[lwip-devel] [bug #43739] Accept not reporting errors about aborted connections

[Joel Cunningham]

Follow-up Comment #2, bug #43739 (project lwip):

I would agree out-of-pcbs should be included in this failure (also
out-of-sockets).  The accept() call in sockets.c will return ENFILE if out of
sockets.

>From the application point of view, if a pending connection can't be handed
off due to failure to allocate connection state (either socket, netconn, or
pcb) it would make sense to be consistent with error handling.

When I encountered this, I had no idea why the connection was being aborted on
the server.  It took considerable debugging in api_lib.c, api_msg.c, and
tcp_in.c to pinpoint the failure.  There are no LWIP_ASSERTs for this
failure.

After looking up the opengroup specification for accept(), that lead me to
consider this a bug.  I would consider it low priority since it just makes
life easier for application developers.

I'm not sure how the backlog should play into this since a full backlog
usually doesn't result in a RST, but ignoring the SYN or ignoring resulting
ACK from listener's SYN+ACK.  The Linux backlog behavior is an interesting
data point:
http://veithen.github.io/2014/01/01/how-tcp-backlog-works-in-linux.html

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