[lwip-devel] [bug #48543] TCP sent callback may prematurely report sent data when only part of a segment is acked

[Ambroz Bizjak]

Follow-up Comment #3, bug #48543 (project lwip):

Here, I've implemented a fix in my fork:
https://github.com/ambrop72/aprinter/commit/a4f6315b4822a25a01a652ff8e162a1839b29d67

I calculate tcp_acked by summing the lengths of the segments that have been
freed due to the ACK. So the stack will not report data as acked until the
entire segment has been acked.

Note if applying this to lwIP some care is needed due to various weirdness
that I have already resolved in my fork:

- lwIP's pcb->snd_buf includes one count for SYN/FIN; in my patch I sum up the
seg->len (no flag counts) and add it to pcb->snd_buf (also no flag counts due
to refactoring).

- Acked segments can be in ->unacked or ->unsent; for some reason the freeing
of ->unsent segments is lower in the code outside of "else if" where the main
ack handling code is. I think it can be moved up and consolidated.

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