Re: [xml] Possible bug with schema validation in combination with xsi:nil

[Thomas Gamper <icicle cg tuwien ac at>]

Am 08.02.2013 11:09, schrieb Thomas Gamper:
> Am 07.02.2013 17:59, schrieb Thomas Gamper:
> > Am 07.02.2013 17:56, schrieb Csaba Raduly:
> > > On Thu, Feb 7, 2013 at 4:47 PM, Thomas Gamper  wrote:
> > > > Hi!
> > > >
> > > > I ran into issues with libxml2 xml validation with schemas as soon 
> > > > as i
> > > > started using the xsi:nil attribute. Attached you find a reduced 
> > > > version of
> > > > the schema I am using (zenotrack-pilot.xsd + all the dependencies 
> > > > it needs)
> > > > and two test cases:
> > > >
> > > > GetNextMessageResponse.xml which does not validate with with xmllint
> > > > (xmllint --schema zenotrack-pilot.xsd GetNextMessageResponse.xml)
> > > > GetMessagesResponse, which is extremely similar to the first 
> > > > testcase, but
> > > > does validate with xmllint (xmllint --schema zenotrack-pilot.xsd
> > > > GetMessagesResponse.xml)
> > > >
> > > > I did try libxml2 2.7.7, 2.7.8 and 2.9.0. I did a debug build of 
> > > > libxml2
> > > > 2.9.0 on Win64 and stepped with the debugger through the code, but 
> > > > it is
> > > > simply to complex for me to understand what is actually going on. 
> > > > All I saw
> > > > was that the nil attribute was recognized as such, but later one 
> > > > validation
> > > > failed for reasons I do not understand.
> > > >
> > > > Probably I am not seeing the obvious, but still I would like to ask 
> > > > for help
> > > > if there is actually something wrong with libxml2 in this case.
> > > It is almost certainly a bug in libxml2: I tried your files with a
> > > validator based on Xerces-C and both passed.
> > >
> > > Csaba
> > The validator integrated into Visual Studio seems to validate both 
> > files fine too.
> >
> > Thanks,
> > TOM
> Ok, I found where the different behavior comes from:
> xmlschemas.c line 26072 where xmlRegExecPushString is called inside 
> xmlSchemaValidatorPopElem, right when we are leaving the offending 
> node (Message element, child of GetNextMessageResponse element)
>
>      libxml2.dll!xmlRegExecPushStringInternal(_xmlRegExecCtxt * 
> exec=0x000000000cb6e200, const unsigned char * 
> value=0x0000000000000000, void * data=0x0000000000000000, int 
> compound=0)  Zeile 3786    C
>      libxml2.dll!xmlRegExecPushString(_xmlRegExecCtxt * 
> exec=0x000000000cb6e200, const unsigned char * 
> value=0x0000000000000000, void * data=0x0000000000000000)  Zeile 
> 4133    C
>      libxml2.dll!xmlSchemaValidatorPopElem(_xmlSchemaValidCtxt * 
> vctxt=0x000000000c973890)  Zeile 26072 + 0x13 Bytes    C
> >    libxml2.dll!xmlSchemaVDocWalk(_xmlSchemaValidCtxt * 
> vctxt=0x000000000c973890)  Zeile 27977 + 0xd Bytes    C
>      libxml2.dll!xmlSchemaVStart(_xmlSchemaValidCtxt * 
> vctxt=0x000000000c973890)  Zeile 28087 + 0xa Bytes    C
>      libxml2.dll!xmlSchemaValidateDoc(_xmlSchemaValidCtxt * 
> ctxt=0x000000000c973890, _xmlDoc * doc=0x00000000080f9ba0)  Zeile 
> 28166    C
>
>
> GetMessagesResponse
>
> xmlRegExecPushStringInternal is called, which in turn calls 
> xmlRegCompactPushString in xmlregexp.c line 3787
> and returns 0.
>
> GetNextMessageResponse
>
> xmlRegExecPushStringInternal is called, which in turn does not call 
> xmlRegCompactPushString,
> and returns -1.
>
> xmlschemas.c line 26073
> if ((ret<0) || ((ret==0) && (!INODE_NILLED(inode))))
>
> The check works with ret == 0, but not with ret = -1. This poses two 
> questions:
> Is the check wrong?
> Or is the regexp matching doing something wrong?
>
> Thanks,
> TOM
So, attached you find a patch diffed against git master which fixes the 
issue. There is no point doing a regexp validation of further content if 
there actually *IS* no further content because the element is nil. I 
also checked that validation of an element which has xsi:nil="true" but 
contains child elements still fails as it should.

Cheers,
TOM

Attachment: xsinil.patch
Description: Text document