Question

I am still confused when it is appropriate to use the Message type in WCF like below

[ServiceContract]
public interface IMyService
{
    [OperationContract]
    Message GetData();

    [OperationContract]
    void PutData(Message m);
}

Why would you want to use it?

Can you use it for streaming?

Thanks

Answer 1

While the reasons listed by Tim are valid, we use messages directly in our services to create one uber routing service.
we have one service that can take any method call you throw at it, Clients are generated by wsdls supplied from multiple sources.

This service would take the message, examine its content and route it accordingly.
So in my opinion if you want to get closer to the wire, or when you dont know the type of incoming messages, you can use the message in the signature directly.

Streaming is a separate concept than message signature, streaming is supported by wcf under very specific bindings and security mechanism and the method signature has to be very specific (i.e it should return/accept stream). Also in streaming the actual stream of data travels outside the scope of soap message.