_nordic.pcapng[/quote]

Thanks a lot for your input!

[quote user="NelsonGoncalves"]Any updates ?[/quote]

Still no news from the development team. My very apologies for that! I will try to push on this one and come back to you.

Regards,

Markus

RE: How to detect that the peer closed a TCP socket

NelsonGoncalves — Fri, 17 Sep 2021 10:27:18 GMT

Hello Markus,

Any updates ? In the meanwhile, I took a look with Wireshark at the network traffic.

On the nRF9160DK I have my TCP listening application running, and I connect to it with from my PC and send ten times a test string. To each one the module replies by upper casing the text. Then my PC application closes the socket. Again, on the module side there is no notification that the client has closed the socket.

From the Wireshark tracing, the TCP packet sequence for when the PC closes the socket is:

PC sends TCP packet with FIN and ACK
Module replies with ACK
PC tries to send, but apparently fails, a TCP packet with RST and ACK

In the attached Wireshark file, my PC (the client) has IP address 192.168.178.29 and the nRF9160 module (the server) has IP address 178.50.73.204. The Wireshark tracing devzone.nordicsemi.com/.../test_5F00_nordic.pcapng

With the debugger, I can see that the application on the nrf9160 module is stuck in the idle task and I don't understand why. could this be related to the issues I am having ?

RE: How to detect that the peer closed a TCP socket

Albrecht Markus Schellenberger — Mon, 30 Aug 2021 07:54:00 GMT

Hello Nelson,

I haven’t received any updates from our development team yet. But I’ll check with them again.

Regards,

Markus

RE: How to detect that the peer closed a TCP socket

NelsonGoncalves — Wed, 25 Aug 2021 11:56:37 GMT

Hello Markus,

Any updates ?

I did not try to update the firmware of the modem because I am using a prototype board, and I don't to risk bricking the only prototype we have.

Regards,

Nelson

RE: How to detect that the peer closed a TCP socket

Albrecht Markus Schellenberger — Thu, 05 Aug 2021 12:55:43 GMT

Thank you, Nelson!

I will be on vacation for the next couple of weeks as well.

Regards,

Markus

RE: How to detect that the peer closed a TCP socket

NelsonGoncalves — Fri, 30 Jul 2021 14:27:30 GMT

Hello Markus,

I could not find the time to update the modem firmware, but I will try it out when I return from hollidays.

Regards,

Nelson

RE: How to detect that the peer closed a TCP socket

Albrecht Markus Schellenberger — Fri, 30 Jul 2021 10:11:56 GMT

Hello Nelson,

[quote user="NelsonGoncalves"]Side note: I will be on vacation the next two and half weeks.[/quote]

thanks a lot for the heads-up.

[quote user="NelsonGoncalves"]Should I also try to update the modem firmware version ?[/quote]

I’m quite sure that this is not a modem issue, but to exclude this one from the list of possible root causes, I would appreciate if you could update and check with the newest mfw as well.

[quote user="NelsonGoncalves"]I tried with NCS v1.6.0 and using poll() for reading from the client socket. Again, when the remote client closes its end, nothing happens on the server side.[/quote]

I’ll inform our development team and let you know as soon as I get any news.

I appreciate your patience!

Regards,

Markus

RE: How to detect that the peer closed a TCP socket

NelsonGoncalves — Fri, 30 Jul 2021 08:36:10 GMT

Hello Markus,

I tried with NCS v1.6.0 and using poll() for reading from the client socket. Again, when the remote client closes its end, nothing happens on the server side. Should I also try to update the modem firmware version ?

Side note: I will be on vacation the next two and half weeks.

Regards,

Nelson

RE: How to detect that the peer closed a TCP socket

Albrecht Markus Schellenberger — Fri, 30 Jul 2021 05:35:01 GMT

Hello again Nelson,

I wonder if you could build your application from NCS v1.6.0 and check if you can reproduce this error?

Regards,

Markus

RE: How to detect that the peer closed a TCP socket

Albrecht Markus Schellenberger — Wed, 28 Jul 2021 09:02:52 GMT

Hello Nelson,

I unfortunately haven’t been able to receive any information from our modem team yet as many of them still are on vacation. I will try to ping them one more time and come back to you as soon as possible.

My apologies for the inconvenience caused!

Regards,

Markus

RE: How to detect that the peer closed a TCP socket

NelsonGoncalves — Tue, 27 Jul 2021 14:25:56 GMT

Hello Markus,

Any updates on this issue ? I tried other alternatives (e.g. reading from the socket and closing it case or error), but this also does not work. After I close the socket, recv() returns -1 but errno is always zero.

[update 28/07/2021] The SO_KEEPALIVE socket option is apparently not available, and using getsockopt() to get the state/error of the client socket also does not detect that the socket was closed.

And sending a custom ping to test the connection is not possible, the protocol does not support it.

Best regards,

Nelson Gonçalves

RE: How to detect that the peer closed a TCP socket

Albrecht Markus Schellenberger — Fri, 16 Jul 2021 10:24:53 GMT

Hello Nelson,

Yes, this should work exactly as you expect. Once peer closes the connection, poll() should return POLLHUP event and the consecutive recv() call should return 0.

I have to check this with out modem team. Due to summer vacation period most of our experts are out of office currently, but I will come back to you as soon as possible.

Regards,

Markus