[lwip-devel] [bug #57018] lwip_select and lwip_connect can not detect "refuse connection request packet"

[Hunkar Ciplak]

URL:
  <https://savannah.nongnu.org/bugs/?57018>

                 Summary: lwip_select and lwip_connect can not detect "refuse
connection request packet"
                 Project: lwIP - A Lightweight TCP/IP stack
            Submitted by: chunkar
            Submitted on: Mon 07 Oct 2019 10:01:55 PM UTC
                Category: TCP
                Severity: 3 - Normal
              Item Group: Faulty Behaviour
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
         Planned Release: None
            lwIP version: 2.1.1

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Details:

I came across an issue while trying to connect to remote TCP server by using
non-blocking socket.After sending the connection request by lwip_connect i am
checking the "writability of the socket by lwip_select and also i am checking
the errno.

But, even if the remote server sends "refuse connection request", lwip assumes
it is connected to remote tcp server.

Note: Just for example, on ubuntu you can send "refuse connection request"
packet to clients when you follow the steps below:
1)nc -l 45678
2)CTRL+Z = stop netcad
3) After stopping netcad, when you send a connection request, ubuntu will send
'refuse' packet to your connection request. When you try to connect with your
mobile phone, it will reported that it can not connect to remote server.
But when you try to connect with a non-blocking socket by using lwIP 2.1.2,
then lwip_connect returns EINPROGRESS and lwip_select, returns 'socket is
writable' / "OK" when the socket receives the 'refuse packet'. 




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