developer reports unexpected behaviour with using libgsf with uncompressed xml
files, i.e. http://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=111468

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Description of problem:
Libgsf's gsf_xml_parser_context() function seems broken when used to
open an uncompressed xml file.  I am working on an application that
does the following:

1.  initializes the library
2.  creates a new gsf input entity using foo=gsf_input_gnomevfs_new()
3.  calls gsf_xml_parser_context(foo)
4.  does some stuff

The problem is that between step 3 and 4, the gsf input entity foo's
cur_offset is set to 10.  This is does even though no data is directly
read by the application.

Since cur_offset is used to calculate the amount of unread data, the
result of this is that gsf_input_remaining returns an incorrect value
and reading gets mixed up.

gsf-libxml.c:gsf_xml_parser_context looks like this:

gsf_xml_parser_context (GsfInput *input)
{
        GsfInputGZip *gzip;
                                                                     
          
        g_return_val_if_fail (GSF_IS_INPUT (input), NULL);
                                                                     
          
        gzip = gsf_input_gzip_new (input, NULL);
        if (gzip != NULL)
                input = GSF_INPUT (gzip);
        else {
                gsf_input_seek(input, 0, G_SEEK_SET);
                g_object_ref (G_OBJECT (input));
        }
                                                                     
          
        return xmlCreateIOParserCtxt (
                NULL, NULL,
                (xmlInputReadCallback) gsf_libxml_read,
                (xmlInputCloseCallback) gsf_libxml_close,
                input, XML_CHAR_ENCODING_NONE);
}

It appears that "gzip = gsf_input_gzip_new (input, NULL);" is what
causes the mixed up cur_offset value.  This make sense because
gsf_input_gzip_new would have to read a few bytes from input in order
to determine if the file is valid gzip'ed data or not.

So...

gsf_xml_parser_context (GsfInput *input)
{
        GsfInputGZip *gzip;
                                                                     
          
        g_return_val_if_fail (GSF_IS_INPUT (input), NULL);

        return xmlCreateIOParserCtxt (
                NULL, NULL,
                (xmlInputReadCallback) gsf_libxml_read,
                (xmlInputCloseCallback) gsf_libxml_close,
                input, XML_CHAR_ENCODING_NONE);
}

...works fine (but only with uncompressed files of course).

Either gsf_input_seek() should be used if gsf_input_gzip_new() fails
or gsf_input_gzip_new() should reset the file cursor before failing.

Version-Release number of selected component (if applicable):
1.8.2

How reproducible:
Always

Steps to Reproduce:
1.  Load an application that uses gsf_xml_parser_context(foo) into
your favorite debugger.

2.  Notice that foo->cur_offset is set to 10d after
gsf_xml_parser_context is executed on an uncompressed file.

Additional info: