DTLS (CoAP) Client not receiving Close Notify alert

[Povilas S]

I am running CoAP client with DTLS enabled on an nRF9161dk.

I poll socket using this code:

 while (1) {
        if (!socket_ready) {
            k_msleep(100);
            continue;
        }

        /* Poll socket */
        err = poll(&fds, 1, 0);
        if (err < 0) {
            LOG_ERR("Poll error: %d", errno);
            continue;
        }

        if (fds.revents & POLLHUP) {
            LOG_ERR("POLLHUP");
            continue;
        }

        if (fds.revents & POLLERR) {
            LOG_ERR("POLLERR");
            continue;
        }

        if (fds.revents & POLLNVAL) {
            LOG_ERR("POLLNVAL");
            continue;
        }

        /* Handle data */
        if (fds.revents & POLLIN) {
            LOG_ERR("POLLIN");
            received = recv(sock, coap_buf, sizeof(coap_buf), 0);

            if (received < 0) {
                LOG_ERR("Socket error:  %d, exit\n", errno);
                continue;
                // break;
            } else if (received == 0) {
                LOG_ERR("Empty datagram\n");
                continue;
            }

            LOG_INF("Packet received, proceeding to handling\n");

            err = client_handle_response(coap_buf, received);
            if (err < 0) {
                LOG_ERR("Invalid response, exit\n");
                break;
            }
        }

        k_msleep(10);
    }

I am able to receive data (POLLIN), but when server closes session and sends close_notify, I am not able to receive POLLHUP.

I've tried nRF SDK 2.6.1 and 2.7.0. Modem FW version: mfw_nrf91x1_2.0.1.

Has anyone else encountered this problem?

[Hakon]

Hello,

do you have an application log from this? Can you also describe in detail what you are doing on the client side and also describe your setup in detail?

[Povilas S]

Nothing much to show from log, since data is missing. As I have mentioned, POLLIN arrives and I am able to call recv() after that. But I am not receiving any of the other "events". Nothing much to add, wireshark shows that close_alert arrives to the device, but it gets lost between that and poll().
Do you have any DTLS setup where you able to receive POLLHUP?

[Hakon]

Povilas S said:

Nothing much to show from log, since data is missing.

you can try to enable

CONFIG_COAP_LOG_LEVEL_DBG=y
CONFIG_NET_LOG=y

That will provide more detailed log output.

[Povilas S]

I don't see any new info coming after enabling these.

[Hakon]

That is kinda strange. You don't get something like this?

[Povilas S]

I don't, and correct me if I am wrong, but the logs you've posted are from CoAP sample and lib? How would it help? The code I've posted is polling socket directly, it is not using any CoAP abstraction for it, only when there is data received from the socket that it gets then parsed using CoAP lib. Am I missing something?

[Hakon]

Okay, it's hard to proceed without having more information. Can you post the application log and a full modem trace (.bin or .mtrace file)? Also, it would be really helpful if you could provide the complete setup to reproduce the issue.