Implemented basic external "execute" function

* enables execution of external programs
** second parameter is passed to stdin
** stdout is captured and returned
** based on booost::process
* this was implemented to enable access to external content preprocessors such as markdown

5 files changed, 115 insertions, 0 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index e09c096..442c215 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -28,6 +28,7 @@ set(
 	src/function/read_xml_file.cc
 	src/function/read_directory.cc
 	src/function/transform.cc
+	src/function/execute.cc
 	src/support/filesystem_context.cc
 	src/support/stylesheet_parameter_guard.cc
 	src/support/xalan_string.cc
diff --git a/README.md b/README.md
index 867de8f..e051979 100644
--- a/README.md
+++ b/README.md
@@ -12,6 +12,7 @@ Contrary to popular opinion I actually like XSLT as a content transformation lan
 - external `read-xml-file` function for read-only access to XML files
 - external `read-directory` function for read-only directory traversal
 - external `transform` function for executing transformations inside transformations
+- external `execute` function for executing external applications and capturing their output
 
 ## Requirements:
 
@@ -21,3 +22,4 @@ Contrary to popular opinion I actually like XSLT as a content transformation lan
 - Apache [Xerces](https://xerces.apache.org/) XML Library
 - Boost [Filesystem](http://www.boost.org/doc/libs/1_55_0/libs/filesystem/doc/index.htm)
 - Boost [Program Options](http://www.boost.org/doc/libs/1_55_0/doc/html/program_options.html)
+- Boost [Process](http://www.highscore.de/boost/process/index.html)
diff --git a/src/function/execute.cc b/src/function/execute.cc
new file mode 100644
index 0000000..f19ba75
--- /dev/null
+++ b/src/function/execute.cc
@@ -0,0 +1,77 @@
+#include "execute.h"
+
+#include <xercesc/dom/DOMDocument.hpp>
+#include <xercesc/dom/DOMImplementation.hpp>
+#include <xercesc/dom/DOMElement.hpp>
+
+#include <boost/process.hpp>
+
+#include "support/xerces_string_guard.h"
+#include "support/dom/result_node_facade.h"
+
+namespace InputXSLT {
+
+xercesc::DOMDocument* FunctionExecute::constructDocument(
+	const InputXSLT::FilesystemContext&,
+	const FunctionBase::parameter_tuple& parameters
+) {
+	const std::string& executablePath(
+		std::get<0>(parameters)
+	);
+
+	const std::string& stdinText(
+		std::get<1>(parameters)
+	);
+
+	xercesc::DOMDocument* const domDocument(
+		xercesc::DOMImplementation::getImplementation()->createDocument(
+			nullptr,
+			*XercesStringGuard<XMLCh>("content"),
+			nullptr
+		)
+	);
+
+	xercesc::DOMNode* const rootNode(
+		domDocument->getDocumentElement()
+	);
+
+	boost::process::context context;
+	context.stdout_behavior = boost::process::capture_stream();
+	context.stdin_behavior  = boost::process::capture_stream();
+
+	boost::process::child process(
+		boost::process::launch(
+			executablePath,
+			std::vector<std::string>{""},
+			context
+		)
+	);
+
+	boost::process::postream& inputStream  = process.get_stdin();
+	boost::process::pistream& outputStream = process.get_stdout();
+
+	inputStream << stdinText;
+	inputStream.close();
+
+	const std::string resultText(
+		(std::istreambuf_iterator<char>(outputStream)),
+		(std::istreambuf_iterator<char>())
+	);
+
+	boost::process::status status = process.wait();
+
+	if ( status.exited() ) {
+		ResultNodeFacade result(domDocument, rootNode, "result");
+
+		result.setValueNode("code",   std::to_string(status.exit_status()));
+		result.setValueNode("output", resultText);
+	} else {
+		ResultNodeFacade result(domDocument, rootNode, "error");
+
+		result.setValueNode("code", std::to_string(status.exit_status()));
+	}
+
+	return domDocument;
+}
+
+}
diff --git a/src/function/execute.h b/src/function/execute.h
new file mode 100644
index 0000000..12167da
--- /dev/null
+++ b/src/function/execute.h
@@ -0,0 +1,28 @@
+#ifndef INPUTXSLT_SRC_FUNCTION_EXECUTE_H_
+#define INPUTXSLT_SRC_FUNCTION_EXECUTE_H_
+
+#include "base.h"
+
+namespace InputXSLT {
+
+class FunctionExecute : public FunctionBase<
+	FunctionExecute,
+	std::string,
+	std::string
+> {
+	public:
+		using FunctionBase::FunctionBase;
+
+	protected:
+		friend FunctionBase;
+
+		xercesc::DOMDocument* constructDocument(
+			const FilesystemContext&,
+			const FunctionBase::parameter_tuple&
+		);
+
+};
+
+}
+
+#endif  // INPUTXSLT_SRC_FUNCTION_EXECUTE_H_
diff --git a/src/plattform_guard.cc b/src/plattform_guard.cc
index d66c8b5..ff4de08 100644
--- a/src/plattform_guard.cc
+++ b/src/plattform_guard.cc
@@ -10,6 +10,7 @@
 #include "function/read_xml_file.h"
 #include "function/read_directory.h"
 #include "function/transform.h"
+#include "function/execute.h"
 
 namespace InputXSLT {
 
@@ -45,6 +46,12 @@ PlattformGuard::PlattformGuard(const std::vector<std::string>& path):
 		xalan::XalanDOMString("transform"),
 		InputXSLT::FunctionTransform(&this->include_resolver_)
 	);
+
+	xalan::XalanTransformer::installExternalFunctionGlobal(
+		customNamespace,
+		xalan::XalanDOMString("execute"),
+		InputXSLT::FunctionExecute(&this->include_resolver_)
+	);
 }
 
 PlattformGuard::~PlattformGuard() {