WCF Problem Serializing a Message Header

Question

Hi guys I have the following code:

public virtual void Initialise()
{ 
    this.AddHeader("SystemContext", this.UserSettings.SystemContext);
}

public virtual void AddHeader(string key, object value)
{
    var customHeader = MessageHeader.CreateHeader(key, this.SystemSettings.SystemServiceNamespace, value);
    OperationContext.Current.OutgoingMessageHeaders.Add(customHeader); 
}

When I try and execute the server after I have run the above code, I get the following error:

Type 'ACSIS.Core.Common.Configuration.UserAcountDetials' with data contract name 'UserAcountDetials:http://schemas.datacontract.org/2004/07/ACSIS.Core.Common.Configuration' is not expected. Add any types not known statically to the list of known types - for example, by using the KnownTypeAttribute attribute or by adding them to the list of known types passed to DataContractSerializer.

Now UserSettings describes SystemContext as being of type IDictionary. I understand that WCF can't magically create objects out of thin air or what ever, so I need to help it out a little.

Is there some way that I can pass the runtime type of object over the wire as well and have it converted back into that type on the other side. I am not using WCF for java to .net SOA stuff or anything like that, I know the concrete type will be on the other side of the wire.

If WCF doesn't really support this (there must be some way though), is there a way I could serialize the data into a binary format, attach the binary to the header and handle serialization myself, using the type information I pass across.

Answer 1

You could try applying the knownType attribute to your service contract, like this:

[ServiceKnownType(typeof(ACSIS.Core.Common.Configuration.UserAcountDetials))]
[ServiceContract]
public interface IMyService
{...

And yes, while it is less elegant, you could use the BinaryFormatter to serialize your header object into a byte[] array, stick that in the header, then de-serialize on the other side. Binary serialization is tricky when it comes to versioning, so you have to be a bit careful.