XML Deserialisation & Malformed XML [modified]

[MrEyes]

Hello all, I have a curious problem relating to XML deserialisation where the deserialiser allows malformed XML to pass through without issue. This needs some further information, so without further ado: I have the following simple schema:

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified" attributeFormDefault="unqualified">
<xs:element name="TestSchema">
xs:complexType
xs:sequence
<xs:element name="Widgets" type="xs:string" nillable="false"/>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:schema>

From this I have created .NET 2 c# classes using the XSD tool, this result in the following class

using System.Xml.Serialization;

[System.CodeDom.Compiler.GeneratedCodeAttribute("xsd", "2.0.50727.42")]
[System.SerializableAttribute()]
[System.Diagnostics.DebuggerStepThroughAttribute()]
[System.ComponentModel.DesignerCategoryAttribute("code")]
[System.Xml.Serialization.XmlTypeAttribute(AnonymousType=true)]
[System.Xml.Serialization.XmlRootAttribute(Namespace="", IsNullable=false)]
public partial class TestSchema {

private string widgetsField;

/// <remarks/>
public string Widgets {
    get {
        return this.widgetsField;
    }
    set {
        this.widgetsField = value;
    }
}

}

This is then added to a simple test project that looks like this:

static void Main(string[] args)
{
//input XML
string rawXml = "<TestSchema>";
rawXml += "<Widgets>A value for widgets</Widgets>";
rawXml += "<LaLa>An element that doesnt exist in the schema</LaLa>";
rawXml += "</TestSchema>";

//deserialise
byte\[\] data = System.Text.Encoding.ASCII.GetBytes(rawXml);
MemoryStream fs = new MemoryStream(data);
TextReader reader = new StreamReader(fs);
XmlSerializer ser = new XmlSerializer(typeof(TestSchema));
TestSchema obj = (TestSchema)ser.Deserialize(reader);
reader.Close();

//output
Console.WriteLine(obj.GetHashCode());
Console.ReadLine();

}

Now all this works, however I wouldn't expect it to! The more eagled eyed will have noticed the following line in the code above:

rawXml += "<LaLa>An element that doesnt exist in the schema</LaLa>";

When the deserialiser is processing the XML string, it seems that a

[MrEyes]

It would seem I have found the solution, a tweak to the code above and malformed XML is no longer allowed:

static void Main(string[] args)
{
//input XML
string rawXml = "<TestSchema>";
rawXml += "<Widgets>A value for widgets</Widgets>";
rawXml += "<LaLa>Hold on whats this an element that doesnt exist in the schema</LaLa>";
rawXml += "</TestSchema>";

//deserialise
XmlSerializer s = new XmlSerializer(typeof(TestSchema));
byte\[\] buffer = ASCIIEncoding.UTF8.GetBytes(rawXml);
MemoryStream ms = new MemoryStream(buffer);
XmlReader reader = new XmlTextReader(ms);

XmlDeserializationEvents deserializationEvents = new XmlDeserializationEvents();
deserializationEvents.OnUnknownAttribute = new XmlAttributeEventHandler(UnknownAttributeEventHandler);
deserializationEvents.OnUnknownElement = new XmlElementEventHandler(UnknownElementEventHandler);
deserializationEvents.OnUnknownNode = new XmlNodeEventHandler(UnknownNodeEventHandler);
deserializationEvents.OnUnreferencedObject = new UnreferencedObjectEventHandler(UnreferencedObjEventHandler);

TestSchema obj = (TestSchema)s.Deserialize(reader, deserializationEvents);

reader.Close();

//output
Console.WriteLine(obj.GetHashCode());
Console.ReadLine();

}

private static void UnknownAttributeEventHandler(object sender, XmlAttributeEventArgs e)
{
//handle event condition
}

private static void UnknownElementEventHandler(object sender, XmlElementEventArgs e)
{
//handle event condition
}

private static void UnknownNodeEventHandler(object sender, XmlNodeEventArgs e)
{
//handle event condition
}

private static void UnreferencedObjEventHandler(object sender, UnreferencedObjectEventArgs e)
{
//handle event condition
}

As you can see in the code above, the XmlSerializer.Deserialize can also take an instance of XmlDeserializationEvents. If this is setup and passed in these events are created and from there I can handle the error condition.

[J4amieC]

Good to know... thanks for posting that!

[MrEyes]

Since posting the original solution I have found that you can also set these event directly on the XmlSerializer

XmlSerializer xmlSerializer = new XmlSerializer(objectType);
xmlSerializer.UnknownAttribute += new XmlAttributeEventHandler(xmlSerializer_UnknownAttribute);
xmlSerializer.UnknownElement += new XmlElementEventHandler(xmlSerializer_UnknownElement);
xmlSerializer.UnknownNode += new XmlNodeEventHandler(xmlSerializer_UnknownNode);
xmlSerializer.UnreferencedObject += new UnreferencedObjectEventHandler(xmlSerializer_UnreferencedObject);

From a functionality point of view I don't suppose it makes any difference at all, however IMHO this method is neater.