Getting Started

Full Duplex

Component: NServiceBus
NuGet Package: NServiceBus (9.x)

Run the solution. Two console applications start-up, Client and Server.

Code walk-through


Look at the messages in the Shared project:

public class RequestDataMessage :
    public Guid DataId { get; set; }
    public string String { get; set; }
public class DataResponseMessage :
    public Guid DataId { get; set; }
    public string String { get; set; }

The two classes here implement the NServiceBus IMessage interface, indicating they are messages. These classes only have properties, each with get and set access. The RequestDataMessage is sent from the client to the server, and the DataResponseMessage replies from the server to the client.


The client console has an input loop:

while (true)
    var key = Console.ReadKey();

    if (key.Key != ConsoleKey.Enter)
    var guid = Guid.NewGuid();
    Console.WriteLine($"Requesting to get data by id: {guid:N}");

    var message = new RequestDataMessage
        DataId = guid,
        String = "String property value"
    await endpointInstance.Send("Samples.FullDuplex.Server", message);

This code performs the following action every time the 'Enter' key is pressed:

  • A new GUID is created and then set in the outgoing headers of the bus using the "Test" key.
  • The bus sends a RequestDataMessage whose DataId property is set to the same Guid and whose String property is set to an XML fragment.
  • A callback is registered and invoked when a response arrives to the request sent. In the callback, the values of several headers are written to the console.


When a RequestDataMessage arrives in the server queue, the bus dispatches it to the message handler found in the RequestDataMessageHandler.cs file in the Server project. The bus knows which classes to call based on the interface they implement.

public class RequestDataMessageHandler :

At start-up, the bus scans all assemblies and builds a dictionary indicating which classes handle which messages. So when a given message arrives in a queue, the bus knows which class to invoke.

The Handle method of this class contains this:

var response = new DataResponseMessage
    DataId = message.DataId,
    String = message.String

await context.Reply(response);

Finally, the bus replies with the response message, sending it to the InputQueue specified in the MsmqTransportConfig section in the app.config of the Client endpoint. The bus knows to send the responses to where the message is sent every time it sends a message from the queue.

When configuring the routing in the bus, continue with the premise of regular request/response communication such that clients need to know where the server is, but servers do not need to know about clients.

Look back at ClientEndpoint.cs to see that it gets the header information from the handler on the server.

Open DataResponseMessageHandler.cs in the Client project and find a class whose signature looks similar to the message handler on the server:

class DataResponseMessageHandler :