Re: [lwip-users] Scan through the heap searching for a free block that is big enough, beginning with the lowest free block.

[Sergio R. Caprile]

If you decide to generate checksums on lwIP, you MUST tell the
controller not to generate them.

You must check arg and newpcb in your tcp_accept() callback, follow the
examples.
Your tcpecho source is different from what I can see on lwIP git. I
won't check further.
I won't check the rest of your coding, particularly because you are
copying memory to places I don't know where they are and to whom they
belong; lest can I know if it fits.

Make sure your modifications to the working server (as you said it
works) happen on a well paced and controlled fashion, in order to make
it easier for you to discover where you break it.