ServiceHost --- WCF Communication Details - Part 1

Introduction

WCF is a programming platform for building a network-distributed system. It is unified programming model which combines features of Web Service, Remoting, MSMQ and COM+. As a .NET developer, you just need to know the APIs that WCF provided, but if you know more about the implementation details, it will help you use WCF efficiently and build a more reliable system.

Background

In the last article, I introduced how to implement a simple WCF service host in process - Create a Self-Hosted WCF Service. Let's use this sample and dig into the WCF inside.

1 - ServiceHost

ServiceHost is the most important class to host our service after we defined the configuration and the provisions of the behaviors and characteristics which the service have. The main work of ServiceHost class is to load the service, configure endpoint, apply security setting and turn on/off a channel to listen to the incoming message.

//SelfHosting.cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.ServiceModel;
using System.ServiceModel.Description;

namespace SelfHostedTest
{
    class Program
    {
        static void Main(string[] args)
        {
            string address = "http://localhost:8090/SelfHostService/EchoSerivce";

            Uri httpUrl = new Uri(address);

            ServiceHost host = new ServiceHost(typeof(SelfHostService.EchoSerivce), httpUrl);

            BasicHttpBinding binding = new BasicHttpBinding();
            host.AddServiceEndpoint(typeof(SelfHostService.IEchoSerivce), new BasicHttpBinding(), address);

            ServiceMetadataBehavior smb = new ServiceMetadataBehavior();
            smb.HttpGetEnabled = true;
            host.Description.Behaviors.Add(smb);

            host.Open();
            Console.WriteLine("Service is host at " + address);
            Console.WriteLine("Host is running... Press <Enter> key to stop");
            Console.ReadLine();
        }
    }
}

1.1 - Create ServiceDescription

No matter what kind of hosting (IIS, WAS, WS..) you used in your project, it all implements through ServiceHost. ServiceHost inherits the ServiceHostBase class. According to the service we configured, ServiceHost creates a ServiceDescription object to describe the service, and copy it to its father ServiceHostBase's behavior Description.

//System.ServiceModel.ServiceHost
public abstract class ServiceHostBase : ...
{
   ServiceDescription description;
}

CreateDescription methods are made to create ServiceDescription. There are several tasks:

• ​Add Service Behavior that is applied when we defined the service.​

[ServiceContract(CallbackContract = typeof(IPushCallback))] public interface IDuplexService {

[OperationContract(isOneWay = true)]

void SendMessage(string data)

}

• ​Initialize ServiceDescription.Name, ServiceDescription.Namespace, ServiceDescription.ConfigurationName
• ​Add ServiceBehavior we defined in the config file (ServiceElement)
• Add ServiceEndpointElement​ according to the endpoint we defined

<system.serviceModel>

<behaviors>
​ <endpointBehaviors>
​ <behavior> ... </behavior>
​ </endpointBehaviors>
</behaviors>
<services>
<service name="HelloworldService">
<endpoint .../>
</service>
</services>
</system.serviceModel>

ServiceDescription is created when we initialize a ServiceHost object. We can call ServiceHost.AddServiceEndpoint methods to add endpoints to Description's endpoint collection.

1.2 - Validate the ServiceDescription is Valid

• ​Service behavior
• Endpoint behavior
• Contract behavior
• Operation behavior

1.3 - Group of Endpoints According to ListenUri and ListenUriMode

ListenUri is a physical address, different endpoint could share the same listenUri, listenUriMode is ensured that the listen uri is unique, it will add a GUID to distinguish the address.

<service name="helloworldService">

<endpoint address="http://127.0.0.1:7777/HelloWorldService"
binding="basicHttpBinding"
contract="SelfHostService.IHelloWorldService"
listenUri="http://127.0.0.1:6666/HelloWorldService"
listenUriMode="Explicit">
</endpoint>
<endpoint address="http://127.0.0.1:8888/HelloWorldService"
binding="basicHttpBinding"
contract="SelfHostService.IHelloWorldService"
listenUri="http://127.0.0.1:6666/HelloWorldService"
listenUriMode="Explicit">
</endpoint>
<endpoint address="http://127.0.0.1:9999/HelloWorldService"
binding="basicHttpBinding"
contract="SlefHostService.IHelloWorldService"
listenUri="http://127.0.0.1:6666/HelloWorldService"
listenUriMode="Unique">
</endpoint>
</service>

Group 1: Endpoint 1

address : http://127.0.0.1:7777/HelloWorldService

listenUri : http://127.0.0.1:6666/HelloWorldService

listenUriMode : Explicit

Endpoint​ 2

address : http://127.0.0.1:8888/HelloWorldService

listenUri : http://127.0.0.1:6666/HelloWorldService

listenUriMode : Explicit

Group 2: Endpoint 3

address : http://127.0.0.1:9999/HelloWorldService

listenUri : http://127.0.0.1:6666/HelloWorldService

listenUriMode : Unique

After group of endpoints, WCF will create a BindingParameterCollection object for each group and use this object to create a very important object --- BindingContext.

ChannelDispather and EndpointDispather are the most important components in WCF Server Side. Each group above has a ChannelDispatcher, each endpoint in the group has an EndpointDispatcher. WCF will build a ChannelListener for each listening address based on BindingContext to listen to the incoming message. We will talk about the Channel Layer in the next article. Find out how WCF listens to an incoming message and how to encode the message through the wire.

Besides, ServiceHost also has an important task to apply the security setting, We will gather the security things to an independent series.