[lwip-devel] [bug #46185] UDP packets are not received after socket rebind

[Andreas Toensfeuerborn]

URL:
  <http://savannah.nongnu.org/bugs/?46185>

                 Summary: UDP packets are not received after socket rebind
                 Project: lwIP - A Lightweight TCP/IP stack
            Submitted by: atoensfeuerborn
            Submitted on: Mon 12 Oct 2015 06:43:48 AM GMT
                Category: UDP
                Severity: 3 - Normal
              Item Group: Faulty Behaviour
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
         Planned Release: 
            lwIP version: 1.4.1

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Details:

In my application I use several interfaces (up to 32). The behaviour described
below can be reproduced easier with more than 1 interface but occurs also with
only 1 interface.

After startup, I create 2 UDP sockets for each interface but do not bind them
because I do not know the IP address yet.

For each socket I have a separate receive thread calling "lwip_recvfrom". The
function returns an error because the socket is not bound and I ignore the
error.

At some point the sockets are bound to an IP address by calling
- lwip_close()
- lwip_socket()
- lwip_bind()

I have been using this kind of implementation with native sockets from
Windows, Linux and VxWorks without any problems.

Most of the time the behaviour after that is correct and packets are received
properly in the receive thread(s).
But sporadically received packets are not delivered to "lwip_recfrom".
The packet is transferred through functions "udp_input" to "recv_udp" but the
mailbox does not deliver the packet to "netconn_recv_data" and therefore to
"lwip_recfrom".

The behaviour is the same under Linux and Windows so I think the mailbox
handling itself is not the source of the problem.

The error seems to occur in case the function "sys_mbox_trypost" is called
before the function "lwip_recvfrom" (netconn_recv_data) is ready to receive
the data.

I have attached to files with (also self made) debug outputs in case the
connection is ok and not ok.
In case the connection is ok, "lwip_recvfrom" is called before "udp_input"
after the rebind.
In case the connection is not ok, "udp_input" is called before
"lwip_recvfrom".








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File Attachments:


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Date: Mon 12 Oct 2015 06:43:48 AM GMT  Name: putty_ok.TXT  Size: 181kB   By:
atoensfeuerborn

<http://savannah.nongnu.org/bugs/download.php?file_id=35162>
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Date: Mon 12 Oct 2015 06:43:48 AM GMT  Name: putty_nok.TXT  Size: 317kB   By:
atoensfeuerborn

<http://savannah.nongnu.org/bugs/download.php?file_id=35163>

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