[Rd] Bug: C-level and _set_rl_word_breaks

[Laurent Gautier]

On 2013-01-31 21:52, Laurent Gautier wrote:
> On 2013-01-31 21:09, Duncan Murdoch wrote:
>> On 13-01-30 9:48 PM, Laurent Gautier wrote:
>>> Hi,
>>>
>>> I filed a bug report in the tracker (id #15169) a short while ago,
>>> along with a patch, but I came back to it to see that there is
>>> relatively little movement or participation on the tracker so I
>>> thought I'd pitch it here (patch attached).
>>>
>>> The function `set_rl_word_breaks` in src/unix/sys-std.c relies on
>>> statically-allocated strings local to the function, making other C
>>> code using the readline library, such as a program embedding
>>> R and using readline as well, at risk of creating a segfault when
>>> trying to free `rl_basic_word_break_characters` or
>>> `rl_completer_word_break_characters` when changing them.
>>>
>>> The issue was noticed when embedding R in Python (rpy2); I had an
>>> ugly hack for a long time (less work than champion the inclusion
>>> of a patch in R) but the iPython developers pushed what could be
>>> demanded from the rpy2 with their "R magic" extension and
>>> so I wrote a patch (and they have made a brittle workaround in
>>> the meantime).
>>>
>>> The fix would be of interest to anyone embedding R in C and using
>>> readline (e.g., language interface developers if the language either
>>> has a console using readline - and chances are that it does - or
>>> an interface to readline).
>>>
>>> The patch attached is against today's R-dev and will likely apply to
>>> current R-2.15 branch. With the patch applied, R is building and is
>>> passing `make check`. It could be slightly expanded by handling
>>> cases where the calloc() or realloc() faills, although not an absolute
>>> priority (if allocating 200 bytes fails, the system might have
>>> bigger worries than keeping R from crashing).
>>
>> I suspect the reason your bug hasn't been dealt with in the 2 weeks 
>> since you posted it is that you don't show any code that illustrates 
>> the problem it causes.  It is much easier to run some code and see 
>> that code that should be valid is causing a crash, than it is to 
>> develop code to illustrate it.
>
> Fair enough. Now I realize that this might be a part of R codebase 
> that is hardly touched; while the problem makes sense to me after 
> spending time on it, a demonstrating what it causes in a minimal 
> example might be best).
>
>> Easily illustrated bugs get solved before hard ones.
>
> I guess I had a free pass since I provide a solution to the bug.
>
>>
>> Your post here gives a lot more detail, but still no code.  This 
>> isn't an area I'd work on (it seems to be a Unix-only bug), but you 
>> might attract someone else to look at it if you include a minimal 
>> self-contained trigger for it.
>
> I'll work on that.

A minimal example to demonstrate the problem is now in the bug tracker. 
It shows that either a C-extension or a part of a application in which R 
is embedded
crash R (segfault) by trying to change break delimiters.

Best,


Laurent


>
> Thanks,
>
> L.
>>
>> Duncan Murdoch
>