Fixed xerces DOM construction related memory leaks

* Wrapped xerces DOM and support class instances in now DomDocumentGuard scope-guard class
* FunctionReadDirectory class contains interal std::stack instance to store DomDocumentGuard instances
** wrapped in std::shared_ptr as FunctionReadDirectory is internally cloned by xalan...
** this is needed as the DOM has to preserved longer than the external function execution scope
* Sadly XMLCh xerces strings have to be manually released
** added appropriate xercesc::XMLString::release calls
* xalan::XercesDOMWrapperParsedSource does not mirror a given xerces DOM but convert it on instantiation
** this is why there is a dedicated finalize member method in InputXSLT::DomDocumentGuard
* In short: I do not like the amount of trickery needed to simply prevent memory leaks in this context
** there sadly doesn't seem to be a substantially easier way to return arbitrary DOM trees from a external function

6 files changed, 101 insertions, 41 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 915a05d..94ade96 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -18,6 +18,7 @@ add_executable(
 	src/function/read_xml_file.cc
 	src/function/read_directory.cc
 	src/support/filesystem_context.cc
+	src/support/dom_document_guard.cc
 )
 
 target_link_libraries(
diff --git a/src/function/read_directory.cc b/src/function/read_directory.cc
index a4284c0..6d643da 100644
--- a/src/function/read_directory.cc
+++ b/src/function/read_directory.cc
@@ -1,25 +1,16 @@
 #include "read_directory.h"
 
-#include <xalanc/XercesParserLiaison/XercesDOMSupport.hpp>
-#include <xalanc/XalanTransformer/XercesDOMWrapperParsedSource.hpp>
-
 #include <xercesc/dom/DOMDocument.hpp>
 #include <xercesc/dom/DOMImplementation.hpp>
 #include <xercesc/dom/DOMElement.hpp>
 #include <xercesc/dom/DOMText.hpp>
 #include <xercesc/util/XMLString.hpp>
 
-#include <sstream>
-
 namespace InputXSLT {
 
 FunctionReadDirectory::FunctionReadDirectory(const FilesystemContext& context):
 	fs_context_(context),
-	parser_() { }
-
-FunctionReadDirectory::FunctionReadDirectory(const FunctionReadDirectory& src):
-	fs_context_(src.fs_context_),
-	parser_() { }
+	documents_(new std::stack<DomDocumentGuard>()) { }
 
 xalan::XObjectPtr FunctionReadDirectory::execute(
 	xalan::XPathExecutionContext&                executionContext,
@@ -35,44 +26,29 @@ xalan::XObjectPtr FunctionReadDirectory::execute(
 		this->generalError(executionContext, context, locator);
 	}
 
-	xercesc::DOMDocument* const inputDom(
-		xercesc::DOMImplementation::getImplementation()->createDocument(
-			nullptr, xercesc::XMLString::transcode("content"), nullptr
-		)
-	);
+	this->documents_->emplace("content");
+	DomDocumentGuard& domDocument = this->documents_->top();
 
-	xercesc::DOMNode* const rootNode = inputDom->getDocumentElement();
+	xercesc::DOMNode* const rootNode = domDocument->getDocumentElement();
 
 	this->fs_context_.iterate(
 		arguments[0]->str(),
-		[&inputDom, &rootNode](const boost::filesystem::path& p) {
-		xercesc::DOMNode* const fileNode = inputDom->createElement(
-			xercesc::XMLString::transcode("file")
-		);
+		[&domDocument, &rootNode](const boost::filesystem::path& p) {
+		XMLCh* buffer = xercesc::XMLString::transcode("file");
+		xercesc::DOMNode* const fileNode = domDocument->createElement(buffer);
+		xercesc::XMLString::release(&buffer);
 
-		xercesc::DOMText* const textNode = inputDom->createTextNode(
-			xercesc::XMLString::transcode(p.filename().string().data())
-		);
+		buffer = xercesc::XMLString::transcode(p.filename().string().data());
+		xercesc::DOMText* const textNode = domDocument->createTextNode(buffer);
+		xercesc::XMLString::release(&buffer);
 
 		fileNode->appendChild(textNode);
 		rootNode->appendChild(fileNode);
 	});
 
-
-	xalan::XercesDOMSupport domSupport(this->parser_);
-
-	xalan::XercesDOMWrapperParsedSource* const parsedSource(
-		new xalan::XercesDOMWrapperParsedSource(
-			inputDom,
-			this->parser_,
-			domSupport
-		)
-	);
-
 	return executionContext.getXObjectFactory().createNodeSet(
-		parsedSource->getDocument()
+		domDocument.finalize()
 	);
-
 }
 
