Restore XML conformant logic for escaping < and > characters

source/MaterialXFormat/External/PugiXML/pugixml.cpp

@@ -3927,7 +3927,7 @@ PUGI__NS_BEGIN
 		xml_encoding encoding;
 	};
 
-	PUGI__FN void text_output_escaped(xml_buffered_writer& writer, const char_t* s, chartypex_t type)
+	PUGI__FN void text_output_escaped(xml_buffered_writer& writer, const char_t* s, chartypex_t type, unsigned int flags)
 	{
 		while (*s)
 		{
@@ -3947,12 +3947,18 @@ PUGI__NS_BEGIN
 					break;
 				case '<':
 					// MaterialX: Allow angle brackets in MTLX serialization.
-					writer.write(*s);
+					if (flags & format_mtlx)
+						writer.write('<');
+					else
+						writer.write('&', 'l', 't', ';');
 					++s;
 					break;
 				case '>':
-					// MaterialX: Allow angle brackets in MTLX serialization.
-					writer.write(*s);
+					// MaterialX: Allow angle brackets in MTLX serialization.					
+					if (flags & format_mtlx)
+						writer.write('>');
+					else
+						writer.write('&', 'g', 't', ';');
 					++s;
 					break;
 				case '"':
@@ -3975,7 +3981,7 @@ PUGI__NS_BEGIN
 		if (flags & format_no_escapes)
 			writer.write_string(s);
 		else
-			text_output_escaped(writer, s, type);
+			text_output_escaped(writer, s, type, flags);
 	}
 
 	PUGI__FN void text_output_cdata(xml_buffered_writer& writer, const char_t* s)

source/MaterialXFormat/External/PugiXML/pugixml.hpp

@@ -256,6 +256,9 @@ namespace pugi
 	// Don't output empty element tags, instead writing an explicit start and end tag even if there are no children. This flag is off by default.
 	const unsigned int format_no_empty_element_tags = 0x80;
 
+	// MaterialX: This flag determines if MaterialX custom output formatting is enabled. THis flag is on by default
+	const unsigned int format_mtlx = 0x100;
+
 	// The default set of formatting flags.
 	// Nodes are indented depending on their depth in DOM tree, a default declaration is output if document has none.
 	const unsigned int format_default = format_indent;

source/MaterialXFormat/XmlIo.cpp

@@ -347,10 +347,19 @@ void readFromXmlString(DocumentPtr doc, const string& str, const FileSearchPath&
 
 void writeToXmlStream(DocumentPtr doc, std::ostream& stream, const XmlWriteOptions* writeOptions)
 {
+    // Check for XML strictness
+    unsigned int flags = format_default;
+    bool strictXML = writeOptions ? writeOptions->strictXML : false;
+    if (!strictXML)
+    {
+        // If not strict add MaterialX specific output formatting.
+        flags |= format_mtlx;
+    }
+
     xml_document xmlDoc;
     xml_node xmlRoot = xmlDoc.append_child("materialx");
     documentToXml(doc, xmlRoot, writeOptions);
-    xmlDoc.save(stream, "  ");
+    xmlDoc.save(stream, "  ", flags);
 }
 
 void writeToXmlFile(DocumentPtr doc, const FilePath& filename, const XmlWriteOptions* writeOptions)

source/MaterialXFormat/XmlIo.h

@@ -70,6 +70,11 @@ class MX_FORMAT_API XmlWriteOptions
     /// XIncludes rather than explicit data.  Defaults to true.
     bool writeXIncludeEnable;
 
+    /// If true output will follow a strict interpretation of the XML specification.  
+    /// If false, then MaterialX customizations which deviate from the XML specification will be allowed.  
+    // Defaults to false. 
+    bool strictXML = false; 
+
     /// If provided, this function will be used to exclude specific elements
     /// (those returning false) from the write operation.  Defaults to nullptr.
     ElementPredicate elementPredicate;

source/MaterialXTest/MaterialXFormat/XmlIo.cpp

@@ -371,3 +371,44 @@ TEST_CASE("Locale region testing", "[xmlio]")
     // Restore the original locale.
     std::locale::global(origLocale);
 }
+
+TEST_CASE("XML strictness", "[xmlio2]")
+{
+    mx::FileSearchPath searchPath = mx::getDefaultDataSearchPath();
+    mx::DocumentPtr stdlib = mx::createDocument();
+    mx::loadLibraries({ "libraries" }, searchPath, stdlib);
+
+    mx::DocumentPtr doc = mx::createDocument();
+    doc->setDataLibrary(stdlib);
+
+    // Create image node with illegal <> characters
+    mx::NodePtr imageNode = doc->addNode("image", "testImage");
+    imageNode->addInputsFromNodeDef();
+    mx::InputPtr fileInput = imageNode->getInput("file");
+    fileInput->setValue("<>");
+
+    // Write to string with default options
+    mx::XmlWriteOptions writeOptions;
+    std::string output_string = mx::writeToXmlString(doc, &writeOptions);
+    // Make sure there are no escaped characters
+    REQUIRE(output_string.find("&lt;&gt;") == std::string::npos);
+
+    // Write with escaped characters enabled
+    writeOptions.strictXML = true;
+    output_string = mx::writeToXmlString(doc, &writeOptions);
+    // Look for escaped characters
+    REQUIRE(output_string.find("&lt;&gt;") != std::string::npos);
+
+    // Read in the document with the escaped characters and verify that the value 
+    // is unescaped properly
+    mx::DocumentPtr readDoc = mx::createDocument();
+    readDoc->setDataLibrary(stdlib);
+    mx::readFromXmlString(readDoc , output_string);
+    imageNode = readDoc->getNode("testImage");
+    REQUIRE(imageNode != nullptr);
+    fileInput = imageNode->getInput("file");
+    REQUIRE(fileInput != nullptr);
+    std::string unescaped_string = fileInput->getValueString();
+    // There should not be any escaped characters in the value string
+    REQUIRE(unescaped_string.find("&lt;&gt;") == std::string::npos);
+}