Boost logo

Boost Users :

From: Paul Giaccone (paulg_at_[hidden])
Date: 2006-01-19 13:06:50

Paul Giaccone wrote:

>How can you deal with a corrupt file when using filters?
>I have a chain of filters that includes a bzip2 and multichar filter
>have written myself. If the read() function fails to find what it
>expects in the file, it returns 0 (meaning "no characters read").
>Otherwise it returns the number of characters read (which should be
>equal to the number of characters requested in the third function
>parameter) or -1 if the end of the file is reached.
>This works fine if the file is as is required, but if it is corrupted in
>any way, the program either hangs or crashes at
> if (s->strm != strm) return BZ_PARAM_ERROR;
>in bzlib.c, with s as a pointer that cannot be read (set to 0xcdcdcdcd).
>I'm working in Microsoft Visual C++ and gcc 3.2.3.
>How should this be handled? I haven't seen anything about it in the
>documentation. I imagine I should throw an exception instead of
>returning 0 (perhaps an iostreams exception?). Given that the crash is
>the bzip2 (bzip2 being the first operation done when deserialising the
>file), where would I put the associated catch block?
OK, I throw an exception if my filter finds an error, but the error is
clearly being caused at the bzip stage. How can I trap that?

Here's a summary of what I am doing:

Filter chain:

        boost::iostreams::filtering_istream in;
        in.push(boost::iostreams::file_source(filename, BOOST_IOS::in |
        boost::archive::xml_iarchive input_archive(in);
        my_data >> BOOST_SERIALIZATION_NVP(my_object);
    catch (MyException e)
        std::cerr << "Error reading archive file " << filename << ": "
<< e.what() << std::endl;
    catch (boost::archive::archive_exception e)
        std::cerr << "Error decoding archive file " << filename << ": "
<< e.what() << std::endl;
    catch (std::ios_base::failure e)
        std::cerr << "Error reading from file " << filename << ": " <<
e.what() << std::endl;

I am deliberatively providing the above with a corrupted file that bzip2
will not be able to understand. None of the "catch"es above are executed.

So how can I catch a problem at the bzip2 stage?

Paul Giaccone

Boost-users list run by williamkempf at, kalb at, bjorn.karlsson at, gregod at, wekempf at