Missing Xerces C++ class to copy attributes of element for use after SAX2 parsing - c++

Question

The documentation of xerces anticipates the need to make a copy of attributes, but the AttributesImpl class doesn't seem to exist. Neither does the facility seem to exist in other associated classes in either the current 3.2.3 version of xerces or previous 2.X
Xerces documentation in the file itself src/xercesc/sax2/Attributes.hpp says:
"The instance provided will return valid results only during the scope of the startElement invocation (to save it for future use, the application must make a copy: the AttributesImpl helper class provides a convenient constructor for doing so)."
See also I've left issue here as a bug in xerces
https://issues.apache.org/jira/browse/XERCESC-2238
Appears I will be stuck instead creating my own version of attributes in which to copy or clone, and not overwritten each new line. Not saving whole document (which would defeat purpose of SAX streaming parse), but the existing framework populating Attributes is pretty convoluted and undocumented. Obviously the library and docs are designed to use the api, not to hack or extend the application.
Is this really correct, AttributesImpl is helper class in the documentation that doesn't actually exist? Neither is there a different class with this functionality to save an element's attributes for later use (outside the handler)?

Answer 1

Below is a working version of an Attributes deep copy utility function. It may be missing a few includes which I'm getting from other includes of my larger file. When I get the chance, I'll try making this a stand alone and update this answer. It still falls short of the Java version utility, due to inaccessible members of RefVectorOf class, because the wrapping class, the Attributes interface and VecAttributesImpl interface, do not provide access to them. https://xerces.apache.org/xerces-j/apiDocs/org/xml/sax/helpers/AttributesImpl.html
Last release of Xerces C/C++ is from 2016, so although marked status active, https://projects.apache.org/project.html?xerces-for_c++_xml_parser , really not so much. Can't vouch for libhunt site, but came up in quick google just now https://cpp.libhunt.com/xerces-c++-alternatives . One can see latest comment here, note use of the phrase "unless a security issue pops up or new committers appear to revive the project" https://issues.apache.org/jira/browse/XERCESC-2238?page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel&focusedCommentId=17571942#comment-17571942
Leaving the status of Xerces C/C++ as active is either a lie or a gross and negligent oversight. This page shows no major release since 2010. https://xerces.apache.org/news.html (C++ is listed below the Java project updates)
#include <xercesc/validators/common/GrammarResolver.hpp>
#include <xercesc/framework/XMLGrammarPool.hpp>
#include <xercesc/sax2/Attributes.hpp>
#include <xercesc/util/RefVectorOf.hpp>
#include "spdlog/spdlog.h"
#define tr XMLString::transcode
static spdlog::logger logger = getLog();
/*
* cloneAttributes
* Uses LocalName as key instead of QName and ignores URI and URI id, id inside RefVectorOf
* but inaccessible to wrapper VecAttributesImpl, and type defaults to CDATA
*/
VecAttributesImpl* cloneAttributes(VecAttributesImpl& attrs, bool useScanner=false){
// from XMLReaderFactory::CreateXMLReader line 49
MemoryManager* const memManager = XMLPlatformUtils::fgMemoryManager;
XMLScanner* scanner;
if(useScanner){
// from void SAX2XMLReaderImpl::initialize() line 124
GrammarResolver* grammarResolver = new (memManager) GrammarResolver(0, memManager); // line 127
// use of 0 from SAX2XMLReaderImpl.hpp line 74 default constructor, XMLGrammarPool* const gramPool = 0
XMLStringPool* URIStringPool = grammarResolver->getStringPool(); // line 128
scanner = XMLScannerResolver::getDefaultScanner(0, grammarResolver, memManager);
// line 42 of XMLScannerResolver::getDefaultScanner uses return new (manager) IGXMLScanner(valToAdopt, grammarResolver, manager);
scanner->setURIStringPool(URIStringPool);
}else{
scanner = NULL;
}
VecAttributesImpl* newAttrs = new VecAttributesImpl(); //VecAttributesImpl is not a vector, it's a wrapper around RefVectorOf
RefVectorOf<XMLAttr> * newRefVectorOf = new (memManager) RefVectorOf<XMLAttr> (32, false, memManager) ;
XMLSize_t atLen = attrs.getLength();
XMLSize_t i;
std::stringstream bruce;
XMLAttr* cpXMLAttr;
for(i = 0;i<atLen;i++){
//Ever QName != LocalName? when URI != ""? logger.debug(format("{}. QName LocalName URI type: {}, {}, {}, {}", i, tr(attrs.getQName(i)), tr(attrs.getLocalName(i)), tr(attrs.getURI(i)),tr(attrs.getType(i)))); // #suppress("Invalid arguments")
cpXMLAttr = new (memManager) XMLAttr
(
0, //URIId, 0 if reading file, but int is inaccessible from attrs, inside RefVectorOf XMLAttr, and getURI(i) returns an XMLCh*
attrs.getLocalName(i),
attrs.getValue(i)
);
if(logger.level() == spdlog::level::debug){
bruce << tr(attrs.getLocalName(i))<<" : "<<tr(attrs.getValue(i))<< " | ";
}
newRefVectorOf->addElement(cpXMLAttr);
}
logger.debug(bruce.str());
newRefVectorOf->size();
logger.debug(newRefVectorOf->size());
//The scanner can actually be set to NULL and the above scanner construction skipped if the VecAttributesImpl isn't scanning.
newAttrs->setVector(newRefVectorOf, newRefVectorOf->size(), scanner, false);
return newAttrs;
}