[xsd-users] Bug in ACE CDR deserialization

[James Frullo]

I just downloaded the latest stable release of xsd (2.3.1), and I tried
compiling and running the "binary" sample under the examples/cxx/tree/binary
directory.  I built ACE by linking to the Multi-threaded Debug DLL version
of the CRT, but I built the sample using the plain Multi-threaded Debug
version.  This brought out a non-obvious bug in the implementation of the
following function:
inline istream<ACE_InputCDR>& operator>> (istream<ACE_InputCDR>& s,
std::basic_string<char>& x)
This function has the following implementation:

        ACE_CDR::Char* r;

        if (!s.impl ().read_string (r))
          throw ace_cdr_stream_extraction ();

        auto_array<ACE_CDR::Char> ar (r);

        x = r;

        return s;

The problem with this is that calling read_string() gives you memory
allocated by ACE.  But auto_array is going to deallocate that memory by
calling delete[].  Since ACE is compiled and linked separately, it is
incorrect to assume that this will work.  In fact, it does not work.  It
crashes because using the build configurations I mentioned above.  The
correct code would be something like:

        ACE_CDR::Char* r;

        if (!s.impl ().read_string (r))
          throw ace_cdr_stream_extraction ();

        try {x = r} catch(...){ACE::strdelete(r);throw;}
        ACE::strdelete(r);

        return s;

Of course, this is ugly.  A nicer way would be to have an ace_auto_str()
class (or whatever).

~James