Part 32 - Message Exchange Patterns in WCF

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In this video we will discuss, the different Message Exchange Patterns that are available in WCF.

Message Exchange Pattern describes how the client and the wcf service exchange messages. WCF supports the following 3 Message Exchange Patterns. The default Message Exchange Pattern in WCF is Request-Reply.
1. Request-Reply (Default)
2. One-Way 
3. Duplex



Request-Reply:
1. This is the default Message Exchange Pattern

2. Client sends a message to a WCF Service and then waits for a reply. During this time the client client stops processing until a response is received from the wcf service.

3. The client waits for the service call to complete even if the operation return type is void.

4. All WCF bindings except the MSMQ-based bindings support the Request-Reply Message Exchange Pattern.

5. IsOneWay parameter of OperationContract attribute specifies the Message Exchange Pattern. The default value for IsOneWay parameter is false. This means that, if we don't specify this parameter, then the Message Exchange Pattern is Request/Reply. So the following 2 declarations are equivalent.
[ServiceContract]
public interface ISampleService
{
    [OperationContract(IsOneWay=false)]
    string RequestReplyOperation();

    [OperationContract(IsOneWay = false)]
    string RequestReplyOperation_ThrowsException();
}

OR

[ServiceContract]
public interface ISampleService
{
    [OperationContract]
    string RequestReplyOperation();

    [OperationContract]
    string RequestReplyOperation_ThrowsException();
}

6. In a Request-Reply message exchange pattern faults and exceptions get reported to the client immediately if any.

Service Implementation:

public class SampleService : ISampleService

{

    // This method simply introduces 2 seconds of artifical processing

    // time using Thread.Sleep(2000) and returns a string

    public string RequestReplyOperation()

    {

        DateTime dtStart = DateTime.Now;

        Thread.Sleep(2000);

        DateTime dtEnd = DateTime.Now;

        return dtEnd.Subtract(dtStart).Seconds.ToString()

            + " seconds processing time";

    }

    // This method throws an NotImplementedException exception

    public string RequestReplyOperation_ThrowsException()

    {

        throw new NotImplementedException();

    }

}

Create a windows client application and add a reference to the WCF service. 

Desing the windows form as shown below.


Here is the client code:

using System;

using System.Windows.Forms;

namespace WindowsClient

{

    public partial class Form1 : Form

    {

        SampleService.SampleServiceClient client;

        public Form1()

        {

            InitializeComponent();

            client = new SampleService.SampleServiceClient();

        }

        private void btnRequestReplyOperation_Click

            (object sender, EventArgs e)

        {

            try

            {

                listBox1.Items.Add("Request-Reply Operation Started @ "

                    + DateTime.Now.ToString());

                btnRequestReplyOperation.Enabled = false;

                listBox1.Items.Add(client.RequestReplyOperation());

                btnRequestReplyOperation.Enabled = true;

                listBox1.Items.Add("Request-Reply Operation Completed @ "

                    + DateTime.Now.ToString());

                listBox1.Items.Add("");

            }

            catch (Exception ex)

            {

                MessageBox.Show(ex.Message);

            }

        }

        private void btnRequestReplyOperation_ThrowsException_Click

            (object sender, EventArgs e)

        {

            try

            {

                listBox1.Items.Add("Request-Reply Throws Exception Operation Started @ "

                    + DateTime.Now.ToString());

                client.RequestReplyOperation_ThrowsException();

                listBox1.Items.Add("Request-Reply Throws Exception Operation Completed @ "

                    + DateTime.Now.ToString());

                listBox1.Items.Add("");

            }

            catch (Exception ex)

            {

                MessageBox.Show(ex.Message);

            }

        }

        private void btnClear_Click(object sender, EventArgs e)

        {

            listBox1.Items.Clear();

        }

    }

}

Next Video: OneWay message exchange pattern