Return str to a callback raise a segfault if used in string formating

[Vincent Vande Vyvre]

Le 14/10/17 à 15:59, Stefan Behnel a écrit :
> Vincent Vande Vyvre schrieb am 13.10.2017 um 13:18:
>> Le 13/10/17 à 12:39, Paul Moore a écrit :
>>> As a specific suggestion, I assume the name of the created file is a
>>> string object constructed in the C extension code, somehow. The fact
>>> that you're getting the segfault with some uses of that string
>>> (specifically, passing it to %-formatting) suggests that there's a bug
>>> in the C code that constructs that string. That's where I'd start by
>>> looking.
> Absolutely.
>
>
>> That was my first idea, because I can verify the instance of PyUnraw is not
>> destroyed when I use the file name, but I was in trouble by the usage of
>> the file name in string formatting.
>>
>> For example I can use the file name into the slot i.e. shutil.copy(fname,
>> "path/renamed.tiff")
>> The file is correctly copied.
>>
>> In fact, I can do anything with the file name except use it in string
>> formatting, then your approach is probably a good way.
>>
>> Into the CPython part I have a c-string pythonized by:
>>      temp = self->outfname;
>>      self->outfname = PyUnicode_FromString(ofname);
>>      Py_XDECREF(temp);
>>
>> and exposed to Python with:
>> static PyMemberDef PyUnraw_members[] = {
>>      {"out_file", T_OBJECT_EX, offsetof(PyUnraw, outfname), 0,
>>       "Path of the decoded file"},
> One more suggestion, in case this is actually your own C code: it's much
> easier to write extension modules in Cython than in plain C and C-API code.
> Much easier. There is a learning curve, sure, but it unburdens you from so
> many pitfalls and boilerplate code that it's always worth switching. And
> you also get faster code as a side-effect. How's that for a tradeoff. :)
>
> Stefan
> (Cython core developer)
>
Thanks, I know Cython but the code is already in C.

This is a lib released as a frontend.  Then usable only in command line.

It's not my own code, my job is to reimplement the main() function of 
the lib in CPython.

The work is nearly complete, I'm in the tests part.

I think I've found the problem, the string (a file path) is modified in 
c with "sprintf, snprintf, ..." And I plan to change that with some 
CPython equivalent function.


Vincent