The WCF Address is a specific location for a service. It is the specific place to which a message will be sent. All WCF services are deployed at a specific address, listening at that address for incoming requests.

A WCF Address is normally specified as a URL, with the first part specifying the transport mechanism, and the hierarchical parts specifying the unique location of the service. For example, http://www.myweb.com/myWCFServices/SampleService is an address for a WCF service. This WCF service uses HTTP as its transport protocol, and it is located on the server www.myweb.com, with a unique service path of myWCFServices/SampleService. The following diagram illustrates the three parts of a WCF service address.

Bindings are used to specify the transport, encoding, and protocol details required for clients and services to communicate with each other. Bindings are what WCF uses to generate the underlying wire representation of the endpoint. So, most of the details of the binding must be agreed upon by the parties that are communicating. The easiest way to achieve this is for clients of a service to use the same binding that the service uses.

A binding is made up of a collection of binding elements. Each element describes some aspect of how the service communicates with clients. A binding must include at least one transport binding element, at least one message encoding binding element (which can be provided by the transport binding element by default), and any number of other protocol binding elements. The process that builds a runtime out of this description allows each binding element to contribute code to that runtime.

WCF provides bindings that contain common selections of binding elements. These can either be used with their default settings or the default values can be modified according to user requirements. These system-provided bindings have properties that allow direct control over the binding elements and their settings.

The following are some examples of system-provided bindings:

BasicHttpBinding, WSHttpBinding, WSDualHttpBinding, WSFederationHttpBinding, NetTcpBinding, NetNamedPipeBinding, NetMsmqBinding, NetPeerTcpBinding, and MsmqIntegrationBinding.

Each one of these built-in bindings has predefined required elements for a common task, and is ready to be used in your project. For instance, the BasicHttpBinding uses HTTP as the transport for sending SOAP 1.1 messages, and it has attributes and elements such as receiveTimeout, sendTimeout, maxMessageSize, and maxBufferSize. You can use the default settings of its attributes and elements, or overwrite them as needed.

A WCF contract is a set of specifications that define the interfaces of a WCF service. A WCF service communicates with other applications according to its contracts. There are several types of WCF contracts such as Service Contract, Operation Contract, Data Contract, Message Contract, and Fault Contract.

[FaultContract(typeof(ProductFault))]
GetProductResponse GetProduct(GetProductRequest request);

namespace MyWCF.EasyNorthwind.MessageContracts
{
  /// <summary>
  /// Service Contract Class - GetProductResponse
  /// </summary>
  [WCF::MessageContract(IsWrapped = false)] 
  public partial class GetProductResponse
  {
    private MyWCF.EasyNorthwind.DataContracts.Product product;
    [WCF::MessageBodyMember(Name = "Product")] 
    public MyWCF.EasyNorthwind.DataContracts.Product Product
    {
      get { return product; }
      set { product = value; }
    }
  }
}

namespace MyWCF.EasyNorthwind.DataContracts
{
  /// <summary>
  /// Data Contract Class - Product
  /// </summary>
  [WcfSerialization::DataContract(Namespace = "http://MyCompany.com/ProductService/EasyWCF/2008/05", Name = "Product")]
  public partial class Product 
  {
    private int productID;
    private string productName;
    [WcfSerialization::DataMember(Name = "ProductID", IsRequired = false, Order = 0)]
    public int ProductID
    {
      get { return productID; }
      set { productID = value; }
    }
    [WcfSerialization::DataMember(Name = "ProductName", IsRequired = false, Order = 1)]
    public string ProductName
    {
      get { return productName; }
      set { productName = value; }
    }
  }
}

namespace MyWCF.EasyNorthwind.FaultContracts
{
  /// <summary>
  /// Data Contract Class - ProductFault
  /// </summary>
  [WcfSerialization::DataContract(Namespace = "http://MyCompany.com/ProductService/EasyWCF/2008/05", Name = "ProductFault")]
  public partial class ProductFault 
  {
    private string faultMessage;
    [WcfSerialization::DataMember(Name = "FaultMessage", IsRequired = false, Order = 0)]
    public string FaultMessage
    {
      get { return faultMessage; }
      set { faultMessage = value; }
    }
  }
}

Messages are sent between endpoints. Endpoints are places where messages are sent or received (or both), and they define all of the information required for the message exchange. A service exposes one or more application endpoints (as well as zero or more infrastructure endpoints). A service can expose this information as the metadata that clients process to generate the appropriate WCF clients and communication stacks. When needed, the client generates an endpoint that is compatible with one of the service's endpoints.

A WCF service endpoint has an address, a binding, and a service contract (WCF ABC).

The endpoint's address is a network address where the endpoint resides. It describes, in a standard-based way, where messages should be sent. Each endpoint normally has one unique address, but sometimes two or more endpoints can share the same address.

The endpoint's binding specifies how the endpoint communicates with the world, including things such as transport protocol (TCP, HTTP), encoding (text, binary), and security requirements (SSL, SOAP message security).

The endpoint's contract specifies what the endpoint communicates, and is essentially a collection of messages organized in the operations that have basic Message Exchange Patterns (MEPs) such as one-way, duplex, or request/reply.

The following diagram shows the components of a WCF service endpoint.

A WCF behavior is a type or settings to extend the functionality of the original type. There are many types of behaviors in WCF such as service behavior, binding behavior, contract behavior, security behavior, and channel behavior. For example, a new service behavior can be defined to specify the transaction timeout of the service, the maximum concurrent instances of the service, and whether the service publishes metadata. Behaviors are configured in the WCF service configuration file. We will configure several specific behaviors in the chapters that follow.

A WCF service is a component that can be called by other applications. It must be hosted in an environment in order to be discovered and used by others. The WCF host is an application that controls the lifetime of the service. With .NET 3.0 and beyond, there are several ways to host the service.

As we have seen in the previous sections, a WCF service has to be hosted in an application on the server side. On the client side, the client applications have to specify the bindings to connect to the WCF services. The binding elements are interfaces, and they have to be implemented in concrete classes. The concrete implementation of a binding element is called a channel. The binding represents the configuration and the channel is the implementation associated with that configuration. Therefore, there is a channel associated with each binding element. Channels stack on top of one another to create the concrete implementation of the binding—the channel stack.

The WCF channel stack is a layered communication stack with one or more channels that process messages. At the bottom of the stack is a transport channel that is responsible for adapting the channel stack to the underlying transport (for example, TCP, HTTP, SMTP, and other types of transport). Channels provide a low-level programming model for sending and receiving messages. This programming model relies on several interfaces and other types collectively known as the WCF channel model. The following diagram shows a simple channel stack:

The metadata of a service describes the characteristics of the service that an external entity needs to understand in order to communicate with the service. Metadata can be consumed by the ServiceModel Metadata Utility Tool (Svcutil.exe) to generate a WCF client and the accompanying configuration that a client application can use to interact with the service.

The metadata exposed by the service includes XML schema documents, which define the data contract of the service, and WSDL documents, which describe the methods of the service.

Though WCF services always have metadata, it is possible to hide the metadata from outsiders. If you do so, you have to pass the metadata to the client side by other means. This practice is not common but it gives your services an extra layer of security. When enabled through the configuration settings through metadata behavior, metadata for the service can be retrieved by inspecting the service and its endpoints. The following configuration setting in a WCF service configuration file will enable metadata publishing for HTTP transport protocol:

<serviceMetadata httpGetEnabled="true" />