Re: [xml] Valgrind problems with xmlParseFile

[Daniel Veillard <veillard redhat com>]

On Thu, Aug 16, 2012 at 10:52:37AM +0100, Alex Bligh wrote:
> We are calling
> xmlParseFile("constantfilename.xml")
> and this is producing Valgrind errors.
>
> On inspection, it appears to be coming from the code snippet below,
> almost certainly the gzdirect call (though the name is lost from
> the stack trace).
>
> Other people have seen this outside libxml and it is probably a zlib
> issue. However, we KNOW our file is not compressed. Is there a way
> that we can do an xmlParseFile and say "please don't even try to
> use a compression handler"?

  Well ... no ! Except by registering your own I/O functions
and feeding the parser yourself but with normal APIs I really want
transparent (de)compression, because well XML compress so well
in general that it's a shame to not do it more often :)

> #ifdef HAVE_ZLIB_H
>        if ((xmlInputCallbackTable[i].opencallback == xmlGzfileOpen) &&
>                (strcmp(URI, "-") != 0)) {
> #if defined(ZLIB_VERNUM) && ZLIB_VERNUM >= 0x1230
>            ret->compressed = !gzdirect(context);
> #else
>            if (((z_stream *)context)->avail_in > 4) {
>                char *cptr, buff4[4];
>                cptr = (char *) ((z_stream *)context)->next_in;
>                if (gzread(context, buff4, 4) == 4) {
>                    if (strncmp(buff4, cptr, 4) == 0)
>                        ret->compressed = 0;
>                    else
>                        ret->compressed = 1;
>                    gzrewind(context);
>                }
>            }
> #endif

  The problem is that if I were to avoid using the autodetection
from zlib, I would have to try to embbed some autodetection in libxml2
and that sounds just the wrong thing to do. Better fix zlib or
get valgrind updated ignore files for zlib.

Daniel

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