 FunctionReadDirectory* FunctionReadDirectory::clone(
diff --git a/src/function/read_directory.h b/src/function/read_directory.h
index e7ee0c4..3c55591 100644
--- a/src/function/read_directory.h
+++ b/src/function/read_directory.h
@@ -6,19 +6,18 @@
 #include <xalanc/XPath/Function.hpp>
 #include <xalanc/XPath/XObject.hpp>
 
-#include <xalanc/XercesParserLiaison/XercesParserLiaison.hpp>
-
-#include <string>
+#include <memory>
+#include <stack>
 
 #include "common.h"
 #include "support/filesystem_context.h"
+#include "support/dom_document_guard.h"
 
 namespace InputXSLT {
 
 class FunctionReadDirectory : public xalan::Function {
 	public:
 		FunctionReadDirectory(const FilesystemContext&);
-		FunctionReadDirectory(const FunctionReadDirectory&);
 
 		virtual xalan::XObjectPtr execute(
 			xalan::XPathExecutionContext&,
@@ -34,7 +33,8 @@ class FunctionReadDirectory : public xalan::Function {
 
 	private:
 		const FilesystemContext& fs_context_;
-		mutable xalan::XercesParserLiaison parser_;
+
+		std::shared_ptr<std::stack<DomDocumentGuard>> documents_;
 
 		const xalan::XalanDOMString& getError(xalan::XalanDOMString&) const;
 
diff --git a/src/support/dom_document_guard.cc b/src/support/dom_document_guard.cc
new file mode 100644
index 0000000..a83345f
--- /dev/null
+++ b/src/support/dom_document_guard.cc
@@ -0,0 +1,45 @@
+#include "support/dom_document_guard.h"
+
+#include <xercesc/dom/DOMImplementation.hpp>
+#include <xercesc/util/XMLString.hpp>
+
+namespace InputXSLT {
+
+DomDocumentGuard::DomDocumentGuard(const std::string& rootNode):
+	parser_(),
+	dom_support_(parser_),
+	root_node_name_(
+		xercesc::XMLString::transcode(rootNode.data())
+	),
+	document_(
+		xercesc::DOMImplementation::getImplementation()->createDocument(
+			nullptr,
+			root_node_name_,
+			nullptr
+		)
+	),
+	parsed_source_() { }
+
+DomDocumentGuard::~DomDocumentGuard() {
+	xercesc::XMLString::release(&this->root_node_name_);
+
+	this->document_->release();
+}
+
+xercesc::DOMDocument* DomDocumentGuard::operator->() {
+	return this->document_;
+}
+
+xalan::XalanDocument* DomDocumentGuard::finalize() {
+	this->parsed_source_.reset(
+		new xalan::XercesDOMWrapperParsedSource(
+				document_,
+				parser_,
+				dom_support_
+		)
+	);
+
+	return this->parsed_source_->getDocument();
+}
+
+}
diff --git a/src/support/dom_document_guard.h b/src/support/dom_document_guard.h
new file mode 100644
index 0000000..decca01
--- /dev/null
+++ b/src/support/dom_document_guard.h
@@ -0,0 +1,36 @@
+#ifndef INPUTXSLT_SRC_SUPPORT_DOM_DOCUMENT_GUARD_H_
+#define INPUTXSLT_SRC_SUPPORT_DOM_DOCUMENT_GUARD_H_
+
+#include <xalanc/XercesParserLiaison/XercesParserLiaison.hpp>
+#include <xalanc/XercesParserLiaison/XercesDOMSupport.hpp>
+#include <xalanc/XalanTransformer/XercesDOMWrapperParsedSource.hpp>
+
+#include <xercesc/dom/DOMDocument.hpp>
+
+#include <string>
+#include <memory>
+
+#include "common.h"
+
+namespace InputXSLT {
+
+class DomDocumentGuard {
+	public:
+		DomDocumentGuard(const std::string&);
+		~DomDocumentGuard();
+
+		xercesc::DOMDocument* operator->();
+		xalan::XalanDocument* finalize();
+
+	private:
+		xalan::XercesParserLiaison parser_;
+		xalan::XercesDOMSupport dom_support_;
+		XMLCh* root_node_name_;
+		xercesc::DOMDocument* const document_;
+		std::unique_ptr<xalan::XercesDOMWrapperParsedSource> parsed_source_;
+
+};
+
+}
+
+#endif  // INPUTXSLT_SRC_SUPPORT_DOM_DOCUMENT_GUARD_H_
diff --git a/src/transformer_facade.cc b/src/transformer_facade.cc
index 01314cd..fbf604c 100644
--- a/src/transformer_facade.cc
+++ b/src/transformer_facade.cc
@@ -59,6 +59,8 @@ int TransformerFacade::execute(
 		domSupport
 	);
 
+	inputDom->release();
+
 	xalan::XSLTInputSource transform(transformation.data());
 	xalan::XSLTResultTarget output(target.data());