Live from TechEd Day 2

Article
06/05/2007

I gave a chalk talk on channel development in the afternoon yesterday. I did a huge experiment for the second-half of the talk, which was to write a custom channel from scratch for the audience. That's the kind of theater that you can pull off in a chalk talk but not a regular breakout session. I started with a completely empty Visual Studio environment, wrote a web service, explained why the web service call crashed due to a protocol issue, and then fixed the crash by writing a custom channel.

We had 46 people in the audience at the start. The capacity of the chalk talk theaters is only 32 people, but we secured about a dozen extra chairs from the lounges and people stood along the back. Capacity was an issue for several of the chalk talks yesterday. I saw one chalk talk for BizTalk that had crammed almost 60 people into the room. If you're in the audience, it starts getting quite warm after a while. The breakout session rooms are quite spacious on the other hand so I haven't seen any problems there. The Orlando venue has a tremendous capacity and a generally good layout.

The only other difficulty was that the standard equipment was a non-adjustable over-ear headset microphone. In addition to making you look like a cross between a call-center worker and a pop star, that type of mic is pretty uncomfortable to wear for an hour and picks up a lot of extra noise if you move around while talking. I tried a half-dozen ways of putting the headset on to fix the issues before the AV guy offered a standard lapel microphone. They had one sitting in the AV case in the room. I don't know why they didn't make the proper equipment available from the start.

I promised at the end of the talk that I'd post some resources.

Ed Pinto and Kenny Wolf are giving a talk "Architecture of Microsoft Windows Communication Foundation and Common Extensibility Points" on Thursday at 4:30 PM.

Steve Maine is giving the buzzword titled talk "Microsoft Windows Communication Foundation Syndication, AJAX and REST Services in Web 2.0 with .NET Framework 3.5" on Friday at 1 PM.

There are six samples that I particularly recommend for channel developers.

Finally, here is the code that was written during the talk. The scenario was based on an HTTP problem I described back in August.

 using System;
using System.Collections.Generic;
using System.Text;
using System.ServiceModel;
using System.ServiceModel.Channels;

public class TechEdChannel : ChannelBase, IRequestChannel
{
   IRequestChannel innerChannel;

   public TechEdChannel(ChannelManagerBase parent, IRequestChannel innerChannel) : base(parent)
   {
      this.innerChannel = innerChannel;

   }
   protected override void OnAbort()
   {
      innerChannel.Abort();
   }

   protected override IAsyncResult OnBeginClose(TimeSpan timeout, AsyncCallback callback, object state)
   {
      return innerChannel.BeginClose(timeout, callback, state);
   }

   protected override IAsyncResult OnBeginOpen(TimeSpan timeout, AsyncCallback callback, object state)
   {
      return innerChannel.BeginOpen(timeout, callback, state);
   }

   protected override void OnClose(TimeSpan timeout)
   {
      innerChannel.Close(timeout);
   }

   protected override void OnEndClose(IAsyncResult result)
   {
      innerChannel.EndClose(result);
   }

   protected override void OnEndOpen(IAsyncResult result)
   {
      innerChannel.EndOpen(result);
   }

   protected override void OnOpen(TimeSpan timeout)
   {
      innerChannel.Open(timeout);
   }

   #region IRequestChannel Members

   public IAsyncResult BeginRequest(Message message, TimeSpan timeout, AsyncCallback callback, object state)
   {
      return innerChannel.BeginRequest(message, timeout, callback, state);
   }

   public IAsyncResult BeginRequest(Message message, AsyncCallback callback, object state)
   {
      return innerChannel.BeginRequest(message, callback, state);
   }

