[lwip-devel] [bug #49684] lwip_netconn_do_writemore(): non-blocking ERR_MEM treated as failure

[Joel Cunningham]

URL:
  <http://savannah.nongnu.org/bugs/?49684>

                 Summary: lwip_netconn_do_writemore(): non-blocking ERR_MEM
treated as failure
                 Project: lwIP - A Lightweight TCP/IP stack
            Submitted by: jcunningham
            Submitted on: Wed 23 Nov 2016 04:10:00 PM GMT
                Category: sockets/netconn
                Severity: 3 - Normal
              Item Group: Faulty Behaviour
                  Status: None
                 Privacy: Public
             Assigned to: jcunningham
             Open/Closed: Open
         Discussion Lock: Any
         Planned Release: None
            lwIP version: git head

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Details:

The current logic in lwip_do_writemore() treats ERR_MEM for non-blocking
sockets as an error that should be propagated to the application.  When
ERR_MEM comes out of the sockets layer, it turns into ENOMEM which most
applications treat as fatal and close the socket rather than waiting in select
for the socket to be writable again

We can instead treat the ERR_MEM case the same as ERR_WOULDBLOCK: mark the
socket as non-writeable, and then writable upon resources opening up.  The
later two steps are already done in lwip_netconn_do_writemore() and
sent_tcp/poll_tcp.  The only piece left is to return ERR_WOULDBLOCK in this
case.

Further, this approach is very similar to how ERR_MEM is handled for blocking
sockets except that the application thread stays blocked until
sent_tcp/poll_tcp indicates resources are available.

Attached is a patch that fixes returning ERR_WOULDBLOCK



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File Attachments:


-------------------------------------------------------
Date: Wed 23 Nov 2016 04:10:00 PM GMT  Name:
0001-api_msg-treat-non-blocking-ERR_MEM-as-ERR_WOULDBLOCK.patch  Size: 2kB  
By: jcunningham

<http://savannah.nongnu.org/bugs/download.php?file_id=39057>

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