TCP connect failed

[FIREWORKmby]

We are trying to add the ability to establish a TCP connection from the development board to a remote TCP server via OTBR to Nordic's matter routine and 52840 development board.

Refer to github.com/.../README_TCP.md, we have set up the network environment, and mentioned in the document, using the shell command on the terminal of success, And we set up a tcp connection with our own tcp server, the effect is similar:

> tcp connect 172.17.0.1 1234

Connecting to synthesized IPv6 address: fdde:ad00:beef:2:0:0:ac11:1

Done

Next, we created our own thread, and called the API provided by OpenThread for network programming instead of shell in the thread, trying to establish a tcp connection, but encountered the connect API returned -1, and there was no more information error.

We captured the connection message passed by the Raspberry PI, and successfully established a TCP connection under shell conditions.

What we now want to know is: on a Matter over Thread device, if you want to write some code to establish a connection with the tcp server and send and receive some tcp content, as the shell command does, whether there is a more direct reference document or code than analyzing the shell source code.

Or: Do you have suggestions on what to check when a connection is Reset by a client (the terminal itself) to abandon the connection? Neither Zephyr nor OpenThread's existing error messages can help us understand why the connection is being abandoned by the terminal?

Look forward to your comments, thank you!

[Marte Myrvold]

Hi,

I have started looking into this and will come back tomorrow.

In the meantime, can you share the code you used for trying to establish a TCP connection?

but encountered the connect API returned -1, and there was no more information error.

Did you check the errno error code? If you are not familiar with this, here is an example of how to use errno:

int err

err = connect(sock, (struct sockaddr *)&server, sizeof(struct sockaddr_in));
if (err < 0) {
	LOG_INF("Connecting to server failed, error: %d, %s", errno, strerror(errno));
	return -errno;
}

Best regards,
Marte

[FIREWORKmby]

We captured the connection message passed by the Raspberry PI, and successfully established a TCP connection under shell conditions：

Create thread, call connect interface failed to establish TCP connection corresponding to：



It seems that in the event of an exception, after the second handshake, the client sends the RST flag to reset the connection, so I wonder why the RST flag was sent during this connection.

[Marte Myrvold]

Hi,

Have you tried connecting to the socket outside of a while loop and without using k_sleep?

Could it be that something in the program interrupts during the TCP connection, like another thread?

Best regards,
Marte

[FIREWORKmby]

hello

I have tried what you say and it has not worked;

Through packet capture, it is found that ECN is successfully opened under the shell, but the code written by myself is not, although I do not know whether it is the cause of connect failure, but I still want to know how to open ECN in tcp connect under cli.

[Marte Myrvold]

Hi,

Have you tested connecting to other servers?

I have not been able to figure out why it fails with your code and not with the CLI. I see that the ot tcp connect command calls a Thread specific function for TCP connection, but there are samples that connect to TCP server by using the socket() and connect() functions as well, such as the Echo client sample.

Best regards,
Marte