TCP Acknowledgement

[Raul]

Hello,

I am trying to print the acknowledgement received by the TCP sender on the CLI but I couldn't make it work. Can anyone help point me in the right direction? Thanks!

[Jonathan Hui]

You can add a call to OutputLine() in TcpExample::HandleTcpSendDone().

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Jonathan Hui

On Fri, Mar 4, 2022 at 12:26 PM Raul <raulpri...@gmail.com> wrote:

Hello,

I am trying to print the acknowledgement received by the TCP sender on the CLI but I couldn't make it work. Can anyone help point me in the right direction? Thanks!

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[Raul]

Hi Jonathan,

I tried OutputLine("%s", aData->mData); and it looks like mData is the data being sent and not the acknowledgement.

So I tried OutputLine("%s", aEndpoint->mReceiveAvailableCallback); and it printed some weird characters. Is this the correct buffer for the acknowledgement and I just need to convert them into ASCII or is it something else?

[Jonathan Hui]

The TCP API does not provide the actual TCP packets. If you really want to dump the contents of the packet, I would suggest using OpenThread log packet dump capabilities and add some code to src/core/net/tcp6.cpp to dump the contents of the packets.

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Jonathan Hui

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[Raul]

Hi Jonathan,

I am just looking for a way to read the additional data appended in the ACK by the listening TCP endpoint.

For context, in our project, our server (the listening TCP endpoint) sends a custom string (e.g., "complete") as sort of an acknowledgement to the connecting TCP endpoint (in our case, a full-thread device) to inform it that all the TCP packets have been received. Currently, when I send a message to the server (e.g., tcp send hello), what is displayed on the cli of the full-thread device is this:

> tcp send hello

Done

> TCP: Reached end of stream

The custom string "complete" is missing.

[Jonathan Hui]

The TCP CLI should output any received bytes before reaching the end of stream (see TcpExample::HandleTcpReceiveAvailable())

Can you provide a pcap file (from tcpdump or sniffer) that shows the TCP packets?

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Jonathan Hui

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[Raul]

Hi Jonathan,

We made a mistake on the string sent by the server. It is fixed now and the TCP CLI did output our expected received bytes. Thank you!