fix(xml): dispatch v2.6/v2.7 namespaces + default unknown to Max

libraries/MTConnect.NET-XML/MTConnect.NET-XML.csproj

@@ -72,6 +72,11 @@
 		<ProjectReference Include="..\MTConnect.NET-Common\MTConnect.NET-Common.csproj" />
 	</ItemGroup>
 
+	<ItemGroup>
+		<!-- Grants MTConnect.NET-XML-Tests reach into the internal helpers (MTConnectVersion, Namespaces) that have no public equivalent. The assembly is not strong-named, so no PublicKey clause is required. -->
+		<InternalsVisibleTo Include="MTConnect.NET-XML-Tests" />
+	</ItemGroup>
+
 	<ItemGroup>
 		<None Include="README-Nuget.md">
 			<Pack>True</Pack>

libraries/MTConnect.NET-XML/MTConnectVersion.cs

@@ -8,7 +8,7 @@ namespace MTConnect
     internal static class MTConnectVersion
     {
         /// <summary>
-        /// Gets the Version of the MTConnect standard being used based on the XML Namespace that is used
+        /// Gets the Version of the MTConnect standard from a raw XML document by extracting the root element's namespace URI and dispatching through <see cref="GetByNamespace"/>.
         /// </summary>
         public static Version Get(string xml)
         {
@@ -17,12 +17,14 @@ public static Version Get(string xml)
         }
 
         /// <summary>
-        /// Gets the Version of the MTConnect standard being used based on the XML Namespace that is used
+        /// Gets the Version of the MTConnect standard from an already-resolved namespace URI. Returns <see cref="MTConnectVersions.Max"/> when the namespace is null, empty, or does not match a declared MTConnect namespace.
         /// </summary>
         public static Version GetByNamespace(string ns)
         {
             if (ns != null)
             {
+                if (Namespaces.Version27.Match(ns)) return MTConnectVersions.Version27;
+                if (Namespaces.Version26.Match(ns)) return MTConnectVersions.Version26;
                 if (Namespaces.Version25.Match(ns)) return MTConnectVersions.Version25;
                 if (Namespaces.Version24.Match(ns)) return MTConnectVersions.Version24;
                 if (Namespaces.Version23.Match(ns)) return MTConnectVersions.Version23;
@@ -40,7 +42,8 @@ public static Version GetByNamespace(string ns)
                 if (Namespaces.Version10.Match(ns)) return MTConnectVersions.Version10;
             }
 
-            return new Version();
+            // unknown namespace → default to latest supported version
+            return MTConnectVersions.Max;
         }
     }
-}
+}

libraries/MTConnect.NET-XML/Namespaces.cs

@@ -18,15 +18,40 @@ internal static class Namespaces
         private static Regex _streamRemoveNamespaceRegex = new Regex(@"\s{1}xmlns:xsi=\""http:\/\/www\.w3\.org\/2001\/XMLSchema-instance\""\s{1}xmlns:xsd=\""http:\/\/www\.w3\.org\/2001\/XMLSchema\""", RegexOptions.Compiled);
         private static Regex _streamNamespaceRegex = new Regex("<MTConnectStreams", RegexOptions.Compiled);
 
+        // XmlDocument.LoadXml delegates to an internal XmlReader whose
+        // DtdProcessing default varies across TFMs and whose XmlResolver
+        // historically resolved external entities. Route the parse through
+        // an explicit XmlReader with DTD processing prohibited and no
+        // resolver so unknown or hostile documents cannot exercise
+        // external-entity or entity-expansion (billion-laughs) paths.
+        // Shared/static so it isn't reallocated on every Get() call.
+        private static readonly XmlReaderSettings _namespaceReaderSettings = new XmlReaderSettings
+        {
+            DtdProcessing = DtdProcessing.Prohibit,
+            XmlResolver = null,
+        };
 
         public static string Get(string xml)
         {
-            var doc = new XmlDocument();
-            doc.LoadXml(xml);
-            if (doc != null && doc.DocumentElement != null)
+            if (string.IsNullOrEmpty(xml)) return null;
+
+            try
             {
-                return doc.DocumentElement.NamespaceURI;
+                using (var stringReader = new StringReader(xml))
+                using (var xmlReader = XmlReader.Create(stringReader, _namespaceReaderSettings))
+                {
+                    // Only the root start-tag's namespace is needed — advance
+                    // to it directly rather than materializing a full
+                    // XmlDocument DOM, which doubles the parse/allocation
+                    // cost for large payloads that get re-parsed for real
+                    // deserialization immediately afterwards anyway.
+                    if (xmlReader.MoveToContent() == XmlNodeType.Element)
+                    {
+                        return xmlReader.NamespaceURI;
+                    }
+                }
             }
+            catch (XmlException) { }
 
             return null;
         }
@@ -478,7 +503,7 @@ internal static class Version12
 
             public static bool Match(string ns)
             {
-                return ns == Devices || ns == Error || ns == Streams;
+                return ns == Assets || ns == Devices || ns == Error || ns == Streams;
             }
         }