[lwip-devel] [bug #35928] BSD sockets functions must set errno for POSIX-compliance

[Mason]

URL:
  <http://savannah.nongnu.org/bugs/?35928>

                 Summary: BSD sockets functions must set errno for
POSIX-compliance
                 Project: lwIP - A Lightweight TCP/IP stack
            Submitted by: mason
            Submitted on: Wed 21 Mar 2012 09:39:03 AM GMT
                Category: sockets
                Severity: 3 - Normal
              Item Group: Faulty Behaviour
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
         Planned Release: 
            lwIP version: 1.4.0

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Details:

I am porting libcurl on top of lwip on a (mostly) POSIX-compliant embedded
platform. In this configuration, libcurl expects a POSIX-compliant network
stack. On a closely related note, cf. task #11879: Add POSIX conformant header
files <https://savannah.nongnu.org/task/?11879>.

lwip provides a BSD sockets compatibility layer which, by default, is not
POSIX-compliant, because none of the sockets function set errno.

cf. set_errno and sock_set_errno macros



#ifdef ERRNO
#ifndef set_errno
#define set_errno(err) errno = (err)
#endif
#else /* ERRNO */
#define set_errno(err)
#endif /* ERRNO */

#define sock_set_errno(sk, e) do { \
  sk->err = (e); \
  set_errno(sk->err); \
} while (0)



Thus, by default, set_errno is a NOP.
(NB: the ERRNO macro is undocumented)

Consider the requirements for connect:
http://pubs.opengroup.org/onlinepubs/9699919799/functions/connect.html

  Upon successful completion, connect() shall return 0;
  otherwise, -1 shall be returned and errno set to indicate the error.

(The same requirement exists for all BSD sockets functions.)

In lwip, the (optional) BSD sockets compatibility layer is compiled
only if LWIP_SOCKET is defined to a non-zero value. If an lwip
integrator needs the sockets layer, it is very likely that he expects
the BSD sockets functions to comply to POSIX.

Thus, if LWIP_SOCKET is defined, I believe the BSD sockets functions
must set errno by default. It might make sense to allow integrators
to disable this feature, but compliance should be the default.

Which means applying the following trivial patch, to remove the
undocumented ERRNO macro.



--- sockets.c   2012-02-23 10:57:12.796875000 +0100
+++ sockets.c   2012-03-20 10:50:40.375000000 +0100
@@ -158,13 +158,9 @@
   ((unsigned)(-(err)) < ERR_TO_ERRNO_TABLE_SIZE ? \
     err_to_errno_table[-(err)] : EIO)
 
-#ifdef ERRNO
 #ifndef set_errno
 #define set_errno(err) errno = (err)
 #endif
-#else /* ERRNO */
-#define set_errno(err)
-#endif /* ERRNO */
 
 #define sock_set_errno(sk, e) do { \
   sk->err = (e); \



An integrator can
#define set_errno(err)
in his port's cc.h if he needs to disable setting errno (why?!)

Please seriously consider this patch, libcurl checks errno all over
the place.




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File Attachments:


-------------------------------------------------------
Date: Wed 21 Mar 2012 09:39:03 AM GMT  Name: patch_sockets.txt  Size: 422B  
By: mason

<http://savannah.nongnu.org/bugs/download.php?file_id=25426>

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