JamesNK/Newtonsoft.Json · error · JsonSerializationException

Unexpected XmlNodeType when getting node name:

Error message

Unexpected XmlNodeType when getting node name: 

What it means

Thrown by XmlNodeConverter.GetPropertyName's default case when an IXmlNode's NodeType is not among the handled element/attribute/PI/comment/text/whitespace types. The converter needs a JSON property name for each node; unhandled node types cannot be named and throw this JsonSerializationException. The message is left unterminated (no value appended) so the offending node type is not echoed.

Source

Thrown at Src/Newtonsoft.Json/Converters/XmlNodeConverter.cs:1124

                    }
                    else
                    {
                        return ResolveFullName(node, manager);
                    }
                case XmlNodeType.ProcessingInstruction:
                    return "?" + ResolveFullName(node, manager);
                case XmlNodeType.DocumentType:
                    return "!" + ResolveFullName(node, manager);
                case XmlNodeType.XmlDeclaration:
                    return DeclarationName;
                case XmlNodeType.SignificantWhitespace:
                    return SignificantWhitespaceName;
                case XmlNodeType.Text:
                    return TextName;
                case XmlNodeType.Whitespace:
                    return WhitespaceName;
                default:
                    throw new JsonSerializationException("Unexpected XmlNodeType when getting node name: " + node.NodeType);
            }
        }

        private bool IsArray(IXmlNode node)
        {
            foreach (IXmlNode attribute in node.Attributes)
            {
                if (attribute.LocalName == "Array" && attribute.NamespaceUri == JsonNamespaceUri)
                {
                    return XmlConvert.ToBoolean(attribute.Value!);
                }
            }

            return false;
        }

        private void SerializeGroupedNodes(JsonWriter writer, IXmlNode node, XmlNamespaceManager manager, bool writePropertyName)
        {

View on GitHub (pinned to 4f73e74372)

Solutions

1. Pre-process the XML to strip or normalize node types the converter does not support (entities, notations, etc.) before serialization.
2. If using a custom IXmlNode wrapper, map unsupported node types to a supported one (e.g. Element/Text).
3. Load the XML with settings that disable DTD/entity expansion to avoid exotic node types.

Example fix

// before: loading XML with DTD produces unsupported nodes
var doc = new XmlDocument(); doc.Load(xmlWithDtd);
JsonConvert.SerializeXmlNode(doc);

// after: load without DTD processing
var settings = new XmlReaderSettings { DtdProcessing = DtdProcessing.Ignore };
using var reader = XmlReader.Create(path, settings);
var doc = new XmlDocument(); doc.Load(reader);
JsonConvert.SerializeXmlNode(doc);

foreach (System.Xml.XmlNode node in doc.SelectNodes("//*"))
{
    if (!IsSupportedForPropertyName(node.NodeType))
        throw new InvalidDataException($"Unsupported XmlNodeType for naming: {node.NodeType}");
}

static bool IsSupportedForPropertyName(XmlNodeType t) =>
    t == XmlNodeType.Attribute || t == XmlNodeType.CDATA || t == XmlNodeType.Comment
    || t == XmlNodeType.Element || t == XmlNodeType.ProcessingInstruction
    || t == XmlNodeType.DocumentType || t == XmlNodeType.XmlDeclaration
    || t == XmlNodeType.Text || t == XmlNodeType.Whitespace
    || t == XmlNodeType.SignificantWhitespace;

static bool IsNameableXmlNode(System.Xml.XmlNodeType t) =>
    t == XmlNodeType.Element || t == XmlNodeType.Attribute || t == XmlNodeType.Comment
    || t == XmlNodeType.ProcessingInstruction || t == XmlNodeType.DocumentType
    || t == XmlNodeType.XmlDeclaration || t == XmlNodeType.Text
    || t == XmlNodeType.Whitespace || t == XmlNodeType.SignificantWhitespace
    || t == XmlNodeType.CDATA;

try { JsonConvert.SerializeXmlNode(doc); }
catch (JsonSerializationException ex) when (ex.Message.Contains("Unexpected XmlNodeType when getting node name"))
{
    throw new InvalidDataException("XML contains an unsupported node type for JSON naming", ex);
}

When it happens

Trigger: Serializing an XML DOM containing a node type the converter does not map to a JSON key, e.g. XmlNodeType.Entity, XmlDataType-like nodes, or implementation-specific node types introduced by a custom IXmlNode wrapper.

Common situations: Loading an XML document with DTD/entity references that produce unusual node types. Using a custom IXmlNode implementation that returns a NodeType outside the handled set. Differences between the XML DOM on different runtimes.

Related errors

• Unexpected XmlNodeType when serializing nodes:
• Value must be an XML object.
• Namespace attribute must have a value.
• Unexpected value type when writing binary: {0}
• CustomCreationConverter should only be used while deserializ

AI-assisted analysis of JamesNK/Newtonsoft.Json@4f73e74372 (2026-08-07). Data as JSON: /api/errors/a6999dfc059dcb01. Report an issue: GitHub.