[xml] Substitution of nested entity references

["Henke, Markus" <Markus_Henke ordat com>]

Hello Daniel,

and sorry to broach that topic again, but i'd hoped
that the approach mentioned below is possibly worth
a comment...  8)

Kidding asside, i really won't to press for something
or get on someone's nerves. It's just that my
(libxml2 based) application (an API for COBOL) is
short to a first release version and i've to decide
whether i've to handle the substitution of nested
entity references on application level or to rely
on libxml.
If it's not intended to do the substitution in
libxml, it's maybe a good idea to point this out in
the docs/reference for xmlNodeGetContent(),
xmlGetProp() and the like!?


TIA, Markus

> -----Original Message-----
> From: Henke, Markus 
> Sent: Wednesday, March 20, 2002 4:08 PM
> To: 'xml gnome org'
> Subject: RE: [xml] xmlNodeGetContent() for XML_ENTITY_REF_NODE
>
>
> Hello,
>
> and please apologize the long response time, but there
> where other things to take care of (among them some holidays...8).
>
> In the meantime i've written a routine that does the (recursive)
> substitution for (nested) entitiy reference, and it works fine for
> me so far (code included below).
> Anyhow, there are some points to clarify before it may be usefull
> for libxml2:
>
> - Is it possible that someone can get a xmlDocPtr to a non
>   well-formed (possibly due to cyclic entity references)
>   document? This could cause serious problems in this
>   routine... 8)
>
> - Is xmlGetDocEntity() the proper way to lookup the entity
>   declaration in that case? There is also xmlGetDtdEntity(),
>   i'm not shure about the difference. Both take a xmlDocPtr
>   as parameter (and i must confess that i haven't had the
>   time by now to examine the source for that...)
>
> - I've assumed that a xmlEntity have only child nodes with
>   type XML_ENTITY_REF_NODE or XML_TEXT_NODE. Is this correct,
>   and if not, which additional cases were to take into
>   consideration?
>
> I would be glad to improve this routine if there is any
> chance that it could be used in libxml2 to resolve nested
> entity references, i guess at least xmlNodeGetContent and
> xmlGetProp() [xmlGetNsProp()] should do so, the reference
> says
> ... Entity references are substituted... e.g.
> ... This does the entity substitution...
>
>
> Thanx & Ciao, Markus
>
>
> ===============================================================
> /**
>  * xmlResolveEntityRef:
>  * @docPtr:  the document pointer
>  * @entityRefPtr:  pointer to a XML_ENTITY_REF_NODE
>  * @contentBufferPtr: pointer to a xmlBuffer for the resolved content
>  *
>  * Does the substitution of an entity reference.
>  * Recursive behaviour for nested references.
>  *
>  * Returns the size of the resolved content or -1 in case of error
>  */
>
> int xmlResolveEntityRef(xmlDocPtr docPtr,
>              xmlNodePtr entityRefPtr,
>              xmlBufferPtr contentBufferPtr)
> {
>       
>   int contentLen = 0;
>   xmlEntityPtr entityDeclPtr = (xmlEntityPtr)NULL;
>   xmlNodePtr nodePtr = (xmlNodePtr)NULL;
>
>   /*** check node type ***/
>   if (entityRefPtr->type != XML_ENTITY_REF_NODE)
>   {
>     xmlGenericError(xmlGenericErrorContext,
>       "xmlResolveEntityRef: Node type != XML_ENTITY_REF_NODE\n");
>     return -1;
>   }
>       
>   /*** lookup entity declaration ***/
>   if (!(entityDeclPtr = xmlGetDocEntity(docPtr, entityRefPtr->name)))
>   {
>     xmlGenericError(xmlGenericErrorContext,
>       "xmlResolveEntityRef: Lookup for entity declaration failed\n");
>     return -1;
>   }
>
>   nodePtr = entityDeclPtr->children;
>   while (nodePtr)
>   {
>     switch (nodePtr->type)
>     {
>       case XML_ENTITY_REF_NODE:
>       {
>         /*** recursive call to xmlResolveEntityRef ***/
>         contentLen += xmlResolveEntityRef(docPtr,
>                           nodePtr, contentBufferPtr);
>         break;
>       }
>       case XML_TEXT_NODE:
>       {
>         /*** read and append (text) node content ***/
>         xmlChar *contStr = xmlNodeGetContent(nodePtr);
>         xmlBufferCat(contentBufferPtr, (const xmlChar*)contStr);
>         contentLen += xmlStrlen((const xmlChar*)contStr);
>         xmlFree(contStr);
>         break;
>       }
>       default:
>       {
>         /*** what shall we do here, could this happen? ***/
>         xmlGenericError(xmlGenericErrorContext,
>           "xmlResolveEntityRef: Unexpected node type: %d\n",
>           nodePtr->type);
>         return -1;
>       }
>     }
>     nodePtr = nodePtr->next;
>   }
>
>   return contentLen;
>
> }
> ==================================================================
>
>
>
> > -----Original Message-----
> > From: Daniel Veillard [mailto:veillard redhat com]
> > Sent: Friday, February 22, 2002 4:07 PM
> > To: Henke, Markus
> > Cc: 'xml gnome org'
> > Subject: Re: [xml] xmlNodeGetContent() for XML_ENTITY_REF_NODE
> >
> >
> > On Fri, Feb 22, 2002 at 03:35:02PM +0100, Henke, Markus wrote:
> > > > I'm not sure you can get this recursive.
> > >
> > >
> > > Hum, you mean nested entity references? Weird, i've never
> >
> >   yep
> >
> > > thought about this. My app instantly crashed as i've tested
> > > it. Smell's like a new debugging session... 8]
> > > I'd hoped that i could pilfer at 'xmlGetProp()', but it won't
> > > do a recursiv entity substitution!?
> > > However, i've to do this and i should manage it since cyclic
> > > entity refs are illegal.
> > > BTW, the libxml parser detects cyclic entity
> > > references but it seems that it loops about 40 times? 
> >
> >   Call me lazy, I need to fix and report only the first one
> >
> > > > Another way would be to change xmlNodeGetContent()
> > > > behaviour on entities nodes.
> > >
> > > I'll try to code a recursiv entity substitution for
> > > XML_ENTITY_REF_NODEs. If it works for me i'll send
> > > it to the list so you can decide if it makes sense to
> > > include it in xmlNodeGetContent() (and possibly
> > > xmlGetProp()...).
> >
> >   Hum, okay,
> >
> > > >   Actually it's a pointer to the associated ENTITY_DEF
> > > > node content's, the subtree are shared.
> > >
> > > I see. Debugging don't show that (at least not obvious).
> >
> >   yes a pointer can't tell if it's shared (wouldn;t that be cool !)
> >
> > > Then xmlSubstituteEntitiesDefault(0) is what i need...8)
> >
> >   probable. it's --noent option for xmllint
> >
> > Daniel
> >
> > -- 
> > Daniel Veillard      | Red Hat Network https://rhn.redhat.com/
> > veillard redhat com  | libxml Gnome XML XSLT toolkit  
> http://xmlsoft.org/
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