[Python-Dev] inet_addr usage in Modules/socketmodule.c? (original) (raw)

Skip Montanaro skip@pobox.com
Fri, 1 Mar 2002 10:47:33 -0600

According to the checkin comment for Modules/socketmodule.c v. 1.91:

Port inet_ntoa and inet_aton to Windows:

- fix unescaped newline in string literal
- removed unused err variable
- Windows doesn't have inet_aton; use inet_addr instead

However, in the man page for inet_addr it states:

This is an obsolete interface to inet_aton, described immediately above;
it is obsolete because -1 is a valid address (255.255.255.255), and
inet_aton provides a cleaner way to indicate error return.

The reason I bring it up is that a request came in today to python-help about python-2.2 on an SX supercomputer, which suggests that the code for handling INADDR_NONE (and thus inet_addr()) is broken:

I have compiled python-2.2 on an SX supercomputer which does not have
inet_pton(). The emulated one in Modules/socketmodule.c is being used
instead. The test for packed_addr against INADDR_NONE fails because:

1) INADDR_NONE is 0xffffffff in SX #include file,
2) long on SX is 8-bytes,
3) inet_addr() returns -1 (0xffffffffffffffff) which is -1, but _not_
   INADDR_NONE. 

Has this problem come up anywhere else with sizeof(long) == 8 and
inet_addr() schizophrenia?

I realize that this may be an OS implementation issue (should
inet_addr() return -1 or INADDR_NONE) but what should/can be done (if
anything) to the Python package in order to address this?

It seems to me the simplest thing to do is to force a "proper" definition of INADDR_NONE with something like

#ifdef INADDR_NONE
#undef INADDR_NONE
#endif
#define INADDR_NONE ((in_addr_t)-1)

if it's not defined and in_addr_t is available. The more correct thing would seem to be to dump inet_addr in favor of inet_aton unless the latter is unavailable.

On the other hand, perhaps just the SX include files are busted and all that has to happen is to override INADDR_NONE for that platform:

#if defined(INADDR_NONE) && INADDR_NONE != ((in_addr_t)-1)
#undef INADDR_NONE
#define INADDR_NONE ((in_addr_t)-1)
#endif

Unfortunately, my mastery of the C preprocessor, casts, and configure is insufficient to determine without some experimentation on a platform I have no acces to if either of these is a workable approach or if there is a better approach that will work on the SX.

Your thoughts?

Skip