tcp sendmsg() EAGAIN handling

RE: tcp sendmsg() EAGAIN handling

Carl Richard — Tue, 15 Sep 2026 13:00:56 GMT

Hello again!

Thanks for the details. Can you verify that you are retransmitting the exact same data when retrying? There is a strict requirement for TLS connections that retries contains the same data. The EAGAIN error indicates that this may not be the case.

The requirement is documented here.

Best regards,
Carl Richard

RE: tcp sendmsg() EAGAIN handling

dpf — Mon, 14 Sep 2026 14:18:27 GMT

>Could you give me some more details about your implementation? Specifically: your nRF Connect SDK version, your modem firmware version and whether you are using TLS or not.

we're using tls + v2.0.0.4 on the nrf9151-laca, and getting to sendmsg() via the zephy'rs offload.

>Also, can you explain how you handle the retries in the application? If you don't want to share implementation data we can make the ticket private.

basically we try twice like:

for (tries = 0; tries < 2; tries++) {

rv = sendmsg((s, msg, flags);

if (rv < 0) {

if (errno == EAGAIN && tries < 1)

continue

return -errno;

}

... udate message iovec ..

}

RE: tcp sendmsg() EAGAIN handling

Carl Richard — Thu, 10 Sep 2026 08:29:03 GMT

Hi dpf!

Thanks for reaching out.

Could you give me some more details about your implementation? Specifically: your nRF Connect SDK version, your modem firmware version and whether you are using TLS or not.

Also, can you explain how you handle the retries in the application? If you don't want to share implementation data we can make the ticket private.

Best regards,
Carl Richard