How do I call client operation for streaming service with MessageContract, that gets and returns a large stream

See more:

C#

WCF

C#4.0

streaming

I have a requirement for a WCF service operation that accepts a large Stream, processes it and returns that stream.

I used an https://msdn.microsoft.com/en-us/library/ms733742.aspx[^] as a reference to what I need (unfortunately, I am not allowed to post links).

Following the advice in that article:

Details:

Because I need to accompany both the input and return streams with MetaData, I decorated the classes with MessageContract attributes, as is required.

Here is a brief run-down of my implementation:

Message Contracts:

[MessageContract]
public class InputStreamMessage
{
    [MessageHeader]
    public InputStreamHeader Header { get; set; }

    [MessageBodyMember(Order = 1)]
    public Stream Data { get; set; }

}

[MessageContract]
public class OutputStreamMessage
{
    [MessageHeader]
    public OutputStreamHeader Header { get; set; }

    [MessageBodyMember(Order = 1)]
    public Stream Data { get; set; }

}

Service Contract:

[ServiceContract]
public interface IStreamService
{
    [OperationContract]
    OutputStreamMessage ProcessStream(InputStreamMessage input);
}

Service Implementation:

 public OutputStreamMessage DoStreamOperation(InputStreamMessage input)
 {
    //Some logic that assigns re
    OutputStreamMessage output = DoSomeNonBufferedProcessing(input);

    return output;
 }

Client-side:

On the client-side, I then generate the service reference, and call the service as below:

private void PerformStreamOperation()
{
    try
    {
        //
        StreamServiceReference.StreamServiceClient client = new StreamServiceReference.StreamServiceReferenceClient();
        client.Open();

        //Set Header and Parameters
        InputMessageHeader header = new InputMessageHeader();

        //...                
        //... initialize header data here
        //...                

        //... do some operation to get input stream
        var inputstream = SomeOperationToGetInputStream();

        //Perform Service stream action
        //         ____ [ Why does the generated method have the following signature, retuning void?]
        //        |     [ If this is expected, how do I use it? ]
        //        |
        //        V 
        client.DoStreamOperation(header, ref inputstream); 


        //...                
        //... Do what you wish with data
        //...                

    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.Message.ToString(), "Stream Processing Error");
    }
}

The MSDN article uses almost the same contract format(without meta data) that exists in the official WCF samples[^]- Look at

[OperationContract]
Stream EchoStream(Stream stream)

But no example of an equivalent MessageContract implementation. The generated service reference method accepts a stream and returns a stream.

Questions:

• I would like to know why the generated service operation does not have a return type when I specified it in the contract?
• If that is expected behaviour, how should I get it to pass on a stream and return a processed stream?
• If I designed my logic wrongly, what would be the recommended way?