[Python-Dev] REVIEW: PyArg_ParseTuple with "s" format and NUL: Bogus TypeError detail string.

[Sean Reifschneider]

Please review this, I'm worried that there are cases where convertitem() is
returning a string that really should be overridden by the argument "help
string".  However, I'm worried that this change will get rid of useful
messages (via the format "; help string"), when there otherwise wouldn't
be.

PyArg_ParseTuple when handling a string format "s", raises a TypeError
when the passed string contains a NUL.  However, the TypeError doesn't
contain useful information.

For example:

   syslog.syslog('hello\0there')
   TypeError: [priority,] message string

This seems to be a thinko in Python/getargs.c at line 331:

   msg = convertitem(PyTuple_GET_ITEM(args, i), &format, p_va,
        flags, levels, msgbuf,
        sizeof(msgbuf), &freelist);
   if (msg) {
      seterror(i+1, msg, levels, fname, message);   <<< Line 331
      return cleanreturn(0, freelist);
   }

This also applies to Python 3 trunk in line 390.

I think that's supposed to be "msg" instead of "message" in the last
argument.  If I change it, I get:

   >>> import syslog; syslog.syslog('hello\0there')
   Traceback (most recent call last):
     File "<stdin>", line 1, in <module>
   TypeError: must be string without null bytes, not str

I think it's safe to change "message" to "msg" because:

   "message" is the "help" string "[priority,] message string",
   but "msg" contains much more useful information.

   "msg" is in the "fall back if the last argument doesn't contain useful
   information" argument position, but "msg" is never NULL.

   "message" only is NULL if the format string doesn't contain ";".

   In every case I can find in the code, convertitem() is returning a
   much more useful string than the help string.

Or perhaps it should do something like:

   if (msg) {
      seterror(i+1, msg, levels, fname, '%s (%s)' % ( msg, message ));

Pardon my mixed C+Python, but you get the idea.

Thoughts?

Thanks,
Sean
-- 
 [...] Premature optimization is the root of all evil.
                 -- Donald Knuth
Sean Reifschneider, Member of Technical Staff <jafo at tummy.com>
tummy.com, ltd. - Linux Consulting since 1995: Ask me about High Availability