   Message FixMessage(Message message)
   {
      if (message == null)
         return null;
      HttpResponseMessageProperty property = (HttpResponseMessageProperty)message.Properties[HttpResponseMessageProperty.Name];
      if (property != null && property.StatusCode == System.Net.HttpStatusCode.Accepted)
      {
         return null;
      }
      return message;
   }

   public Message EndRequest(IAsyncResult result)
   {
      return FixMessage(innerChannel.EndRequest(result));
   }

   public EndpointAddress RemoteAddress
   {
      get { return innerChannel.RemoteAddress; }
   }

   public Message Request(Message message, TimeSpan timeout)
   {
      return FixMessage(innerChannel.Request(message, timeout));
   }

   public Message Request(Message message)
   {
      return FixMessage(innerChannel.Request(message));
   }

   public Uri Via
   {
      get { return innerChannel.Via; }
   }

   #endregion
}

public class TechEdChannelFactory : ChannelFactoryBase, IChannelFactory<IRequestChannel>
{
   IChannelFactory<IRequestChannel> innerFactory;

   public TechEdChannelFactory(IChannelFactory<IRequestChannel> innerFactory) : base()
   {
      this.innerFactory = innerFactory;
   }
   protected override IAsyncResult OnBeginOpen(TimeSpan timeout, AsyncCallback callback, object state)
   {
      return innerFactory.BeginOpen(timeout, callback, state);
   }

   protected override void OnEndOpen(IAsyncResult result)
   {
      innerFactory.EndOpen(result);
   }

   protected override void OnOpen(TimeSpan timeout)
   {
      innerFactory.Open(timeout);
   }

   #region IChannelFactory<IRequestChannel> Members

   public IRequestChannel CreateChannel(EndpointAddress to, Uri via)
   {
      return new TechEdChannel(this, innerFactory.CreateChannel(to, via));
   }

   public IRequestChannel CreateChannel(EndpointAddress to)
   {
      return new TechEdChannel(this, innerFactory.CreateChannel(to));
   }

   #endregion
}

public class TechEdBindingElement : BindingElement
{
   public TechEdBindingElement()
      : base()
   {
   }

   protected TechEdBindingElement(TechEdBindingElement element)
      : base(element)
   {
   }

   public override BindingElement Clone()
   {
      return new TechEdBindingElement(this);
   }

   public override IChannelFactory<TChannel> BuildChannelFactory<TChannel>(BindingContext context)
   {
      IChannelFactory<TChannel> innerFactory = base.BuildChannelFactory<TChannel>(context);
      return (IChannelFactory<TChannel>)new TechEdChannelFactory((IChannelFactory<IRequestChannel>)innerFactory);
   }

   public override bool CanBuildChannelFactory<TChannel>(BindingContext context)
   {
      if (typeof(TChannel) != typeof(IRequestChannel))
         return false;
      return base.CanBuildChannelFactory<TChannel>(context);
   }

   public override T GetProperty<T>(BindingContext context)
   {
      return context.GetInnerProperty<T>();
   }
}

[ServiceContract]
public interface IService
{
   [OperationContract(Action="*", IsOneWay=true)]
   void DoNothing();
}

public class Service : IService
{
   public void DoNothing()
   {
      Console.WriteLine("Did nothing.");
   }
}

class Program
{
   static void Main(string[] args)
   {
      string uri = "https://localhost:8000/";

      TextMessageEncodingBindingElement be = new TextMessageEncodingBindingElement();
      be.MessageVersion = MessageVersion.None;

      Binding binding = new CustomBinding(
         new OneWayBindingElement(),
         new TechEdBindingElement(),
         be,
         new HttpTransportBindingElement()
         );

      ServiceHost host = new ServiceHost(typeof(Service));
      host.AddServiceEndpoint(typeof(IService), binding, uri);
      host.Open();
      ChannelFactory<IService> factory = new ChannelFactory<IService>(binding, new EndpointAddress(uri));
      factory.Open();
      IService proxy = factory.CreateChannel();
      proxy.DoNothing();
      factory.Close();
      host.Close();
      Console.ReadLine();
   }
}

Next time: Live from TechEd Day 3

Live from TechEd Day 2

Additional resources