[lwip-devel] [bug #56964] lwIP2.1.2 assumes it connected to remote server altough remote server sends "refuse" for the connection reques

[Hunkar ciplak]

URL:
  <https://savannah.nongnu.org/bugs/?56964>

                 Summary: lwIP2.1.2 assumes it connected to remote server
altough remote server sends "refuse" for the connection reques
                 Project: lwIP - A Lightweight TCP/IP stack
            Submitted by: chunkar
            Submitted on: Sun 29 Sep 2019 10:38:44 AM UTC
                Category: TCP
                Severity: 3 - Normal
              Item Group: Feature Request
                  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 using lwip_connect, i am checking the
errno and then i checking whether it writable or not by using the lwip_select.
As known, when lwip_select returns "OK" then, it means client got connected to
remote server successfully but lwip_connect and lwip_select does not return
any error, although the connection request is refused by the 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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