So, out-of-the-box, WCF doesn't believe in XML validation. It treats the XML as a message format, reading the information out which appears correct and ignoring the rest. This has the advantage of being very liberal in what the service will accept.
The trouble comes when things like the ordering of elements start to matter. It could be argued that ordering of the structures shouldn't be important, that you can indicate ordering with information in the data itself (dates, times or index properties, for example). In your trivial case, the ordering doesn't actually matter, since you can read and comprehend the information regardless of the order it's presented in. I am sure your actual case is much more valid, so I won't labour this point further.
In order to validate the XML structure, you need access to the message in the WCF pipeline. The easiest way in is to use an IClientMessageInspector impementation which validates the message and attach it to your client using a behaviour.
Assuming you want to do this with XML schema validation against an XSD, you would create an inspector like this:
class XsdValidationInspector : IClientMessageInspector
{
private readonly XmlSchemaSet _schemas;
public XsdValidationInspector(XmlSchemaSet schemas)
{
this._schemas = schemas;
}
public void AfterReceiveReply(ref Message reply, object correlationState)
{
// Buffer the message so we can read multiple times.
var buffer = reply.CreateBufferedCopy();
// Validate the message content.
var message = buffer.CreateMessage();
using (var bodyReader
= message.GetReaderAtBodyContents().ReadSubTree())
{
var settings = new XmlReaderSettings
{
Schemas = this._schemas,
ValidationType = ValidationType.Schema,
};
var events = new List<ValidationEventArgs>();
settings.ValidationEventHandler += (sender, e) => events.Add(e);
using (var validatingReader
= XmlReader.Create(bodyReader, settings))
{
// Read to the end of the body.
while(validatingReader.Read()) { }
}
if (events.Any())
{
// TODO: Examine events and decide whether to throw exception.
}
}
// Assign a copy to be passed to the next component.
reply = buffer.CreateMessage();
}
public object BeforeSendRequest(
ref Message request,
IClientChannel channel) {}
}
The accompanying validation behaviour isn't especially complicated:
class XsdValiationBehavior : IEndpointBehavior
{
private readonly XmlSchemaSet _schemas;
public XsdValidationBehavior(XmlSchemaSet schemas)
{
this._schemas = schemas;
}
public void AddBindingParameters(
ServiceEndpoint endpoint,
BindingParameterCollection bindingParameters) {}
public void ApplyClientBehavior(
ServiceEndpoint endpoint,
ClientRuntime clientRuntime)
{
clientRuntime.MessageInspectors.Add(
new XsdValidationInspector(this._schemas));
}
public void ApplyDispatchBehavior(
ServiceEndpoint endpoint,
EndpointDispatcher endpointDispatcher) {}
public void Validate(ServiceEndpoint endpoint){}
}
You can either create some configuration elements and apply the behaviour via config, or you can do so programatically by modifying the client's channel factory before you open the client connection. Here's the programmatic approach:
var schemaMarkup = @"<xsd:schema xmlns:xsd='http://www.w3.org/2001/XMLSchema'>
<xsd:element name='Program'>
<xsd:complexType>
<xsd:sequence>
<xsd:element name='One' minOccurs='1' maxOccurs='1'/>
<xsd:element name='Two' minOccurs='1' maxOccurs='1'/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
</xsd:schema>";
var schema = new XmlSchema();
using (var stringReader = new StringReader(schemaMarkup));
{
var events = new List<ValidationEventArgs>();
schema.Read(stringReader, (sender, e) => events.Add(e));
// TODO: Check events for any errors.
}
var validation = new XsdValidationBehavior(new XmlSchemaSet { schema });
client.ChannelFactory.Behaviours.Add(validation);
